SEXUAL REPRODUCTION IN
PLANTS
Types of flowers
Self-pollination vs Cross-pollination
Insect-pollinated vs Wind-pollinated
Fertilisation
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FLOWERS
Unisexual
Flower with either the male
part or the female part
male and female
flowers can be
found on same
plant (Monoecious
plant)
e.g. maize plant
Bisexual
Flower with both the male and
female parts
male and female
flowers are borne
on separate trees
(Dioecious plant)
e.g. hibiscus, morning
glory, string bean
plant
e.g. papaya plant
(see next slide)
Mrs Theresa Teo GE2003
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papaya flowers
Mrs Theresa Teo GE2003
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maize flowers
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POLLINATION
• 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.
Mrs Theresa Teo GE2003
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Pollen
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POLLINATION
Flower A of Plant A
Flower B of Plant B
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.
Mrs Theresa Teo GE2003
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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 windpollinated 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
1.
Flowers are large, brightlycoloured and scented
Flowers are smaller and scentless
with dull coloured petals
2. Nectar present
3. Stamens and stigma hidden
inside petals. Filaments not
pendulous. Flowers face
upwards
4. Stigma is sticky so that pollen
grains that land on it cannot be
easily shaken off
Nectar absent
Stamens and stigma hang out of
the flower. Filaments are long
and pendulous. Flowers hang
down for easy shaking
Stigma is larger with feathery
branches for catching pollen
grains. Not sticky
5. Pollen grains are large and
Pollen grains are smaller,
heavy with rough surface for
smoother and light, easily blown
sticking to insect’s body.
by wind. Larger number of
Smaller number producedMrs Theresa Teo GE2003
pollen grains produced
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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.
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