NCERT Solutions Class 12 Biology Chapter 1

NCERT Solutions Class 12 Biology Chapter 1: Reproduction in Organisms

The NCERT Solutions Class 12 Biology Chapter 1 is about reproduction in all living organisms. Reproduction is a natural process of producing offspring by conjoining chromosomes. Pre-existing living beings perform this practice to balance the stability of life. NCERT Solutions Class 12 Biology Chapter 1 deals with the process of birth among animals and plants that ensures species generation. In contrast, every species has to experience ageing and eventually die at a certain age. 

By referring to Extramarks’ NCERT Solutions Class 12 Biology Chapter 1, students can attain clear information on types of reproduction. These notes have been crafted by expert faculty to help the learners have deeper understanding of the subject and hence score good grades.

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Key Topics Covered In NCERT Solutions Class 12 Biology Chapter 1

Life Span:

Life span is the period which begins from birth and ends with the natural death of an organism. Reproduction is an essential biological process by which an organism will give birth to another similar organism.

Some basic facts about reproduction are given below. 

• Reproduction is the procedure that ensures the continuation of species from generation to generation. It leads to the evolution of genetic variation.
• The variation in genetics is inherited during reproduction.
• Asexual reproduction is defined as the form of reproduction in which only one parent is involved.
• Sexual reproduction is the reproduction in which two parents of the opposite sex are involved in fusing male and female gametes.

Asexual Reproduction:

• In asexual reproduction, only one parent participates in producing the youngsters. Correspondingly, the babies produced are identical to each other and the parents.
• Asexual reproduction is commonly seen in unicellular organisms, animals, and plants with relatively simple organisms. Additionally, it can also be seen in multicellular organisms.

Asexual Reproduction in Animals:

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

1. Fission:

• Fission, generally known as binary fission, occurs in prokaryotic microorganisms and a few multicellular organisms.
• After the development phase, the organisms are split into independent organisms. Few single-celled eukaryotes go through binary division via mitosis.
• In various organisms, part of an individual is separated, and a second individual is formed.
• For example, in many asteroid echinoderms, this process occurs when the central disk separates.
• Some of the sea anemones and a few polyps will also reproduce via division.
• In a few cases, it is seen that the nucleus divides multiple times by amitotic divisions. This leads to the formation of many new copies of nuclei. Cytoplasmic division does not happen during this time. However, the Cytoplasm will accumulate around each nucleus. 
• Consequently, many unicellular and seedless offspring will be formed from a single cell. This particular method of propagation is known as multiple fission. For example, Amoeba and Paramecium.

Differences Between Binary and Multiple Fission:

2. Budding:

• The budding is a kind of asexual reproduction that happens from the advancement of part of a cell or a particular area of the body that leads to the separation of the original organism into two individuals.
• The budding process is ordinary in some invertebrates, such as corals and hydras.
• In hydras, a bud is produced that grows up and detaches from the main body. While 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 called sporogenesis. It is a shape of asexual reproduction that includes spores. Spores, is derived from “sporā.”, which means “seed”. And “genesis means ‘birth’ or ‘origin. Spores are dormant reproductive cells that are identical to seeds in that, where they serve as units of multiplication.
• As spores are distinct from the seeds, they lack the embryo created by the fusion of male and female gametes.
• Spores have thick walls and are contrary to various adverse conditions such as high temperatures and low humidity.
• When the conditions are favourable, they will germinate to give birth to fresh individuals. Spores are built in some plants and fungi.

4. Fragmentation:

• Fragmentation indicates the breaking up of the parent organism into fragments, and each particle is capable of becoming a new organism. This is noticed in fungi, for example, yeasts and lichens, moulds, cyanobacteria, vascular and non-vascular plants, and animals.   
• This form of asexual reproduction in animals may be unintentional. Human activity, predation, and other environmental elements can cause them to break up into fragments.

Asexual Reproduction in Plants:

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

1. Fission:

Fission is known to be the simplest of all asexual methods. It is generally established in fungi and algae. Single-cell stem cells split mitotically to form two identical daughter cells and the mother. Every daughter cell eventually becomes an independent organism.

2. Buds:

• Some algae bear branches of Advent, like in the case of Dictyota, Fucus, buds like in Protosiphon Yeast, and mushrooms produce sprouts.
• These compositions result from uneven division and hold fast to the mother cell. Eventually, they divide and mature into a new organism.

3. Fragmentation:

• The process of fragmentation is very familiar in plants. It is a very traditional way of plant vegetative reproduction.
• The fragmentation process materialises when rooting branches are torn or detached from the leading group due to mechanical pressure or other reasons.
• Different plants have divergent mechanisms.

4. Spore formation:

• Asexual reproduction in plants arises from a wide variety of motile and non-motile spores, also known as conidia.
• Ciliated motile asexual spores, called zoospores, are created by algae and fungi. The zoospores swim in water for some metres with the assistance of flagella connected to them. In the later stage, they directly progress into new independent individuals under good conditions. Examples are Oedogonium and Ulothrix.
• Few of the fungi are terrestrial too. These have non-flagellated and non-motile spores or conidia. These spores are therefore transparent in weight and dry. They have a strong coat and are well altered for dispersal by wind. For example, Penicillium, and Aspergillus.
• The constituent which bears the actual spores is defined as the sporangium. The sporangium exists on a sporophyte. It guides the sporophyte, which multiplies rapidly in an asexual manner to give rise to vast numbers of spores. Few ferns, for example, Nephrolepis, bear spores are multiplied asexually by them. Those plants are homosporous, meaning they own only one type of spore throughout their lifetime.
• Gymnosperms and Selaginella (pteridophyte) are heterosporous because they bear two types of spores.

Vegetative Propagation:

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

1. Natural Methods:

With natural propagation methods, the maturing of a new plant from an organ of the mother plant transpires under suitable environmental conditions. These altered organs can enlarge from the stem, leaf, root, or flower.

Vegetative propagation:

• By roots: Asparagus, sweet potatoes, and dahlias.
• Through the leaves: The shoots flourish on the leaf edges with this process. These buds aid in generating new plants, as in Bryophyllum.
• Through flower buds: In plants such as oxalis and agave, flowers.
• Buds generate new plants, and in Dioscorea, axillary buds do so.
• Through the stem: Corridors noticed in the grass, dislocations formed in Pistia, runners in Nephrolepis, and runners in mint plants. 

2. Artificial Methods: 

In this Class of methods, only a tiny part of the plant organ is used for obtaining a complete fresh plant. The most standard methods used are cutting, layering, and grafting.

1. Cutting:

In cutting, a tiny piece of root is cut, and when planted in moist soil, it will lead to the artificial inducement and expansion of adventitious roots, for example, in lemon.

Rose, hibiscus, sugarcane, and chrysanthemum plants are refined by cuttings that entail stem pieces with nodes. The tiny cuttings are planted in moist soil to grow new plants. Underground parts of the stem lead to the development of adventitious roots, whereas buds develop and blossom on the aerial parts of stems. The new plants are in a normal state known as cutting. Later, these cuttings are transplanted in various prepared places.

1. Layering: 

This method is used for growing rose, grape, lemon, jasmine and hibiscus. The lowest branches of these plants are bent slightly and shielded with soil in such a manner that the tip of the branch protrudes from the ground, and the middle part of the plant is inside the earth. It will then flourish adventurous roots from this buried area of ​​the plant’s stem. This branch is cut off and excluded from the mother plant, whereby a new plant is obtained.

1. Grafting: 

Grafting is carried out on plants with trouble forming roots or by those that generally have a frail root system.

• This method involves connecting two plants of the same or non-identical species. This is achieved by joining the tissues of the two plants directly. When brought into contact, the meristematic tissue of two plants divides and multiplies. As a result, the cells of each plant fuse.
• The rooted plant is known as the stem plant. While the plant that is grafted onto it is called the sprout. A plant is chosen as the “scion” with superior and desirable properties. The stock is generally challenging, robust, and resilient. Mango, pear, apple, citrus, guava, lychee and many other fruit plants are collected and kept.
• The graft can be of different kinds. Namely, bud graft, tongue graft and lateral graft, wedge graft, and crown graft, depending on the joining of the two parts.

Significance of Vegetative Reproduction:

• Vegetative reproduction is a perfect reproduction method in plants in which we want to preserve parental characteristics.
• It is suitable for plants that are less efficient sexually, have poor seed viability, tiny seeds, long seed dormancy, etc. 
• They can also be easily expanded by this method.
• Vegetative propagation is ideal for obtaining disease-free plants.
• The needed characters can be brought together from two varieties by using Grafting.

Sexual Reproduction:

• Sexual reproduction includes the origination of male and female gametes, either by the same individual or by different individuals of the opposite sex.
• The initiated gametes fuse to form the zygote, which grows into a new organism. It is an arduous and slow process compared to asexual reproduction.
• Since this process is the fusion of male and female gametes, the children are not exactly identical to the parents. . 
• Even with different external morphology, physiology and anatomy, sexual reproduction in plants, animals, and fungi patterns are similar. All organisms go through general development before reproductive growth. Only when they are reproductively mature can they breed sexually. General growth is called the juvenile phase and the vegetative phase in the case of plants. 
• The processes and procedures of sexual reproduction are fundamentally similar in all organisms. The systems which are associated with sexual reproduction are pretty different.
• In every case, sexual reproduction is characterised by the fusion of the male and female gametes of the species.       

For clarity, these sequential events can be examined as three different stages: pre-fertilisation, fertilisation, and post-fertilization.

Pre-Fertilisation Events: 

1. Gametogenesis:

• Gametogenesis is explained as the procedure of the formation of gametes. There are two kinds of gametes; male and female gametes extracted from male and female parents. Gametes are the haploid (n) in nature.
• Gametes that are identical in appearance are called isogametes or homogametic. They are morphologically and physiologically alike. For example, Cladophora and Ulothrix.
• Most sexually reproducing organisms have morphologically and physiologically distinct kinds of gametes called heterogametes or isogametes. The male gametes are tiny and more active. On the other hand, the female gametes are larger and sluggish. The male gametes are sperm or antherozoid, and the female gamete is called ovum or egg.
• Gametes are haploids all the time. The parent might be either haploid or diploid. A haploid parent creates gametes which are haploid by mitotic division.
• Various fungi organisms, Monera, algae, Bryophyta, gymnosperms, angiosperms, and most animals are diploid. This is where meiosis turns out to produce haploid gametes.
• In diploid organisms, when meiocytes, i.e. gamete stem cell and diploid 2n, undergo meiosis, one set of chromosomes is assembled into each gamete.

2. Gamete transfer:

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

• Many male gametes do not reach female gametes, so male gametes are consolidated in huge numbers correlated with female gametes.
• In angiosperms, pollen grains move the male gametes. The ovule consists of the ovules. Pollen grains are generated on the anthers and transferred to the stigma. This phenomenon is called pollination. Pollination demands the involvement of external agents such as insects, wind, animals, and water.
• The pollen grains sprout in the stigma, and the pollen tubes that move the male gametes reach the ovule and eject two gametes near the ovule.
• In bisexual animals, the organism has to grow a unique mechanism for the transmission of gametes since male and female gametes are formed in different individuals, which is essential for fertilisation.

Fertilisation: 

• The fusion of both gametes, i.e. male and female, is called syngamy. In this, a diploid zygote is formed. This method is known as fertilisation.  
• In most fish, algae, and amphibians, syngamy occurs outside the body of organisms. This category of gamete fusion is called external fertilisation. This is seen in frogs and bony fish, where many offspring are produced. They are highly vulnerable to predators, which threatens their survival.  
• Syngamy develops in the organism’s body in plants, i.e. fungi, pteridophytes and mosses; birds, reptiles, and mammals. Hence the process is called internal fertilisation. The mobile male gametes reach the egg and fuse with it, which occurs inside the female body.
• In seed plants, the motionless male gametes are carried to the female gametes through pollen tubes.

 Post-Fertilization Events:

1. Zygote:

• The shaping of the zygote is standard in sexual reproduction. It is diploid. With external fertilisation, the zygote is developed in the external environment (water), while with internal fertilisation, the zygote is shaped in the body by organisms
• The further growth of the zygote depends on the organism’s life cycle and the conditions to which it is sensitive. In organisms such as fungi and algae, the zygote builds a thick wall resistant to desiccation and damage and usually goes between a dormant phase before germination.
• Some unicellular animals form the zygote nucleus. This type of sexual reproduction is known as conjugation.  
• The zygote is the essential link that ensures the continuity of species between organisms from one generation to the next.

2. Embryogenesis:

• Embryogenesis indicates the method of embryo development from the zygote. The zygote undergoes cell differentiation and cell division (mitosis) during embryogenesis.
• Cell divisions will lead to a rise in the number of cells in the developing embryo. In contrast, cell differentiation assists the group of cells undergoing certain modifications to form specialised tissues and organs to shape organisms.
• In animals, if the zygote’s growth happens in the female parent’s body, it is known as viviparous. 
• In egg-laying animals such as birds and reptiles, fertilised eggs covered by a hard calcareous shell are deposited in a safe place. After an incubation period, the babies hatch.
• Besides, the zygote evolves into a cub that emerges from the mother’s body in viviparous animals such as mammals, including humans. The probability of survival of the offspring is higher with live-bearing organisms due to adequate embryonic care and safety.

NCERT Solutions Class 12 Biology Chapter 1: Exercises and Answer Solutions

The NCERT Solutions Class 12 Biology Chapter 1 exercise and answer solutions are based on NCERT books. Every exercise is compiled to add more value to the chapter. Students may refer to various study materials such as revision notes, past years’ questions papers, and essential questions and learn more about NCERT and CBSE solutions from the Extramarks’ website. 

NCERT Solutions Class 12 Biology Chapter 1 is explained in detail by the subject experts working at Extramarks. In addition to Chapter 1, students can access CBSE solutions for all other Biology chapters of Class 12.

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NCERT Solutions Class 12 Biology Chapter 1 Ex 1.1

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NCERT Exemplar Class 12 Biology

All solutions and problems are given to help students prepare for their final examinations. These Exemplar questions are a little more complex and cover every concept introduced in Class 12 Biology chapters.

Students will fully understand the concepts covered in each chapter by practising this NCERT exemplar for Class 12 Biology. 

Below given is the list of study materials students can refer to.

• NCERT Solutions
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• CBSE Past Years’ Question Papers
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Exemplars provide the best solutions to the problems that students come across. To match the ideas taught in each class and provide the most outstanding practising materials or worksheets for students, these questions strictly follow updated 2022-23 CBSE guidelines.

Key Features of NCERT Solutions Class 12 Biology Chapter 1

The key features of NCERT Solutions Class 12 Biology Chapter 1 are as under:

• Class 12 Biology Chapter 1 NCERT Solutions will help students formulate their answers well in the examination. 
• In these notes, the theory is described in detail. Students can write to-the-point answers by covering the right notes on the Extramarks’ website. 
• Experienced teachers in the respective subject write the concepts.