Chapter 2: Sexual Reproduction in Plants

By the end of this chapter, you will be able to:

a) recognise the flower structures that are involved in the processes of pollination, fertilisation, fruit and seed development and outline their functions.

b) know the process of pollination, fertilisation and fruit formation.

c) understand the difference between cross and self-fertilisation and the advantages of each method.

d) differentiate between seeds and fruits structurally and functionally.

e) understand the importance of dispersal.

f) recognise the structures and the types of fruits and seeds and relate their structures to their methods of dispersal.

Keywords

1. androecium
2. ovules
3. anthers
4. calyx
5. corolla
6. cross fertilisation
7. pedicel
8. perianth
9. petals
10. pistil
11. placenta
12. dispersal
13. pollen grain
14. epicalyx
15. fertilisation
16. filament
17. flower
18. fruit
19. gametes
20. gynoecium
21. ovary
22. pollination
23. receptacle
24. seed
25. self-pollination

Introduction

Sexual Reproduction in Plants Plants are known to reproduce both asexually and sexually. In Chapter 1, you looked at the various ways plants can reproduce asexually.

In this chapter, you are going to discover how the seeds that are used in sexual reproduction come about. you are going to carry out activities in which you will examine the special organs of a plant that are involved in sexual reproduction and how they eventually form seeds that contain the embryos that later give rise to other plants.

2.1 Flower structure and function

During your study of sexual reproduction you will learn that it involves the fusion of male and female gametes. The male gamete is produced by the anthers while the female gamete is produced by the ovary. The organs of sexual reproduction are born in the flower. The flower is a special reproductive organ that has structures that are adapted for pollination and fertilisation Flowering plants are the most common plants.

They can be found everywhere in school compounds, floral gardens, bushes on the roadsides, and in peoples gardens. You cannot fail to get a flower in all seasons. In the next activity, you are going to investigate flower structure in detail.

Activity 2.1 Investigating structure of a flower and functions of different parts

Key question

What are the functions of the different parts of a flower parts?

What you need

Flowers of different types

Hand lens

Biology textbook

Razorblade

Scalpel/razorblade

Notebook

Pen

Manila paper

Marker

Figure 2.1: A flower

Figure 2.2:

What to do

1 Working in groups collect different flowers from the environment and examine them.

2 Cut one of the flowers longitudinally and examine the structures, draw and label the half flower.

3 Relate structures identified to those shown in Figure 2.1.

4 Using a Biology textbook, label the parts of the flower of Figure. 2.1 and state the functions of each part indicated on the diagram.

5 Compare your findings with the rest of the class, then pin up the harmonised information on the class noticeboard.

2.2 Pollination

In order for sexual reproduction to occur, the pollen grains have to be moved by some means e.g wind, water or by insects like bees from the anthers to the stigma of the flowers.

Activity 2.2 Finding the meaning of pollination

Key question

What is pollination?

What you need •

Notebook

Pen

Biology textbooks

Computer with internet connection

What to do

1 Working in pairs make a research and discuss the term pollination.

2 Write down the information you have discovered and discussed.

3 Present the information to the rest of the class and harmonise the information with the rest of the class.

4 Pin up the harmonised copy on the class noticeboard.

Types of Pollination

Sexual Reproduction in Plants There are two types of pollination. In the next activity you will discuss the type of pollination.

Activity 2.3 Discussing the types of pollination

Key question

1 What are the types of pollination?

What you need

1. Notebook
2. Pen
3. Biology textbook
4. Computer with internet connection

What to do

1 In groups, study the illustration in Figure 2.2(a) and 2.2(b).

2 Discuss and identify the types of pollination taking place in each.

3 Describe the types of pollination identified in (2) above.

4 Research and discuss the advantages of each type of pollination.

5 Share your findings, harmonise the results and pin your work on the class noticeboard.

Agents of pollination

Transfer of pollen from the anther to stigma can be aided by some agents. In the following activity, you are going to identify the agents of pollination.

Activity 2.4 Finding out how flowers are adapted to different agents of pollination

Key question

How are flowers adapted to different agents of pollination?

What you need

Different types of flowers

Notebook

Pen

Biology textbook

Computer with internet connection

What to do

1 In groups discuss agents of pollination.

2 Examine the differences between flowers provided.

3 What are the characteristics of each flower? List them down.

4 Identify the agents of pollination for each flower.

5 State how each flower is adapted to the agent of pollination.

6 Make a write-up and present your work to the rest of the class.

7 Harmonise your work through class discussion and pin it up on the noticeboard.

2.3 Fertilisation

The male and female gametes are brought together and fuse in the process of fertilisation. The next activity, you will investigate on the process of fertilisation in a flower.

Activity 2.5 Investigating the process of fertilisation

Key question

What is fertilization?

What you need

Biology textbook

Computer with internet connection

Notebook

Pen

Pencil

Manila paper

Marker

2.4 External and internal structure of seeds and fruits

The end product of fertilisation is the formation of seeds and fruits. Most seeds are inside fruits though some seeds are naked.

Activity 2.6 Examining the structure of a seed

Key question

What is a seed and what makes up a seed?

What you need

Relevant Biology textbooks

Computer with internet connection

Manila paper

Notebook

Pen

Pencil

Seeds (beans and maize grains)

Knife or razor blade or scalpel.

Marker

What to do

1 Working in groups research on what seeds are and seed structure from Biology textbooks/internet.

2 Obtain and examine the seeds.

3 Use soaked bean seeds overnight to help you see the different parts properly.

4 Identify the different structures you discovered from your research and make a well labeled drawing of the external structures of the seed.

5 State the functions of the parts of the seed identified.

6 Cut through the seed longitudinally and observe the internal structures.

7 Make a neat well labeled drawing of the internal structure of the seed.

8 State the meaning of the term seed.

9 Present your group work to the class.

10 Harmonise the external and internal structures of seeds

11 Pin up your work on the class noticeboard.

What is a fruit?

A fruit is a fertilised ovary.

Activity 2.7 Finding out what a fruit is

Key question

What is a fruit?

What you need

A variety of fruits

Notebook

Manila

Marker

What to do

1 In groups research and discuss the meaning of the term fruit.

2 Make a write-up and present it to the class.

3 Harmonise your findings with the rest of the class.

4 Pin up your harmonised work to the class noticeboard.

Fruits differ in their surface appearance but on close observation, you will find that fruits have common structures that can be used to tell what is a fruit and what is not.

In this activity, you are going to examine the external structure of a fruit to identify these structures.

Activity 2.7 (b) Examining the external structure of a fruit

Key question

What make up the external structure of a fruit?

What you need

Fruits: tomato, mango or Manila avocado

Marker Notebook

Pen

Biology textbook

Computer with internet connection

What to do

1 In groups examine the external structure of a fruit.

2 Draw and label external parts of a tomato, mango or avocado.

3 Research in a Biology textbook or internet for the functions of the parts of the fruit and indicate them on the diagram.

4 Present your work to the rest of the class.

5 Pin up harmonised work in the class noticeboard.

Activity 2.7 (c) Examining the internal structure of a fruit

Key question

What makes the internal structure of a fruit?

What you need

A fruit: mango, tomato or •

Manila avocado •

Marker

Notebook

Knife

Pen

Biology textbook

What to do

1 Make a section through a mango, tomato or avocado fruit.

2 Examine the internal structure of a fruit.

3 Draw and label the internal structure of the mango, tomato or avocado fruit.

4 State the functions of the internal fruit parts.

5 Discuss and show your work to the rest of the class.

6 Hang the harmonised work on the class noticeboard.

Fruits have many structures internally. Each of these structures is important for the fruit.

2.5 Fruits differ in their internal structures as well.

In this activity, you are going to examine the internal parts of a fruit and identify the structures inside. Fruit and seed dispersal If all the seeds of a plant fell beneath the parent plant, the seedlings would be crowded that few would have a chance to grow.

Activity 2.8 Investigating the meaning of fruit and seed dispersal

Key question

What do you understand by the terms fruit and seed dispersal?

What you need •

Biology textbook

Notebook

Computer with internet •

Pen connection

What to do

1 In groups, research and discuss the meaning of fruit and seed dispersal.

2 Make a write-up of your findings.

3 Report your findings to the class.

4 Harmonise your information and pin it up on the class noticeboard.

In some plants the seeds or fruits are easily scattered to new areas because of their modification in structure. The scattering of fruits and seeds from their parent plants is known as dispersal. By means of dispersal the overcrowding of plant populations is prevented.

Activity 2.9 Examining the adaptation of the different seeds and fruits that aid their dispersal

Key question What are the adaptations of seeds and fruits for dispersal?

What you need

Various seeds

Manila paper

Marker

Different types of fruits e.g. black jack/ desmodium/castor oil/tobacco /bean/ ground nut/tridax banana/orange, mango/avocado/tomato/passion.

Pen

Pencil

Notebook

What to do

1 Examine the seeds and fruits provided.

2 Using observable characteristics, identify how each is adapted for dispersal.

3 Discuss the advantages and disadvantages of seed and fruit dispersal.

4 Show your group findings to the class.

5 Pin harmonised information on the class noticeboard.

Chapter Summary

In this chapter, you have learnt that:

1. plants in addition to asexual reproduction can reproduce sexually through production of fruits and seeds.
2. the organs for sexual reproduction in plants are the flowers.
3. sexual reproduction in plants involves several processes which include: – pollination, fertilisation fruit and seed formation.
4. pollination requires agents like insects wind and flowers are adapted differently for each type of pollination.
5. fertilisation can be self within the same plant or cross between separate plants of the same species.
6. dispersal is the scattering of fruits and seeds from parent plants.
7. it is necessary to avoid overcrowding around the parent plant.
8. fruits and seeds are specifically modified for their mode of dispersal. a seed consists of an embryo distinguished into a plumule and radicle, a food store (endosperm /cotyledon) and a testa.
9. a fruit consists of several seeds enclosed in a fruit wall.
10. a fruit differs from a seed by having two scars whereas a seed has one scar.

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