Biology and Health Sciences

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• UNIT 1 Biodiversity and classification

  URLs: 2
• UNIT 2 Introduction to Classification

  

  

  
  

  Oral activity
  In groups, discuss these questions.
  1. How do we know that something is living?
  2. Make a guess about the number of different animals and plants in
  Rwanda. Do you think it is a large number or a small number?
  3. Th ink of ways in which you could put these organisms
  into groups.
  4. Do you know the scientific name for some of these organisms?

  
  

  

   Topic 1: Biodiversity and classification

  
  

  The importance of classification
  In the oral activity, you talked about how many different organisms there are
  in Rwanda. No doubt you realized that there are a large number of different
  living things in our country. In fact, there are more than 2,000 different types
  of plants and 500 different types of animals in our country.

  
  

  Activity 2.1
  Work in pairs. Look at the pictures below, and then answer the questions.

  
  

  

  Figure 2.2 Living and non-living things

  
  

  1. Draw a table with two columns. In one column, write down all the
  living things that you can see in the picture. In the other column, write
  down all the non-living things.
  2. How did you decide which things were living and which were not?
  3. Of the non-living things:
  a) Which were always dead?
  b) Which were once alive, but are now dead?
  4. Draw another table with two columns. In one column, write down
  the names of all the animals you can see in the picture. In the other
  column, write down the names of all the plants.
  5. How did you decide which things were animals and which were plants?

  
  

  Scientists need to sort all living things into groups so that they can recognise
  and study them more easily. When you were sorting the living things into
  plants and animals in the activity, you were classifying them. There are so
  many different organisms on Earth that scientists need to sort them into
  groups. Classification means sorting things into groups. Think back to how
  you sorted the living things. You put those that shared certain characteristics
  into the animal group, and those that shared certain other characteristics
  into the plant group.
  Sorting, or classifying, things into groups according to their similarities
  and differences is called classification, or taxonomy.
  Scientists sometimes change the way they classify an organism as they
  learn more about it. Taxonomists use information from many branches of
  Biology to classify organisms; for example, genetics, biochemistry and fossils.

  
  

  Unit 2: Introduction to classification 

  
  

  The concept of hierarchical classification
  In Activity 2.1, you grouped different living organisms into two groups:
  animals and plants. However, there are thousands of different organisms
  in these two groups, so scientists must classify them into smaller groups.
  Taxonomists study more similarities and differences between different
  organisms so that they can classify them into smaller and smaller groups.
  Th is is called hierarchical classification.

  
  

  The five kingdom system

  Organisms are grouped into five big groups, called kingdoms. Th e
  kingdoms are Animals, Plants, Fungi, Protoctista and Monera.
  Th e features that are used to group organisms into these
  kingdoms are: body structure, method of getting food and method of
  reproduction.
  Th e kingdoms are further divided into smaller groups called phyla,
  classes, orders, families, genera and species. See Figure 2.3.
  

  
  

  • Each kingdom is divided into phyla.
  • Each phylum is divided into classes.
  • Each class is divided into orders.
  • Each order is divided into families.
  • Each family is divided into genera.
  • Each genus is divided into species.
  

  
  

  

  

  Topic 1: Biodiversity and classification

  
  

  The diagram below shows two classification hierarchies. A hierarchy is a
  way of arranging groups from the biggest group to the smallest. The first is
  for a fig tree and the second is for a cat.
  Figure 2.4 The classification hierarchy for a fig tree (A) and a cat (B)
  Kingdom

  
  

  

  
  

  
  

  
  

  

  
  

  
  

  Figure 2.4 The classification hierarchy for a fig tree (A) and a cat (B)

  
  

  Unit 2: Introduction to classification

  The binomial system
  

  Usually, we use an organism’s common name, for example, ‘cat’. However,
  the word for ‘cat’ is different in different languages. So, people in different
  parts of the world use different words to describe the same organism. This
  makes it difficult for scientists to accurately communicate their findings
  about an organism accurately.
  To solve this problem, the biologist Linnaeus developed a system
  accurately give an organism two Latin names. Using two names is called
  the binomial system. The first word in the name is the genus to which the
  organism belongs. So for a cat, this would be Felis. The second name is
  the species to which the organism belongs. A species is a group of closely
  related organisms that are able to breed with
  one another and produce offspring that can
  also reproduce. The species name for a cat
  is domesticus. So the scientific name for a
  domestic cat is Felis domesticus.
  Let us look at another example, one
  from the plant kingdom. Yellow commelina
  is a plant found commonly in Rwanda.
  Its scientific name is Commelina africana.
  The name Commelina is its genus name.
  All commelina plants have the same genus
  name. The africana part of the name is the
  species name. Only one kind of commelina
  plant has the species name. So Commelina
  africana is the scientific name for a particular
  kind, or species, of commelina plant.

  

  
  

  Figure 2.5 Yellow commelina, or Commelina africana

  
  

  
  

  

  

  Figure 2.6 A scientific name
  written by hand (A), and the
  same name in print (B)

  How to write scientific names
  

  Look again at the scientific names you have learnt about in this unit: Ficus
  carica, Felis domesticus and Commelina africana. What do you notice about
  how they are written?
  • The first name is the name of the genus the organism belongs to; it
  starts with a capital letter.
  • The second name is the name of the species the organism belongs to; it
  starts with a small letter.
  • When written by hand, the two names must be underlined separately;
  when they are printed, they must be in italics. See Figure 2.6.

  
  

  Characteristics of organisms in the five kingdoms
  Table 2.2 shows characteristics and examples of organisms in
  each kingdom.

  
  

  Topic 1: Biodiversity and classification

  
  

  Table 2.2 Characteristics of organisms in the five kingdoms

  
  

  
  

  Kingdom	Characteristics	Examples
  Animalia	• The organisms’ cells do not have a cell wall. • The organisms are multicellular, feed on other organisms, and move around.	Snail, mosquito, snake, bird forest cobra
  Plantae	• The organisms’ cells have a cell wall. • The organisms contain a green substance called chlorophyll and make their own food through photosynthesis.	Moss, fern, maize, fig tree fern
  Fungi	• The organisms reproduce by means of spores and not seeds. • The organisms do not photosynthesise.	Toadstool, mould, yeast toadstool
  Protoctista	The organisms are single cells or colonies of single cells.	Amoeba, paramecium paramecia
  Monera	• The organisms are single cells that do not have a membrane-bound nucleus; they are prokaryotic. • They are the smallest and simplest of all organisms.	Bacterium bacteria

  
  
  

  Exercise 2.1

  1. Name the five kingdoms of organisms.
  2. Identify the kingdom to which each of the organisms described
  belongs.
  a) It has a cell wall and chloroplasts.
  b) It is a single cell.
  c) It reproduces by means of spores.
  3. Arrange the classification groups below into the correct order. Start
  with the group that contains the smallest number of organisms.

  
  
  

  family	species	order	genus	phylum	kingdom	class

  
  
  Unit 2: Introduction to classification

  Exercise 2.2

  1. Give the correct name or word for each of the following:
  a) the biologist who developed the binomial system
  b) a system that groups things into smaller and smaller groups
  c) the naming and classification of organisms.
  2. Match each animal’s
  common name with
  its scientific name. To
  help you, here are some
  Latin words translated
  into English:
  mel = honey;
  taurus = bull;
  terra = earth;
  sapiens = wise
  

  
  

  
  

  Common name	Scientific name
  2.1 Earthworm	A. Homo sapiens
  2.2 Honeybee	B. Bos taurus
  2.3 Rhinoceros	C. Panthera leo
  2.4 Cow	D. Apis mellifera
  2.5 Hippopotamus	E. Diceros bicornis
  2.6 Lion	F. Lumbricus terrestris
  2.7 Human	G. Hippopotamus amphibius

  
  
  

  Homework
  

  Copy the table, and then complete it by putting the following animals into
  their correct groups:
  buffalo, earthworm,
  hyena, hare, cheetah,
  jellyfish, lynx.
  (Hint: all the
  animals belong to
  one group, but only
  some belong to
  other groups, too.)

  
  

  
  

  Kingdom	Animalia
  Phylum	Chordata
  Class	Mammalia
  Order	Carnivora
  Family	Felidae (cats)

  
  Use simple identification keys

  Scientists use identification keys to help them to identify unknown
  organisms. A key is a list of characteristics. Scientists compare the
  characteristics of the unknown organism with the descriptions on the
  key, and so can classify the organism.
  You will use a dichotomous key in the next activity (‘di’ means
  ‘two’). A dichotomous key consists of pairs of statements about a
  characteristic of a particular organism.

  
  

  
  

   Topic 1: Biodiversity and classification

  
  

  Activity 2.2

  Work in pairs. Look at pictures A to D alongside, and read the example of a
  dichotomous key. Then, answer the questions.

  
  

  Example of a dichotomous key
  We can identify the animals A, B, C and D by using a dichotomous key
  like this one:
  1. Has legs ________________________ See 2
  Has no legs ____________________ Snake
  2. Has two legs _________________ Chicken
  Has more than two legs __________ See 3
  3. Has six legs _______________ Grasshopper
  Has eight legs __________________ Spider
  

  
  

  1. The key has three steps. Each step has a pair of statements which
  describe the animals. Notice that each pair of statements in the key
  divides the animals into two groups. What characteristic is used in this
  key to group and identify the animals?
  2. Step 1 of the key separates the animals that have legs (A, B and C) from
  those that do not have legs (D). The first statement in Step 1 says that if
  the animal has legs, we should move on to Step 2. The second statement
  says that if the animal has no legs, it is a snake. Therefore animal D is
  identified as a snake.
  3. Read Step 2 of the key. The first statement says that if the animal has
  two legs, it is a chicken. Of the three remaining animals (A, B and
  C), only B has two legs. Therefore, animal B is a chicken. This leaves
  two animals (A and C), which have more than two legs. The second
  statement tells us to go on to Step 3 to identify these
  two animals.
  4. Step 3 identifies an animal with six legs as a grasshopper. Therefore,
  animal C is a grasshopper. Using the second statement in Step 3, can
  you identify animal A?
  5. Your teacher will display some specimens or pictures of different
  organisms in the classroom. Identify their observable characteristics,
  and then try to make a dichotomous key using their characteristics so
  that someone else could identify them.

  

  

  
  

  
  

  Unit 2: Introduction to classification

  Checklist of learning:

  In this unit, I have learnt:

  There are many different organisms on Earth, and scientists classify them into groups.
  There are five groups, called kingdoms, which each have many organisms; the kingdoms are:
  Animalia, Plantae, Fungi, Protoctista and Monera.
  The kingdoms are further divided into smaller and smaller groups; this is called hierarchical
  classification.
  The groups in the kingdoms are: phyla, classes, orders, families, genera and species.
  Organisms have two names in the binomial system: a genus name and a species name.
  Animals have cells without a cell wall, are multicellular, can move around, and feed on other
  organisms.
  Plants have cells with cell walls, contain chlorophyll and can make their own food through
  photosynthesis.
  Fungi reproduce by spores instead of seeds and do not photosynthesise.
  Protoctista are single-celled organisms.
  Monera are single cells without a membrane-bound nucleus.
  To appreciate the need for classification of organisms.

  
  

  Self-assessment
  

  1. Copy the table, and then complete it by putting the following animals into their correct groups:
  cow, perch, locust, lion, donkey, leopard.
  (Hint: all the animals belong to one group, but only some belong to other groups, too.)

  
  

  
  

  Kingdom	Animalia
  Phylum	Animalia
  Class	Chordata
  Class	Mammalia
  Order	Carnivora
  Family	Felidae (cats)

  
  
  

  
  

  Topic 1: Biodiversity and classification

  
  

  2. Figure 2.7 shows four animals: A, B, C and D. Construct a dichotomous key that can be used to identify the animals.

  
  

  A:
  

  B:

  C:

  D:

  3. In groups, discuss the dichotomous keys that you constructed.

  
  

  
  

  
  

  
  

  
  

  
  
  
  

  
  

  
  
  

  
  

  
  
  

  
  

  
  

  
  

  
  

  
  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  

  
  
• UNIT 3 The external structure and importance of flowering plants

  UNIT 3 The external structure and
  

               importance of flowering plants

            
  

  Key unit
  competence:

  To be able to analyse
  the external structure
  of a typical fl owering plant
  

  
  

  Cross-cutting issue:

  Environment and
  sustainability: We
  need to ensure that
  we use sustainable
  farming practices in
  

  Rwanda.
  

  At the end of this unit, you should be able to:

  • Identify the external parts of a fl owering plant
  • Describe how plant organs are organized into systems
  • Explain the functions of roots, stem and leaves in plants
  • Identify diff erent root, stem, and leaf modifi cations
  • Describe the external structural modifications shown by roots, stem and
  leaves
  • Explain the importance of fl owering plants
  • Diff erentiate fl owering plants from other plants
  • Observe the external structure of leaves and root modifi cations and how
  they carry out other functions
  • Explain the diff erence between fi brous and tap root systems
  • Carry out home observation on the importance of fl owering plants and
  submit a report
  • Appreciate the importance of food storage organs in plants and the value
  of roots and leaves to man.
  

  
  

  Oral activity
  

  In groups, think about what you learnt in Upper Primary. Th en, talk about
  the answers to these questions.
  1. What is the main function of a flower?
  2. Put the following terms in the correct order: germination, seed
  dispersal, fertilisation, pollination.
  3. Describe how some plants, such as avocado and cassava, can reproduce asexually.
  

  
  

  A
  

  

  B
  

  

  
  

  C
  

  

  
  

  Figure 3.1 The flowering plants maize (A), sorghum (B) and cassava (C) are important food crops.

  Topic 1: Biodiversity and classification

  
  

  The external structure of a
  flowering plant
  

  Flowering plants are a large group of
  plants and trees. They all have flowers,
  bear fruit and produce seeds. They are
  organisms that are made up of different
  organs, which are called stems, leaves,
  

  flowers and roots.
  

  
  

  Monocotyledonous and
  dicotyledonous plants
  

  There are two main types of flowering
  plants: monocotyledonous and
  dicotyledonous plants. All flowering
  plants have seeds with cotyledons, or
  seed leaves. Some plants have just one
  cotyledon and others have two. Table 3.1
  shows the main differences between these
  

  two groups.

  
  

  

                              Table 3.1 Differences between monocotyledonous and dicotyledonous plants

  
  

  
  

  Monocotyledons	Dicotyledons
  One seed leaf, or cotyledon	Two seed leaves, or cotyledons
  Fibrous roots	Tap root
  Flower parts are in multiples of three	Flower parts are in multiples of four or five
  Narrow leaves with parallel veins	Leaves with a net-like pattern of veins
  Examples: grasses and cereal plants, such as maize and sorghum	Examples: mangoes, avocados, beans and figs

  
  Experiment 3.1

  Work in pairs.
  You will need: a typical dicotyledonous plant with roots, e.g. a bean plant
  or black jack; a hand lens
  Procedure
  1. Identify the following parts on your flowering plant: shoot system,
  root system, bud, node, internode, leaves, stem, flowers, fruits, roots.
  

  Use Figure 3.2, above, to help you.

  
  

  Unit 3: The external structure and importance of flowering plants

  A. Runner Stolon                                         B. rhizome
  

  

  C. Stem tuber                                                   D. CORM

  
  

  
  

  Figure 3.3 Examples of
  modified stems: strawberry (A),
  ginger (B), potato (C), yam (D)

  
  

  2. Note the main features of the stem and root.
  3. Make a large drawing of your plant specimen, showing all the parts
  you have identified. Label the diagram carefully.
  Exercise 3.1
  1. Suggest the functions of all the plant parts you identified in
  Experiment 3.1.
  2. How does the plant you observed in the experiment differ from a
  maize plant?
  The stem
  The stem is the part of a flowering plant that usually grows above the
  ground. A stem has buds and side shoots, and bears leaves. Most stems are
  green as they contain chlorophyll.
  The place where a leaf grows from a stem is called a node. The length of
  a stem between the leaves is called an internode.
  Functions of the stem
  The stem:
  • transports water and mineral salts from the roots to other parts of the
  plant
  • transports sugars (food) from the leaves to all other parts of
  the plant
  • supports and holds buds and leaves so that they can get enough
  sunlight for photosynthesis
  • holds flowers in the best position for pollination
  • supports the fruits and seeds in the best position for dispersal
  • makes food for the plant through the process of photosynthesis.
  Modified stems
  Most stems have similar functions, but some stems are modified so they
  can do other jobs. Modified stems have features that help them to do
  a particular job. For example, some stems can be modified for asexual
  reproduction. Plants with such stems can make new plants using their
  modified stems. The stems can produce small, identical new plants at their
  ends, or roots can form where a stem touches the ground, and a new plant can grow from there.

  
  

  Topic 1: Biodiversity and classification

  
  

  For example, in strawberries, bananas and sisal, suckers and stolons can be
  used to make new plants.
  Some stems are modified for food storage, for example, ginger,
  potatoes, yams and strawberries. Figure 3.3, on page 28 shows some
  

  modified stems.

  
  

  Experiment 3.2

  
  

  Work on your own.
  You will need: specimens or photographs of the following: a rhizome
  of ginger, a canna lily, couch grass or potato; a creeping stem of oxalis; a
  corm of coco yam; a stolon of a strawberry; a hand lens
  Procedure
  1. Examine the different types of stems provided. Note the main
  features of each stem.
  2. Suggest the function of each stem and note how it is suited to
  its function.
  3. Make a drawing of each different stem type, and label the drawings carefully.
  

  
  

  Experiment 3.3

  
  

  Work in groups.
  You will need: a carrot or sweet potato; a potato; a piece of ginger; a
  stolon of sweet potato
  Procedure
  Carefully examine the specimens, and then answer the questions.
  Questions
  1. Explain why potatoes, sweet potatoes and carrots are called tubers.
  2. What makes a potato a stem and not a root?
  3. Give two functions that different types of modified stems can carry out.

  
  

  Unit 3: The external structure and importance of flowering plants
  

  Leaves

  
  

  Leaves are attached to a plant’s stem at the nodes by a stalk called a petiole
  (see Figure 3.4). Leaves are usually thin, wide and flat in shape. The
  wide, flat area of a leaf is called the lamina. Leaves are the main organs of
  photosynthesis.
  Leaves are green because their cells contain a lot of chlorophyll, to
  capture the sunlight that falls on the leaf.
  The structure of a leaf is closely related to the job it has to do for the
  plant. The thin, flat lamina means that leaves have a large surface area.
  Carbon dioxide can easily get into the leaf. The large surface area can also
  trap lots of sunlight for photosynthesis. Leaves have a system of veins which
  bring water and minerals to the cells and carry away the sugar made by
  photosynthesis. The main vein, which connects with the petiole, is called
  the midrib.
  The top layer of a leaf is covered by a waxy waterproof layer called the
  cuticle. The cuticle prevents water loss through the surface of
  the leaf.
  The arrangement of the veins on a leaf can vary a lot. The veins
  of a monocotyledonous plant run in parallel lines. The leaves of a
  dicotyledonous plant have a network of branching veins.
  The size and shape of leaves can also vary (see Figure 3.5). Leaves
  can be split into several parts or have smooth, toothed or lobed edges
  (margins). Many of these features help us to identify different types of

  plants.

  
  

  

  
  

  Figure 3.5 Leaves can have different shapes and sizes.

  Topic 1: Biodiversity and classification

  
  

  Functions of leaf parts
  

  Table 3.2 describes the functions of the different parts of the leaf.

  
  

  Table 3.2 Parts of the leaf and their functions
  

  
  

  Part	Function
  Petiole	• Carries food made by photosynthesis from the leaf to the   stem • Transports mineral salts and water from the stem to the leaf • Supports the leaf
  Midrib	• Supports the lamina • Carries water and mineral salts from the petiole   to the lamina • Transports food from the lamina to the petiole
  Veins	• Support the lamina • Distribute water and mineral salts within the lamina • Collect food from the lamina
  Lamina	• Contains chlorophyll for trapping light energy,    which is needed for photosynthesis

  
  Modified leaves
  As with stems, some leaves are modified for different functions. Some of the
  most common modifications enable the plant to:
  • Prevent animals from eating the plant. Such leaves are usually prickly,
  poisonous or have an unpleasant taste.
  • Prevent water loss. These leaves often have a thick, shiny, waxy layer
  on their surface. They may be reduced to spines (e.g. a cactus), or be
  covered with a layer of tiny hairs. Some leaves are curled up to prevent
  water leaving the leaves.
  • Store water. These leaves are fleshy and used to store water.
  • Store food; examples include onion and garlic.
  

  
  

  Figure 3.6 Examples of leaf
  modifications: a cactus (A),
  onion (B) and succulent (C)
  

  
  

  Activity 3.1

  Work in groups.
  1. Collect at least three different types of leaves.
  2. Draw a table to show the differences between the leaves.
  3. Make a labelled drawing of any one of the leaves, showing its
  

  
  

  Unit 3: The external structure and importance of flowering plants

  Flowers:

  Flowers are the reproductive organs of a plant.
  Some flowers form individually on stems, whilst
  others are arranged in clusters. An arrangement
  of flowers on a stem is called an inflorescence.
  Figure 3.7 shows the main parts of a flower.
  Flowers produce the male and female sex cells,
  which are called gametes. The female sex cells
  are inside the ovules. The male sex cells are
  inside the pollen gains.
  

  

  
  

  Experiment 3.4

  Work in groups. Complete the experiment, and then answer
  the questions.
  You will need: a razor blade; a hand lens; a large flower such as hibiscus;
  a grass flower
  Procedure
  1. Compare the characteristics of both flowers.
  2. Carefully dissect the hibiscus flower to observe all its parts.
  Questions
  1. Explain why some parts of a flower are brightly coloured.
  2. Name at least eight parts that you saw on the hibiscus flower.
  3. Make a labelled drawing to show the main parts of a flower.

  
  

  Exercise 3.2

  1. Give the meaning of each of these terms.
  a) petiole
  b) pollination
  c) monocotyledon
  2. a) List the functions of leaves.
  b) Describe two ways in which leaves are suited to their functions.
  3. A plant has a tap root, two cotyledons and a flower with eight petals.
  Is this a monocotyledonous or a dicotyledonous plant?

  Topic 1: Biodiversity and classification

  
  

  The external structure of a root system
  The root system of a flowering plant develops from the radicle of the
  embryo in the seed. Most roots are white, cream or brown in colour. They
  do not contain chlorophyll and so cannot photosynthesise.
  There are two main types of root systems.
  • A tap root system consists of a single main root with smaller lateral,
  or side, roots branching from it. Tap root systems are found in
  dicotyledonous plants, for example black jack, carrot and bean. See
  Figure 3.8A.
  • A fibrous root system is made up of many roots that grow
  from one point and that have side roots branching from them.
  Monocotyledonous plants, such as maize and elephant grass, have a
  fibrous root system. See Figure 3.8B.
  

  
  

  Functions of roots
  The main functions of roots are to:
  • hold the plant firmly in the soil
  • absorb water and minerals from the soil
  • transport water and minerals to the stem.
  

  
  

  
  

  Figure 3.8 Root systems:
  a tap root (A) and fibrous
  root (B)

  Experiment 3.5

  Work in groups.
  You will need: specimens or photographs of the following: a bean plant,
  an onion, couch grass or a maize plant, a carrot; a hand lens
  Procedure
  Use the hand lens to observe the different types of root systems in
  the specimens.
  Questions
  1. Suggest two functions of roots.
  2. a) Draw and label the parts of the bean plant’s root system.
  b) What is the function of each part labelled?
  3. Identity the type of root for each plant.
  4. a) What root modifications can you see?
  b) What are the functions of modified roots?

  
  

  Unit 3: The external structure and importance of flowering plants

  Modified roots

  Roots can also be modified to carry out other functions. While most
  roots are underground, sometimes roots grow above the ground for extra
  support, for example maize and sugarcane. These are called prop roots.
  Aerial roots grow above the ground and are used for gaseous exchange.
  This is the exchange of oxygen and carbon dioxide between the inside and
  outside of the root. Many plants that grow in mangroves have aerial roots.
  Prop roots can grow from aerial roots to give the plant extra support; for
  example, maize and sugarcane. Some plants have roots that are used for
  food storage; for example, carrot and sweet potato.
  Some modified roots enable the plant to reproduce asexually.
  Examples include sweet potato and cassava.
  

  
  

  

  Figure 3.9 Examples of modified roots: aerial roots (A), prop roots (B), a storage
  root (C), clasping root (D), buttress root (E), breathing root (F) and stilt root (G)
  

  
  

  Experiment 3.6
  

  
  

  Work in groups.
  You will need: specimens or photographs of the following: prop roots
  of maize or sugarcane; clasping roots of vanilla; aerial roots of Ficus;
  buttress roots of flamboyant tree; breathing roots of white mangrove;
  stilt roots of red mangrove; storage root of carrot or sweet potato;
  a hand lens
  Procedure
  1. Examine the roots of your specimens, and then make a list of all the
  root modifications you can see.
  2. Describe the main features of each root.
  2. Describe how each root type is suited for its functions.
  3. Make labelled drawings of the different root types.
  

  
  

  Topic 1: Biodiversity and classification
  

  
  

  Homework:

  1. Collect at least four plants with different types of root systems.
  2. What type of root system does each plant have?

  
  

  The importance of flowering plants
  

  Flowering plants are important for the following reasons.
  • They are a food source for many organisms.
  • Plants help to maintain a balance of gases in the atmosphere. They
  remove carbon dioxide from the air, and release oxygen into it during
  photosynthesis.
  • They are important food crops for humans, for example, maize, wheat
  and sorghum.
  • They provide shelter for many animals, such as birds and monkeys.
  • Many trees are a source of timber, which is used in construction, to
  make furniture and for firewood.
  • Some plants can be used to make medicines, for example, the quinine
  tree is used in anti-malarial medicines.
  • Some plants, such as cotton, can be used to make fabrics.
  • Plants help to make our surroundings beautiful
  

  
  

  Activity 3.2

  Work on your own.
  1. Find out more about the importance of flowering plants.
  2. Try to find examples of plants in Rwanda that are used for some of the
  things listed above.
  3. Write up your findings as a report, and then hand it in to your teacher
  to be marked.
  

  
  

  Homework
  

  1. Do your own investigation on the importance of flowering plants in
  your own home and community. See if you can think of any more
  functions of flowering plants. Present your findings in a report.
  2. Discuss your report with your group.
  

  Activity 1.1
  

  Research the growing of plants using hydroponics. Find out how this
  practice works, and explore its advantages and disadvantages.
  

  
  

  Unit 3: The external structure and importance of flowering plants
  

  Checklist of learning
  In this unit, I have learnt:

  Flowering plants have flowers, bear fruits and produce seeds.
  Flowering plants consist of roots, stems, leaves and flowers.
  There are two main groups of flowering plants: monocotyledons and dicotyledons.
  The stem is usually green, and it is above the ground.
  The stem holds the leaves and flowers in place, transports water and mineral salts to the leaves,
  transports sugars from the leaves to other parts of the plant, and makes food
  by photosynthesis.
  Some stems are modified for asexual reproduction and food storage.
  Leaves are the main organs of photosynthesis, and they are well adapted for this function.
  Some leaves are modified for water and food storage, and to prevent water loss.
  Flowers are the reproductive organs of flowering plants.
  There are two types of root systems: tap roots and fibrous roots.
  Roots hold the plant in the soil, and absorb and conduct water and mineral salts from the soil into
  the plant.
  Some roots are modified for food storage, extra support and asexual reproduction.
  Flowering plants are important because they balance gases in the atmosphere, provide food
  and shelter for animals, and are food crops; they beautify our environment and can be used in
  construction, to make furniture, medicines and fabrics, and as firewood.
  

  
  

  Peer assessment:

  1. Ask your partner to give the correct word or term for each of these descriptions.
  a) the thin, flat, wide area of a leaf
  b) a root system that has one main root and small lateral roots
  c) plants that have their flower parts in multiples of three.
  2. Draw a picture of a flower, showing all its parts. Then, ask your partner to label
  the picture.
  3. Explain to your partner how a leaf is adapted to enable it to photosynthesise.
  4. Explain to your partner why both eucalyptus and paspalum are used in Rwanda to prevent soil erosion.
  

  
  

  Topic 1: Biodiversity and classification
  

  Formal assessment
  

  1. Identify animals A to H below by using the key.
  

  
  

  

  

  
  

  
  

  
  

  Formal assessment

  KEY
  1. Animal has four legs �������������������������������������������� See 3
  Animal has fewer or more than four legs ��������������������������� See 2
  2. Animal has two long legs ������������������������������ Blue crane
  Animal has eight legs and two pincers ��������������������������� Scorpion
  3. Animal has horns ������������������������������������������ See 4
  Animal does not have horns ���������������������������������� See 5
  4. Horns are straight and pointed ������������������������������� Duiker
  Horns are large and curved ���������������������������������� Buffalo
  5. Animal is covered with fur ����������������������������������� See 6
  Animal is covered with scales ����������������������� Nile monitor lizard
  6. Animal has speckled fur all over its body ��������������������� Mongoose
  Animal has dark fur on some parts of its body �������������������� See 7
  7. Animal has dark fur on its legs �������������������������� Bat-eared fox
  Animal has dark fur on its back and tail �������������� Black-backed jackal
  (8)
  2. What type of plant structure is each of the following?
  (3)
  3. Complete the table by filling in the missing information.

  
  

  Kingdom	Features	Example
  3.1	Have many cells. Need to eat other organisms.	Chimpanzee
  3.2	Can photosynthesise.	3.3
  Fungi	3.4	3.5
  3.6	Are single-celled. Have a nucleus	Amoeba
  Monera	3.7	Bacterium

  (7)
  

  4. a) Make a labelled drawing to show the structure of a flower. (8)
  b) Name two types of root systems. (2)
  c) List three reasons why flowering plants are important. (3)
  5. Find out about biodiversity in Rwanda by researching the following:
  • indigenous plants and animals in Rwanda
  • the names of some endangered species in Rwanda
  • the importance of conservation in Rwanda.
  Present your information as a poster. (14)
  Total marks: 45

  Formal assessment

  
  

  Organisation and maintenance of life

  
  

  Sub-topic Cell structure
  Unit 4 Magnifying instruments and biological drawings
  Unit 5 Plant and animal cells
  Unit 6 Levels of organisation in multicellular organisms
  Sub-topic Nutrition
  Unit 7 Food nutrients and diet
  Sub-topic Gas exchange and smoking
  Unit 8 Structure and functions of human gaseous exchange system
  Sub-topic Co-ordination in plants and animals
  Unit 9 Tropic responses
  Sub-topic Support and locomotion
  Unit 10 Skeletal systems of organisms
  

  
  

  

  
  
• UNIT 4 Magnifying instruments and biological drawings

  Key unit
  competence
  To be able to explain
  the components and
  demonstrate proper
  use and care of a
  hand lens and light
  microscope.

  Cross-cutting issue
  Environment and
  sustainability: Think
  about how you dispose
  of microscopes and
  other old pieces of
  technology. How can
  you do this in a way
  that doesn’t damage
  the environment?

  At the end of this unit, you should be able to:
  • Explain why we need to use magnifying instruments
  • Identify a given unknown specimen
  • Recall that a hand lens is a simple magnifying glass for observing relatively small
  objects
  • Identify the different components of a light microscope and explain their
  functions
  • Recall that microscopes are delicate instruments that need great care
  • Explain that the light microscope has various levels of magnification
  • List the features of a good biological drawing
  • Explain that magnification is the number of times larger an image is than the
  object (specimen) under the microscope
  • Manipulate a hand lens to observe relatively small specimens
  • Manipulate a light microscope to observe various specimens from prepared
  slides
  • Illustrate the biological specimens observed under a light microscope
  • Illustrate well labelled biological diagrams of specimens
  • Compare the relationship between the actual size of the specimen and its image
  • Measure and calculate the magnification of a given specimen
  • Appreciate the need for using a light microscope and a hand lens in observation
  of specimens
  • Show perseverance when making scientific observations
  • Show care and proper use of the magnifying instruments.

  Oral activity
  In your groups, think about what you learnt in previous grades.
  Th en, brainstorm the answers to these questions.
  1. Give two reasons why scientists need to observe things using
  instruments that make these things bigger.
  2. Work out a defi nition of the word ‘magnify’.
  3. Discuss whether you have ever used a magnifying instrument.
  If you have, then describe what you used it for and what you saw.

  Figure 4.2 Microscopes are important  instruments for observation.

  Topic 2: Organisation and maintenance of life

  Why do we need magnifying instruments?

  Biologists make many observations when they work. Observations enable
  them to see the details of living things. Many things are too small for us
  to see using only our eyes, so they need to be made bigger, or magnified.
  There are two instruments that biologists use for this. When they work
  outside the laboratory, they can use a hand lens. Inside the laboratory, they
  can use a microscope.

  Hand lenses
  A hand lens is a magnifying instrument that is held in the hand. We use it
  to look at small things, such as insects, flowers and animal parts, that are
  too big to put on a microscope slide.

  Microscopes
  The first microscope was invented by Robert Hooke in 1665. He used it
  to look at cells. Today, we can use powerful microscopes to see viruses,
  bacteria and cells. There are many types of microscopes.

  

  Figure 4.3 Hand lens

  

  Figure 4.4 The first
  microscope, invented by
  Robert Hooke, in 1665

  Experiment 4.1

  Work in groups.
  You will need: a hand lens; a light microscope; newsprint; moss plants; a
  pencil; paper
  Procedure
  1. Place the lens just above the newsprint, and then look down through
  the lens.
  2. Move the lens closer to your eyes, and then further away from your
  eyes.
  3. Repeat step 2, above, using a moss plant. Identify the small green
  leaves and the tiny transparent rhizoids.
  Questions
  1. How does the image appear when the hand lens is close to the object
  and when it is further away from the object?
  2. Make a simple drawing of a moss plant, and label the structures you
  have identified; for example, the leaves, rhizoids and stem.

  Unit 4: Magnifying instruments and biological drawings

  Parts of a microscope

  In the following experiment, you will learn about the different parts of a
  light microscope and what the function of each part is.

  Experiment 4.2

  Work in groups.
  You will need: a microscope, or you can use the diagram below if your
  school does not have a microscope
  Procedure
  
  1 eyepiece – the lens that
  you look through; it
  usually has 10× or 15×
  power
  2 body tube
  3 nosepiece – holds two or
  more objective lenses; it is
  rotated to change power
  4 objective lenses – lenses
  of different magnification;
  the shortest lens has the
  lowest power; the longest
  lens has the highest
  power
  5 stage clip – holds the
  slide in place
  6 stage – the flat platform
  where you place your
  slides; it can be moved left
  and right to view the slide
  and up and down to focus
  7 diaphragm – a rotating
  disk with holes of different
  sizes; it is used to vary
  the intensity and size of
  the cone of light that is
  projected upwards into the slide

  8 condenser – focuses the
  light onto the slide
  9 light source – bulb or
  lamp; if the microscope
  has a mirror, it is used
  to reflect light from an
  external light source up
  through the bottom of
  the stage
  10 coarse focusing knob –
  brings the specimen into
  focus under a low-power
  objective lens; it cannot
  be used with high-power
  objective lens
  11 fine focusing knob –
  brings the specimen into
  focus under mediumand
  high-power
  objective lenses
  12 light switch – turns the
  light source on

  

  Topic 2: Organisation and maintenance of life

  The functioning of a microscope
  If your school does not have enough microscopes, your teacher will
  demonstrate how to use one correctly.
  Activity 4.1
  Work in pairs or groups.
  1. Carefully carry a microscope to your workbench or desk using both
  hands. One hand should be on the arm of the microscope and the other
  underneath, below the base.
  2. Identify the different parts of the microscope using Figure 4.5, on
  page 42, to help you. Do not touch the surface of the lenses.
  3. Turn the nosepiece so that the objective lens with the lowest
  magnification is in position.
  4. Turn the coarse focus knob and observe what happens to the objective
  lens.
  5. Turn the mirror so that light is reflected through the lens.
  

  Activity 4.2
  Work in the same pair or group you were in for Activity 4.1. Your teacher
  will give you a slide with a specimen on it. Follow these steps to view the
  specimen using your microscope.
  1. Make sure that the lowest power objective lens is in place.
  2. Turn the coarse focus knob until the lens is as far away from the stage
  as possible.
  3. Put the slide onto the stage and clip it in place. Move the slide until the
  specimen is directly under the lens.
  4. Slowly turn the coarse focus knob until the specimen is in focus. You
  can use the diaphragm above the mirror to change the amount of light
  passing through the specimen.
  5. Once the specimen is in focus with one lens, it will be nearly in focus
  with the other lenses. Now you will need to turn only the fine focus
  knob.
  6. Turn the nosepiece so that a more powerful objective lens is in place
  above the slide.
  7. Use the fine focus knob to bring the specimen into focus.

  Unit 4: Magnifying instruments and biological drawings

  How to store a microscope

  Microscopes are expensive instruments that must be used and stored with
  care.
  1. Place the lowest power objective above the stage, and turn the coarse
  focus knob so that the lens is as far away from the stage
  as possible.
  2. Make sure that there is no water on the stage. Use a tissue to clean it if
  there is.
  3. Store the microscope in a box or with a cover over it.

  Experiment 4.3

  Work in groups.
  You will need: a microscope; a hand lens; slides; glycerine; a razor blade;
  pollen grains; cover slips; a needle; forceps or small tweezers;
  a dropper; an onion bulb; iodine solution; a dead fly or mosquito
  Procedure

  Part A

  1. Use the hand lens to look at the insect specimen.
  2. Discuss how much detail you can see.

  
  

  Part B
  You will now prepare a slide for viewing using a light microscope. Look
  at Figure 4.6, on page 45, to help you as you work.
  1. Make sure that the glass slide is clean. Use a tissue to clean it if it is
  dirty. Try to hold the slide on the edges.
  2. Place a small drop of iodine in the centre of the slide (see A in Figure
  4.6).
  3. Use forceps to peel off the thin outer layer that surrounds the fleshy
  white storage leaves of the onion (see B). This layer is the epidermis;
  it is made up of a single layer of cells.
  4. Carefully, use a razor blade to cut off a small piece of the epidermis,
  about one centimetre square.
  5. Place the piece of onion skin in the drop of iodine (see C). Try to
  flatten it against the slide, using the needle.
  6. Hold one side of the cover slip as shown in the diagram, and slowly
  lower it on top of the iodine (see D). Do this carefully to avoid
  trapping air bubbles.
  

  Topic 2: Organisation and maintenance of life

  7. If there is iodine around the slip cover, clean it away using a tissue
  (see E).
  8. Place the slide onto the stage of the microscope (see F).
  Part C
  1. Adjust the microscope to view the specimen (as you learnt to do in
  Activity 4.2).
  2. Make an accurate drawing of what you see.
  3. Make other slides using specimens such as a fly’s wing and pollen
  grains. Use glycerine instead of iodine for these slides.

  

  Figure 4.6 Preparing a specimen for viewing under a microscope
  Questions
  1. List two differences between a hand lens and a microscope.
  2. Give one advantage of using a hand lens and one advantage of using
  a microscope for magnifying specimens.
  3. Explain why you must NOT use the coarse focus adjustment knob
  when the high power objective is in place.

  Care of a microscope
  Microscopes are expensive instruments that can be damaged easily, so it is
  important to handle them with care. These are some of the ways of caring
  for a microscope.
  1. Always place the microscope in its box when it is not in use, or cover it
  with a plastic cover.
  2. Avoid touching any lens surface of the condenser and objectives. Polish
  these regularly using a tissue.

  Unit 4: Magnifying instruments and biological drawings

  Never force the coarse and fine focus adjustments beyond the end of
  their range of movement.
  4. Always carry a microscope by the arm and stand, and use
  two hands.
  5. Keep the stage dry and clean.
  6. Always cover the specimen on the slide with a cover slip, to protect the
  objective lens.
  7. Always move the lens up when focusing, to avoid breaking
  the slide.
  8. Clean the mirror occasionally using a tissue.
  9. Never unscrew the lens components.

  Biological drawings
  Biologists need to make careful and accurate observations. They need to
  record what they see, and so they need to draw accurate biological drawings
  of their specimens. We can learn the skill of drawing biological specimens
  accurately, through practice.
  A good biological drawing should:
  • have a detailed, underlined title at the top of the page
  • have smooth, fairly thin, solid pencil lines made by controlled
  movements of the hand
  • be large enough to show all the parts
  • be neat
  • show the magnification (you will learn about this in the
  next section).

  

  Topic 2: Organisation and maintenance of life

  Magnification
  The magnification of a specimen is a measure of how much bigger it is when
  viewed with a hand lens or a microscope compared with its actual size.
  The magnification of a hand lens is usually written on it. Hand lenses can
  magnify specimens between 2 and 6 times.
  For a light microscope, the magnification of each lens is written on its
  side. It can be written in the form of ‘×40’, or ‘40×’ or simply ‘40’. There are
  two lenses: the eyepiece lens and the objective lens. The total magnification
  of an image through a microscope is calculated
  as follows:
  Total magnification of microscope = eyepiece magnification × objective
  lens magnification

  Worked example: Calculate total magnification
  A learner views a specimen using a microscope with an eyepiece lens that has a
  magnification of 10×. She uses an objective lens of 50×.
  What is the total magnification?
  We use this formula.
  Total magnification = eyepiece magnification × objective lens magnification
  So total magnification = 10 × 50
  = 500×

  Magnification of biological drawings

  When you draw a specimen, you usually also magnify it. Your drawing will
  be bigger than the image that you see through the hand lens or microscope.
  If you have an image or biological diagram of a specimen, you can work
  out how many times it has been magnified. You work with three factors
  when working out the magnification of an object. These are:
  • the image size (how large an image is or how big a drawing of the
  specimen is)
  • the actual size of the specimen (how large it is in the real world)
  • the magnification (how much larger the image size is compared with
  the actual size; how many times the image has been enlarged).
  We use this formula to work out the magnification of a drawing.
  
  In this formula, size could be length or breadth, but the same measurement
  must be taken of both the specimen and the drawing.
  Always include a magnification or scale bar on your drawing.

  Unit 4: Magnifying instruments and biological drawings
  

  Worked example: Calculate magnification of a drawing
  Uwimana measures a bean seed. It is 3 cm long. She makes a biological
  drawing of the seed. The length of the seed in her drawing is 15 cm. By
  how much has the bean seed been magnified?
  

  

  This means that the drawing is five times bigger than the bean
  specimen.

  Exercise 4.1

  1. A leaf measures 4 cm in length. A diagram of the leaf that appears in
  a Biology textbook measures 12 cm. By how much has the leaf been
  magnified?
  2. A group of learners use a microscope to view a cell. The eyepiece lens
  magnifies objects 10× and the objective lens that they use magnifies
  25×. What is the total magnification?

  Homework

  1. Collect two biological specimens. They can be a flower, leaf or plant
  you collected outside the classroom.
  2. Use a hand lens to view your specimens.
  3. Make careful biological drawings of your specimens. Label anything
  you can. Remember to give the magnification of
  your drawing.
  4. Which part of this activity did you find the most difficult? Explain
  what you would do differently if you had to do the activity again.

  Exercise 4.2

  1. Copy Figure 4.7, on page 46, to practise biological drawing.
  2. A learner looks through a microscope using a 20× eyepiece lens and
  a 40× objective lens. What is the total magnification that the learner
  is using?

  Topic 2: Organisation and maintenance of life

  Checklist of learning
  In this unit, I have learned that:
  Biologists use two types of instruments to observe things: hand lenses and microscopes.
  These instruments magnify things, which means that they make them appear larger than their actual
  size.
  A hand lens is often used outside on fieldtrips as it is easy to carry and use.
  Microscopes are used in laboratories, and specimens can be seen at higher magnifications than
  when using a hand lens.
  The different parts in a microscope are designed to make it function properly.
  Biologists need to observe specimens and record their observations by drawing biological drawings.
  The total magnification of a specimen when viewed with a microscope can be calculated by
  multiplying the eyepiece magnification by the objective lens magnification.
  The magnification of a biological drawing of a specimen can be calculated by measuring the size of
  the drawing and dividing it by the actual size of the specimen.

  Self-assessment

  1. Name two types of instruments that can be used to magnify things.
  2. Complete the table.

  Eyepiece magnification	Objective lens magnification	Total magnification
  5×	25×
  10×		100×

  
  
  

  3. Look at the drawing of a bee.                                      4. Provide labels for the micros part A to E.

  If the bee’s actual length is 1,5 cm, how                         
  many times has it been magnified
  in the drawing?                                                       

  

  
  

  
  

  
  

                   

          

  
  

  
  

  
  
  

  
  

  
  

• UNIT 5 Plant and animal cells

  Key unit                                                                                  
  

  To be able to differentiate between
  animal and plant cells using a light microscope.

  Cross-cutting issue
  Standardisation
  culture: When chemical products are purchased, they should be of a high standard or quality. It’s important that they will be disposed of or recycled to avoid harming our environment and human life in general.

  At the end of this unit, you should be able to:
  • Explain the role of a cell in a living organism
  • Describe the structure of a plant and animal cells
  • Identify the diff erent parts of the cell
  • Explain the uses of the various structures seen under the light microscope in
  the plant and animal cell
  • Explain that cells with high rates of metabolism contain large numbers of
  mitochondria for suffi cient energy
  • Organize a science practical setup according to given instructions
  • Prepare slides of human cheek cells and epidermal cells of an onion
  • Explain the diff erences in the structure of plant and animal cells seen under a
  light microscope
  • Demonstrate that plant and animal cells diff er in shape
  • Appreciate the importance of cells in organisms
  • Show perseverance when observing slides of plant and animal cells
  • Pay attention while handling delicate slides and sharp instruments to avoid
  injury.

  Oral activity:

  In your groups, think about what you learnt in the previous unit and earlier
  grades. Th en, brainstorm the answers to these questions.
  1. Arrange these structures in the correct order, starting with the smallest
  structure: tissue,  organ, cell,organism.
  2. What different types of microscopes are available for biologists to use
  to view cells?
  3. How would a biologist choose the type of microscope he or she should use
  to view a cell?

  

  Figure 5.1 A plant cell, as seen under a high-power
                   microscope. 

  Topic 2: Organisation and maintenance of life

  The cell
  Cells are the basic units of all living organisms. Cells are made of molecules
  such water, proteins, carbohydrates and fats. Th ese molecules are made
  up of atoms such as carbon, hydrogen and oxygen. Cells are the building
  blocks of living organisms.
  Some organisms, such as bacteria, are made up of only one cell. Th ese
  are called unicellular organisms (‘uni’ means ‘one’). Other organisms,
  such as humans and trees, are made up of many cells. Th ey are called
  multicellular organisms (‘multi’ means ‘many’).
  Because cells are too small to be seen with the naked eye, scientists
  use microscopes to see the structure of cells. Sometimes they use powerful
  microscopes called electron microscopes to view structures that are too
  small to be seen with a light microscope.

  Hint
  Microscopes are useful for identifying organisms that cause
  diseases in Rwanda

  Structures found in plant and animal cells
  All cells have the same basic structure. Cells contain cytoplasm and
  organelles. Th e cytoplasm is a living, jelly-like substance in which the
  organelles are found. Many chemical reactions take place inside the
  cytoplasm. It is made mainly from water, in which substances such as
  sugars and gases are dissolved. Th e organelles in the cytoplasm carry
  out special functions inside the cell. Examples of organelles include the
  nucleus, chloroplasts and mitochondria. A cell membrane surrounds the
  cytoplasm.

  Figure 5.2 shows typical plant and animal cells and their organelles.

  

  
  Unit 5: Plant and animal cells

  Experiment 5.1
  Work in groups.
  You will need: a microscope; prepared slides of onion epidermis and
  human cheek cells; drawing paper
  Procedure
  1. Look at Activity 4.1, on page 43, to remind yourself how to use a
  microscope to view specimens.
  2. View the prepared slides that your teacher will give you.
  3. Make careful drawings of the two different types of cells using
  Figure 5.3, below, to help you. Only draw the structures that you
  can see on the slide.

  Questions
  1. Mention two things that you did to ensure that you avoided any
  injuries whilst doing this activity.
  2. How do the two types of cells differ in shape?
  3. Which structures are present in the onion cells but absent in the
  cheek cells?
  4. What was the total magnification that you used to view
  these specimens?

  

  

  Figure 5.3 A micrograph of an onion epidermis (A) and human cheek cells
  (B), as seen under a light microscope

  Topic 2: Organisation and maintenance of life

  Unit 5: Plant and animal cells 53
  

  There are many different types of plant and animal cells. Although they all
  have slightly different structures (depending on their functions), they all
  have these organelles:
  • cell membrane
  • nucleus
  • mitochondria
  • vacuole
  • cytoplasm.

  Cell membrane
  The cell membrane surrounds the cytoplasm and keeps the cell contents
  in place. It is selectively permeable, which means that it can control the
  movement of substances into and out of the cell.
  Nucleus
  The nucleus is the control centre of the cell. It is easily seen inside the cell.
  The nucleus is round and found near the centre of an animal cell and on the
  side of a plant cell.

  

  Figure 5.4 The nucleus, as seen using an electron microscope,
  is the control centre of the cell.

  The nucleus plays an important role when the cell divides to make new
  cells. It contains the hereditary, or genetic, information that is passed from
  parents to their offspring during reproduction.

  Unit 5: Plant and animal cells

  Mitochondria
  Mitochondria (singular = mitochondrion) are the organelles inside plant
  and animal cells where the reactions of cellular respiration take place.
  Energy that the cell can use is made in the mitochondria. Some cells,
  depending on their function, have more mitochondria than others. For
  example, muscle cells (which need a lot of energy to work) have several
  thousand mitochondria.
  Vacuoles
  Vacuoles are organelles that usually contain fluid. They are surrounded by
  a membrane. Animal cells have small vacuoles or no vacuoles. The fluid
  in animal vacuoles often contains substances such as enzymes, or stored
  food or waste products. Plant cells have large vacuoles that take up a lot of
  space inside the cell. Plant vacuoles usually contain water and dissolved
  substances, such as mineral salts and food molecules. Plant vacuoles are
  important for keeping the cell rigid.
  Activity 5.1
  Work in pairs.
  Use the library or the Internet to find out about the structure and the
  functions of each of the following cell organelles: nucleus, mitochondrion,
  ribosome, Golgi body, endoplasmic reticulum, lysosome and chloroplast.

  Exercise 5.1
  1. Define each of these terms:
  a) unicellular
  b) multicellular
  c) organelle
  2. Give one example each of a unicellular and a multicellular organism.
  3. What is the function of each of the following?
  a) the cell membrane
  b) the nucleus
  4. Which organelle in the cell makes energy?
  5. a) What is sometimes stored inside vacuoles?
  b) What is the difference between the vacuoles found in animal
  cells and those found in plant cells?

  Topic 2: Organisation and maintenance of life

  Structures that are found only in plant cells
  Two important structures are found in plant cells but not in animal cells:
  cell walls and chloroplasts.
  Cell wall
  The cell wall is a rigid structure found around the outside of plant cells. It is
  not living, and it is made up of a substance called cellulose.
  The cell wall gives the plant cell its shape. Because the cell wall is rigid, it
  protects the contents of the cell. It is fully permeable, which means that
  substances can move freely into and out of the cell through the cell wall.
  Chloroplasts
  Chloroplasts are the organelles found in plant cells that carry out the
  process of photosynthesis. They contain a green pigment called chlorophyll.
  Chloroplasts are also found in the cells of algae and
  some bacteria.

  Exercise 5.2
  1. a) What is the function of the cell wall in plants?
  b) What substance is the cell wall made of?
  2. a) What is the function of chloroplasts?
  b) What pigment is found inside chloroplasts?

  Differences in the structure of plant and animal cells
  Although plant and animal cells have many features in common, there are
  some obvious differences. Table 5.1 lists the main differences between plant
  and animal cells.

  Table 5.1 The main differences between plant and animal cells

  	Plant cell	Animal cell
  Shape	• Have cell walls • The cell wall is rigid and has a fixed shape	• Do not have cell walls • Because there is no cell wall, they vary in shape
  Chloroplasts	Contain chloroplasts, which are used for photosynthesis	Animals do not photosynthesise, so cells do not have these organelles
  Vacuoles	Have a large, central vacuole	Have no vacuoles or one or more small vacuoles (which are much smaller than plant vacuoles)

  Unit 5: Plant and animal cells

  Homework

  Copy this table, and then complete it.

  
  

  	Plant cell	Animal cell
  Shape
  Outer covering
  Organelles
  Vacuoles

  
  Checklist of learning
  In this unit, I have learned that:

  Cells are the basic units of life; they are the building blocks of living organisms.
  Some organisms consist of only one cell (unicellular), whilst other are made up of many cells
  (multicellular).
  We can view cells using either a light microscope or an electron microscope.
  All cells contain cytoplasm and organelles such as a nucleus, mitochondria, a cell membrane and
  vacuoles.
  The cytoplasm is a jelly-like substance in which the organelles are found inside the cell.
  The cell membrane surrounds the cytoplasm and controls what goes in and out of the cell.
  The nucleus is the control centre of the cell and contains hereditary material.
  Mitochondria are the organelles in the cell where energy is made; cells that need more energy, such
  as those found in muscles, have more mitochondria.
  Vacuoles are membrane-bound organelles that contain fluid; plants have large vacuoles and animals
  have no vacuoles or small vacuoles.
  Only plant cells have a cell wall, which gives the cell a rigid shape and allows substances to pass in
  and out of the cell.
  Chloroplasts are organelles in plant cells where the reactions of photosynthesis take place.

  Topic 2: Organisation and maintenance of life
  

  Self-assessment

  1. Match the organelles in Column A with the correct function in Column B.

  Column A	Column B
  1.1 Nucleus	A. Living, jelly-like fluid in which reactions take place inside the cell
  1.2 Mitochondria	B. Control centre of the cell
  1.3 Cell wall	C. Produces energy
  1.4 Cell membrane	D. Controls what goes in and out of the cell
  1.5 Chloroplast	E. Photosynthesis takes place here
  1.6 Cytoplasm	F. The rigid structure on the outside of plant cells that keeps the shape of the cell

  2. Give the meaning of each of these terms.
  a) permeable   c) enzymes
  b) hereditary   d) photosynthesis

  3. Draw a table to show the differences between a plant and an animal cell. Include these headings: Shape, Outer covering, Organelles, Vacuoles.

  
  
  
• UNIT 6 Levels of organisation in multicellular organisms

  Key unit
  competence
  To be able to explain specialisation of cells, and the link between levels of organisation
  in multicellular organisms

  Cross-cutting issue

  Comprehensive sexuality education: Understanding what healthy cells are and how they function in
  the body, enables us to live a happy, healthy life.

  At the end of this unit, you should be able to:
  • Recall that a cell is a basic structure of an organism
  • Describe the diff erent types of cells in this unit and state their functions
  • Describe the diff erent cell structures found in animals and plants and how
  they relate to their functions
  • Identify diff erent levels of organisation in multicellular organisms
  • Observe and illustrate diff erent types of cells and tissues under light
  microscope or micrographs
  • Categorize plant and animal tissues using observation of micrographs or
  slides
  • Illustrate well labelled structures of xylem and phloem tissue from slides or
  micrographs of sections of vascular plants
  • Sequence the levels of organization of multicellular organisms from the
  simplest to the most complex
  • Diff erentiate the relationship between the structure and function of
  specialised cells
  • Appreciate the complexity of life from the tiny cell through to the tissue,
  organ, system and organism levels of organisation
  • Be aware that an organism is a complex organisation of cells, an important
  unit of life.

  Oral activity

  
  

  Figure 6.1 Red blood cells are part of blood and are specialised
  to transport oxygen.
  

  In pairs, think back to what you learnt in the last two units. Th en, brainstorm the answers
  to these questions.
  1. Why is the cell referred to as the ‘basic
  unit of life’?
  2. Are all cells the same? If not, in what
  ways are they diff erent?
  3. What structures do plant cells have to
  help them carry out photosynthesis?
  4. Are all organisms made up of many
  cells? What do we call single-celled
  organisms? What do we call organisms
  that consist of many cells? Give an
  example of an organism that has many
  cells in its body.

  Topic 2: Organisation and maintenance of life

  Cell specialisation
  In the previous unit, you learnt about plant and animal cells. Not all cells
  look the same or work in the same way. Th ere are many different types
  of cells and each type can carry out different functions. For example, in
  animals, cells in muscles are specialised to bring about movement. These
  cells contain lots of mitochondria so that they can make energy for the
  muscles to work.
  Blood cells in animals are another specialised type of cell. They
  transport oxygen. A plant’s leaf cells are specialised to perform
  photosynthesis, whereas its root cells are adapted to take in water and
  nutrients from the soil. Th e cells are able to do these different functions
  because they are slightly different in structure from one another.
  In this unit you will find out more about some specialised cells in
  animals and in plants. You will also learn how their structure is linked to
  their functions.
  

  Hint
  Understanding how our bodies are made up can be useful in health related careers
  in Rwanda.

  Examples of some specialised animal cells
  In this section, we look at examples of different types of animal cells
  whose structures have been adapted to enable them to perform different
  functions.

  Ciliated cells
  Ciliated cells have tiny hair-like structures, called cilia, on their surfaces.
  Th ere are also other specialised cells, called goblet cells, amongst the
  ciliated cells. Goblet cells make a substance called mucus.
  Ciliated cells line the surfaces of some parts of the body, such as the air
  passages. Air passages take air to and from the lungs. Th e cilia trap dust
  particles and stop them from going into the lungs. Mucus from the goblet
  cells also traps dust.
  Ciliated cells are also found in the female reproductive organs. You will
  learn about their function in this part of the body later on.

  

  Nerve cells
  Nerve cells, or neurons, are specialised to conduct nerve impulses in the
  nervous system. They carry information from one part of the body to
  another part.
  Nerve cells are long and thin, and are grouped together in bundles
  to form nerves. Their shape makes them suitable for conducting nerve
  impulses over long distances.

  

  Unit 6: Levels of organisation in multicellular organisms

  Red blood cells
  Red blood cells are specialised cells that are found in the blood. They
  transport oxygen around the body.
  Red blood cells are small and have an unusual shape. They are referred to
  as biconcave discs. This shape gives them a large surface area on which oxygen
  molecules can bond. Red blood cells do not have a nucleus. They are packed
  full of a special substance called haemoglobin. Haemoglobin attracts oxygen
  molecules, which makes red blood cells well suited for carrying oxygen around
  they body. The cells are elastic, so they can easily squeeze through narrow
  tubes in the blood system.

  Exercise 6.11. Give the meaning of each of these words.
  a) specialised c) neurons
  b) cilia d) haemoglobin
  2. a) What is the function of ciliated cells?
  b) List two ways in which ciliated cells are adapted to
  their function.
  3. a) What is the function of red blood cells?
  b) List two ways in which red blood cells are suited to
  their function.
  c) Make a neat, labelled drawing of some red blood cells.

  Sperm cells
  Sperm cells are male sex cells. They are made inside the male reproductive
  system in structures called the testes.
  Sperm cells are specialised for joining, or fusing, with
  the female sex cell, the egg. Sperm cells have a tail, called a
  flagellum, which they use to swim. Because sperm cells can
  move, we say that they are motile. There are large numbers
  of mitochondria in the middle region of a sperm cell. These
  mitochondria make energy to help the flagellum to move.
  The flagellum enables the sperm cell to swim towards the
  egg when it is inside the female reproductive system.
  In the head of the sperm, there are special enzymes
  inside the acrosome. These enzymes break down the
  membrane around the female egg cell. The sperm nucleus
  contains genetic material. The nucleus enters the egg
  cell and fuses with the nucleus of the female egg during
  fertilisation.

  

  Topic 2: Organisation and maintenance of life

  Egg cells
  Egg cells are female sex cells. They are also called ova (singular = ovum).
  They are produced in the ovaries of the female reproductive system.
  Egg cells are large cells that have a large nucleus, and they can be seen
  with the naked eye. The cytoplasm contains many nutrients. Each egg cell
  has a special cell membrane that allows only one male sperm cell to pass
  through it. There is genetic material in the egg’s nucleus. The egg and sperm
  nuclei fuse to form a single cell,
  called a zygote.

  

  Exercise 6.2

  1. Give the meaning of each of these words.
  a) flagellum
  b) motile
  c) acrosome
  d) zygote
  2. a) What is the function of sperm cells?
  b) List three ways in which sperm cells are suited to
  their function.
  c) Make a neat, labelled drawing of a sperm cell.
  3. a) What is the function of egg cells?
  b) What happens when a sperm cell meets an egg cell?
  c) How is the egg cell suited to its function?

  Unit 6: Levels of organisation in multicellular organisms

  

  Unit 6: Levels of organisation in multicellular organisms

  Xylem cells
  Xylem cells are sometimes called xylem vessels. They transport water
  up from the roots to the other parts of the plant.
  Xylem cells are non-living cells. The end of each cell has holes in
  its wall and the cells are arranged one on top of the other, to form a
  long narrow tube. These tubes, rather like long straws, are ideal for
  transporting water.
  Phloem cells
  Phloem is a living tissue. It transports food made by the leaves during
  photosynthesis to all parts of the plant. Figure 6.8 shows the difference
  between the xylem and phloem. In the xylem, water flows in one
  direction only from the roots to the leaves. In the phloem, the food
  flows in both directions.
  Mesophyll cells
  Most cells inside a leaf are found between the upper and lower
  surfaces. (see Figure 6.9). This region of the leaf is called the mesophyll.
  Mesophyll cells are specialised for photosynthesis, which is their main
  function. Look at the diagram below, which shows the inside of a leaf.
  There are two types of mesophyll cells and they are found in
  different places in the mesophyll. These cells are called palisade
  mesophyll cells and spongy mesophyll cells. Palisade mesophyll cells
  are long, thin cells which are full of chloroplasts. They are found near
  the upper surface of the leaf. It is easy for them to trap lots of light in
  this position. Spongy mesophyll cells also have lots of chloroplasts and
  they are loosely packed in the leaf. This makes it easy for gases, such as
  carbon dioxide, which is needed for photosynthesis, to move into and
  out of these cells.

  

  

  Topic 2: Organisation and maintenance of life

  Unit 6: Levels of organisation in multicellular organisms 63

  Exercise 6.3
  1. Draw a mind map to show what you have learnt about these animal
  cells: ciliated cells, red blood cells, nerve cells, sperm cells, egg cells.
  Refer to pages 59 to 61 for help.
  2. Draw a mind map to show what you have learnt about these plant
  cells: root hair cells, xylem cells, mesophyll cells. Refer to pages 61
  and 62 for help.

  Experiment 6.1
  Work in groups.
  You will need: a microscope; prepared slides or micrographs
  Procedure
  1. Use a microscope to look at the prepared slides of different tissues
  that your teacher will give you. Remember the rules for using a
  microscope. If your school does not have slides, use the micrographs
  that your teacher gives you.
  2. Identify the tissues shown in the slides/micrographs. Decide which
  slides/micrographs show plant tissue and which show animal tissue.
  Discuss the reasons for your choice in your group.
  3. Can you identify specialised cells in the tissue specimen?
  4. Draw labelled biological diagrams of each tissue specimen in the
  slides/micrographs.

  Organisation in multicellular organisms
  There are four levels of organisation in multicellular organisms such as
  plants and animals: cells, tissues, organs and organ systems. An organism
  is made up of many organ systems which enable it to function for life.
  Cells
  These are the most basic units of life. There are many different types
  of cells in a multicellular organism. They are specialised to do a
  certain function.

  Unit 6: Levels of organisation in multicellular organisms

  Tissues
  In multicellular organisms, similar cells are grouped together to form
  tissues. A tissue is a group of specialised cells that have a similar structure
  and function. For example, muscle tissue is composed of muscle cells,
  which function to help the animal move, by contracting and relaxing.
  Examples of tissues in plant leaves are xylem, phloem and mesophyll.
  As you have learnt, xylem is made up of xylem cells, which are able to
  transport water. Phloem transports food in the plant. Xylem and phloem
  are found in leaf veins. Mesophyll tissue is made up of mesophyll cells and
  makes food.
  Organs
  Organs are structures that are made up of tissues. For example, your
  stomach is an organ for digesting your food. A particular organ may
  contain several different tissues. For example, your stomach contains
  muscle tissue (for mixing up the food) as well as glandular tissue (which
  produces digestive juices). Animal organs include the skin, heart, liver,
  brain, lungs and kidneys. Roots, stems, flowers, leaves and fruits are plant
  organs.
  Organ systems
  Organ systems are the highest level of organisation. A system consists
  of several organs working together to perform a function of life. For
  example, your digestive system consists of your stomach and your intestines
  (amongst other organs), which function to digest your food. In plants, the
  leaves, stems and roots work together to form a transport system.

  

    Topic 2: Organisation and maintenance of life

  

  Figure 6.11 Levels of organisation of a multicellular plant organism: cell, tissue,
  organ, organ system

  Homework
  1. Define each of these words.
  a) cell
  b) tissue
  c) organ
  d) organ system
  2. Give an example for each of the words in question 1.
  3. Make a simple drawing showing organisation in multicellular
  organisms. Use Figure 6.10, on page 64, and Figure 6.11, above,
  to help you.
  4. Name two animal tissues and two plant tissues.

  Advantages of specialisation of cells
  Specialisation of cells occurs only in multicellular organisms and not in
  unicellular organisms.
  Cell specialisation gives these advantages to multicellular organisms.
  • It enables them to grow bigger.
  • It enables them to carry out complex processes. Different cells carry out
  different functions.
  • Specialised cells can work together to form tissues, organs and organ
  systems.

  Exercise 6.4
  1. Arrange these structures in the correct order, starting with the
  smallest.

  
  

  organ	tissue	cell	organ	system organ

  
  2. Give definitions for each of these words.
  a) specialisation
  b) permeable
  c) zygote
  d) motile

  Topic 2: Organisation and maintenance of life

  Checklist of learning
  In this unit, I have learned that:
  In multicellular organisms, cells are specialised to perform certain functions.
  Examples of specialised cells in animals include ciliated cells, nerve cells, red blood cells, sperm cells
  and egg cells; examples in plants include root hair cells, xylem cells and mesophyll cells.
  A group of similar cells is called a tissue.
  Plant tissues, such as mesophyll tissue and xylem and phloem tissue, consist of similar cells that are
  structurally adapted to their functions.
  Mesophyll tissue in the leaves contains cells with lots of chloroplasts, where the reactions of
  photosynthesis take place; xylem tissue transports water around the plant.
  Animal tissues, such as muscle tissue, consist of similar cells that work together to perform a
  function.
  Organs consist of many tissues that work together to do a certain function.
  Animal organs include the skin, heart, liver, brain, lungs and kidneys; plant organs include roots,
  stems, flowers, leaves and fruits.
  An organ system consists of many organs working together, for example, the digestive system in
  animals and the transport system in plants.
  The specialisation of cells in multicellular organisms gives them advantages over unicellular
  organisms.

  Peer assessment

  Complete the questions, and then swap your answers with a friend for marking.
  1. What is another name for nerve cells?
  2. Which organelles are found in high numbers in muscle cells? Why is this so?
  3. Explain the functions of each of these cells: a) red blood cells b) xylem cells.
  4. Look at the micrographs, and then answer these questions.
  a) Identify each type of cell
  shown in pictures A to D.
  b) Identify each type of cell
  as either an animal cell or
  a plant cell.
  c) Give one function for each
  type of cell.
  d) Explain how cell D is
  suited to its function

  A B

  CD

• UNIT 7 Food nutrients and diet

  Key unit
  competence
  To be able to analyse the different food nutrients and their significance to the
  human body.

  Cross-cutting issue
  Peace and values
  education:

  When you are working in pairs or as a group during an activity, work in unity and respect each
  other’s point of view.

  At the end of this unit, you should be able to:
  • Explain the importance of the classes of foods
  • List the main sources of food nutrients
  • List the chemical elements that make up carbohydrates, fats and proteins
  • Explain that large molecules consist of smaller molecules joined together
  • State that a balanced diet is eating a variety of foods containing all the
  nutrients and in the correct proportions
  • Explain that people have different dietary needs, dependant on age, gender
  and activity levels including pregnant and breastfeeding mothers
  • Explain the effects of malnutrition
  • Explain that obesity is the build-up of excess fat in the body due to excess
  intake of calories
  • Apply knowledge of deficiency symptoms to identify the different deficiency
  diseases among individuals
  • Test for carbohydrates, proteins and lipids in different food samples
  • Demonstrate the different functions of water, mineral salts and vitamins in the
  body
  • Acknowledge the importance of having a balanced diet and its relation to age
  and gender
  • Appreciate the need for a specific diet for individuals who carry out strenuous
  activities like sports and manual labour.
  • Take care when using reagents to test for food types
  • Appreciate the myths and values communities attach to certain foods
  • Adopt and develop healthy eating habits by eating a balanced diet.

  

  Figure 7.1 Healthy food means healthy people.

  Oral activity
  In groups, answer these questions.
  1. Make a list of your favourite foods
  or the foods you usually eat.
  2. Can you think of the nutrients that
  these foods contain?
  3. Try to work out the functions of
  each of these food nutrients.

  Topic 2: Organisation and maintenance of life

  Food nutrients
  Nutrients are chemical substances that organisms need to live. In Unit 1 you
  learnt that all living things need nutrition in order to live. Animals get their
  nutrients from the food they eat. Plants get their nutrients from the air,
  water and soil.
  Food nutrients give organisms:
  • energy for daily activities
  • the building blocks for growth and cell repair
  • substances that enable the organisms to function properly and stay
  healthy.
  There are six types, or classes, of food nutrients: carbohydrates, proteins,
  lipids (fats and oils), vitamins, mineral salts and water. Food nutrients are
  made up of elements such as carbon, hydrogen and oxygen, and sometimes
  nitrogen, phosphorus and sulphur.
  Sources of food nutrients
  Table 7.1 shows sources of food nutrients for human beings.
  Table 7.1 Sources of nutrients

  Food nutrients	Foods
  Carbohydrates (sugars and starches)	Bread, pasta, potatoes, cassava, maize, sorghum, rice, fruits, sweets, sugar
  Lipids (fats and oils)	Nuts, fish oils, meat, milk, butter, cheese, cooking oil
  Proteins	Meat, milk, chicken, fish, eggs, groundnuts, soya beans, seeds
  Vitamins	Fruits, vegetables, meat, fish, milk, wholegrain cereals, nuts
  Mineral salts	Salt, milk, meat, fruits, fish, eggs
  Water	Drinking water, fruit and vegetable juices, food

  
  

  Sources of nutrients.

  

  Unit 7: Food nutrients and diet

  Activity 7.1
  Working in pairs, answer these questions.
  1. Identify the nutrients present in the food sources A and B.

  AB

  Figure 7.2 Sources of food.

  2. Keep a journal of the food that you eat over a week. Bring the list to
  school, and discuss it with your partner.
  a) Is your list of foods similar to your partner’s list? If it is not, how is
  it different?
  b) Did your list of foods change during the week? If it did, explain
  why.
  c) Were any of the food nutrients missing from your lists?

  Carbohydrates
  Carbohydrates are nutrients made up of the elements carbon (C),
  hydrogen (H) and oxygen (O). Some carbohydrates, such as glucose, are
  small, simple molecules. Other carbohydrates, such as starch and cellulose,
  are large, complex molecules.
  Simple sugars such as glucose are the basic units of all carbohydrates.
  We call these units sugars, or monosaccharides (‘mono’ means ‘single’ and
  ‘saccharide’ means ‘sugar’). Examples of monosaccharides include glucose
  and fructose. Monosaccharides can join together to form disaccharides; for
  example, sucrose. Polysaccharides, such as starch, are made up of many
  single units (‘poly’ means ‘many’).

  Topic 2: Organisation and maintenance of life

  Figure 7.3 shows how polysaccharides are formed.

  

  Figure 7.3 Formation of large carbohydrates.

  Starch is an important storage carbohydrate in plants. Glycogen is an
  important storage carbohydrate in animals. It is stored in the muscles and
  liver. Cellulose is another large carbohydrate. It is found in plant
  cell walls.

  Lipids
  Lipids are fats and oils. Fats are lipids that are solids at room temperature.
  They are used mainly to store energy in the bodies of living things. Like
  carbohydrates, lipids are made of the elements carbon (C), hydrogen (H)
  and oxygen (O). Lipid molecules consist of one molecule of glycerol joined
  to three long fatty acid molecules.

  

  Figure 7.4 A lipid molecule consists of a glycerol molecule joined to three fatty
  acid molecules.

  Proteins
  Proteins are nutrients made up of the elements carbon (C), hydrogen (H),
  oxygen (O) and nitrogen (N). Some proteins also contain the element
  sulphur (S). Proteins are large molecules that consist of chains of smaller
  molecules called amino acids. There are over 20 different types of amino
  acids. They can be joined in different combinations to make many different
  proteins.

  

  Unit 7: Food nutrients and diet

  The importance of food nutrients
  Table 7.2 shows the importance of the different food nutrient groups.
  Table 7.2 Food nutrient groups and their importance

  Food nutrients	Importance
  Carbohydrates (sugars and starches	• Provide the body with energy
  Lipids (fats and oils)	• Provide energy • Help with absorption of fat-soluble vitamins A, D, E and K • Form a layer beneath the skin that insulates the body and reduces heat loss • Form a layer around organs to provide protection from injury
  Proteins	• Needed for growth • Needed for repair of damaged tissues • Needed for producing the enzymes required for chemical reactions in the body
  Vitamins	Needed in small amounts for different functions in the body, for example: • Vitamin C is needed to fight infections and heal wounds, and for healthy bones, teeth, skin and gums • Vitamin D helps the body to absorb calcium from food, which is needed for healthy bones and teeth
  Mineral salts	Needed in small amounts for many different functions in the body, for example: • Iron is needed to make haemoglobin, a substance in red blood cells that transports oxygen around the body • Calcium is needed for strong bones and teeth
  Water	• Needed for chemical reactions in the cells • Keeps body temperature constant • Helps the movement of joints • Helps digestion of food • Helps to remove poisonous substances from the body

  
  Food tests
  We can test for the presence of food nutrients in different foods. In the next
  activity, you will work in groups to find out whether food samples contain
  carbohydrates, proteins or fats. You will use chemicals called reagents to do
  this. Remember to work carefully while doing these experiments.

  Topic 2: Organisation and maintenance of life

  Experiment 7.1
  Tests for carbohydrates, proteins and lipids.
  You will need: some bread, maize porridge or other complex carbohydrate;
  test tubes; a white tile; droppers; iodine solution; cooked chicken; meat or
  egg; butter; water; nuts (crushed); sodium hydroxide solution; copper
  sulphate solution; ethanol; test tube racks; permanent markers; test strips
  for testing proteins, fats and glucose (if your school has these)
  Procedure
  Part A
  1. Copy the table below. You will need this to record your results.

  		Colour change
  Food sample	Iodine	Biuret test	Ethanol
  1. Bread
  2. Maize porridge
  3. Chicken
  4. Meat
  5. Egg
  6. Butter

  
  2. Set up your test tubes in a test tube rack. For each test, you need to
  test all your food samples. Use the marker pen to label each test tube
  with the number that matches the table.

  Part B

  Starch is a carbohydrate. We can easily test for its presence in a food
  sample by using iodine.
  1. Put a small piece of
  each food sample
  into a test tube or
  onto a white tile.
  2. Use a dropper and add
  two drops of iodine to
  each food sample.
  3. Observe what happens,
  and then record any
  colour changes in
  the table.

  

  Figure 7.6 Test for carbohydrates

  Unit 7: Food nutrients and diet

  Part C
  We test for proteins in a food sample by using the Biuret test. If proteins
  are present in the food, it will turn purple when we add sodium
  hydroxide solution (colourless) and copper sulphate solution (blue) to
  the sample. If there are no proteins in the food, the sample will remain
  blue.
  1. Put a small piece of each food
  sample into a test tube and add
  some water.
  2. Use a dropper to add about
  20 drops of sodium hydroxide
  solution to the test tube.
  3. Use another dropper to add
  about 2 drops of copper sulphate
  solution to the test tube.
  4. Gently shake each test tube.
  5. Observe what happens, and then
  record any colour changes in
  the table.

  

  Figure 7.7 Test for proteins.

  Part D
  We test for lipids by using organic
  solvents such as ethanol. If lipids
  are present, they will dissolve in
  the ethanol. When water is added
  to the ethanol, the water will
  turn milky.
  1. Put a small piece of each food
  sample into a test tube and add
  some ethanol. Shake the test tube
  well and then allow the contents
  to settle.
  2. Add the same amount of water to
  the test tube and shake it well.
  3. Observe what happens, and then
  record what you see.

  

  Figure 7.8 Test for lipids.

  Questions
  1. Make a list of the foods that you tested that contained carbohydrates,
  proteins and lipids. Some food samples may contain more than one
  nutrient.
  2. Did you take any precautions when you were doing these tests?
  3. Is there anything that you would change if you did the tests again?

  Topic 2: Organisation and maintenance of life

  A balanced diet
  A person’s diet consists of all the foods and liquids that he or she eats and
  drinks. A balanced diet gives us all the nutrients we need in the right
  amounts, as well as enough energy for our body to function well. The
  amount of energy we need is measured in kilojoules (kJ).

  

  Figure 7.9 A balanced diet includes foods from all five food groups.

  You have learnt about the groups of food nutrients your body needs to stay
  healthy. Your body needs different amounts of each food nutrient. The ‘pie
  chart’ in Figure 7.9 shows the relative amounts of each food group that we
  need for a balanced diet. Water is also an essential part of a balanced diet.

  Unit 7: Food nutrients and diet

  Table 7.3 describes the importance of each food group and gives the
  proportion each group should make up in the diet.
  Table 7.3 Food groups and their percentages in the diet

  Food group	Importance	Examples	% of diet
  Carbohydrates	Provide energy for growth and development. Wholegrain forms are best because they provide extra fibre.	Bread, maize and cassava	33%
  Fruits and vegetables	These foods provide vitamins and minerals needed for a healthy immune system. They also provide fibre. You should aim to eat five portions of these foods per day.	Bananas, spinach and tomatoes	33%
  Dairy foods	These foods provide fat for energy, protein for muscle and nerve development, calcium for bone development and vitamins for fighting infections.	Milk, yoghurt and sour milk	15%
  Non-dairy proteins	These foods provide protein needed for muscle and nerve development, and for tissues to repair after infections.	Meat, eggs, beans	12%
  Foods high in sugar or fat	These foods should be limited to prevent excessive weight gain or problems with blood sugar.	Cakes, biscuits, fried foods,chocolate and cooldrinks	7%

  
  Activity 7.2
  Work in pairs.
  The amount of energy different people need is shown in the bar chart in
  Figure 7.10. Look at the chart, and then answer the questions.

  

  Figure 7.10 The amount of energy needed by different people

  1. Which person needed:
  a) the most energy b) the least energy?
  2. Explain your answers to question 1.

  Topic 2: Organisation and maintenance of life

  Balanced diets for different people
  In Activity 7.3 you saw that different people need different amounts
  of nutrients and energy. A person’s needs depend on their age, gender,
  level of activity and whether or not the person is ill. For example, males
  need more energy per day than females of all ages, and people with very
  active jobs need more energy than people who stay seated all day.
  Young people
  Children grow quickly and are very active, so they need a diet that provides
  lots of food nutrients and energy. When they reach their teenage years,
  they have times of rapid growth called growth spurts, when extra nutrients
  and energy are needed. A balanced diet for a school child should contain
  similar proportions of foods to those shown in Figure 7.9 (see page 75), but
  in amounts that provide them with enough energy. The child should also
  drink plenty of water.

  Pregnant and breastfeeding women
  Pregnant and breastfeeding women need more energy per day than the
  average adult woman. A pregnant woman needs extra nutrients and energy
  for the healthy growth and development of her baby.
  A balanced diet for a pregnant woman should contain similar
  proportions of foods to an average adult woman, but should include extra
  fruits and vegetables, dairy foods, non-dairy proteins and water.
  A breastfeeding woman needs extra energy and nutrients to make
  breast milk. Her diet should contain similar proportions of foods to an
  average adult woman, but with extra carbohydrates, dairy foods, non-dairy
  proteins and water.
  Sports players
  People who play sport need extra energy for their sporting activities. They
  also need extra nutrients to build and repair their muscles and to replace
  the minerals lost in their sweat. A balanced diet for people who play sport
  should contain similar proportions of foods to a healthy man or woman,
  but should include extra carbohydrates and non-dairy proteins, as well as
  extra water and other fluids.

  Unit 7: Food nutrients and diet

  Nutritional disorders
  A nutritional disorder is also called malnutrition. It happens when a
  person’s body has either too little or too much of a certain food nutrient.
  As a result, their body does not grow or function properly. Examples of
  nutritional disorders include deficiency diseases, starvation, obesity and
  constipation.
  There are many reasons for malnutrition. It can be caused by poverty,
  where people are either too poor to buy enough food, or can only buy cheap
  food that does not provide all the nutrients they need. Malnutrition can
  also be caused by poor food choices and poor cooking methods.

  Deficiency diseases
  Deficiency diseases occur when a person has too little of a vitamin or
  mineral. Examples of deficiency diseases include scurvy, rickets and
  anaemia.

  

  Figure 7.12 The gums and teeth of a person with scurvy
  

  

  Table 7.4, on page 79, shows the causes, symptoms and prevention of some
  deficiency diseases.

  Topic 2: Organisation and maintenance of life

  

  Starvation Starvation occurs when a person does not eat enough food. There are  two forms ofstarvation: marasmus and kwashiorkor.
  Marasmus is caused by not eating enough of almost all nutrients, but especially energy-rich foods such
  as carbohydrates, fats and proteins. Marasmus causes extreme loss of body fat and muscle. A sufferer
  of marasmus is very thin. Other symptoms of marasmus include lack of energy, severe hunger and
  swelling of the hands and feet. Kwashiorkor occurs when a person’s diet does not include enough proteins, vitamins and minerals. Mainly children are affected. Sufferers have a swollen stomach, while
  the rest of their body is very thin and has little muscle. Other symptoms
  of kwashiorkor include changes in hair colour, skin rashes, swollen hands and feet, and loss of appetite.

  

  Unit 7: Food nutrients and diet

  

  Figure 7.15 Obesity can lead
  to serious health problems.

  Obesity
  Obesity is caused by eating a diet that contains
  too many energy-rich carbohydrates and fats.
  These foods are usually called junk foods and
  contain very few nutrients. The body stores the
  extra energy as body fat. Obesity can lead to
  serious health problems such as heart disease,
  stroke and diabetes.

  Impact of deficiency diseases
  Deficiency diseases can affect a person negatively if they are left untreated.
  Some of the effects are: stunted growth, increased likelihood of getting
  infections, blindness (in the case of untreated vitamin A deficiency), being
  unable to take part in everyday activities, deformity, and death.
  When children get sick, parents or guardians and other family
  members have to care for them. So, there is less time to do other activities
  that are necessary for the family’s well-being. This can have negative effects
  on the family.
  At a community and national level, caring for sick people takes
  up valuable resources that could be used for the development of the
  community and nation. In this way deficiency diseases, which are easily
  preventable, can slow down the development of the community and nation.

  Case study
  Work in pairs. Read the case study and then discuss how soya milk can
  improve children’s health.
  Life-saving soyamilk
  Soyamilk contains all the proteins necessary to replace meat and milk.
  In a village in eastern Rwanda, women have learnt how to extract soya
  milk from soya beans. Soyamilk contains more proteins than cow’s milk
  and many adults and children prefer it. Malnutrition amongst children
  in this area has decreased in the last few years since the women’s soya
  milk production has started. There has also been a decrease in the
  number of childhood illnesses in this area.
  Constipation
  Constipation occurs when a person does not eat enough fruits and vegetables.
  Their stools become hard and difficult to pass. We can prevent constipation
  by eating food rich in fibre and by drinking plenty of water.

  Topic 2: Organisation and maintenance of life

  Unit 7: Food nutrients and diet 81
  

  Activity 7.3
  Work in pairs.
  1. a) Discuss with your partner some of the nutritional disorders that
  occur in your local community.
  b) What impact do these disorders have on:
  i) an individual
  ii) a family
  iii) a community
  iv) the nation?
  2. Kalisa recorded the number of children at his local clinic that suffered
  from nutritional disorders over three months. His results are shown in
  this table.
  

  
  

  a) How many children in total had kwashiorkor?
  b) In which month were there the most children with anaemia?
  c) Which foods should children with anaemia eat?
  d) Which vitamin and mineral should children with rickets eat more
  of in their diet?

  Homework
  Draw a table with three columns: Disease, Cause, Prevention. Complete
  the table using the information about nutritional disorders that you learnt
  in the section above (see pages 78 to 80).
  

  Exercise 7.1
  1. Name six food nutrients.
  2. Give an example of a food that contains:
  a) carbohydrates b) proteins c) vitamins.
  3. Name the elements that are found in each of the following:
  a) carbohydrates b) proteins c) fats.
  4. Give the basic units of each of the following:
  a) carbohydrates b) proteins c) fats and oils.
  5. What is a balanced diet?
  6. Name three deficiency diseases.

  Unit 7: Food nutrients and diet

  Checklist of learning
  In this unit, I have learned that:
  All living things need food nutrients to provide energy, build and repair cells and
  keep them functioning properly.
  The main food groups are carbohydrates (sugars and starches), proteins, lipids (fats and oils),
  vitamins, mineral salts and water.
  Different foods contain different nutrients.
  Simple carbohydrates are made up of single sugars, such as glucose; complex carbohydrates, such as
  starch and glycogen, consist of many single sugar units joined together.
  Lipid molecules are made up of a molecule of glycerol and three fatty acids.
  Protein molecules are large molecules that are made up of amino acids.
  Foods can be tested using reagents to find out which nutrients they contain.
  A balanced diet contains all the food nutrients that a person needs in the right quantities.
  Different people need different diets depending on their age, gender, level of activity and whether or
  not they are ill.
  A nutritional disorder occurs when a person does not have enough food or when their diet is lacking
  certain vitamins or minerals.
  Scurvy, rickets, anaemia, starvation and obesity are examples of nutritional disorders.
  

  Topic 2: Organisation and maintenance of life

  Self-assessment
  1. Match the word in Column A with the correct statement in Column B.

  

  2. Name the reagents that are used to test for the presence of the following in a food sample:
  a) proteins
  b) starch.
  3. A family has four members: an 80-year-old grandfather, a 35-year-old father, and 28-year-old
  pregnant mother, and a 2-year-old boy.
  a) Between the boy and the grandfather, who should be given more milk?
  b) Why?
  4. Miss Umutoni visited a doctor as her gums were bleeding and she complained that she was always
  tired. The doctor told her to eat two oranges, spinach and plenty of red meat every day for one
  month. After two weeks, Miss Umutoni felt better and went
  to thank the doctor.
  Discuss the causes of Miss Umutoni’s symptoms, and explain why her treatment
  was successful.
  5. Describe any two nutritional disorders. Include the causes, prevention and treatment of each
  disorder.

  Unit 7: Food nutrients and diet

  
  
  

• UNIT 8 Structure and functions of the human gas exchange system

  Key unit
  competence

  To be able to describe the structure and functions of the human gas exchange system.

  Cross-cutting issue Environment and sustainability:
  Breathing safe air ensures good health. Rwandans strive to maintain a clean environment by planting trees and conserving them. The areas of Umutara and Bugesera have been transformed by planting trees.

  Oral activity
  In groups, think back to your earlier grades. Th en, discuss these questions.
  1. What is
  respiration?
  2. Why does      
  respiration take
  place in the cells of
  the body?
  3. Which gas is
  needed for
  respiration?
  4. Which gas is
  produced by
  respiration?
  5. Name the
  respiratory organs
  in humans.
  6. Do all organisms
  have the same
  respiratory
  organs?
  7. Try to remember
  the pathway that
  air follows when
  we breathe in
  until it reaches the
  respiratory organs.

                                                                                              Figure 8.1 We need oxygen to make energy for exercise.

  Topic 2: Organisation and maintenance of life

  Structure of the human gas exchange system
  Most living organisms need oxygen gas (O2) for respiration. You learnt
  in Unit 1 that respiration is a characteristic of living things. During
  respiration, glucose is broken down using oxygen, to release energy in cells.
  During this process, carbon dioxide (CO2) is produced as a waste product.
  So, the cells must take in O2 and get rid of CO2 at the same time. The
  movement of gases across a surface or a membrane in opposite directions is
  called gas exchange. Gas exchange enables the movement of gases. It takes
  place in our lungs and in our cells.

  How does gas exchange work?
  In Figure 8.2, you can see that O2
  molecules move from one side of
  the gas exchange surface to the other
  side. The O2 molecules move from the
  side where there are lots of them to
  the side where there are fewer of them.
  The CO2 molecules move in the opposite
  direction through the gas exchange
  surface. However, they too move from
  where there is a high concentration of
  CO2 molecules to where there is a lower
  concentration of CO2 molecules.
  The movement of molecules
  from a place where they are in a high
  concentration to a place where they are
  in a lower concentration is called diffusion.
  So, gas exchange takes place by diffusion.
  Do not confuse gas exchange with breathing in mammals. Breathing is
  the movement of air into and out of the lungs.

  The structure of the lungs
  Air moves in and out of the lungs. Humans get the oxygen they need from
  the air. They get rid of carbon dioxide in the air that leaves the lungs. The
  lungs are part of the gas exchange system in humans.
  Air is taken in from the outside, or inhaled, through the nose and
  mouth. The nose has two nostrils, which lead to the nasal cavity. The nasal
  cavity is lined with hairs and mucus, which filter and moisten the incoming
  air. They also trap dirt and bacteria. Blood vessels warm the air as it passes through the nasal cavity.

  Unit 8: Structure and functions of the human gas exchange system

  Air passes from the nasal cavity down a tube called the trachea, or windpipe. There is a flap of
  cartilage at the top of the trachea that flaps over it during swallowing. This stops food from entering
  the trachea. The trachea is held open by C-shaped rings of cartilage.
  The trachea branches into two smaller tubes called bronchi (singular = bronchus). One
  bronchus leads to each lung and branches into many smaller tubes called bronchioles. The
  bronchioles end in many bunches of small, thinwalled air sacs called alveoli (singular = alveolus).
  The alveoli are the gas exchange surfaces. The alveoli provide a very large surface area for gas
  exchange. The inside surfaces of the alveoli are kept moist by water that diffuses out of the blood.
  The walls of the alveoli are only one cell thick, and many small blood capillaries surround them.

  Experiment 8.1
  Dissect a lung.
  You will need: a dissecting set; plastic sheeting; a hand lens; a lung of
  a goat, sheep or cow (with the trachea and bronchi intact); water; a
  container; a towel; soap; disinfectant; rubber tubing
  Procedure
  1. Wash the lungs carefully with enough water to remove the blood. Do
  not allow water to enter the trachea.
  2. Place the lungs on a piece of plastic sheeting on a bench. Position the
  lungs so that you can see the tubes leading into them. You may have to
  cut away some pieces of flesh to fully expose the lungs.
  3. Use Figure 8.3, above, to identify the various parts of the lungs.
  4. Insert the rubber tubing into the trachea. Take a deep breath, and blow
  into the lungs very hard. Do you notice any movement of the lungs?
  Describe this movement. Do you think your lungs behave in a similar way when you breathe in? Explain your answer.

  Topic 2: Organisation and maintenance of life

  5. Examine the sides of the trachea and bronchi very closely. Do you see
  the rings on the trachea and bronchi? What colour are these rings?
  Next, feel the sides of the trachea and bronchi, and then the surface of
  the lungs. Do you notice any differences between them? Describe these
  differences.
  6. The thin layer of skin covering the lungs is called the pleural
  membrane. What do you think is the function of this membrane?
  7. Bend the trachea until the open end faces downwards, and then let
  it go. Was it easy to bend? What happened to the trachea when you
  let go? Next, try to close the trachea by squeezing it with your fingers,
  and describe what you feel. What happens to the trachea after you stop
  squeezing it? What function do the rings have?
  8. Cut off one bronchus from the trachea to separate a lung. Next, cut
  along the bronchus until you expose the inside of the lung. Use the
  hand lens to see whether the bronchus divides further into smaller
  tubes. What are these sub-divisions of the bronchus called? What
  other details inside the lung have you observed? Describe the inside of
  the lung.
  9. Figure 8.3, on page 86, shows the human lung in detail. Could you see
  this much detail when you examined the lung? Why can you not see
  the alveoli?
  10. Put the lungs and other parts into the container and bury them in the
  ground. Carefully wash the bench and plastic sheeting with soap, and
  then disinfect them.
  11. Wash your hands thoroughly with soap.

  Table 8.1 describes the functions of the different parts of the human gas
  exchange system.

  Table 8.1 Functions of parts of the human gas exchange system

  

  Unit 8: Structure and functions of the human gas exchange system

  Exercise 8.1
  1. Draw a labelled diagram of the human lungs.
  2. Describe the function of each of the following:
  a) rings of cartilage
  b) mucus inside the trachea and bronchi.
  3. What are alveoli?
  4. The inside of the lung is spongy. Explain the word ‘spongy’.
  5. Copy the table below, and then complete it.

  

  Gas exchange in humans

  In humans, gas exchange takes place in two places: in the alveoli in the lungs and in the cells of the body.
  Gas exchange in alveoli Air, which contains oxygen, is breathed into the lungs. Oxygen moves from the alveoli into the blood in the capillaries that surround the alveoli. Carbon dioxide moves out of the blood into the alveoli. Carbon dioxide is breathed out.

                                                                                       

  Topic 2: Organisation and maintenance of life

  Gas exchange in cells
  Blood containing oxygen flows from the heart to the body cells.
  Oxygen molecules move by diffusion from a high concentration in the blood towards a region where there is less oxygen inside thecells. Inside the cell, oxygen is used in the process of respiration.
  Carbon dioxide is made during respiration in the cells. This means that there is a high concentration of carbon dioxide molecules inside the cells. Carbon dioxide moves out of the cells into the
  blood where there is a lower carbon dioxide concentration.

  

  Experiment 8.2
  Make a model to demonstrate breathing.
  You will need: rubber bands or string; a glass rod; a rubber sheet of a size that will cover the
  bottom of a bell jar; a bell jar; two balloons; a Y-shaped tube; a rubber bung or cork
  Procedure
  1. Using a rubber band, tie the glass rod to the rubber sheet. Secure the rubber sheet
  around the open end of the bell jar using rubber bands. The rubber sheet represents the
  diaphragm.
  2. Tie a balloon around each arm of the Y-shaped tube. Push the other end of the tube
  through a rubber bung or a cork. The balloons represent the lungs and the Y-shaped tube
  represents the trachea and bronchi. Assemble the apparatus as shown in Figure 8.6, below.
  3. Pull the rubber sheet downwards using the glass rod. This represents an inhalation. Note
  what happens to the balloons when the rubber sheet is pulled downwards. Explain what
  happens.
  4. Push the rubber sheet upwards using the glass rod. This represents an exhalation. Note
  what happens to the balloons when the rubber sheet is pushed upwards. Explain what happens.

  

  Unit 8: Structure and functions of the human gas exchange system

  Activity 8.1
  Work in pairs.
  1. Use a microscope to examine the microscope slides that your teacher
  will give you. You can also use the micrographs in Figure 8.7 if you do
  not have slides.
  2. Make a labelled drawing of what you see. What magnification did you
  use?

  

  Figure 8.7 Micrographs showing alveolar cells (A) and ciliated epithelium (B)

  Exercise 8.2
  1. Explain the difference between:
  a) gaseous exchange and breathing
  b) diffusion and breathing.
  2. List the pathway for air from the nose into the lungs.
  3. Name two places where gas exchange takes place in humans.
  4. a) What type of cells line the trachea?
  b) How are these cells specialised for their function?
  5. Research gaseous exchange in the following animals:
  a) insects
  b) fish
  c) spiders.

  Topic 2: Organisation and maintenance of life

  Checklist of learning
  In this unit, I have learned that:
  Gas exchange is the movement of gas molecules across a surface or membrane which is called the
  gas exchange surface.
  The movement of gas molecules takes place by diffusion.
  All organisms need to make energy through respiration, so they need oxygen and they produce
  carbon dioxide.
  In humans, gas exchange takes place inside the lungs and in the cells of the body.
  The human gas exchange system consists of the nostrils, nasal passages, trachea, bronchi,
  bronchioles and alveoli.
  The walls of the alveoli are only one cell thick; the alveoli are surrounded by small blood capillaries.
  Air, which contains oxygen, is breathed in; oxygen molecules diffuse through the walls of the alveoli
  into the blood.
  Blood that contains oxygen flows to the cells of the body; oxygen molecules diffuse across the cell
  membrane into the cell, where they are used for respiration.
  Carbon dioxide diffuses out of the cells into the blood.
  Blood that contains carbon dioxide flows into the lungs; carbon dioxide molecules diffuse through
  the walls of the alveoli into air in the lungs, and are breathed out.

  Self-assessment
  Choose the correct answer.
  1. What are the tiny sacs in the lungs called?
  A bronchi B alveoli C capillaries
  2. What happens during gas exchange in the lungs?
  A Oxygen passes into the blood and carbon dioxide passes out of the blood.
  B Oxygen passes out of the blood and carbon dioxide passes into the blood.
  C Oxygen and carbon dioxide pass into the blood.
  3. Which structures does the trachea lead to in the lungs?
  A pleural membranes B bronchioles C bronchi
  4. The alveoli are suited for gas exchange because they have:
  A a small surface area B a large surface area C walls that are many cells thick
  5. The cilia in the air passages:
  A trap dust B trap bacteria C trap dust and bacteria

  Unit 8: Structure and functions of the human gas exchange system

• UNIT 9 Tropic responses

  Not available
• UNIT 10 Skeletal systems of organisms

  Not available
• UNIT 11 Classifi cation of diseases

  Key unit
  competence
  To be able classify diseases and explain ways of preventing the spread of infectious diseases.

  Cross-cutting issue

  Comprehensive
  sexuality education:

  Rwandans need to ensure that they lead healthy lifestyles so that they can contribute to the Rwandan economy. HIV/AIDS is a serious disease that impacts on the lives of many Rwandans as well as the country’s economy.
  

  At the end of this unit, you should be able to:

  • Define good health as a state of mental, social and physical wellbeing
  • Define disease as any physical or mental disorder or malfunction with a
  characteristic set of signs and symptoms
  • Explain how infectious diseases (cholera, tuberculosis, malaria, Ebola, HIV/
  AIDS) are spread
  • Explain ways in which infectious and non-infectious diseases can be
  prevented
  • Classify diseases into infectious, non-infectious, inherited, degenerative,
  social, mental, eating disorder and deficiency diseases
  • Adopt and encourage the practices that enhance good health
  • Be aware that the clearing of bushes and grasses in the habitats of the
  anopheles mosquitoes and the treatment of the stagnant water for the
  anopheles larvae are necessary for eradicating malaria.

  Oral activity

  Some people are healthy, but others are sick. Sometimes sick people need to
  go to hospital. In groups, talk about these questions.
  1. What is good health?
  2. Name some
  diseases that
  occur in your
  community.
  3. Discuss whether
  or not people get
  these diseases
  from
  other people.
  4. Talk about ways
  to prevent sick
  people from
  spreading disease.
  5. Work out a
  defi nition for the
  terms ‘disease ’ and‘good health’. 
  

  Topic 3: Health and disease

  Health and disease When we say that a person is in ‘good health’, we mean that the person is in a good mental, physical and social state. The word ‘disease’ refers to a physical or mental disorder or malfunction that has a particular set of signs and symptoms. A person that has a disease is sick and may need to be treated by a health worker. Some diseases do not cause symptoms, so we may not know that the person is sick. However, other diseases cause a clear set of signs and symptoms.
  

  

  Figure 11.3 A nurse taking care of a patient in hospital

  Activity 11.1
  Work on your own.
  You may have heard the saying ‘prevention is better than cure’. Describe five
  good practices that can prevent a person from getting
  a disease.
  Practices that promote good health
  We can follow these good practices to prevent disease and stay healthy.
  • Eat a balanced diet.
  • Eat at regular intervals.
  • Get enough sleep.
  • Maintain good hygiene of the body, clothes, the home
  and foods.
  • Drink safe water.
  • Exercise regularly.
  • Avoid eating too much salt.
  • Wash your hands before each meal and after going to
  the toilet.
  

  Activity 11.2
  Work in groups.
  Design a poster to show how washing your hands helps to prevent the spread of infectious diseases. Include information about how and when we must wash our hands.
  

  Unit 11: Classification of diseases
  

  Types of diseases
  There are two main types of diseases: infectious and non-infectious
  diseases.
  Infectious diseases
  Infectious diseases are diseases that are passed on, or transmitted, to a
  person by another organism, such as a bacterium or virus. Organisms that
  cause disease are called pathogens. They attack the body’s cells or release
  poisons called toxins. Nearly all pathogens are micro-organisms, so they
  are microscopic. When a person has an infectious disease, he or she can
  spread it to another person. Table 11.1 lists some examples of pathogens
  and the infectious diseases that they cause.
  Table 11.1 Pathogens and infectious diseases
  

  

  

  

  Topic 3: Health and disease

  The spread and prevention of infections
  You have learnt that infectious diseases can be transferred, or
  transmitted, from one infected person to another. Another name for
  an infectious disease is a communicable disease. Communicable
  diseases are transmitted by infections.
  Figure 11.7 A patient suffering from tuberculosis (TB), which is
  an infectious disease
  Infectious diseases can spread through:
  • water (e.g. cholera); these are called
  waterborne diseases
  • air (e.g. measles, tuberculosis)
  • blood (e.g. HIV/AIDS)
  • sexual intercourse (e.g. gonorrhoea).
  There are several ways to prevent the
  spread of infectious diseases, including the
  following:
  • Inform and warn people about a
  particular infectious disease, for
  example, cholera or Ebola fever. Offer
  health education at all levels of the
  country.
  • Improve public hygiene measures; for
  example, remove the remains of dead
  animals, have rubbish collection points
  around schools and cities, and provide
  safe drinking water and sewage systems.
  • Isolate or quarantine infected people in
  places where they have little contact with                                       
  people other than health workers.
  • Immunise people against infectious
  diseases. This is an injection that
  helps our bodies to fight a disease.
  • Build more healthcare centres.

  Unit 11: Classification of diseases

  Activity 11.3
  Work in groups.
  1. What is an infection?
  2. a) Find out the names of at least five infectious diseases.
  b) Research how each of these diseases is transmitted, and then
  suggest preventive measures for each one.

  

  3. The wall chart below shows some ways to prevent cholera. Analyse it,
  and then answer these questions.
  a) Use the wall chart to suggest ways to prevent cholera.
  b) Suggest any two other ways to prevent cholera.
  c) How can we help someone with cholera?

  

  Experiment 11.1
  Work in pairs. Follow the steps on the next page to prepare an oral
  rehydrating solution (ORS) that you can use as a first aid to help a patient
  suffering from cholera. ORS is a mixture that is made from clean water,
  table salt and sugar.

  Topic 3: Health and disease

  You will need: sugar (table sugar); table salt; two teaspoons; a clean onelitre
  bottle with a lid; boiled water; a clean measuring cylinder or any
  suitable container; soap
  Procedure
  1. Wash your hands with soap and water. Wash the teaspoons, bottle
  and measuring cylinder with soap and clean water and leave them to
  dry.
  2. Put 750 ml of boiled water into the bottle.
  3. Measure out one level teaspoonful of table salt. Remove half of the
  salt from the spoon. Add the remaining half (2,5 ml) to the water in
  the bottle.
  4. Measure out one level teaspoon of sugar (use the other teaspoon to
  level the sugar with the edge of the spoon). Add the teaspoonful of
  sugar (about 5 ml) to the 750 ml of water in the bottle.
  5. Repeat step 4 until you have added six level teaspoonsful (30 ml) of
  sugar.
  6. Put the lid on the bottle and shake it until all the sugar and salt
  have dissolved. You have now prepared an oral rehydration solution
  (ORS). Taste it; it should be no more salty than the tears from your
  eyes.

  Non-infectious diseases
  Non-infectious diseases cannot be passed from one person to another by
  living organisms. They develop because the body does not work properly,
  or they may be caused by a person’s lifestyle. Examples include sickle cell
  anaemia, allergies, ageing, osteoporosis, cancer, cardiovascular diseases,
  eating disorders, deficiency diseases and mental illnesses.
  Activity 11.4
  Work on your own.
  Kalisa and Nyirasafari still have their grandparents, who are 90 years old.
  They like to visit their grandparents. One day, their grandmother fell and
  broke her arm. The doctor said that her arm broke because of osteoporosis,
  which is an age-related disease.
  1. Do research in the library or on the Internet, and then explain the
  words ‘ageing’ and ‘osteoporosis’.
  2. What are the signs of ageing?
  3. How can we take care of a person who is ageing?

  Unit 11: Classification of diseases

  Sickle cell anaemia
  Sickle cell anaemia is a disease of the red blood cells. Sickle-shaped red
  blood cells are unable to carry oxygen as well as normal red blood cells can.
  They can also easily get stuck in narrow blood vessels. This prevents oxygen
  from reaching the cells of the body.

  

  Sickle cell anaemia is caused by a change in a gene that makes haemoglobin,
  the molecules that give your blood its red colour. Haemoglobin helps red
  blood cells to carry oxygen from the lungs to all the cells in the body.
  The sickle cell gene is passed from one generation to the next. If both
  a mother and father have the sickle cell gene and pass it to their child, then
  their child will have sickle cell anaemia. If only one parent has the sickle cell
  gene and it is passed to his or her child, then the child will be able to make
  both normal and sickle cell haemoglobin. This child will be a carrier of the
  sickle cell gene. There are tests available to find out if a child has sickle cell
  anaemia. Although
  there is no cure for sickle cell anaemia, medications can relieve
  the symptoms.
  Allergies
  An allergy is a reaction by the immune system to a substance in the
  environment. A substance that causes an allergy is called an allergen.
  Some people are allergic to certain foods, for example, nuts or shellfish, or
  to substances in the environment, for example, dust, pollen or pesticides.
  When someone is allergic to something, they sneeze, get itchy eyes, get a
  rash or have swelling on their body. There are different medicines available
  to treat allergies.

  Topic 3: Health and disease

  Ageing
  Ageing is the process of becoming older. Many
  physical, mental and social changes take place. For
  example, older people do not walk or think as fast as
  younger people do. Ageing is a natural process that we
  will all go through.
  Osteoporosis
  Osteoporosis is a bone disease that occurs mostly in
  women after menopause. The bones become very
  porous, and they break easily and heal slowly. The
  disease can lead to curvature of the spine after the
  vertebrae collapse.
  Cancer
  Cancer is a non-infectious disease that develops when cells of the
  body do not divide normally. Cancer can start almost anywhere in a
  person’s body. Cancer may lead to the growth of tumours. There are
  many ways to treat cancer, but it is important to find it early on.
  Cardiovascular diseases
  These are diseases of the heart and blood vessels. Examples include
  coronary heart disease (CHD) and strokes. CHD can lead to a heart
  attack, which is when the heart muscles do not get enough oxygen. A
  stroke occurs when too little oxygen is transported to the brain cells.
  Eating disorders
  Eating disorders lead to diseases that are caused by undereating or
  overeating. You have already learnt about some diseases that occur
  from undereating, such as kwashiorkor and marasmus.
  Obesity is caused by eating more food calories than are used up
  by physical activity. Excess energy is stored as fat. Obesity is becoming
  more common as people eat more unhealthy ‘fast’ foods and spend
  less time exercising.
  Deficiency diseases
  Deficiency diseases occur when a person’s diet lacks certain vitamins
  and minerals. For example, a deficiency of vitamin C can lead to
  scurvy. You learnt about some of these diseases in Unit 7 in Table 7.4,
  on page 79.

  

  Unit 11: Classification of diseases

  Mental illnesses
  Diseases that affect a person’s mind include depression, anorexia and
  schizophrenia. There are many ways to treat these diseases. Table 11.2
  summarises different types of diseases and gives examples of each disease.

  Activity 11.5
  Work in groups.
  1. Look at the diseases given in the blocks below.

  

  Put each disease into one of these categories:
  a) infectious disease
  b) non-infectious disease
  c) inherited disease
  d) eating disorder
  e) deficiency disease.
  2. Name four other diseases, and classify each disease into one of the
  groups above.

  Table 11.2 Different diseases and their descriptions
  

  

  Topic 3: Health and disease

  Exercise 11.1
  Look at Table 11.2, on page 120, and then answer these questions.
  1. Name:
  a) three infectious diseases
  b) two inherited diseases
  c) one degenerative disease.
  2. Give the meaning of the following terms:
  a) degenerative disease
  b) social disease
  c) deficiency disease.
  3. Which vitamin is deficient when a person has:
  a) scurvy
  b) rickets?
  

  Activity 11.6
  Work in pairs. Look at the photographs below, and then comment on the
  health of each child.

  

  Unit 11: Classification of diseases

  Homework
  1. List five types of diseases.
  2. Explain the meaning of each of these terms.
  a) infectious disease
  b) hypertension
  c) immunisation
  d) haemoglobin
  3. Copy the table below, and then complete it.

  

  Checklist of learning
  In this unit, I have learned that:
  A person’s health includes their mental, social and physical well-being.
  There are two main types of diseases: infectious and non-infectious diseases.
  Infectious diseases are caused by pathogenic organisms, and they can be transmitted from one
  person to another unless preventive measures are taken.
  Preventing the spread of infectious diseases is important and includes quarantine
  and immunisation.
  Cholera is an infectious disease that is caused by a bacterium and spread through contaminated
  water.
  Some diseases are non-infectious; they include sickle cell anaemia, allergies, ageing, osteoporosis,
  cancer, cardiovascular diseases, eating disorders, deficiency diseases and mental illnesses.

  Topic 3: Health and disease

  Peer assessment
  1. Ask your partner to look at the pie chart, and then to tell you, according to the data presented,
  which disease causes:
  a) the most deaths b) the fewest deaths.

  

  Number of deaths caused by the main non-infectious diseases worldwide
  Source: http://www.who.int/gho/ncd/mortality_morbidity/ncd_premature_text/en
  2. Describe to your partner two measures for preventing the spread of infectious diseases.
  3. We often hear in the news that people in refugee camps die from cholera. Ask your partner to
  explain factors that make cholera common in such camps.
  4. a) Discuss with your partner the preventive measures the Rwandan government uses to eradicate
  malaria.
  b) Despite the measures taken by the government, malaria still causes the death of many
  Rwandans. What factors are causing this failure to eradicate malaria?
  5. The Rwandan government encourages its citizens to participate in sport. Discuss with your partner
  the impact that sport can have on our health.

  Unit 11: Classification of diseases

• UNIT 12 Human reproductive system

  Not available
• UNIT 13 Puberty and sexual maturation

  Not available
• Unit 14: Reproduction, pregnancy and childbirth

  Key unit competence To be able to analyse the process of reproduction, pregnancy and childbirth.

  Cross-cutting issue Comprehensive sexuality education: Unintended pregnancies and teenage pregnancies may lead to health problems as well as social and economic difficulties. Healthy pregnancies, childbirth, antenatal and postnatal care are essential for all Rwandan women.

  At the end of this unit, you should be able to: 

  • Describe male and female reproductive systems 

  • Explain the process of fertilisation 

  • Explain how a pregnancy occurs 

  • Describe the signs of pregnancy, and the stages of foetal development and childbirth 

  • Define maternal mortality and list major causes of maternal mortality 

  • Describe ways that poverty and gender inequality lead to death among pregnant women and how these outcomes can be prevented

   • List health risks associated with early pregnancy and birth 

  • Analyse using simulations of stages of pregnancy and discuss the signs and behavioural symptoms of pregnancy 

  • Appreciate the importance of the steps that should be taken to promote safe pregnancy and childbirth 

  • Show concern about maternal mortality as an issue in the region.

  Oral activity In groups, discuss these questions.

   1. Name two main functions of the human reproductive system. 

  2. During which time in a woman’s menstrual cycle is she most likely to fall pregnant after unprotected sex? 

  3. Discuss how unintended pregnancy can occur.

  4. What are the consequences of unintended pregnancies?

  

  The male and female reproductive systems 

  In unit 12 you learnt about the male and female reproductive organs and how they are involved in reproduction. Reproduction is the production of offspring or new individuals from their parents. Human reproduction is sexual reproduction, as it requires sex cells, or gametes, from male and female parents. The gametes fuse, or join, to form a new cell. A new organism develops from this cell. The reproductive organs are important for two reasons: they play a role in sexual intercourse and, in females, they provide a place for a new baby to develop. You will find out about these two roles in this unit.

  Exercise 14.1 1. 

  List the parts of the male reproductive system in which: 

  a) sperm are produced 

  b) semen leaves the male body. 

  2. Write down the pathway of an ovum from the time it is released until it leaves the female body.

   3. In which part of the female reproductive system do the following take place? 

  a) fertilisation 

  b) development of the foetus

  Sexual intercourse

   The male sex cells, or sperm, are produced in the testes of the male reproductive system. 

  So the sperm need to be transferred to the inside of the female body to enable one of them to fuse with the ovum. This takes place during sexual intercourse. Sexual arousal occurs when a man and a woman interact and their senses are stimulated. The pulse rate, breathing rate and blood pressure increases. The male penis fills with blood and becomes erect. 

  The external female reproductive parts become sensitive to touch and the vagina secretes mucus for lubrication during intercourse. T

  he erect penis is placed inside the vagina. In the male, the movement of the penis inside the vagina stimulates a reflex and causes ejaculation.

  This is a rhythmic muscular contraction of the male reproductive system from the testes to the penis. It results in the release of semen from the urethra. Male orgasm happens at the same time as ejaculation.

   In the female, the to and fro movement of the penis also leads to orgasm. An orgasm is the peak of sexual arousal and is a combination of pleasurable physical and emotional sensations.
  

  Fertilisation 

  During sexual intercourse, the male ejaculates between two and six millilitres of semen that contains about 300 million sperm. Semen is deposited inside the female vagina near the cervix. Sperm in the semen swim upwards into the oviducts. 

  If an ovum is in an oviduct, the sperm can reach it within five minutes. The ovum is surrounded by a tough outer coat that makes it difficult for the sperm to penetrate into the ovum. After a few minutes, the strongest sperm passes through the coat around the ovum and attaches to the membrane. Only the head of the sperm penetrates the ovum; the tail stays outside. The nuclei of the ovum and the sperm fuse; this is called fertilisation. The fertilisation event is called conception – a new human being has been created. The new cell that forms after fertilisation is called a zygote.
  

  
  

  Foetal development 

  After fertilisation, the zygote continues to divide. It divides into two cells, then four, then eight, and so on. Eventually a ball of cells is formed. After about seven days, it develops into a fluid-filled cavity surrounded by a single layer of cells. The cilia move the ball of cells down the oviduct towards the uterus. After about ten days, the ball of cells burrows into the wall of the uterus. This process is called implantation. There it continues to divide into more specialised cells and an embryo is formed. From the eighth week until birth (around 40 weeks), the developing organism is called a foetus.