Reproduction in Organisms Class 12th Notes - Free NCERT Class 12 Biology Chapter 1 Notes - Download PDF

Don't you wonder how the species of any organism survive from year to year? In this chapter, you're gonna study that how reproduction takes place in different-different organisms as it becomes a vital process and without this process, species cannot survive for long, so they need to produce their generation. Through the NCERT notes for class 12 biology chapter 1 reproduction in the organism, you will be able to solve all the doubts and questions of this chapter. These class 12 Biology chapter 1 notes will help to score good marks in the exams.

1. What is life span?

It is the period from birth to the natural death of an organism that represents the life span of an organism. From organism to organism it can vary from even less than a day to more than 400 yrs. It is important to know that life spans of organisms are not necessarily correlated with their sizes, for example: the sizes of crows and parrots are not very different yet their life spans show a wide difference. Similarly, if we talk about trees then a mango tree has a much shorter life span as compared to a peepal tree.

Given below is the lifespan of some organisms:

But always remember that, the death of every individual organism is a certainty, that is no individual is immortal, except single-celled organisms.

2. What is Reproduction?

Reproduction is the biological process in which an organism gives rise to their young ones/offspring that are similar to them. These offspring grow, mature, and in turn, produce new offspring.

Importance of reproduction:

(i) It enables the continuity of the species.

(ii) It maintains and balances life on the earth.

(iii) It creates variations and evolution among the population.

There are many factors like an organism's habitat, its internal physiology and several other factors that are collectively responsible for how they reproduce.

Based on whether there is the participation of one organism or two in the process of reproduction, there are two types of reproduction:

(i) Asexual reproduction

(ii) Sexual reproduction

3. Asexual reproduction:

In this method of reproduction, a single individual (parent) is capable of producing offspring. As a result, the offspring that are produced through asexual reproductions are not only identical to one another but are also exact copies of their parents.

They are also called clones because they are morphologically and genetically similar to each other and this reproduction is common among single-celled organisms.

Different types of asexual reproduction are given below:

A. Fission

Further fission can be classified as:

Binary fission

In binary fission of asexual reproduction, the body of an individual divides into two equal halves and produces offspring.

It can be following types:

2 Multiple fission

In multiple fission of asexual reproduction the division of the parent body into many daughter organisms, e.g. Amoeba,

Plasmodium, Monocystis (all Protozoa).

B. Budding:

It is an outgrowth of buds that develops, grows, and constricts at the base and eventually gets separated from the parent body and mature into new organisms, for example, yeast and Hydra. Remember that the complex budded condition is called torala stage.

C. Sporulation:

Sporulation is the reproduction process which occurs by tiny, single-celled and thin-walled spores that are extremely resistant to environmental extremes. These spores are liberated in the surrounding medium to grow up into many individuals. This reproduction commonly occurs in Monera, Protista, Fungi and Algae.

Spore formation can be of different types and these are given below:

In plants, there are different units of vegetative propagation such as tuber, runner, offset, rhizome, sucker, bulb and they all have the capability to give rise to their new offsprings. Whereas, these structures are also known as vegetative propagules.

4. Sexual reproduction

Sexual reproduction is quite different from asexual one as it involves the formation of the male and female gametes, either by the same individual or by different individuals of two opposite sex. These gametes fuse to form the zygote which develops to form the new organism.

As compared to asexual reproduction, this is little slow process and due to the fusion of male and female gametes, it results in those offspring that are not necessarily identical to the parents or even amongst themselves.

Juvenile phase:

Organisms which are able to reproduce sexually have to reach a certain stage of growth and maturity in their life, before they can reproduce and this period of growth is called the juvenile phase which is similar to the vegetative phase in plants and this phase is also of variable duration in different organisms.

Oestrus cycle and Menstrual cycle:

In non-primate mammals for example: cows, sheep, rats, deers, dogs, tigers, etc., such changes are called the oestrus cycle whereas in primates, for example: monkeys, apes, and humans it is called the menstrual cycle.

Important events of sexual reproduction :

pre-fertilisation

fertilisation

post-fertilisation

Pre-fertilisation Events

Pre-fertilisation is the event that includes all the events of sexual reproduction prior to the fusion of gametes. The two main pre-fertilization events are gametogenesis and gamete transfer.

Gametogenesis : It is the process of formation of the two types of gametes that are male and female gametes. Whereas gametes are haploid through the parent plant body from which they arise and they may be either haploid or diploid. Haploid parent produces gametes by the process named mitotic division.

The figures mentioned below are showing the diversity of sexuality in different organisms:

1. Cockroach: Unisexual Animal

2. Earthworm: Bisexual Animal

3. Sweet Potato Flower: Bisexual Flower

Gamete Transfer : After their formation, male and female gametes must be physically brought together to facilitate fusion (fertilisation).

Pollination : It is the process that take place in cross pollinating plants which includes dioecious plants, as it facilitates the transfer of pollen grains to the stigma for fertilisation. Pollen grains germinate on the stigma and the pollen tubes carrying the male gametes reach the ovule and discharge male gametes near the egg.

2. Fertilisation Events

Fertilisation is the process in which male and female gamete fuse with each other to form a diploid zygote. This process is also called syngamy. When the fertilization takes place inside the body of the organism it will be called external fertilisation and when it takes place inside the body of an organism it will be called internal fertilization .

Parthenogenesis is the process in which zygote formation takes place without any fertilisation.

Post-fertilisation Events

Post-fertilisation events are those which take place after the fertilisation process; formation of the zygote in sexual reproduction.

Zygote Formation:

Organisms in which external fertilisation takes place, the zygote will form in the external medium; water, or any safe environment, whereas, organisms in which external fertilisation takes place, the zygote will form inside the body of the organism itself. Further development of the zygote depends on the type of life cycle and the environment the organism is exposed to.

3. Embryogenesis:

It is the process where the development of the embryo from the zygote takes place. During the process of embryogenesis, the zygote undergoes the process of cell division that is mitosis and cell differentiation to increase the number of cells in the developing embryo and cell differentiation.

It helps the groups of cells to undergo certain modifications to form specialised tissues and organs to form a complete organism.

In oviparous types of animals like reptiles and birds, the fertilised eggs are covered by a type of hard shell that is a calcareous shell.

And after the formation of the embryo from the zygote, the ovules develop into the seed. And then the ovary develops into the fruit that develops a thick wall which is called a pericarp and its function is to protect them.

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Chapter wise NCERT  link

1- NCERT Exemplar Class 12 Biology Solutions Chapter 1 Reproduction in Organisms

2- NCERT Chapter 3 Human Reproduction class 12 Biology