CBSE Board Class XII – NCERT Biology
Chapter 1, Reproduction in Organisms
(NCERT solutions of Class 12 Biology textbook chapter exercise questions)
Question 1: Why is reproduction essential for organisms?
Solution: Reproduction is the ability of all living organisms to produce young ones (offspring) similar to themselves in most of characters. The offspring grow, mature and produce new offsprings thus, completing the cycle of birth, grow and death. This way reproduction enables the continuity of the species generation after generation.
Question 2: Which is better mode of reproduction sexual or asexual? Why?
Solution: Sexual reproduction is a better mode of reproduction because though the events of sexual reproduction are elaborate and complex but they follow a regular sequence.
Question 3: Why is the offspring formed by asexual reproduction referred to as clone?
Solution: Asexual reproduction does not involve the formation or fusion of gametes. Thus, a single parent is capable of producing offsprings. The offsprings so produced are identical to each other and are exact copies of their parent. They are morphologically and genetically similar individuals so, they are referred to as clone.
Question 4: Offspring formed due to sexual reproduction have better chances of survival; why? Is this statement always true?
Solution: Sexual reproduction involves the formation and fusion of gametes. These gametes are male and female either from same individual or by different individuals of the opposite sex. These gametes fuse (syngamy) to form zygote which develops to form new organism. This way the offsprings are not identical to themselves or to their parents.
These offsprings are genetically different from their parents as variations appear due to new combinations of genes during crossing over, chance of seggregation of chromosomes and chance of fusion of gametes. Thus, there are more chances of elimination of unfavourable traits in sexual reproduction so giving better survival to the offsprings. No, the above statement is not always true. If the mother is suffering from any major disease or any other ailment the offspring may not survive.
Question 5: How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Solution: In asexual reproduction the participation of two organisms is not required, no gametes are formed. Somatic cells of the parent undergo mitotic divisions and produce the offsprings. So, the next generation will be the exact copy of the parent.
Sexual reproduction is generally biparental. It involves the production of specialised sex cells i.e. male and female gametes. They undergo fusion and form zygote. It involves the process of fertilisation. During fertilisation both the parental traits fuse and variations appear. The offsprings are genetically different from the parents. Thus, giving better chances of survival for the most favourable ones. It plays important role in evolution.
Question 6: Distinguish asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
1. Always uniparental reproduction.
2. No gametes are formed.
3. It involves only mitotic divisions.
4. No fusion of gametes occurs.
5. Offsprings are genetically similar to the parents.
6. Rate of reproduction is faster.
7. Units of reproduction can be whole parent body or bud or body fragment.
8. Occurs in lower invertebrates and lower chordates and plants with simple organizations.
1. Generally biparental except Taenia, Fasciola.
2. Male and female gametes are formed.
3. Meiosis occurs at the time of gamete formation and mitosis occurs after fertilization.
4. Male and female gametes fuse to form zygote.
5. Offsprings are genetically different from the parent.
6. Rate of reproduction is slower.
7. Unit of reproduction are gametes.
8. Found in higher plants and animals.
Vegetative reproduction involves a single parent and there is no formation and fusion of gametes; hence, it is considered as asexual reproduction.
Question 7: What is vegetative propagation? Give two suitable examples.
Solution: Vegetative propagation is the process of formation or regeneration of new plants from a portion of a vegetative part of the plant.
E.g., Eyes of potato, Leaf buds of Bryophyllum. (See figures below)
Question 8: Define: (i) Juvenile phase, (ii) Reproductive phase, (iii) Senescent phase
Solution: (i) Juvenile Phase
Period of growth of an organism from birth till attaining reproductive maturity is called "juvenile phase".
In plant, it is called vegetative phase.
In perennial plants, vegetative growth continues through the year. It is more in spring and rainy season and less during winter and summer season.
(ii) Reproductive Phase
Period in the life of an organism after it attains sexual maturity and starts reproducing is called "reproductive phase". In perennial plants, flowering occurs in particular season of every year. In biennial plants, flowering occurs in a particular season. E.g. cabbage, radish, carrot and sugar beet.
(iii) Senescent Phase
The period in the life cycle of an organism between the end of sexual maturity and death. Degradative/Deteroriate changes takes place in the structure/function of organs.
Question 9: Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Solution: In sexual reproduction, separate male and female gametes fuse to form a zygote which develops to form embryo and later, a complete organism. It is an elaborate and complex process. It involves slow multiplication and units of reproduction are haploid gametes. Since, the offsprings are genetically different from the parents as variations appear due to new genetic combinations during crossing over, chance of seggregation of chromosomes, and chance of fusion of gametes. So, better chances of survival are there in the next generation. This leads to selection of better traits at each generation and ultimately to the evolution.
For rest exercise questions (10 – 18) and Solutions of CBSE Hot Questions for Chapter 1, Reproduction in Organisms, click below –