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SEXUAL REPRODUCTION IN PLANTS

Types of flowers

Self-pollination vs Cross-pollination

Insect-pollinated vs Wind-pollinated

Fertilisation

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FLOWERS

Unisexual Bisexual

Flower with either the male part or the female part

Flower with both the male and female parts

male and female flowers can be found on same

plant (Monoecious plant)

e.g. maize plant

male and female flowers are borne on separate trees

(Dioecious plant)

e.g. papaya plant (see next slide)

e.g. hibiscus, morning glory, string bean

plant

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papaya flowers

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maize flowers

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• What is pollination?– To reproduce sexually, you need to fuse a male sex cell with a

female sex cell.– The male sex cell must be brought to the female sex cell. In

animals, there is the mating process.– How about for plants? They can’t move from place to place!– They need an external agent and since it is the male sex cell

which are contained in the pollen grains that gets transferred , the process of transferring the pollen grains from the male part of the flower to the female part is known as pollination.

– Pollination must occur before fertilisation can occur.

POLLINATION

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Pollen

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POLLINATION

Flower B of Plant BFlower A of Plant A

Flower B of Plant A

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Self-Pollination vs Cross Pollination

• SELF-POLLINATION

– Pollen grains falling on the stigma of the same flower or of a different flower but of the same plant

– Not favoured because offspring weaker and less adaptable to changes in the environment.

– Analogy : Marrying within same family

• CROSS-POLLINATION

– Pollen grains falling on the stigma of another flower of the same kind but on a different plant

– Favoured because offsprings healthier and has more variety.

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Self-pollination vs Cross-pollination

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How does a plant ensure there are more chances of cross-

pollination than self-pollination?

1. Presence of dioecious plants 2. For those with bisexual flowers, the male

and female parts of the flower mature at different times

3. The male and female parts of a bisexual flower may be some distance away or at a certain position such that self-pollination is difficult.

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Helpers of Pollination• Pollen cannot move on its own from the anther to

the stigma. • Help must be given.• The insects and the wind help in transferring the

pollen.• However, insects and wind are very different

helpers so insect-pollinated flowers and wind-pollinated flowers must look very different from each other to facilitate the process.

• How different are they?

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Insect-pollinated Flowers vs Wind-pollinated Flowers

2. Nectar present Nectar absent

4. Stigma is sticky so that pollen grains that land on it cannot be easily shaken off

Stigma is larger with feathery branches for catching pollen grains. Not sticky

5. Pollen grains are large and heavy with rough surface for sticking to insect’s body. Smaller number produced

Pollen grains are smaller, smoother and light, easily blown by wind. Larger number of pollen grains produced

1. Flowers are large, brightly- coloured and scented

Flowers are smaller and scentless with dull coloured petals

3. Stamens and stigma hidden inside petals. Filaments not pendulous. Flowers face upwards

Stamens and stigma hang out of the flower. Filaments are long and pendulous. Flowers hang down for easy shaking

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Insect pollinated flower

e.g. Hibiscus

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wind pollination - grass flower

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Grass flower

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Wind pollination

e.g. Maize, grass

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Sexual parts of a flower

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Releasing the pollens

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Fertilization

When all the ovules have been fertilised, the petals, stamens, stigma and style are no longer needed. They will usually wither and fall away, leaving an ovary in which the ovules are developing into seeds.