mrs theresa teo ge2003 1 sexual reproduction in plants lesson 4: germination of seeds
TRANSCRIPT
Mrs Theresa Teo GE2003 1
SEXUAL REPRODUCTION IN PLANTS
Lesson 4:
GERMINATION OF SEEDS
Mrs Theresa Teo GE2003 2
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 3
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?
Mrs Theresa Teo GE2003 4
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.
Mrs Theresa Teo GE2003 5
Seed
Mrs Theresa Teo GE2003 6
• 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?
ACTIVITY 1
Mrs Theresa Teo GE2003 7
Cross section of a Seed
Mrs Theresa Teo GE2003 8
Cotyledon
Mrs Theresa Teo GE2003 9
Pea fruit from flowers
Mrs Theresa Teo GE2003 10
GerminationThe growth of the embryo out of the testa so that it becomes anchored in the soil to become a seedling.
For respiration of cells in the embryo.
To activate enzymes in the cotyledon to digest the stored food for the growing embryo.
Conditions for germinating
1 Water
2 Oxygen
3 Suitable temperatureFor enzymes to function.
Mrs Theresa Teo GE2003 11
Germination
Mrs Theresa Teo GE2003 12
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.
Mrs Theresa Teo GE2003 13
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.
Mrs Theresa Teo GE2003 14
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.
Mrs Theresa Teo GE2003 15
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
Mrs Theresa Teo GE2003 16
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.
Mrs Theresa Teo GE2003 17
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.
Mrs Theresa Teo GE2003 18
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.
Mrs Theresa Teo GE2003 19
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.