NCERT Class 11-Biology: Chapter – 15 Plant Growth and Development Part 9 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Long Answer Type Questions

Question 1:

Some varieties of wheat are known as spring wheat while others are called winter wheat. Former variety is sown, and planted in spring and is harvested by the end of the same season. However, winter varieties, if planted in spring, fail to flower or produce mature grains within a span of a flowering season. Explain, why?


Some plants are dependent on exposure to low temperature for flowering. This is called verbalisation. It allows plant to have adequate time to reach maturity. The ‘spring’ variety of wheat are sown in the spring and is harvested by the end of the same season while Winter varieties if planted in spring would normally fail to flower or produce mature grain within a span of a the flowering season so they are sown in autumn. Then they take time to germinate and over winter they come out as seedlings. After that, they resume growth in the season of spring. Following which they are harvested around midsummer.

Winter wheat

Winter Wheat

Spring Wheat

Spring Wheat

Question 2:

It is known that some varieties of wheat are sown in autumn but are harvested around next mid-summer.

a. What could be the probable reason for this?

b. What term is used for this promotion of flowering under low temperature?

c. Which plant hormone can replace the cold treatment?


a. Varieties of wheat which are the winter varieties would not normally flower in in a single flowering season available.

When they are planted in autumn, they take their time to germinate and over the winter period, seedlings are noticed which resumes its normal growth during the spring season so get harvested around the next midsummer.

b. Promotion of flowering under low temperature is called vernalization.

It is one of the important adaptations of plants growing at high altitudes to ensure that flowering occurs during the summer or warmer temperatures giving time for the development of seed in the plant.

c. The plant hormone that can replace the cold treatment is called gibberellin.

Plants that need cold treatment require photoperiodism to induce flowering in them. Without this treatment, vernalization has no effect. But it is observed that when these plants are treated with gibberellins (GA) , they undergo flowering without subjecting the plants to cold environment and photoperiodism. Gibberellins are seen not only to substitute vernalization but also photoperiodism.

Vernalization- It is a process of cooling of seeds during its period of germination to induce faster flowering in them.

Photoperiodism: Physiological response of plants to day or night length or light exposure.

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