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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

(gamete) with a female sex cell (gamete).– The male gamete must be brought to the female gamete. 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 gametes

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

Help! I’m covered in pollen!

Pollination• Pollination is the transfer of pollen grains

from the anther to the stigma of a flower.– The pollen grains can be transferred within the

same flower.

stigma pollen grains from anther

Pollination• Pollination is the transfer of pollen grains

from the anther to the stigma of a flower.– The pollen grains can also be transferred from

one flower to another.

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Self-pollination vs Cross-pollination

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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

– less adaptable to changes in the environment.

– Analogy : Marrying within same family

– If parent plant has a genetic disease, it will be passed on to offspring.

• CROSS-POLLINATION

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

– offspring has more variety. Genetic variation.

– Offspring inherit traits from both parents can be good, but can be a bad thing too! E.g. genetic defect, disease, etc.

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

pollination than self-pollination?

1. Presence of dioecious plants (plant has only male or only female parts)

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

All about Flowers!• You can infer the method of pollination and

what type of pollinator (if animal pollinated) by observing the flower!

• Observe the size, shape, colour, presence of nectary

• Smell

http://www.colours.phy.cam.ac.uk/pollination-game/

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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.