Reproduction in Organism Class 12 Notes CBSE Biology Chapter 1 (Free PDF Download)

Section–A (1 Mark Questions)

1. Name the organism that produces gemmule as an asexual reproductive structure?

Ans. Gemmules are the asexual reproductive structures produced by sponges.

2. “The offsprings produced by asexual reproduction are referred to as clones”. Why?

Ans. During asexual reproduction, there is no fusion of gametes and a single parent divides and redivides to produce the offspring. Hence, the offsprings are morphologically and genetically similar to the parents and therefore referred to as clones.

3. Among the annual and the perennial plants, which one has a shorter juvenile period. Explain.

Ans. The entire life cycle of an annual plant has to be completed in one year which is shorter than that of the perennial plants. Hence, it has a shorter juvenile period.

4. Rearrange the following events in the sequence in which they occur in the sexual reproduction of flowering plants: embryogenesis, fertilization, gametogenesis, pollination.

Ans. The sequence of events in sexual reproduction are as follows:

Gametogenesis → Pollination → Fertilization → Embryogenesis

5. Write the names of vegetative propagules in the following:

(i) Agave

(ii) Byophyllum

Ans. (i) Bulbil

(ii) Adventitious buds in the notches of leaf

Section–B (2 Mark Questions)

6. What are the two inherent characteristics of Amoeba and yeast that favor asexual reproduction in them?

Ans. The two inherent properties of Amoeba and yeast that help them to reproduce asexually are:

• They have relatively simple structures and can divide very quickly.

• They are uniparental.

7. Why is potato tuber considered as a stem though it is an underground part? Give two reasons in support of your answer.

Ans. The potato is referred to as a stem because:

• It has nodes and internodes.

• It can form plantlets from the buds present over the nodes.

8. Define fragmentation and vegetative propagation.

Ans. The definition of fragmentation and vegetative propagation is:

• Fragmentation is an asexual mode of reproduction. In this, the parent organism splits into several parts and each part grows into a new individual. For eg., Hydra.

• Vegetative propagation is an asexual mode of reproduction occurring in plants. The formation of a new individual from any vegetative part of the plant body is called vegetative reproduction. The structures which are used in vegetative propagation are called vegetative propagules. E.g., Eyes of potato.

9. Explain by giving two examples if there is a relationship between the size and the lifespan of an organism.

Ans. There is no relationship between the size and lifespan of an organism. For e.g.,

• The size of a crow and a parrot is the same but a crow can live for 15 years while a parrot, 140 years.

• The mango tree and the banyan tree have the same size but the lifespan of a mango tree is shorter than that of the banyan tree.

10. Give the chromosome number in the gametes of the following if the number of chromosomes in their meiocyte is as follows:

(i) Dog - 78, (ii) Housefly - 12, (iii) Rice - 24,  (iv) Onion - 16

Ans. (i)  Dog - 39, (ii) Housefly - 6, (iii) Rice - 12, (iv) Onion - 8

11. What is Gametogenesis? Support your answer with a suitable example.

Ans. Gametogenesis is the biological process by which diploid or haploid cells undergo cell division and differentiation to form mature haploid gametes. In humans, during the process of gametogenesis, two different types of gametes are formed. 

1. Male gametes are called sperm.

2. Female gametes are called the ovum.

PDF Summary - Class 12 Biology Reproduction in Organisms Notes (Chapter 1)

Life Span: The period which begins from birth and ends with the natural death of an organism is known as its life span.

Reproduction is an important biological process by which an organism will give rise to another organism similar to itself.

• Some basic facts about reproduction are discussed below.

• Reproduction is the process that ensures that species are continued from generation to generation. It leads to the development of genetic variation.

• This variation in genetics is inherited during reproduction.

• Reproduction in which only one parent is called asexual.

• Reproduction in which two parents of the opposite sex are involved in the fusion of male and female gametes is known as sexual reproduction.

Fig: Binary fission in amoeba

Fig: Sexual Reproduction

Asexual Reproduction

• In this asexual reproduction, only one parent participates in producing the offspring. As a result, the offspring produced are identical to each other and also to the parents.

• Asexual reproduction is most commonly seen in unicellular organisms, as well as in plants and animals with relatively simple organizations. It is also seen in organisms that are multicellular.

Asexual Reproduction in Animals

The most commonly seen modes of asexual reproduction  in the case of animals are as follows:

1. Fission: 

• Fission, commonly known as binary fission, takes place in prokaryotic microorganisms and a few multicellular organisms too.

• After a growth period, the organism is split into independent organisms. Some single-celled eukaryotes go through binary division via mitosis.

• In different organisms, part of an individual is separated and a second individual is formed.

• For example, in lots of asteroid echinoderms, this technique takes place while the central disk separates.

• Some sea anemones and a few polyps also reproduce via division.

• In some cases, it is seen that the nucleus divides several times by amitotic divisions. This leads to the formation of several new copies of nuclei. Cytoplasmic division does not take place during this time. The cytoplasm will accumulate around each nucleus. 

• Therefore, many unicellular and seedless offspring are formed from a single cell. This method of propagation is known as multiple fission. Eg Amoeba and Paramecium.

Differences Between Binary and Multiple Fission-

2. Budding

• The budding is a type of asexual reproduction that occurs from the growth of part of a cell or a region of the body that leads to the separation of the original organism into two individuals.

• The budding process is common in some invertebrates such as corals and hydras.

• In hydras a bud is formed that grows up and detaches from the main body; whereas in sprouting corals the bud does not fall off and reproduces as part of a new colony.

3. Sporulation or Spore Formation:

• Sporulation is also known as sporogenesis. It is a form of asexual reproduction that involves spores. Spores, from "sporā" which means "seed" and "genesis" which means "birth" or "origin", are dormant reproductive cells that are similar to seeds in that they serve as units of multiplication.

• As spores are different from the seeds, they lack the embryo created by the fusion of male and female gametes.

• Spores have thick walls and are very resistant to various adverse conditions such as high temperatures and low humidity.

• When the conditions are right, they germinate to give birth to new individuals. Spores are found in some plants and fungi.

4. Fragmentation: 

• Fragmentation refers to the breaking up of the parent organism into fragments and each fragment is capable of becoming a new organism. This is observed in fungi (e.g. yeasts and lichens), moulds, vascular and nonvascular plants, cyanobacteria, and animals (e.g. stars, planarians, and many annelids). 

• This form of asexual reproduction in animals can also be unintentional. Human activity, predation, and other environmental factors can cause them to break up into fragments.

Asexual Reproduction in Plants

The  modes of asexual reproduction  which are seen commonly  in plants are:

1. Fission: It is known to be the simplest of all asexual methods. It is commonly found in fungi and algae. Single-cell stem cells divide mitotically to form two identical daughter cells and the mother. Each daughter cell eventually becomes an independent organism.

2. Buds:

• Some algae produce branches of Advent like in the case of Dictyota, Fucus, or buds like in Protosiphon. Like yeast, mushrooms produce sprouts.

• These structures are the result of uneven division and adhere to the mother cell. Eventually, they separate and mature into a new organism.

3. Fragmentation

• The process of fragmentation is very common in plants. It is a very common way of plant vegetative reproduction.

• The process of fragmentation occurs when rooting branches are torn or detached from the main group due to mechanical pressure or some different reason.

• Different plants have different mechanisms.

4. Spore formation:

• Asexual reproduction in plants takes place by many varieties of motile and non-motile spores which are also known as conidia.

• Ciliated motile asexual spores, which are known as zoospores are produced by algae and fungi. These zoospores swim in water for some of the time with the help of flagella attached to them. In the later stage, they directly develop into new independent individuals under favorable conditions. e.g. Ulothrix, and  Oedogonium.

• Some of the fungi are terrestrial too. These have non-flagellated and non-motile spores/ conidia. These spores are therefore light in weight and dry. They have a tough coat and are well adapted for dispersal by wind. E.g. Penicillium, Aspergillus.

• The structure which bears the true spores is defined as the sporangium. The sporangium is present on a sporophyte. It helps the sporophyte multiplies rapidly in an asexual manner to generate large numbers by spores. Some ferns, for example, Nephrolepis bear spores and reproduce asexually by them. These plants are homosporous; this means that they possess only one kind of spore in their entire lifetime.

• While in Selaginella (pteridophyte) and gymnosperms are heterosporous because of the fact that they bear two types of spores.

Vegetative Propagation

It is a type of process in which new plants are obtained without the production of sexual structures i.e seeds or spores. It involves the propagation of plants through different types of vegetative parts such as the rhizome, sucker, tuber, bulb, etc. In this, a fusion of the male and the female gamete does not take place and requires only one parent. This is grouped into natural and artificial. 

(i) Natural Methods:

• With natural propagation methods, the development of a new plant from an organ of the mother plant takes place under suitable environmental conditions; These altered organs can develop from the stem, leaf, root, or even the flower.

Vegetative propagation 

• By roots: sweet potatoes, asparagus, and dahlias.

• Through the leaves: With this method, the shoots develop on the leaf edges. These buds help in producing the new plants, as can be seen in Bryophyllum.

• Through flower buds: In plants such as agave and oxalis, flower buds produce new plants and in Dioscorea axillary buds do so.

• Through the stem: corridors observed in the grass, dislocations found in Pistia, runners in Nephrolepis, and runners in mint plants. 

(ii) Artificial Methods: 

In this type of method, only a small part of the plant organ is utilized for obtaining a new complete plant. Amongst them, the most common methods which are used are cutting, layering, and grafting.

1. Cutting

• In cutting, a small piece of root is cut and when planted in moist soil, it will lead to the artificial inducement and development of adventitious roots. For example, in lemon.

• In Rose, sugarcane, hibiscus, and chrysanthemum plants are developed by cuttings that involve stem pieces with the presence of nodes. The small cuttings are planted in moist soil to develop new plants. Underground parts of the stem leading to the development of adventitious roots, whereas buds develop and sprout on the aerial parts of stems. The new plants are in a common language known as cutting. Later, these cuttings are transplanted in different prepared places.

2. Layering: This method is used for growing rose, lemon, grape, hibiscus, and jasmine. The lower branches of these plants are bent a little bit and covered with soil in such a way that the tip of the branch protrudes from the ground and the middle part of the plant is inside the soil. It will then develop adventurous roots from this buried area of ​​the stem of the plant, at that time this branch is cut off and separated from the mother plant, whereby a new plant is obtained.

(c) Grafting: Grafting is carried out on plants that are having difficulty in forming roots or that generally have a weak root system.

• This method involves joining two plants of the same or different species, this is achieved by connecting the tissues of the two plants directly to The. When brought into contact, the meristematic tissue of both plants divides and multiplies, and finally the cells of each plant fuse. 

• The rooted plant is called the stem plant. The plant that is grafted onto it is called the sprout. A plant is selected as the "scion" that has superior and desirable properties. The stock is generally strong, robust, and resilient, mango, apple, pear, citrus, guava, lychee, and many other fruit plants are obtained and kept in this way.

• The graft can be of several types, namely, bud graft, lateral graft, and tongue graft, wedge graft, and crown graft, depending on the methods of joining the two parts.

Significance of Vegetative Reproduction

• Vegetative reproduction is an ideal method of reproduction in plants in which we want to preserve parental characteristics.

• It is best for plants that are less efficient sexually, small seeds, long seed dormancy, poor seed viability, etc. They can also be easily multiplied by this method.

• Vegetative propagation is useful for obtaining disease-free plants.

• By using grafting, the desired characters can be brought together from two varieties.

Sexual Reproduction

• Sexual reproduction involves the formation of male and female gametes, either by the same individual or by different individuals of the opposite sex.

• The formed gametes fuse to form the zygote, which develops into a new organism. It is a complex and slow process compared to asexual reproduction.

• Since it is the fusion of male and female gametes, the offspring are not identical to the parents or between them. 

• Even with different external morphology, anatomy, and physiology, sexual reproduction in the patterns of plants, animals, and fungi is similar. All organisms go through general growth before reproductive growth. Only when they are reproductively mature can they reproduce sexually. General growth is called the juvenile phase and, in the case of plants, the vegetative phase. 

• The procedures and processes of sexual reproduction are fundamentally similar in all organisms. The structures which are associated with sexual reproduction are quite different.

• In all cases, sexual reproduction is characterized by the fusion of the male and female gametes of the species.                                                

• For the sake of simplicity, these sequential events can be examined as three different stages, namely pre-fertilization, fertilization, and post-fertilization.

Pre-Fertilization Events

1. Gametogenesis:

• Gametogenesis is defined as the process of the formation of gametes. There are two types of gametes; male and female gametes derived from male and female parents, respectively. Gametes are the haploid (n) in nature.

• Gametes that are similar in appearance are called isogametes or homogametic. They are morphologically and physiologically similar (e.g. Cladophora, Ulothrix).

• Most sexually reproducing organisms have two morphologically and physiologically distinct types of gametes called heterogametes or anisogametes. The male gametes are smaller and more active whereas the female gametes are larger and sluggish. The male gametes are called antherozoid or sperm and the female gamete is called egg or ovum.

• Gametes are always haploids. The parent may be either haploid or diploid. A haploid parent produces gametes which are haploid by mitotic division.

• Various organisms of the Monera, fungi, algae, and Bryophyta, gymnosperms, angiosperms, and most animals are diploid. This is where meiosis occurs to produce haploid gametes.

• In diploid organisms, when meiocytes (gamete stem cell, diploid 2n) undergo meiosis, only one set of chromosomes is built into each gamete.

Types Of Gametes

(a)Isogametes of Cladophora

(b)Fucus

(c)Human Beings

Diversity of Sexuality in Organisms

2. Gamete transfer

After their formation, the male and female gametes must come into contact for fertilization. The male gamete is generally mobile and the female gamete is generally stationary. Gamete transfer requires an appropriate medium. to transfer.

• A large number of male gametes do not reach female gametes, so that male gametes are synthesized in very large numbers as compared with female gametes.

• In angiosperms, pollen grains carry the male gametes and the ovule contains the ovules. Pollen grains are produced on the anthers and transferred to the stigma. This phenomenon is known as pollination. Pollination requires the involvement of external agents such as insects, animals, wind, and water.

• The pollen grains germinate in the stigma and the pollen tubes that carry the male gametes reach the ovule and eject two gametes near the ovule.

• In bisexual animals, the organism has to develop a special mechanism for the transmission of gametes, since male and female gametes are formed in different individuals and this is essential for fertilization.

Fertilization

• The fusion of both gametes i.e male and female is known as syngamy. In this, a diploid zygote is formed. This process is known as fertilization.  

• In most algae, fish, and amphibians, syngamy occurs outside the body of organisms. This type of gamete fusion is called external fertilization. This is seen in bony fish and frogs, where large numbers of young are produced. extremely vulnerable to predators, which threatens their survival.  

• Syngamy occurs in the body of the organism in plants (ie fungi, mosses, and pteridophytes) as well as in reptiles, birds, and mammals. Hence the process is called internal fertilization. The mobile male gametes reach the egg and fuse with it, which takes place within the female body.

• In seed plants, the immobile male gametes are transported to the female gametes through pollen tubes.

Post-Fertilization Events

1. Zygote

• The formation of the zygote is common in sexual reproduction. It is diploid. With external fertilization, the zygote is formed in the external environment (water), while with internal fertilization, the zygote is formed in the body by organisms.

• The further development of the zygote depends on the life cycle of the organism and the environment to which it is exposed. In organisms such as algae and fungi, the zygote develops a thick wall that is resistant to desiccation and damage and usually goes through a dormant phase. before germination.

• Some unicellular animals (z that form the zygote nucleus. This type of sexual reproduction is called conjugation.  

• The zygote is the vital link that ensures the continuity of species between organisms from one generation to the next.

Fig: Zygote formation

2. Embryogenesis

• Embryogenesis is defined as the process of development of the embryo from the zygote. During embryogenesis, the zygote undergoes cell division (mitosis) and cell differentiation.

• Cell divisions will lead to the increase in the number of cells in the developing embryo, while cell differentiation helps the group of cells undergo certain modifications to form specialized tissues and organs to form organisms.

• In animals, if the development of the zygote takes place in the body of the female parent, it is called viviparous. 

• In egg-laying animals such as reptiles and birds, fertilized eggs, which are covered by a hard calcareous shell, are deposited in a safe place in the environment. After an incubation period, the young hatch.

• On the other hand, in viviparous animals such as mammals, including humans, the zygote develops into a cub that emerges from the mother's body. The chances of survival of the young are greater with live-bearing organisms due to adequate embryonic care and protection.

Fig: Stages of embryonic development

• In the case of Angiospermic plants, the zygote is formed, inside the ovule. Once fertilization takes place, different parts like the sepals, petals, and stamens of the flower fall off. The pistil is the only part that remains attached to the plant.

• In plants:

1. The zygote develops into an embryo.

2. Ovule develops into a seed

3. The integument of the ovule develops into a seed coat.

4. The ovary develops into a fruit.

5. Ovary wall develops into pericarp and is protective in function.

• After dispersal, seeds germinate under favourable conditions to produce new plants

Advantages of Sexual Reproduction

Here are a few advantages of sexual reproduction: 

• The offsprings produced through sexual reproduction has greater adaptability and survival changes due to its variations. 

• Since there is a fusion of male snd female gametes in sexual reproduction, the offspring produced are genetically diverse. 

• It leads to the evolution of new species. 

• It increases the variation in the population due to the genetic diversity, which is not possible in asexual reproduction as there is no fertilization.

NCERT Class 12 Revision Notes Biology Chapter 1 Solution

Class 12 Biology chapter 1 revision notes are both straightforward as well as concise in their explanation of various topics. They depict the causes and need for an asexual and sexual form of reproduction in details.

This section, in general, discusses the asexual, sexual and fission methods of reproduction.

Revision Notes Class 12 Chapter 1 - Types of Reproduction

Class 12 notes Reproduction in organisms discusses that reproduction is a common phenomenon among living beings which is aimed to sustain race continuity. In other words, the offspring after growing up, give birth to the next generation, thereby continuing the cycle. Reproduction process performs a specific function which is mentioned below.

• It enables permanence of the genus.

• Reproduction upholds existence on the earth.

• It generates distinction among inhabitants.

This procedure to create offspring is based on habitat, physiology, etc. of organisms. Based on the partaking of single or multiple organisms. (a) Asexual reproduction and (b) Sexual reproduction.

NCERT Solutions Chapter 1 Class 12 Biology Revision Notes - Asexual Reproduction

This process is practised among single parents to produce the next generation. These offsprings are morphologically and genetics wise similar to each other. They display similar traits to the birth parent and therefore referred to as a clone. Ideally, the somatic cell is where the reproduction process starts.

Asexual reproduction is frequent among single-celled living beings, plants and animals with effortless organisations. Biology class 12 chapter 1 revision notes details that a cell separation is a form of this process in protists like monerans, bacteria, etc.

Class 12 Biology Revision Notes Solution Chapter 1 - Forms of Asexual Reproduction

Class 12 revision notes chapter 1 further discusses the ways of asexual reproduction practised among organisms. They practice dual fission, vegetative propagation, manifold fission, sporulation, fragmentation, budding, and regeneration.

This process can be done manually by utilising roots, stems, leaves, bulbils and turions among plants.

Reproduction in Organism Class 12 Biology Revision Notes - Sexual Reproduction

Revision Notes Class 12 Biology Chapter 1 next discusses sexual reproduction practised among animals and plants. It involves an arrangement of a male and female chromosome to form an offspring. The children born out of this conjugation are non-identical to each other and their parents.

Ideally, all sexually reproducing organisms distribute a parallel prototype of reproduction. There are two phases in sexual reproduction, namely maturity and juvenile phase. Juvenile is the period between being born and sexual adulthood which is known as a vegetative phase in plants. The end of these phases ascertains the beginning of reproductive one.

Class 12 Biology chapter 1 revision notes has vast topics related to reproduction. These topics, like menstruation, oestrous, gametes, etc., are needed to be understood. Young learners need to revise these theories from quality study material which can be found in Vedantu.

They offer free notes, solutions, live classes, etc., on different topics and subjects. To answer the questions confidently in exams, download the app today!