Biology and Health Sciences

             importance of flowering plants

B

C

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

Topic 1: Biodiversity and classification

                            Table 3.1 Differences between monocotyledonous and dicotyledonous plants

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.

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.

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.

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.

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)

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 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.

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.

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?

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)

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?

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.

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

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

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.

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.

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

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.

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.

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

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