CBSE Class 8 Science Chapter 9: Reproduction in Animals NCERT Solutions

Solution: Reproduction is a fundamental biological process that ensures the continuity of life on Earth. Its primary importance lies in the continuation of a species from one generation to the next. Without reproduction, a species would eventually die out. It also allows for the propagation of characteristics and traits, maintaining the identity of the species over time. Essentially, reproduction is the mechanism that allows life to persist and evolve.

Solution: Fertilization in human beings is a form of sexual reproduction that involves the fusion of male and female gametes. The male reproductive organs produce numerous microscopic male gametes called sperms. The female reproductive organs produce a female gamete called an ovum (egg). During sexual intercourse, sperms are transferred into the female reproductive tract. If ovulation has occurred, a sperm may travel to meet the ovum, typically in the fallopian tube. The fusion of a sperm nucleus with the ovum nucleus results in the formation of a single diploid cell called a zygote. This process is known as internal fertilization. The zygote then begins to divide and develop into an embryo, which implants in the wall of the uterus and continues to grow.

Solution:

1. Internal fertilization occurs (i) in female body. This is because the fusion of sperm and ovum takes place within the female reproductive system.
2. A tadpole develops into an adult frog by the process of (iii) metamorphosis. Metamorphosis is a biological process where an animal undergoes a dramatic change in form from its immature to adult state.
3. The number of nuclei present in a zygote is (ii) one. A zygote is formed by the fusion of one sperm nucleus and one ovum nucleus, resulting in a single nucleus containing the combined genetic material.

Solution:

(a) Oviparous animals give birth to young ones. (False). Oviparous animals lay eggs, while viviparous animals give birth to young ones.

(b) Each sperm is a single cell. (True). A sperm is the male gamete, which is a single cell specialized for fertilization.

(c) External fertilization takes place in frog. (True). Frogs typically reproduce in water, where the female lays eggs and the male fertilizes them externally.

(d) A new human individual develops from a cell called gamete. (False). A new human individual develops from a zygote, which is formed by the fusion of two gametes (sperm and ovum).

(e) Egg laid after fertilization is made up of a single cell. (True). The fertilized egg, or zygote, is initially a single cell. If it is laid as an egg (like in birds or reptiles), it starts as this single cell and develops further.

(f) Amoeba reproduces by budding. (False). Amoeba reproduces primarily by binary fission, not budding.

(g) Fertilization is necessary even in asexual reproduction. (False). Fertilization is the fusion of gametes, which occurs in sexual reproduction. Asexual reproduction does not involve gametes or fertilization.

(h) Binary fission is a method of asexual reproduction. (True). Binary fission is a common mode of asexual reproduction in unicellular organisms like Amoeba and bacteria.

(i) A zygote is formed as a result of fertilization. (True). Fertilization is the process that leads to the formation of a zygote.

(j) An embryo is made up of a single cell. (False). An embryo is a multicellular organism that develops from a zygote through repeated cell division and differentiation.

Solution:

Here are two key differences between a zygote and a fetus:

1. Cellularity: A zygote is a single-celled structure formed immediately after fertilization. In contrast, a fetus is a multicellular stage of development that results from the repeated division and differentiation of the zygote.
2. Development of Body Parts: A zygote does not have any defined body parts; it is simply a fertilized egg. A fetus, however, develops recognizable body parts such as limbs, organs, and other structures, becoming more complex over time.