NCERT answers of CBSE Class 12 Biology Chapter 1, Reproduction in Organisms


CBSE Board Class XII – NCERT Biology

Chapter 1, Reproduction in Organisms

(NCERT solutions of Class 12 Biology textbook chapter exercise questions)

To see answers of Question 1 – 9 please click below
Question 10: Explain why meiosis and gametogenesis are always interlinked.
Answer: Meiosis occurs at gametogenesis stage in diploid organisms during gamete formation. As a result, the gametes become haploid. By the fusion of two such haploid gametes, a diploid zygote is formed, and it develops involving mitotic divisions. Thus, meiosis maintains the characteristic number of chromosomes constant.
In this way, meiosis and gametogenesis are always interlinked.
Question 11: Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n):
(a) Ovary  (b) Anther (c) Egg (d) Pollen (e) Male gamete (f) Zygote
(a) Diploid (b) Diploid (c) Haploid (d) Haploid (e) Haploid (f) Diploid
Question 12: Define external fertilisation. Mention its disadvantages.
Answer: External Fertilisation- When fusion of gametes occurs outside the body of organisms (in the external medium like water), the process is called "external fertilisation".
Its major disadvantages are as follows:
1. A large nunnery of gametes are required.
2. A large number of offsprings are produced.
3. Chances of gametic fusion are less.
4. The chances of syngamy are less.
5. The offspring formed are extremely vulnerable to predators, which threaten their survival upto adulthood.
6. They are also exposed to harsh environmental condition.
Question 13: Differentiate between a zoospore and a zygote.
CBSE Class 12 NCERT Biology - Reproduction in Organisms (Zoospores of Chlamydomonas image)
Fig: Zoospores of Chlamydomonas
1. They are involved with asexual reproduction.
2. Zoospores are formed in simple plants, algae, or fungi.
3. They are microscopic motile structures formed from parent body. No gametic fusion is involved.
 CBSE Class 12 NCERT Biology - Reproduction in Organisms (image of Zygote)
Fig: Zygote
1. They are involved in sexual reproduction.
2. Zygote is formed in complex organisms.
3. This is formed because of fusion of male and female gametes.

Question 14: Differentiate between gametogenesis from embryogenesis.
1. Gametogenesis involves the formation of haploid gametes in the gonads.
2. It leads to fertilisation.
3. It is of two types:
(a) spermatogenesis, and
(b) oogenesis.
4. It is variable in different organisms.
1. Embryogenesis involves the transformation of zygote into a multicellular organism.
2. It leads to birth.
3. It is a complex process which involves:
(a) gametogenesis, (b) fertilisation, (c) cleavage, (d) gastrulation, (e) organogenesis.
4. It includes a definite series of phases which are fundamentally similar in all sexually reproducing organisms.
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Question 15: Describe the post-fertilisation changes in a flower.
Answer: Post-fertilisation changes in a flower:
1. After fertilisation, the sepals, petals and stamens of the flower wither and fall off.
2. The pistil remains attached to the plant.
3. The zygote develops into an embryo (embryogenesis) inside the ovule.
4. The ovule develops into a seed.
5. The ovary transforms into the fruit with a thick wall, called pericarp.
6. The seeds are dispersed after maturity.
Question 16: What is a bisexual flower? Collect 5 bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Answer: Flowers which contain both stamen and pistil are called hermaphrodite or bisexual flowers e.g., sweet potato.
[For second answer, consult your schoolteacher]
Question 18:  Why are offsprings of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Answer: In oviparous animals, the development of zygote takes place outside the body of the female parent i.e. they lay fertilised egg in safe environment. These eggs are covered by hard calcareous shells and hatch young ones after a period of incubation. Because of lack of proper parental care and risk of predators, the offspring of oviparous animals are at a greater risk for survival. On the other hand, in viviparous animals, the zygote develops into a young one inside the body of the female organism. After attaining a certain age of growth, the young ones are delivered out of the body of female organism. Thus, due to proper embryonic care and protection, the chances are survival of young ones is greater in viviparous organisms.
To see answers of Question 1 – 9 and Solutions of CBSE Hot Questions and Value Based Questions (VBQs) for Chapter 1, Reproduction in Organisms, please click below:

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