In the cycle of life, reproduction is a vital process. Each organism leaves its progeny by means of sexual or asexual reproductive methods. Between the phase of life and death, an organisms go through a biological process to give rise to offspring, which grow and mature into new organisms. The chapter mainly discusses about the topics:
- Asexual Reproduction
- Sexual Reproduction
The NCERT Solutions for Class 12 Reproduction in Organism throws light on following topics:
Asexual Reproduction: A single individual or parent can give rise to a young one similar to itself. The offspring are not only identical, but are the exact copies of parent organisms. This method of reproduction is commonly found in single-celled organisms and in organisms with simple organizations. In Protista and Monera, the individual organisms divide into two to give rise to offspring. It also involves the process of binary fission. In some other organisms like yeast, the structures called buds that are initially attached to the organism detach and mature to form new individuals. Asexual reproduction is also made possible by some specialized asexual reproductive structures in organisms like fungi and few algae. Some of the examples for these structures include zoospores, conidia, gemmules, etc.
Vegetative reproduction is also very much common in plants, which is again a type of asexual types of reproduction. Reproduction is achieved in plants with structures like runner, rhizome, tuber, offset, bulb, and sucker. These are also termed as vegetative propagules. Also, in Bryophyllum, one can find structures called nodes which modify into stems and can grow independently.
Sexual Reproduction: The CBSE Class 12 Biology Chapter 1 further discusses about sexual reproduction. This mode of reproduction involves the formation of male and female gametes, which fuse to form a structure called zygote, which develops into a new organisms. The structures maybe produced in the same organism of different organisms. Although the morphology and physiology differs in organisms undergoing sexual reproduction, the pattern remains constant across plants, fungi or animals. Every organism has to attain growth and maturity, before it can reproduce sexually, which is often referred to as juvenile phase. The end of juvenile phase, also called as vegetative phase in plants marks the start of reproductive phase.
Some of the important events in the process of sexual reproduction are:
- Pre-Fertilization Events: Involves the events prior to the fusion of male and female gametes. The main phenomenon in this phase are: (I) Gametogenesis- process of formation of gametes, maybe homogametes or heterogametes and (II) Gamete Transfer- Transfer of gametes to a medium or site to fuse. This mainly depends on the nature and method of carriage of gametes.
- Fertilization: This event involves the fusion of gametes. It is also referred to as syngamy and leads to the formation of a zygote which is diploid in nature. The process of fertilization maybe I) External fertilization- Fertilization occurs outside the body of the organisms or II) Internal Fertilization: Fertilization occurs inside the body of the organism.
- Post-Fertilization Events: It involves all the events that occur after the formation of the zygote. Few of the most important events are I) Initial development of Zygote and II) Embryogenesis: Formation of Embryo from a Zygote.