#109 Formation of seed, conditions affecting germination

The fertilised ovule divides by mitosis to form a seed containing the embryo plant and food stores called cotyledons.

• The wall of the ovule forms the seed testa (coat).
• The ovary wall develops into a fruit, which may be fleshy (e.g. plum) or a dry pod (e.g. lupin or pea).

Structure of a non-endospermic seed 

Try this

Figure below shows a section through a bean flower.

a) Name the parts labeled A and B                                                   [2 marks]

b) This flower is insect-pollinated. Suggest how parts C, D and E help in pollination of this flower.                                                               [3 marks]

c) After pollination, the ovules develop into seeds. Describe the events which occur after pollination and which result in the formation of seeds    [4 marks]

Answer

a) A: ovule, B:sepal

b) C (petal) are large and colourful to attract insects

    D (stigma) is sticky and lies in the way of the insects to cllect pollen

    E (anther) produces pollen and lies in the way of the insects 

                     to transfer pollen on to their bodies.

c) Four points form:

- pollen grains germinate

- pollen tube grows down the style

- through the micropyle

- into the ovule

- the male nucleus fuses with the female nucleus

- reference to fertilisation

Environmental conditions affecting germination 

1.Water: 

• absorbed through microphyle until radicle is forced out of testa
• activate enzymes for converting soluble food stores in the cotyledons down to soluble food ---> for growth + energy production of baby plant.  

2.Oxygen: respiration ---> release energy ---> growth

3.Warmth/temperature: enzymes present in the seed get activated and work best at optimum temperature (20-40⁰C) which trigger growth in the baby plant.

4. Light intensity: high or very low light intensity does not allow enzymes to function normally. 

* Light may or may not be necessary for germination. 

Seeds of many species germinate equally well in light and darkness. Others have been found to germinate to higher percentages in light while a smaller proportion germinate better in darkness.

Studies have shown that small seeds often require light for germination while large seeds are usually indifferent to their exposure to light. These results support the general gardening rule that says that the larger the seed, the deeper it should be planted in the soil.

More informatiton on Seed germination requirements.