Class 12th Biology Chapter 1 - (Reproduction In Organisms) Removed From Syllabus For 24-2025

NCERT Solutions for Class 12 Biology Chapter 1 : This chapter is about Reproduction in Organisms. We are going to cover the topics like Reproduction, Modes of Reproduction, Asexual Reproduction and Sexual Reproduction. We have prepared this article very carefully and tried to include all those important topics and notes from the chapter which you can use in your preparation for 12th exam or any other upcoming competitive exams. 

 

In this chapter we have covered all the topics related to Reproduction in Organisms which are listed below:-

1. Reproduction 
2. Modes of reproduction 
3. Asexual reproduction 
4. Vegetative propagation in plants 
5. Importance of vegetative propagation 
6. Limitation of vegetative propagation 
7. Sexual reproduction 
8. Events in sexual reproduction
9. Sexuality in plants
10. Sexual reproduction in flowering plants
11. Sexuality in animals
12. Parthenogenesis
13. Oestrus and Menstrual Cylcles 

 

                                           Reproduction in Organisms

 

Reproduction

The process by which the formation of new individuals of same kind with slight genetic , structural and physiological variation  is known as reproduction.

Types of reproduction in organism

1.Asexual reproduction

2.Sexual reproduction

1. Asexual reproduction

 When a single organisms is capable of producing its own kind and are genetically identical then this process is known by asexual reproduction.

 

It takes place through budding , fragmentation, spores , etc

Asexual reproduction may take place by following methods.

1.Fission

The body of the organism after attaining a certain size it simply divides into two or more parts having a part of nucleus.

Two types of fission

Binary fission

In this method two individuals are formed from a single parents.The fission may be irregular, transverse or longitudinal.

Multiple fission

In this method the parent body is divided into many daughters organisms like Plasmodium vivax or malarial parasite.

2.Budding

In this process the protoplast bulges out in the form of a bud and it is separated from the mother cell.

3.Gemmule formation

All fresh water and marine sponges reproduce asexually by exogenous buds known as gemmules.

4.Regeneration

The power of replacement or regenerate of lost parts is called regeneration.Ex-Hydra

5.Fragmentation

In this method the thallus breaks into smaller fragments and they have capability to grow independently into a new thallus.ex- Algae-Ulothrix.

 

2 . sexual reproduction

The development  of the new individual which takes place by the fusion of two sex cells ,one male gamete and the other one which is female gamete .

The Zygote is formed by the fusion of sperm ( male)

Ovum (female) gametes and when they meet they form embryo.

 

Lifespan of some organisms

1.Tortoise.        150-200 years

2.Rose plant.    6-10 years

3.Rice plant.      4 -7 months

4.Butterfly.        1-2 weeks

5.Parrot               140 years

6.Horse.              60 years

Vegetative propagation in plants

When  new plants regenerate from the vegetative part then it is known as vegetative reproduction or propagation.

Two types of vegetative propagation in plants are

Natural vegetative propagation

Artificial vegetative propagation

Natural vegetative propagation

When a new plant grows from the detached portion  the body of mother plant under a suitable control like soil, air , sunlight, etc. this process is known as natural vegetative propagation.

1.leaves

 In the leaves of a plant there grows a foliar bud on the leaf margin which grows into new plants.Ex-Begonia, Bryophyllum

 

Artificial vegetative propagation

 A new plant grows when the portion is separated from the mother plant.It take place by some methods which are known as layering , cutting , etc.

1.Grafting

 

The process of joining the parts of two different plants in one plant as a manner that they live as one plant.

 

 

Propagation by plant tissue culture OR Micropropagation

The technique of propagation which involves the cell, tissue and organ culture is known as Micropropagation.

Tissue culture technique is used for orchids, ornamental plants, etc.

Importance of vegetative propagation

It is important because it is the easier , less costly and  faster  process of multiplying plants which have seed dormancy.

Clone

The plants which are multiplied by vegetative propagation are copies of the parent ,and they are derived from an individual is called a clone.

Limitation of vegetative propagation

They are easily uprooted during storms.

It requires technical experts.

It does not involve meiosis and fusion of gametes.

Events.in Sexual reproduction

Pre -Fertilization

Fertilization

Post -fertilization

Pre -Fertilization

Fusion of gametes in sexual reproduction is knows as pre Fertilization .Two events are

Gametogenesis and gamete transfer.

Fertilization

The transfer and coming of gametes together is the most critical events .

Fusion of male and female gamete is known as syngamy.

It results in formation of diploid zygote.

In aquatic organisms syngamy occurs outside the body of organisms and this is known as external Fertilization.

In plants and animals the gamete fusion takes place inside the body it is known as internal fertilization.

Post fertilization events

 After the formation of zygote in sexual reproduction is called post fertilization events.

Embryogenesis.

Development of embryo from the zygote is known as embryogenesis.

Sexuality in plants

Plants are of two kinds.

1.Bisexual or Staminate or Dioecious

Examples. Papaya

2.Unisexual or pistillate or monoecious

Examples.Coconut

Sexual reproduction in flowering plants

Diploid sporophytic phase and haploid gametophytic phase are the two phases in the life cycle of angiosperms.

Process of sexual reproduction

Microsporogenesis

The formation of microspores from the sporogenous tissue is called Microsporogenesis.

 Development Of male gametophyte

The mother cell of the mail gametophyte is microspore or pollen grain.

Later on,they divide into two unequal cells. Smaller one is generative cell and lager is vegetative cell.The generative cell divides mitotically to form two non motile male gametes.

 

Sexuality in animals

In animals sperms and ova are produced which is known as gonads. The male testis produce sperms and female gonad is known by ovary.

 

Oviparous and viviparous  organisms

Based on development of zygote which takes place inside or outside the body of the female parent or whether they lay fertilized or unfertilized eggs or give birth to young ones.They are classified into oviparous and viviparous organisms.

 

Parthenogenesis

In sexual reproduction in which development of eggs occurs without the participation of sperm cells.

Oestrus vs Menstrual Cycle

In primates monkeys , humans.The female exhibit cyclical changes in the activities of ovaries and accessory ducts is known as menstrual cycle.

The sexual activities of the females occur cyclically outside these cycles the female do not have any sexual activity is known as oestrus cycle.

In non primates like cows , dogs .The female receives the male only at certain periods and this is known as breeding season.

 

Oogenesis

The process which are involved in the growth and maturation of ovum in preparation for Fertilization is called oogenesis.

Parthenocarpy 2018

The formation of fruits without the process of Fertilization.

Pollination

The transfer of pollen grains from the anther of flower to the stigma of the other flower or same flower .

 Autogamy or Self Pollination

The transfer of pollen grains from the anther of flower to the stigma of the same flower .

Cross Pollination

The transfer of pollen grains from the anther of flower to the stigma of the another flower .

Geitonogamous

If the cross Pollination is occurred on the two flowers of same plant.

Xenogamy

If the cross Pollination is occurred on the two flowers of different plants.

Nucellus

The parenchymatous body which is present on the ovary which develops the ovule within it.

The nucleus is protected by one or two sheath which is knows as integuments

Micropyle

The small opening at the one end of the integument.

Megasporogenesis

The development of megaspore within ovule or megasporangium .

Embryogenesis

The process by which the development of mature embryo from diploid zygote takes place is called embryogenesis.

Double Fertilization

 The fusion of male nucleus with the egg and the other with polar nuclei which is unique to angiosperms is known as double Fertilization.

A phenomenon first discovered by S.G.Nawaschin 1897 in Lilium and Fritillaria species.

 

 

Funicle

The stalk by which the ovule is attached to the placenta is called funicle.

 

Totipotency

It is defined as that every living cell is capable of regenerating a whole organism.

Spermatogenesis

In this process the spermatogonia undergo through Meiosis and transform into spermatozoa.

Sexual cycle

The physiological and structural changes which are associated with sex.

SEED

It is the mature ovule which contains the embryonic plant and have stored food material and protective coat .

Parthenogenome or parthenote

The organism that  has developed parthenogenetically.

Chromosome numbers in meiocytes  2n and gametes n of some eukaryotic organisms.

Plant species

Organisms	Chromosome numbers in gametes (n)	Chromosome numbers in meiocytes (2n)
Zea mays or maize	10	20
Allium cepa or onion	8	16
Pyrus malus or apple	17	34
Nicotiana tabacum or tobacco	24	48
Oryza sativa or Rice	12	24
Triticum vulgare or wheat	21	42

 

Animal species

Organisms	Chromosome numbers in gametes (n)	Chromosome numbers in meiocytes (2n)
Culex pipiens or mosquito	3	6
Musca domestica or house fly	6	12
Rattus rattus or rat	21	42
Canis familiarise or dog	39	78
Homo Sapiens or human	23	46
Felis domesticus or cat	19	38

 

Types of asexual spores in fungi

Sporangiospores 

Conidia

Asexual reproduction	Sexual reproduction
Fast process	Slow process
No gametes formed	Gametes are formed
More offspring	Less offspring

 

Juvenile phase

 The organisms have to reach to a certain stage of growth and maturity in their life before they can reproduce sexually.

 

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