Reproduction in Organisms class 12 NCERT Solution chapter 1 Explanation and summary
NCERT Solution for class 12 Reproduction in organisms chapter 1 In this I covered whole chapter and all the related information in this chapter ,like summary ,Notes, Explanation
Reproduction in Organisms class 12 Intoduction
Reproduction is a fundamental biological process that ensures the continuity of life on Earth. In the realm of biology, the study of reproduction in organisms is a crucial component. Reproduction is not only vital for the survival of individual species but also plays a key role in maintaining biodiversity. This multifaceted process encompasses a variety of mechanisms across different organisms, from simple unicellular organisms to complex multicellular organisms.
Reproduction in Organisms class 12 About the Author
Born in November 1904 in Jaipur (Rajasthan) Panchanan Maheshwari
rose to become one of the most distinguished botanists not only of India
but of the entire world. He moved to Allahabad for higher education
where he obtained his D.Sc. During his college days, he was inspired
by Dr W
Dudgeon, an American missionary teacher, to develop interest
in Botany and especially morphology. His teacher once expressed that
if his student progresses ahead of him, it will give him a great satisfaction.
These words encouraged Panchanan to enquire what he could do for
his teacher in return.
He worked on embryological aspects and popularised the use of
embryological characters in taxonomy. He established the Department
of Botany, University of Delhi as an important centre of research in
embryology and tissue culture. He also emphasised the need for initiation
of work on artificial culture of immature embryos. These days, tissue
culture has become a landmark in science. His work on test tube
fertilisation and intra-ovarian pollination won worldwide acclaim
He was honoured with fellowship of Royal Society of London (FRS),
Indian National Science Academy and several other institutions of
excellence. He encouraged general education and made a significant
contribution to school education by his leadership in bringing out the
very first textbooks of Biology for Higher Secondary Schools published
by NCERT in 1964
Reproduction in Organisms class 12 Definition
Reproduction in organisms is the biological process by which new individuals of the same species are produced, ensuring the continuity of life. It involves the creation of offspring, either through asexual means, where a single parent gives rise to genetically identical or nearly identical progeny, or through sexual means
where specialized reproductive cells (gametes) from two parents fuse, resulting in offspring with a unique combination of genetic material. Reproduction is essential for the perpetuation of species, genetic diversity, and adaptation to changing environments. The process varies across different organisms and encompasses a range of mechanisms and strategies.
Reproduction in Organisms class 12 Important Notes
- Types of Reproduction
- Asexual Reproduction
- Involves a single parent.
- Offspring are genetically identical to the parent.
- Common methods include binary fission, budding, and spore formation.
- Sexual Reproduction:
- Involves the fusion of gametes (sperm and egg).
- Offspring inherit a combination of genetic material from both parents.
- Promotes genetic diversity within a population
- Asexual Reproduction
- Asexual Reproduction
- Binary Fission:
- Common in unicellular organisms like bacteria.
- The cell divides into two identical daughter cells
- Common in organisms like hydra and yeast.
- New individuals develop as outgrowths or buds on the parent.
- Spore Formation:
- Spores are reproductive cells capable of developing into new individuals.
- Examples include fungi and some plants.
- Binary Fission:
- Sexual Reproduction:
- Formation of specialized reproductive cells (gametes).
- Involves meiosis, resulting in haploid gametes (sperm and egg)
- Fusion of sperm and egg to form a zygote.
- Restores the diploid number of chromosomes.
- Embryonic Development:
- Zygote undergoes cell division and differentiation to form an embryo.
- Occurs in the uterus in mammals and in various locations in other organisms.
Reproduction In Organisms class 12 Explanation
Each and every organism can live only for a certain period of time. The period from birth to the natural death of an organism represents its life span. Life spans of a few organisms are given in Figure 1.1. Several other organisms are drawn for which you should find out their life spans and write in the spaces provided. Examine the life spans of organisms represented in the Figure 1.1. Isn’t it both
Interesting and intriguing to note that it may be as short as a few days or as long as a few thousand years? Between these two extremes are the life spans of most other living organisms. You may note that life spans of organisms are not necessarily correlated with their sizes; the sizes of crows and parrots are not very different yet their life spans show a wide difference. Similarly, a mango tree has a much shorter life span as compared to a peepal tree. Whatever be the life span
Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself. The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. Reproduction enables the continuity of the species, generation after generation. You will study later in Chapter 5 (Principles of Inheritance and Variation) how genetic variation is created and inherited during reproduction.
There is a large diversity in the biological world and each organism has evolved its own mechanism to multiply and produce offspring. The organism’s habitat, its internal physiology and several other factors are collectively responsible for how it reproduces. Based on whether there is participation of one organism or two in the process of reproduction, it is of two types. When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual. When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction
1.1 ASEXUAL REPRODUCTION
In this method, a single individual (parent) is capable of producing offspring. As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent. Are these offspring likely to be genetically identical or different? The term clone is used to describe such morphologically and genetically similar individuals
Let us see how widespread asexual reproduction is, among different groups of organisms. Asexual reproduction is common among single-celled organisms, and in plants and animals with relatively simple organisations. In Protists and Monerans, the organism or the parent cell divides by mitosis into two to give rise to new individuals (Figure1.2).Thus, in these organisms cell division is itself a mode of reproduction
Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly grows into an adult (e.g., Amoeba, Paramecium). In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells). Under unfavourable condition the Amoeba withdraws its pseudopodia and secretes a three-layered hard covering or cyst around itself.
This phenomenon is termed as encystation. When favourable conditions return, the encysted Amoeba divides by multiple fission and produces many minute amoeba or pseudopodiospores; the cyst wall bursts out, and the spores are liberated in the surrounding medium to grow up into many amoebae. This phenomenon is known as sporulation
Meaning of this word pseudopodiospores” (Pseudopodiospores” refers to spores or reproductive structures that exhibit characteristics resembling pseudopodia, often associated with certain amoeboid or protist organisms.)
Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures (Figure 1.3). The most common of these structures are zoospores that usually are microscopic motile structures. Other common asexual reproductive microscopic motile structures. Other common asexual reproductive structures are conidia (Penicillium), buds (Hydra) and gemmules (sponge)
You have learnt about vegetative reproduction in plants in Class XI.What do you think – Is vegetative reproduction also a type of asexual reproduction? Why do you say so? Is the term clone applicable to the offspring formed by vegetative reproduction? While in animals and other simple organisms the term asexual is used unambiguously, in plants, the term vegetative reproduction is frequently used. In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring (Figure1.4). These structures are called vegetative propagules.
Meaning of this word unambiguously : (“Unambiguously” means in a manner that is clear, straightforward, and without any ambiguity or uncertainty.)
Obviously, since the formation of these structures does not involve two parents, the process involved is asexual. In some organisms, if the body breaks into distinct pieces (fragments) each fragment grows into an adult capable of producing offspring (e.g., Hydra). This is also a mode of asexual reproduction called fragmentation
You must have he ard about the scourge of the water bodies or about the ‘terror of Bengal’. This is nothing but the aquatic plant ‘water hyacinth’ which is one of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water, which leads to death of fishes. You will learn more about it in Chapters 13 and 14. You may find it interesting to know that this plant was introduced in India because of its beautiful flowers and shape of leaves. Since it can propagate vegetatively at a phenomenal rate and spread all over the water body in a short period of time, it is very difficult to get rid off them.
Are you aware how plants like potato, sugarcane, banana, ginger,dahlia are cultivated? Have you seen small plants emerging from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger? When you carefully try to determine the site of origin of the new plantlets in the plants listed above, you will notice that they invariably arise from the nodes present in the modified stems of these plants. When the nodes come in contact with damp soil or water, they produce roots and new plants. Similarly, adventitious buds arise from the notches present at margins of leaves of Bryophyllum. This ability is fully exploited by gardeners and farmers for commercial propagation of such plants.
It is interesting to note that asexual reproduction is the common method of reproduction in organisms that have a relatively simple organisation, like algae and fungi and that they shift to sexual method of reproduction just before the onset of adverse conditions. Find out how sexual reproduction enables these organisms to survive during unfavourable conditions? Why is sexual reproduction favoured under such conditions? Asexual (vegetative) as well as sexual modes of reproduction are exhibited by the higher plants. On the other hand, only sexual mode of reproduction is present in most of the animals.
1.2 SEXUAL REPRODUCTION
Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex. These gametes fuse to form the zygote which develops to form the new organism. It is an elaborate, complex and slow process as compared to asexual reproduction. Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves. A study of diverse organisms–plants, animals or fungi–show that though they differ so greatly in external morphology, internal structure
and physiology, when it comes to sexual mode of reproduction, surprisingly, they share a similar pattern. Let us first discuss what features are common to these diverse organisms. All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually. That period of growth is called the juvenile phase. It is known as vegetative phase in plants. This phase is of variable durations in different organisms. The end of juvenile/vegetative phase which marks the beginning of the reproductive phase can be seen easily in the higher plants when they come to flower. How long does it take for marigold/rice/wheat/coconut/ mango plants to come to flower? In some plants, where flowering occurs more than once, what would you call the inter-flowering period – juvenile or mature
Observe a few trees in your area. Do they flower during the same month year after year? Why do you think the availability of fruits like mango, apple, jackfruit, etc., is seasonal? Are there some plants that flower throughout the year and some others that show seasonal flowering? Plants–the annual and biennial types, show clear cut vegetative, reproductive and senescent phases, but in the perennial species it is very difficult to clearly define these phases. A few plants exhibit unusual flowering phenomenon; some of them such as bamboo species flower only once in their life time
generally after 50-100 years, produce large number of fruits and die. Another plant, Strobilanthus kunthiana (neelakuranji), flowers once in 12 years. As many of you would know, this plant flowered during September-October 2006. Its mass flowering transformed large tracks of hilly areas in Kerala, Karnataka and Tamil Nadu into blue stretches and attracted a large number of tourists. In animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour. The reproductive phase is also of variable duration in different organisms. Can you list the changes seen in human beings that are indicative of reproductive maturity?
Meaning of this word morphological : “Morphological” refers to the study or description of the form and structure of organisms or their parts.
Among animals, for example birds, do they lay eggs all through the year? Or is it a seasonal phenomenon? What about other animals like frogs and lizards? You will notice that, birds living in nature lay eggs only seasonally. However, birds in captivity (as in poultry farms) can be made to lay eggs throughout the year. In this case, laying eggs is not related to reproduction but is a commercial exploitation for human welfare. The females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase. In non-primate mammals like cows, sheep, rats, deers, dogs, tiger, etc., such cyclical changes during reproduction are called oestrus cycle where as in primates (monkeys, apes, and humans) it is called menstrual cycle. Many mammals, especially those living in natural, wild conditions exhibit such cycles only during favourable seasons in their reproductive
Table 1.1: Chromosome Numbers in Meiocytes (diploid, 2n) and Gametes (haploid, n) of Some Organisms. Fill in the Blank Spaces.
|Name of organism
|Chromosome number Chromosome number
in meiocyte (2n)
in gamete (n)
|Ophioglossum (a fern)
In diploid organisms, specialised cells called meiocytes (gamete mother cell) undergo meiosis. At the end of meiosis, only one set of chromosomes gets incorporated into each gamete. Carefully study Table 1.1 and fill in the diploid and haploid chromosome numbers of organisms. Is there any relationship in the number of chromosomes of meiocytes and gametes
188.8.131.52 Gamete Transfer After their formation, male and female gametes must be physically brought together to facilitate fusion (fertilisation). Have you ever wondered how the gametes meet? In a majority of organisms, male gamete is motile and the female gamete is stationary. Exceptions are a few fungi and algae in which both types of gametes are motile (Figure1.7a). There is a need for a medium through which the male gametes move. In several simple plants like algae, bryophytes and pteridophytes, water is the medium through which this gamete transfer takes place. A large number of the male gametes, however, fail to reach the female gametes. To compensate this loss of male gametes during transport, the number of male gametes produced is several thousand times the number of female gametes produced
Reproduction In Organisms class 12 summary
Reproduction enables a species to live generation after generation.Reproduction in organisms can be broadly classified into asexual and sexual reproduction. Asexual reproduction does not involve the fusion of gametes. It is common in organisms that have a relatively simple organisation such as the fungi, algae and some invertebrate animals. The offspring formed by asexual reproduction are identical and can be referred to as clones. Zoospores, conidia, etc., are the most common asexual structures formed in several algae and fungi. Budding and gemmule formation are the common asexual methods seen in lower animals.Prokaryotes and unicellular organisms reproduce asexually by cell division or binary fission of the parent cell. In several aquatic and
terrestrial species of angiosperms, structures such as runners,rhizomes, suckers, tubers, offsets, etc., are capable of giving rise to new offspring. This method of asexual reproduction is generally referred to as vegetative propagatio Sexual reproduction involves the formation and fusion of gametes.It is a complex and slower process as compared to asexual reproduction. Most of the higher animals reproduce almost entirely by sexual method.Events of sexual reproduction may be categorised into pre-fertilisation, fertilisation and post-fertilisation events. Pre-fertilisation events include gametogenesis and gamete transfer while post-fertilisation events include the formation of zygote and embryogenesis.
Reproduction In Organisms class 12 Question and Answer
Question 1: Differentiate between asexual and sexual reproduction.
Asexual reproduction involves a single parent and results in genetically identical offspring, while sexual reproduction involves two parents and produces genetically diverse offspring through the fusion of gametes.
Question 2: Explain the importance of genetic diversity in evolution.
Genetic diversity, generated through sexual reproduction, provides the raw material for natural selection and adaptation. It allows populations to respond to environmental changes and contributes to the long-term survival and evolution of species.
Question 3: Describe the process of binary fission in unicellular organisms.
Binary fission is a form of asexual reproduction in which a single-celled organism divides into two identical daughter cells. The cell duplicates its genetic material and then splits into two, each with a complete set of genetic information.
Question 4: How does fertilization contribute to genetic variation in sexually reproducing organisms?
Fertilization involves the fusion of gametes, combining genetic material from two parents. This results in offspring with unique combinations of genes, enhancing genetic diversity within a population.
Question 5: What is the role of hormones in the regulation of the menstrual cycle in females?
Hormones such as estrogen and progesterone regulate the menstrual cycle in females. They control the development of the uterine lining, ovulation, and the preparation for pregnancy, orchestrating the complex reproductive process.
Question 6: Explain the significance of spore formation in fungi.
Spore formation in fungi is a means of asexual reproduction. Spores are resistant structures that can disperse in various environments, aiding in the colonization of new areas and ensuring the survival of the fungal species.
Question 7: Compare the advantages and disadvantages of asexual and sexual reproduction.
Asexual reproduction is efficient but lacks genetic diversity, limiting adaptability. Sexual reproduction provides diversity but demands more energy and resources. The balance between the two depends on environmental conditions.
Question 8: Discuss the role of gametogenesis in sexual reproduction.
Gametogenesis is the formation of specialized reproductive cells (gametes) through meiosis. It ensures the production of haploid gametes, which, upon fertilization, restores the diploid number in sexually reproducing organisms.
Reproduction In Organisms class 12 MCQ
Question:1 What is the primary purpose of reproduction in organisms?
- A. Increase in body size
- B. Preservation of species
- C. Energy production
- D. Adaptation to the environment
Question:2 Which of the following is an example of asexual reproduction?
- A. Fertilization
- B. Budding
- C. Meiosis
- D. Pollination
Question:3 In sexual reproduction, the fusion of gametes leads to the formation of
- A. Zygote
- B. Spore
- C. Gemmule
- D. Clone
Question:4 Binary fission is a common method of asexual reproduction in
- A. Animals
- B. Plants
- C. Bacteria
- D. Fungi
Question:5 What is the significance of genetic diversity in a population?
- A. It reduces adaptability
- B. It hinders evolution
- C. It increases susceptibility to diseases
- D. It enhances adaptability and survival
Question:6 Which hormone is responsible for the regulation of the menstrual cycle in females?
- A. Testosterone
- B. Estrogen
- C. Progesterone
- D. Insulin
Question:7 What is the primary role of spore formation in fungi?
- A. Asexual reproduction
- B. Sexual reproduction
- C. Pollination
- D. Fertilization
Question:8 During which process does gametogenesis occur?
- A. Binary fission
- B. Budding
- C. Meiosis
- D. Mitosis
Question:9 Which term is used to describe the temporary extensions of the cell membrane and cytoplasm in amoeboid cells?
- A. Pseudopodia
- B. Cilia
- C. Flagella
- D. Microvilli
Question:10 Why is genetic diversity crucial for the long-term survival of a species?
- A. It increases the risk of extinction
- B. It limits adaptation
- C. It ensures variability for environmental changes
- D. It leads to genetic uniformity
In conclusion, the study of “Reproduction in Organisms” in Class 12 Biology explores the essential processes that ensure the continuation of life. Asexual and sexual reproduction showcase diverse strategies employed by organisms, influencing genetic diversity and adaptability. From binary fission in bacteria to the complex hormonal regulation of the menstrual cycle, the subject offers a comprehensive understanding of how life perpetuates,