12 Biology


Extra Questions

Question 1: What is reproduction?

Answer: The biological process through which an organism gives rises to young ones (offspring) similar to itself, is called reproduction.

Question 2: What are the different types of reproduction? Explain each type in brief.

Answer: There are two types of reproduction, viz. asexual reproduction and sexual reproduction.

Asexual Reproduction: When a single parent participates in reproduction, and gamete formation does not take place; it is called asexual reproduction. Offspring which are produced by means of asexual reproduction are identical or clones to their parent.

Sexual Reproduction: When two parents (of opposite sexes) participate in reproduction, and gamete formation takes place; it is called sexual reproduction. In some examples of sexual reproduction, a single parent may produce both the male and female gametes and participate in reproduction.

Question 3: What do you understand by binary fission?

Answer: Binary fission is a type of asexual reproduction. This method is common in unicellular organisms. In this method, the mother cell undergoes mitotic cell division to produce two daughter cells. Binary fission is seen in Protista and Monera.

Question 4: What do you understand by budding?

Answer: This is a type of asexual reproduction. Reproduction by budding can be seen in yeast. In this method, the cell undergoes unequal division and produces small buds. The buds separate from mother cell on maturation and start life as new individuals.

Question 5: What is spore formation?

Answer: Spore formation is a method of asexual reproduction. Some species of algae and fungi reproduce by spore formation. Special asexual reproductive structures are formed in these organisms. Zoospores are the most common structure among such asexual reproductive structures. Zoospore is usually a microscopic motile structure.

Question 6: What is vegetative propagation?

Answer: When reproduction takes place through vegetative parts rather than reproductive parts in these plants, it is termed as vegetative propagation. In this method, a new plant is produced from roots, leaves or stems. Examples of vegetative propagules are; eyes of potato, rhizome of ginger, bulbil of agave, leaf buds of bryophyllum, offset of water hyacinth, etc.

Question 7: What is juvenile phase?

Answer: The period of growth before onset of sexual maturity is called juvenile phase. This phase is called vegetative phase in plants.

Question 8: What do you understand by oestrous cycle?

Answer: The cyclical changes in females of non-primates during reproductive phase are called oestrous cycle. In this case, the animal resorbs the endometrium in case pregnancy does not happen.

Question 9: What is menstrual cycle?

Answer: The cyclical changes in females of primates during reproductive phase are called menstrual cycle. In this case, the animal sheds the endometrium in case pregnancy does not happen. Endometrium is shed in fragments along with blood by means of menstrual flow.

Question 10: Which are the key pre-fertilisation events?

Answer: Gametogenesis and gamete transfer

Question 11: What is isogamous condition?

Answer: In some species the two gametes are similar in appearance, and it is not possible to categorise them into male and female gametes. Such condition is called isogamous condition.

Question 12: What is anisogamous or heterogamous condition?

Answer: In majority of sexually reproducing organisms, the gametes are of two morphologically distinct types. Such condition is called anisogamous or heterogamous condition. The smaller gamete is the male gamete and is called antherozoid or sperm. The larger gamete is the female gamete and is called the egg or ovum.

Question 13: What is the difference between a staminate flower and a pistillate flower?

Answer: A staminate flower produces only the male gametes, while a pistillate flower produces only the female gamete.

Question 14: Why do organisms produce male gametes in significantly large numbers compared to the number of female gametes?

Answer: In most of the organisms, female gamete is stationary while the male gamete is motile. The male gamete needs to be physically brought near the female gamete to facilitate fertilization. During the process of transfer majority of male gametes are lost in transit. To compensate for this loss of male gametes during transport; organisms produce male gametes in several thousand times the number of female gametes produced.

Question 15: What is parthenogenesis?

Answer: The female gamete in some organisms develops to form a new organism without fertilization. This phenomenon is called parthenogenesis, e.g. some lizards, rotifers, honeybees and some birds (turkey).

Types of Reproduction

Patterns in Sexual Reproduction

Gamete Transfer

NCERT Solution

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