Transcript Pollination - P5 GE Science 2011

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)
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papaya flowers
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maize flowers
Mrs Theresa Teo GE2003
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POLLINATION
• 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.
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Pollen
Help! I’m covered
in pollen!
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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.
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 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
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
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Insect pollinated flower
e.g. Hibiscus
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wind pollination - grass flower
Mrs Theresa Teo GE2003
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Grass flower
Mrs Theresa Teo GE2003
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Wind pollination
e.g. Maize, grass
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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/
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.
Mrs Theresa Teo GE2003
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