Short Questions and Answers
One mark question with answers
1. The testa is usually
(a) thick and leathery
Answer: (a) thick and leathery
2. The seed remains attached to the pericarp by a short stalk called
(b) seed stalk
(c) both a and b
Answer: (c) both (a) and (b)
3. The radical, plumule and the hypocotyl together form the
(a) embryonic axis
(c) both a and b
Answer: (c) both (a) and (b)
4. Coleorrhiza is
(a) covering of radicle
(b) covering of plumule
(c) plumule and rudimentary sheath
(d) radical and root cap
Answer: (a) covering of radicle
5. In exalbuminous seeds, the food is generally stored in
Answer: (a) cotyledons
6. The remains of nucellus present in the seed constitute
Answer: (c) perisperm
7. The aleurone layer in maize grains is especially rich in
Answer: (a) proteins
8. In cereal grain, single cotyledon is represented by
Answer: (c) scutellum
9. Caryopsis is
(a) one seeded fruit
(b) two seeded fruit
(c) multi seeded fruit
Answer: (a) one seeded fruit
10. Which tissue makes up the embryo of a seed?
Answer: (b) meristematic
Two marks questions with answers
1.What is epigeal germination? Give examples.
Answer: During the germination of seeds, the cotyledons are raised above the surface of the soil due to rapid elongation of hypocotyl. This type of germination where the cotyledons are raised above the soil surface is known as epigeal germination. Epigeal germination is found in the seeds of Dolichos, castor, Cucurbita, tamarind, Helianthus, Carica papaya, sunflower, onion etc.
2. What is hypogeal germination?
Answer: In some seeds and grains, the cotyledons are not pushed upwards. They remain under the surface of the soil during germination. In this case, the epicotyl that is the portion of the axis just above the cotyledons grow faster and push the plumule upwards. As the cotyledons remain under the surface of the soil, they do not turn green but they supply food material to the growing seedling from the reserve stock. This type of germination is called hypogeal germination. Hypogeal germination is found in dicotyledonous seeds of Cicer, Pisum, Mangifera, groundnut etc., and in many monocots like wheat, rice, maize, coconut, date palm, etc.
3. What is seed dormancy?
Answer: In many plant species, the seeds fail to germinate for some period after maturation and harvest even if suitable conditions for germination are provided to them. This state of inactivation of seeds may be due to some internal factors that inhibit the process of germination and is referred to as seed dormancy.
4. How does the seed coat affect seed germination?
Answer: The seed coat or testa of most of the seeds are hard, tough and dehydrated forming a protective covering around the embryo. It is impermeable to water and oxygen gas and it does not allow them to reach the embryo thereby suppressing germination. The hard seed coat offers mechanical resistance for the growth of the germinating embryo e.g., Capsella, Lepidium.
5. What is scarification?
Answer: Sometimes the hard seed coat resist germination. Such seeds, however, readily germinate if the seed coat is artificially removed either by chemical treatment or by mechanical means. This process is called scarification. It is the rupturing of seed coats by abrasion through machine threshing, filling, chipping, vigorous shaking, etc.
6. How does the condition of embryo cause dormancy?
Answer: The embryo may be immature and rudimentary when the seeds ripe and it may take some time to get fully developed, causing a period of dormancy. In some other cases, however, the embryo may be fully developed when the seed matures but it fails to germinate immediately due to some internal factors causing physiological immaturity as in case of seeds of apple, pear, cherry etc.
7. What does stratification mean?
Answer: To overcome dormancy caused by the embryos, seeds can be induced to germinate early if they are stored in moist well-aerated and low temperature condition. This process is called stratification.
Three marks questions with answers
1. What do you understand by quiescence state of seed?
Answer: Germination may not always be prevented due to dormancy. Sometimes seeds may be quite capable of germination but they fail to germinate due to the non-availability of sufficient moisture or temperature. This state is called quiescence state of seed and the seed and the embryo are called quiescent seed and quiescent embryo.
The quiescence state of seed is usually referred to a state of suppression of embryo growth imposed by external factors outside the seeds. On the other hand, dormant state is the suppression of embryo growth due to internal factors within the seeds. Thus, dormancy is defined as the condition of seed when it fails to germinate even though the environmental conditions usually considered favourable for active growth is present.
2.What is the role of abscisic acid in seed dormancy?
Answer: Arabidopsis a member of Brassicaceae family has been used to demonstrate the role of abscisic acid in seed dormancy. It has several ecotypes some of which are abscisic acid deficient while the wild types have abscisic acid. Abscisic acid deficient mutants are not dormant and readily germinate at maturity. Exogenously applied abscisic acid in these seeds could not induce dormancy. Not only this, paternal or maternal abscisic acid also failed to induce dormancy when reciprocal crosses were made between wild types and abscisic acid deficient types. Dormancy was shown by these seed only when the embryo itself produced abscisic acid. The influence of abscisic acid on seed dormancy is also contributed by the concentration of other hormones. For example, in most plants, it has been observed that as the level of indole acetic acid and gibberellic acid declines, the concentration of abscisic acid increases.
3. Explain the role of gibberellic acid in seed dormancy.
Answer: Seeds of some wild plant species require light or cold to induce germination. These changes in the conditions are usually associated with changes in gibberellin levels, therefore, the dormancy of such seeds can be overcome by application of gibberellin. It may be a natural regulator in the process of germination. In barley, application of gibberellic acid has been found to stimulate α-amylase secretion in the aleurone layer of the seed. The α-amylase consists of multiple isozymes. Besides this, β-amylase and other starch-degrading enzymes such as proteases are involved in mobilizing the food reserve in the endosperm. Mobilization of food reserves probably facilitates seed germination.
4. Explain the role of chemicals in seed dormancy.
Answer: Presence of some chemical substances such as coumarin, phenolic acid, para-ascorbic acid etc., and hormone like abscisic acid in the embryo, endosperm or seed coat of certain seeds may induce dormancy. Such seeds fail to germinate so long as the concentration of these chemical remains high. Concentration of such chemical substances and growth inhibitors can, however, be reduced by various treatments such as chilling exposure to fluctuating temperature, exposure to light, treatment with growth promotors like gibberellins and cytokinins and chemicals like thiourea, potassium nitrate etc. Seeds subjected to chilling or treatment with low temperature results in the breaking down of abscisic acid and promotion of gibberellic acid synthesis. This helps in releasing the seed dormancy caused due to the presence of inhibitors.
5. What is vivipary? Give examples.
Answer: Some plants, which grow in sea coasts show a special kind of germination known as vivipary. In this case, the seed germinates while it is inside the fruit, which remains attached to the plant. The radicle of the soil grows rapidly and comes out piercing the fruit wall. It elongates and becomes stout. Later on, due to its weight, the fruit gets detached from the plant and falls vertically down. The elongated portion of the radicle pierce into the soil and soon develops lateral roots which gives anchorage to the growing seedling. The plumule grows upwards and gives rise to the shoot for example, Rhizophora etc.
6. What are the conditions necessary for germination of seeds?
Answer: (1). Moisture: For the germination of the seeds and grains, availability of water or moisture is the most important condition. The protoplasm of the cells of the seed remains almost inactive or in a dormant state at a very low moisture content. When the moisture content of the soil is increased, their vital activity is also accelerated.
(2). Oxygen: Oxygen is essential for respiration of the growing cells. Respiration helps in the liberation of a great amount of energy required for the various growth processes of the embryo.
(3). Temperature: A number of physiological processes occur within the seed during germination of the seeds. Therefore, suitable temperature is always necessary for germination. At a very low or high temperature, respiration and other vital processes are retarded or completely checked.