REPRODUCTION IN FLOWERING PLANTS

Reproduction is the production of new generation of individuals of the

same species. It is one of the fundamental characteristics of living

organisms.

Structure of the flower

A flower is interpreted as a modified leaf of a plant which is highly

specialised for reproduction. It can be bisexual or unisexual, depending on

a plant species. Bisexual and unisexual flowers are called complete and

incomplete flowers respectively. Flowers are the main reproductive organs

of flowering plants.

There is great variation in morphology among flowers of different species,

but generally, a typical flower has the four main floral parts described

below.

1. Sepals form the outermost ring of floral leaves. They are

collectively termed as calyx. Sepals are small, green and

morphologically leaf-like in structure located at the base of the

flower.

The main function of sepals (Calyx) includes;

❖ Protecting the inner parts of a flower during the bud stage.

❖ They also carry out photosynthesis since they contain

chlorophyll.

❖ In some plants they are brightly coloured to attract insects

for pollination

2. Petals form a ring of floral parts next to the calyx. The collection

of petals is called corolla. In insect pollinated flowers, petals are

brightly coloured and have glandular swellings referred to as

nectaries at the base. Nectaries release a sugary substance known

as nectar which attracts insects. The sepals and petals are

collectively referred to as perianth.

The main function of petals

❖ Attract insects for pollination.

❖ They also offer protection to the inner parts of the flower

and they are large to provide a broad landing area for

insects.

3. The stamen is the male reproductive organ of a flower. The male

reproductive structures are collectively referred to as the

androecium. Stamen consists of anthers and a stalk or filament.

The anther consists of four pollen sacs containing pollen grains

which are powdery substance. The filament is a thin long stalk that

supports the anthers on its top.

The main function of anthers is to produce pollen grains which

contain the male gametes.

4. Pistil is the female part of the flower. The female reproductive

structures are also called gynoecium. Pistil consists of three parts

namely stigma, style, and ovary.

❖ The style connects stigma to the ovary. The style is hollow

to allow growth of the pollen tube during fertilisation.

❖ Stigma is a glandular sticky structure found as the swelling

at the tip of the style. It receives the pollen grain during

pollination.

❖ The ovary is an expanded hollow base which contains

ovules. Ovules are unfertilised female gametes. They are

attached to the ridges of a soft fleshy tissue called the

placenta. After fertilisation, the ovary develops into a fruit

while ovules develop into seeds.

The other parts of the flower

5. Flower stalk or pedicel is the modified branch or stem on which

the flower develops. The branch of each flower is called a pedicel.

6. Receptacle is a swelling that develops at the tip of the flower stalk

into which the floral parts are attached in rings or whorls. Basing

on the position of ovary, there are two types of ovaries namely:

Inferior ovary and superior ovary.

❖ Inferior ovary is the ovary positioned below the attachment

of the petals, sepals and stamens. In this case, other floral

parts occur above the ovary. A flower with inferior ovary

is referred to as epigynous flower. Examples include

guava, rose and apple flowers.

❖ Superior ovary is the ovary positioned above the

attachment of the petals, sepals and stamens. The ovary

develops above the position of the other floral parts. A

flower with a superior ovary is referred to as hypogynous

Figure: 3.1 general structure of the Hibiscus flower

flower. Examples include orange, Hibiscus sp and bean

flowers.

Figure;3.2:exteral structure of the Hibiscus flower

Types of Reproduction in plants

Sexual Reproduction; this is the type of reproduction which involves two

individuals. One parent is a male and the other is a female. Sexual

reproduction involves sperms and eggs which are specialised sex cells

called gametes. It occurs when the sperm from the male parent is fused

with the egg from the female parent to produce a new organism.

Asexual Reproduction

Asexual reproduction is the type of reproduction whereby only a single

individual give rise to new offspring. It does not involve the fusion of

gametes. As a result, the offspring reproduced asexually are genetically

identical to their parents.

There are different forms of asexual reproduction depending on the type of

organism. These forms include the following:

❖ Fission

In this form of asexual reproduction, a parent separates into two or

more individuals of equal size. Fission can be binary or multiple

fission

❖ Fragmentation

This is a form of asexual reproduction where by an organism

breaks down into fragments (pieces) and each fragment develops

into a mature organism containing features identical to those of the

parent

❖ Spore formation (sporulation) this is the type of asexual

reproduction whereby an organism reproduces new organisms by

reproductive cells called spores. Spores are small unicellular

structures which are capable of developing into new individuals

❖ Vegetative propagation; in plants asexual reproduction is called

vegetative propagation. This occurs when a new plant grows from

a fragment of a parent plant or through specialised reproductive

structures such as leaves, roots, stems or buds.

Figure; 3.3: Section through a dormant bulb

Advantages of asexual reproduction

❖ Only one parent is required

❖ Ensure genetic stability

❖ Rapid multiplication

Disadvantages of asexual reproduction

❖ No variation

❖ Most of spores are lost

❖ Increase competition of resources

Pollination

Pollination is the transfer of pollen grains from the anthers to the stigma

of a flower.

Types of pollination

❖ Self – Pollination is the transfer of mature pollen grains from the

anther of a flower to the stigma of the same flower or to the stigma

of another flower on the same plant. In self-pollination, the male

parts of the flower are located above the female parts, thus the

pollen grain fall easily onto the stigma. For self- pollination to take

place the plant must have both male and female flowers on the

same plant. Examples include peas, maize and Hibiscus sp.

❖ Cross-Pollination is the transfer of mature pollen grains from the

anther of one flower to the stigma of a flower of another plant of

the same species as shown. Examples include pawpaw, maize and

sorghum.

Agents of Pollination

In other plants there is a wide gap between the anther and stigma and since

the pollen grains are immobile, they must be carried from the anther to the

stigma. In such plants, wind, water, animals and insects act as the agents

of pollination. Each species of plant employs its own particular agent of

pollination and has features which enable them to carry out that kind of

pollination. These agents of pollination are also known as pollinators.

Wind-pollination

In wind pollinated flowers, wind transfers pollen grains from anthers to

the stigma. The anther and the stigma of wind pollinated flowers are

exposed. This makes it easy for the wind to blow the pollen that can easily

land on the stigma. Examples include flowers of most grasses such as rice,

maize and sorghum. Wind-pollinated flowers are also referred to as

anemophilous flowers

Features wind-pollinated flower

❖ Have small petals and not brightly coloured

❖ Nectaries are absent

❖ Produce large quantities of pollen grains

❖ Pollen grains are relatively light and small

❖ Not scented

Insect-Pollination

Insects visit a flower and are dusted with pollen grains from the ripe

stamens. When they visit another flower some of the pollen is transferred

to the stigma. Insects such as bees, butterflies and moths aid in pollination

of flowers. Insect-pollinated flowers are also known as entomophilous

flowers. The term entomophilous is derived from the word entomophily

which means to be carried by insects.

Features of Insect-Pollinated flowers

❖ Have large coloured petals

❖ Nectaries are present

❖ Less pollen grains are produced

❖ Scented

❖ Nectaries present

❖ Small stigma, sticky to hold pollen and enclosed within flower

❖ Pollen grains are relatively large and heavy.

Figure; 3.4: Wind Pollinated Flower

(iii)Give five reasons which suggest the pollinator you named in

(a)(ii)

(b) (i) Briefly explain the importance of pollination in specimen A.

(ii)Describe how the process of fertilization is likely to occur in

specimen A.

(i)

Identify which one developed from an ovum? Give two reasons

(ii)

which one developed from the ovary? Give one reason.

(d) using a scalpel, prepare a longitudinal section of specimen A. Then

draw a well labeled diagram of the cut surface of specimen A to

show its internal parts and external structures.

1.(a)(i)

Specimen

Common name

Hibiscus flower

Orange fruit

Bean seed

(ii) The agent of pollination in specimen A is insect.

(iii) Five reasons which suggest the agent of pollination is insect are: -

Specimen A have: -

❖ Brightly coloured petals to attract insect insects

❖ It is large in size-to attract insect,

❖ Have nectar-to attract insects,

❖ pollen grains are sticky-so that they can stick easily to insect’s

body parts.

❖ Sweet scented – to attract insects.

b.(i)The importance of pollination in specimen A,

Pollination leads to the fertilization of ovules that matures to seeds and

fruits. The seeds that can create more hibiscus plants (Specimen A).

(ii) Fertilization on flowering plant.

Fertilization is the fusion of the nuclei of the male gamete with that of the

female gamete to form a zygote.

Fig: Diagram of specimen A

Example

You have been provided with specimens L, M and N.

(a) (i)Identify specimens L,M and N by their common names

(ii) Which part of a plant are specimens L,M and N?

(b) Observe specimen N carefully, Then;

(i)

Name the structures which constitute the female and male parts

of specimen

(ii)

Explain how specimen N manages to attract insects for

pollination

(iii)

Explain how fertilization process takes place in specimen N.

tube) from specimen N. Then;

(d) (i) Draw a well labeled diagram of the specimen

(ii) Identify which part of the specimen receives the male gametes

during pollination

(iii) Identify which part of the specimen transfers the male

gametes to the place where fertilization takes place.