Seeds: Structure and Germination

Seeds: Structure and Germination

• Enlarged Mature ovary -  Fruit

• Mature ovule -  Seed

Types of seeds: (on the basis of endosperm)

• Albuminous

• Exalbuminous

Types of seeds:

• Monocotyledonous seed (one cotyledon)

• Dicotyledonous seed (two cotyledons)

Conditions Required for germination:

• Water

• Suitable temperature(25 degree Celsius 35 degree Celsius)

• Oxygen

Maize grain

• It is a single seeded fruit

• Fruit wall and seed coat fuse together to form a protective layer known as grain

• On one side of the grain occurs a small oval light coloured area

• Remaining majority part of the grain contains endosperm

• Endosperm and embryo are well separated by a thin epithelial layer

• The outermost layer of the endosperm, rich in protein, is known as the aleurone layer

• The embryo consists of a single cotyledon here, called scutellum

• The radical is enclosed in a protective sheath called coleorhiza

• The plumule is enclosed in a protective sheath called coleoptile

Frequently Asked Questions (FAQ):

Very Short Answer Type

1. Are the following statements true (T) or false (F)?

1. Some seeds have no cotyledons at all. (T/F)

2. Maize grain is a fruit and not a seed. (T/F)

3. Seeds fallen in a flower bed from the previous crop usually do not germinate until the next sowing season. (T/F)

4. Oxygen is necessary for the germination of seeds. (T/F)

2. Name the following:

1. A monocotyledonous endospermic seed - Bean

2. A chemical used in experiments, which absorbs oxygen. - Pyrogallic acid

3. Part of the plumule above the embryonic axis of the seed. - Epicotyl

4. A plant which shows viviparous germination. - Rhizophora

5. The layer of the endosperm of maize, rich in protein. - Aleurone layer

6. A seed with folded plumule leaves. - Bean

3. Fill in the blanks:

1. In bean seeds,   hypocotyl   faster and the seeds are brought   above    ground.

2. Coleorhiza is a protective layer of radicle and coleoptile protects the rolled plumule.

3. A seed is protected by   testa   and   tegmen .

4. Seeds absorb water through micropyle which also helps in diffusion of respiratory gases.

5. Rice, wheat and maize are rich in   starch   food.

Short Answer Type

4. What is the difference between an embryo and a seed?

	Embryo	Seed
1	It is contained within a seed	It contains the embryo
2	It is a tiny living plant formed by the fusion of male and female nuclei	It is a mature ovule formed after fertilisation
3	It is a part of a seed	It is the entire seed
4	No protective seed coat is present	It is covered by a protective seed coat

5. Give two examples each of endospermic (albuminous) seeds and non-endospermic (exalbuminous) seeds.

• Endospermic (albuminous) seeds - Cereals (monocot), Poppy (dicot), palm, Custard apple

• Non-endospermic (exalbuminous) seeds - Vallisneria (monocot), gram (dicot),  mango 

6. Germinated grams are considered highly nutritive. What is the reason for this belief?

The cotyledons absorb food from the endosperm, making it highly nutritive. Hence, the germinated grams are rich in starch,  proteins, vitamins and minerals.

7. Why do we not use the terms ‘maize fruit’ and ‘maize seed’? What do we say instead?

Maize grain is actually a fruit in which the fruit wall and the seed coat have fused together to form a protective layer. Hence, we do not use the terms ‘maize fruit’ and ‘maize seed’. We call such fruits as grains. 

Long Answer Type

8. What are the functions of the following in a seed?

1. Seed coat - It protects the delicate inner parts of the seed from injury and infections.

2. Micropyle - 

1. Seed absorbs water through the micropyle for the embryo during germination.

2. It provides passage for the diffusion of respiratory gases for the growing embryo.

3. It provides passage for the  germinating root to come out of the seed.

3. Cotyledons - 

1. They provide nutrition to the  germinating embryo

2. They protect the embryo during germination

4. Radicle - It is the first part of the seedling to emerge from the seed 

1. to enhance water uptake from the soil and 

2. to anchor the plant in the soil

5. Plumule - It forms the future shoot to start performing photosynthesis before the food stored in the cotyledons finishes.

9. Suggest an experiment to prove that a suitable temperature is necessary for germination.

Let us take two beakers labelled A and B. Let us place some gram seeds on wet cotton wool in both the beakers. Let us put beaker A in refrigerator and beaker B at ordinary room temperature. 

In a day or 2, we observe that the seeds in beaker B have germinated quite well, but the seeds of beaker A may not have germinated. This experiment proves that a suitable temperature is necessary for germination.

10. Sometimes the potatoes kept in a basket during the late rainy season start giving out small shoots. Would you call it germination? Give reason in support of your answer.

Germination is the development of a plant from a seed after a period of dormancy. Hence, yes, we call it germination when sometimes the potatoes kept in a basket during the late rainy season start giving out small shoots. 

11. Give two differences in each of the following pairs:

1. Epigeal germination and hypogeal germination

	Epigeal Germination	Hypogeal Germination
1	Hypocotyl elongates faster	Epicotyl elongates faster
2	Cotyledons are pushed above the ground	Cotyledons remain underground
3	Usually occurs in dicotyledonous seeds	Usually occurs in monocotyledonous seeds

2. Coleorhiza and coleoptile

	Coleorhiza	Coleoptile
1	It protects the radicle of the seed	It protects the plumule of the seed
2	It remains underground	It comes above the soil during germination
3	It never turns green	It becomes green and does photosynthesis

3. Bean seed and maize grain

	Bean Seed	Maize Grain
1	It is a dicotyledonous seed	It is a monocotyledonous seed
2	It has no endosperm	It has a large endosperm
3	It has a large embryo	It has a small embryo
4	The plume is large	The plumule is very small
5	Hilum and micropyle are clearly present	Hilum and micropyle are not clearly visible
6	Seeds are separately contained in a fruit called pod	Seed wall and fruit wall are fused to form a single grain with no separate seed

12. Differentiate between germination and vivipary.

	Germination	Vivipary
1	It is the process of formation of a seedling from the embryo	Seed germinates inside the fruit while it is still attached to the parent plant
2	It starts with the development of root	It ends with the development of root

13. Justify the statement that the maize grain is ’a one seeded fruit’

The maize grain is a ’a one seeded fruit’ because the fruit wall and the seed coat have fused to form a single protective layer. We call such fruits ‘grain’.

14. What is the role played by the hypocotyl in epigeal germination?

After emergence of the radicle, the hypocotyl emerges and lifts the growing tip (usually including the seed coat) above the ground, bearing the embryonic leaves (cotyledons) and the plumule that gives rise to the first true leaves.

15. With regard to germination in bean, answer the following:

1. State the function of the ‘micropile’

1. Seed absorbs water through the micropyle for the embryo during germination.

2. It provides passage for the diffusion of respiratory gases for the growing embryo.

3. It provides passage for the  germinating root to come out of the seed.

2. Name the part of the seed that grows into the seedling. 

Embryo

3. Name the part of the seed that provides nutrition for the growing seedlings.

Cotyledon

4. Draw a neat labelled diagram of a mature bean seed.