Biology - Class Twelve
REPRODUCTION IN ORGANISMS
NCERT Solution - Part-2
Answer:
| Asexual Reproduction | Sexual Reproduction |
|---|---|
| Single parent is involved in reproduction. | Two parents are involved in reproduction. |
| Gametes are not formed. | Two types of gametes are formed. |
| Fertilization is not involved. | Fertilization is an important step in sexual reproduction. |
| Progeny is a clone of its parent. | Progeny can never be a clone of its parents. |
| Is a simple process; involving only mitosis. | Is a complex process; involving both meiosis and mitosis. |
Since vegetative propagation involves a single parent and no gamete formation is required, hence it is also considered as a type of asexual reproduction.
(7) What is vegetative propagation? Give two suitable examples.
Answer: Most of the flowering plants reproduce sexually, but many of them also have the capability to produce a new plant through their vegetative parts; such as roots, stems and leaves. When a new plant is formed from vegetative part, this is called vegetative propagation. Example: A stem cutting from a rose plant gives rise to a new plant. Pieces of potato tuber give rise to new plants.
(a) Juvenile phase,
Answer: The phase before an organism attains sexual maturity is called the juvenile phase. In humans, the juvenile phase lasts till the beginning of puberty.
(b) Reproductive phase,
Answer: The phase when an organism attains sexual maturity and is ready and capable of sexual reproduction is called reproductive phase.
(c) Senescent phase.
Answer: The phase when an organism loses its capability of sexual reproduction is called senescent phase.
Question-(9) Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Answer: Sexual reproduction entails many advantages. Sexual reproduction facilitates selection of suitable genes to be transferred to the next generation. Sexual reproduction enables some organism to take better care of progeny. It also facilitates variations and thereby evolution. Hence, in spite of its complexities; higher organisms have resorted to sexual reproduction.
Question-(10) Explain why meiosis and gametogenesis are always interlinked?
Answer: A gamete is a haploid cell. Haploidy is necessary in gametes because fertilization involves fusion of two nuclei which results in doubling the number of chromosomes in zygote. We know that haploid cells are formed only after meiosis, hence meiosis is always interlinked with gametogenesis.