Frank Solutions for Chapter 9 Seeds: Structure and Germination Class 9 Biology ICSE

Exercises


1. Define the following:
(a) Seed
(b) Germination
Answer
(a) Seed is defined as a fertilized mature ovule which possesses an inactive embryo and reserve food for its further development.
(b) The process by which the dormant embryo of the seed resumes active growth and forms a seedling is known as germination.

2. Explain the following terms:
(a) Albuminous seed
(b) Dormancy
(c) Hypogeal germination
(d) Epigeal germination
Answer
(a) Albuminous seed – In some dicotyledons and monocotyledons, the food is stored mainly in the endosperm. Such seeds are called albuminous seeds. Example - Seeds of castor, cereals and grasses.

(b) Dormancy - Seed dormancy is a condition of plant seeds that prevents germination under optimal environmental conditions. Here the seed is in a state of apparent inactivity and will not grow even if favorable conditions are provided, until a definite time has elapsed.

(c) Hypogeal germination – In this germination, the seed remains inside the soil since epicotyl elongates faster than hypocotyl. Hence the cotyledons remain inside the soil. Example – Wheat, rice, pea, mango.

(d) Epigeal germination – It is a type of germination in which cotyledons are pushed above the soil into the air and light. This occurs due to rapid growth and elongation of the hypocotyl. Example – Bean, cotton, castor, papaya, onion, tamarind.

3. A seed is provided with all the conditions necessary for germination. Yet it fails to germinate. Explain.
Answer
This is because the seed is in a state of dormancy. In this case, even if all the favorable conditions are provided, the seed remains in a state of apparent inactivity and only germinates after a definite time has elapsed.

4. Give the functions of the following:
(a) Seed coat 
(b) Micropyle
(c) Endosperm 
(d) Cotyledon
Answer
(a) Seed coat is the outer covering of seed. It protects the inner contents of the seed.
(b) Micropyle allows entry of water into the embryo.
(c) Endosperm contains stored food mostly as starch.
(d) Cotyledons store food material for the embryo.

5. Name the following:
(a) The part of the seed which gives out the shoot.
(b) The protective sheath covering the radical in the maize grain.
(c) The part of castor seed that stores food.
(d) The small opening through which water enters the seeds.
(e) What is formed from radical and plumule?
(f) In which part of the maize-seed food is stored?
(g) The type of germination in which the cotyledons come above ground.
(h) The type of germination in which the cotyledons stay below the ground.
(i) Lightest seed.
(j) Largest seed.
Answer
(a) Plumule
(b) Coleorhiza
(c) Endosperm
(d) Micropyle
(e) Root and shoot
(f) Endosperm
(g) Epigeal germination
(h) Hypogeal germination
(i) Orchis seed
(j) Seed of Lodoicea moldivica

6. Differentiate between:
(a) Coleorhiza and Coleoptile.
(b) Albuminous seed and Exalbuminous seed.
(c) Epigeal germination and Hypogeal germination.
Answer
(a) Difference between Coleorhiza and Coleoptile
Cleorhiza Coleoptile
It is the outer sheath covering the radicle in certail seeds. It is the outer sheath covering the plumule in certain seeds.

(b) Difference between Albuminous seed and Exalbuminous seed
Albuminous seed Exalbuminous seed
These seeds possess endosperm These seeds lack endosperm
In such seeds, food is stored mainly in endosperm In such seeds, food is stored only in the cotyledons
Examples - Castor, cereals, grasses Examples - pea, gram, lentil

(c) Difference between Epigeal germination and Hypogeal germination
Epigeal germination Hypogeal germination
Here cotyledons are pushed above the soil Here cotyledons remain inside the soil
Here hypocotyl grows and elongates faster than epicotyl Here epicotyl grows and elongates faster than hypocotyl
Examples - Bean, cotton, castor, papaya Examples - Wheat, rice, groundnut, mango

7. Give two examples each of:
(a) Dicotyledonous albuminous seeds.
(b) Monocotyledonous albuminous seeds.
(c) Dicotyledonous non-endospermic seeds showing hypogeal germination.
(d) Monocotyledonous endospermic seeds showing hypogeal germination.
Answer
(a) castor, papaya
(b) grasses, wheat
(c) pea, mango
(d) wheat, rice

8. Briefly, explain the factors that are necessary for germination.
Answer
The factors necessary for germination are:
  1. Water - Water is essential for seed germination since protoplasm becomes active only when saturated with water. Water facilitates the necessary chemical changes in food material. Also enzymatic reaction occurs only in the water medium. Water when imbibed by the seed coat makes it soft and swollen. Then the seed coat bursts open, helping the embryo come out easily.
  2. Temperature - A suitable temperature is essential for seed germination since many physiological processes occur within the seed during germination. Seeds fail to germinate below 0°C or above 45°C. Optimum temperature for seed germination is 15-30°C.
  3. Oxygen – During germination, embryo resumes growth and for this energy is required. This energy comes from the oxidation of food material stored in the endosperm or cotyledons. This process requires oxygen.

9. Describe three beans experiment. What does it demonstrate?
Answer
Apparatus required for three beans experiment are beaker, bean seeds and wooden piece. The air-dried seeds are attached to a piece of wood, one at each end and one in the middle. This is then placed in a beaker and water is poured into it till the middle seed is half immersed in it. The beaker is then left in a warm place for a couple of days. From time to time, water is added to maintain the original level. It is observed that after a couple of days that the bean in the middle germinates normally since it has sufficient water, oxygen and temperature. The bottom seed gets sufficient water and temperature but not oxygen hence it may develop a radicle but doesn’t grow further. The upper seed gets oxygen and temperature but not water and hence fails to germinate.
This experiment shows that water, temperature and oxygen are essential for seed germination and that germination will not occur if any one of these factors are absent.

10. Explain, why seeds sown in too deep in the soil fail to germinate.
Answer
If the seeds are sown too deep in the soil, they may not get sufficient oxygen required for
respiration and hence will fail to germinate.

11. Describe the structure of a seed by suitable diagram.
Answer
A typical seed consists of the following parts:
  1. Seed coat - It is the outer covering of the seed and develops from the integument of the ovule. Its outer layer is called testa and inner layer is called tegmen. seed coat protects the inner parts of the seed.
  2. Micropyle - It is a small pore present near the hilum which allows entry of water into the embryo.
  3. Embryo - It is the miniature plant present inside the seed coat. it develops from the fertilized egg. The embryo of a mature seed consists of cotyledons (or seed leaves), plumule, hypocotyl and radicle.
    Dicots have two cotyledons joined by a stalk whereas monocots have one cotyledon joined to the embryo. cotyledons store food material for the embryo.
  4. Endosperm - It is a food reserve present in certain seeds. such seeds are called endospermic seeds.

12. Every question has four options. Choose the correct answer:

(i) Food is stored in the seeds of castor
(a) in radicle
(b) in plumule
(c) in cotyledons
(d) in endosperm
Answer
(d) in endosperm

(ii) Caruncle is present in
(a) wheat
(b) maize
(c) paddy
(d) castor bean
Answer
(d) castor bean

(iii) Essential condition for germination is
(a) water
(b) oxygen
(c) temperature
(d) all the above
Answer
(d) all the above

(iv) Hypogeal germination is present in
(a) pea
(b) bean
(c) castor
(d) maize
Answer
(d) maize

(v) Largest seed is
(a) double coconut
(b) coconut
(c) heartnut
(d) walnut
Answer
(a) double coconut

(vi) The collective term for the stages that lead to the formation of seedling from a seed is
(a) dormancy
(b) germination
(c) viability
(d) none of these
Answer
(b) germination
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