Topic outline

  • General

  • 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


     KingdomCharacteristics 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 â€¢ 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 â€¢ 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.