Transcript Lesson3-SexualRepInPlants(Germination)

SEXUAL REPRODUCTION IN
PLANTS
Lesson 4:
GERMINATION OF SEEDS
Mrs Theresa Teo GE2003
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Revision of Previous Lesson
• We have discussed in great detail :
pollination, fertilisation and seed dispersal in
flowering plants.
• Let’s move on to the next and last stage in the
reproduction of plants
– germination.
Mrs Theresa Teo GE2003
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ACTIVITY 1
• Each group will be given some bean seeds (green
beans, red beans, broad beans and green peas)
• These bean seeds have been soaked in water until
they are soft.
• For each seed, examine the outside carefully.
What do you notice?
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ACTIVITY 1
• Hilum : a long scar at one edge of the testa. It
marks the region where the seed stalk was
attached.
• Micropyle : a small opening at one end of the
hilum where water enters the seed. It is also
where the pollen tube entered the ovule. If you
squeeze the seed gently, you might notice water
oozing out through the micropyle.
• Seed coat or Testa : Thick hard coat that protects
the seed.
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Seed
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ACTIVITY 1
• Remove the testa to reveal the seed leaves also
known as cotyledons. They are thickened with food
reserves (i.e. starch and proteins). The young plant
will use these food reserves initially until they have
green leaves of their own.
• Separate the cotyledons. What do you see?
• Draw what you see in your journal. Label the seed
leaves/ cotyledons.
• Where do you think the baby plant is?
• Can you tell which is the shoot, which is the root?
Mrs Theresa Teo GE2003
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Cross section of a Seed
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Cotyledon
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Pea fruit from flowers
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Germination
The growth of the embryo out of the testa so that it becomes
anchored in the soil to become a seedling.
Conditions for germinating
1 Water
To activate enzymes in the cotyledon to digest the stored food for the
growing embryo.
2 Oxygen
For respiration of cells in the embryo.
3 Suitable temperature
For enzymes to function.
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Germination
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Germination of Seeds
• Light is not one of the conditions for
germination of seeds.
• It is only necessary after the seed leaves
appear. Why?
• Some seeds also do not germinate as soon as
they are shed even though the conditions are
very favourable. They have a dormant
period.
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ACTIVITY 2 (Worksheet 3-6)
• Let’s grow some bean seeds.
• You may wish to grow maize grains too.
Maize grains are special. They are actually
fruits. The fruit wall as fused with the testa of
the seed.
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ACTIVITY 2
• Experiment 1 :
– In pot A : Grow some green bean seeds with their
seed coats removed.
– In pot B : Grow the same number of green bean
seeds with their seed coats intact.
Aim : To find out if the presence of a seed coat
affects the rate of germination of the bean seeds.
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ACTIVITY 2
• Experiment 2 :
– In pot A : Grow five green bean seeds.
– In pot B : Grow twenty green bean seeds.
Aim :
• To find out if overcrowding affects the rate of
germination of seeds.
• To find out if overcrowding affects the growth of seeds
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ACTIVITY 2
• Experiment 3 :
– In pot A : Grow some green bean seeds in the dark.
– In pot B : Grow the same number of green bean seeds in
the light.
Aim :
To find out if the presence of light affects the rate of germination of
seeds
To find out if the presence of light affects the growth of seeds.
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NON-FLOWERING PLANTS/FUNGI
• Finally, we wrap up this topic with the way the
above plants reproduce.
• They have no flowers.
• Examples of non-flowering plants : algae, seaweeds,
mosses, liverworts, ferns.
• Reproduce by spores.
• Spores : tiny spherical cell
• Millions of spores are found inside spore capsules.
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Mosses and Ferns
• The spore capsule of a moss is at the top of a stalk
which sticks out of the leafy part of the plant.
• The spore capsule of the fern are located in groups at
the underside of the fronds (name given to the leaf
of the fern.)
• When the spore capsules are ripe, they open and
scatter the spores which may then be carried further
by wind.
• If they land on favourable soil, they start to grow.
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Fungi
• Fungi e.g. bread mould also reproduce by spores.
• Bread mould looks like a mass of fine threads from
which branches grow upwards. At the end of each
branch is a spore case from which spores are
released and furthered dispersed by wind.
• Mushrooms, another type of fungi have spores found
on the underside of its cap in between the gills of the
cap.
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