NCERT Solutions Class 10 Science Chapter 8: How Do Organisms Reproduce? (Free PDF)

In NCERT Solutions Class 10 Science Chapter 8, we have provided notes of what you have learnt in the chapter with important points. These notes will help you recap the chapter within minutes and will serve you as a quick method of revision. After that, you will find solutions to the exercise in the book. Let’s proceed!

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Download NCERT Solutions Class 10 Science Chapter 8 How Do Organisms Reproduce Free PDF

Do organisms create exact copies of themselves?

We start NCERT Solutions Class 10 Science Chapter 8 with the basic concept of how organisms create copies of themselves. Let’s begin!!

• Reproduction at its most basic level will involve making copies of the blueprints of body design. The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be created. A basic event in reproduction is the creation of a DNA copy. 

• Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other. DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its cellular apparatus. Effectively, a cell divides to give rise to two cells.

• No bio-chemical reaction is reliable. Therefore, it is only to be expected that the process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may not be identical to the original. Some of these variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. This inbuilt tendency for variation during reproduction is the basis for evolution, as we will discuss in the next chapter.

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Importance of variation

• The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species. 
• If some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Variation is thus useful for the survival of species over time.

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Modes of Reproduction Used by Single Organisms

In this section of NCERT Solutions Class 10 Science Chapter 10, we will learn about Fission, Fragmentation, Regeneration, and Vegetative Propagation.

Fission

Fission is the splitting of unicellular organisms to create two or more similar organisms. 

• Many different patterns of fission have been observed. Many bacteria and protozoa simply split into two halves during cell division. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

• Leishmania (which causes kala-azar) shows more organisation in their bodies during fission. In them, binary fission occurs in a definite orientation because of the flagella. Yeast produces single buds that separate and grow. 

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Fragmentation

• Some multicellular organisms can still reproduce by simple methods such as the spirogyra which on maturation, breaks up into smaller fragments and each one grows into an individual spirogyra. 
• Although, this is not true for every multi-cellular organism. 
• Multi-cellular organisms, therefore, need to use more complex ways of reproduction because their bodies are formed by clusters of cells developing into specialised tissues. 

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Regeneration

• Certain simple organisms such as the Hydra and Planaria can be cut into pieces and each piece will grow into a separate organism. This is known as regeneration. 
• This is carried out by specialised cells. However, it is not the same as reproduction. 

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Vegetative Propagation

In many plants, their parts such as leaves, roots, stems, etc can grow into each individual separately under certain specific conditions. Examples of the same include sugarcane, roses, grapes, Bryophyllum, etc. This is useful for plants such as bananas, oranges, etc that have lost their ability to produce seeds. Another advantage of the same plants produced by vegetative propagation are genetically similar to the parent plant in terms of characteristics. 

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Spore Formation

Many multicellular organisms produce thread-like structures called hyphae which have blobs called sporangia on them (example: Bread Mould i.e. Rhizopus) containing spores in them which produce new organisms. 

All the above-mentioned modes are Asexual Modes of Reproduction.

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Sexual Reproduction

Further in this section of NCERT Solutions Class 10 Science Chapter 8, we will explore sexual reproduction.

The mode of reproduction where two individuals of opposite sexes are involved in the production of a new one is known as sexual reproduction. 

Why the sexual mode of reproduction?

• In a population, for it to survive, variations are important. While DNA-copying mechanisms are not accurate, they are precise enough to make the generation of variation a fairly slow process. 
• If the DNA copying mechanisms were to be less accurate, many of the resultant DNA copies would not be able to work with the cellular apparatus and would die. 
• Two different individuals in a population would have quite different patterns of accumulated variations. Since all of these variations are in living individuals, it is assumed that they do not have any really bad effects. 
• Combining variations from two or more individuals would thus create new combinations of variants. Each combination would be novel since it would involve two different individuals. 
• The sexual mode of reproduction involves the combining of DNA from two different individuals, thus ensuring variations. Now, to avoid doubling up of the DNA in a new organism, a process called meiosis occurs which divides the cells, thus halving the DNA amount and restoring the number of chromosomes in the new individual thus formed. 
• The zygote formed would need energy for its development hence for the same purpose, the germ cells become specialised in such a manner that one becomes enlarged and is called a female gamete and contains food stores and the other one becomes small for its mobility towards the other germ cell and is known as the male gamete. 

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Sexual Reproduction in Flowering Plants

Some flowers may be unisexual such as papaya and watermelon, while others may be bisexual and contain both the organs i.e. stamens as well as pistils. 

Stamens are the male reproductive organ and produce pollens that are yellow and pistils are located in the centre of a flower. The pistil consists of 3 parts:- the stigma which is a sticky platform for pollens to stick, the style which is a long slender structure connecting the stigma to the ovary and lastly the ovary which contains ovules. Ovules contain egg cells. 

Pollens are transferred from the stamen through a medium and they land on the stigma. Then a pollen tube is formed which carries two germ cells to the ovary where the fertilisation occurs in the ovule forming a zygote. If the pollens are transferred from the stamen of a flower to the stigma of the same flower, then it is known as self-pollination, otherwise it it is known as cross-pollination. 

After fertilisation, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off. The seed contains the future plant or embryo which develops into a seedling under appropriate conditions. This process is known as germination.

Also Read: Class 11 Morphology of Flowering Plants NCERT Notes

Reproduction in Human Beings

In the early teenage years, a whole new set of changes occurs that cannot be explained simply as body enlargement. Instead, the appearance of the body changes. Proportions change, new features appear, and so do new sensations.

Some of these changes like the appearance of hair on the body are common between boys and girls, while others such as the development of breasts in girls and voice cracking in boys are different. These changes take place in the teenage years and happen over a period of time. These depict the sexual maturation of an individual. As the rate of general body growth begins to slow down, reproductive tissues begin to mature. This period during adolescence is called puberty.

 Now, in sexual reproduction, the gametes of two individuals need to come in contact with each other to form a new individual. The actual transfer of germ cells between two people needs special organs for the sexual act, such as the penis when it is capable of becoming erect. In mammals such as humans, the baby is carried in the mother’s body for a long period and will be breast-fed later. The female reproductive organs and breasts will need to mature to accommodate these possibilities. 

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Male Reproductive System

The male germ cells are carried in sperms which are produced at a temperature lower than that of the body in the testes located in the scrotum outside the abdominal cavity. The sperms are passed from the testes through the vas deferens to the urethra that forms the common passage for both, sperms as well as urine. The prostate gland and the seminal vesicles pour their secretion thus creating a fluid that makes the transfer of the sperm easier. The sperms mainly consist of genetic material and a long tail for mobility.

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Female Reproductive System

The female germ cells or eggs are made in the ovaries. Once puberty is attained, eggs in the ovary mature and every month ovaries start to release one egg that is carried to the womb by fallopian tubes. The two oviducts or fallopian tubes unite into an elastic bag-like structure known as the uterus. The uterus opens into the vagina through the cervix.

During intercourse, the sperm travel to the oviduct from the vagina, through the cervix to fertilise the egg and form a zygote that starts dividing and forms a ball of cells or embryo. The embryo is implanted in the lining of the uterus where it continues to grow and develop organs to become a foetus. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta which is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. 

The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta. The development of the child inside the mother’s body takes approximately nine months. The child is born as a result of rhythmic contractions of the muscles in the uterus.

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What happens when the egg is not fertilized?

If the egg is not fertilized, it lives in the uterus for one day, after that it is removed from the body with the thick endometrial lining from the uterus along with blood and mucous through the vagina. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

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Reproductive Health

Here are some important points about reproductive health:

• During sexual intercourse, many diseases can be transmitted from one person to another such as bacterial, and viral infections, Gonorrhea, syphilis, warts, HIV-AIDS, etc. Using a covering, called a condom, for the penis during sex helps to prevent transmission of many of these infections to some extent. 
• Also, unwanted pregnancy is another concern that will make major demands on the body and the mind of the woman.
• These contraceptive methods fall into several categories. One category is the creation of a mechanical barrier so that sperm does not reach the egg. Condoms on the penis or similar coverings worn in the vagina can serve this purpose. Another category of contraceptives acts by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur. These drugs commonly need to be taken orally as pills.
•  However, since they change hormonal balances, they can cause side effects too. Other contraceptive devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy. Again, they can cause side effects due to irritation of the uterus. 
• Certain surgical methods such as vasectomy in males and tubectomy in females are another method to prevent unwanted pregnancy. 

• For a healthy society, the female-male sex ratio must be maintained. Because of reckless female foeticides, child sex ratio is declining at an alarming rate in some sections of our society, although prenatal sex determination has been prohibited by law. For a healthy society, the female-male sex ratio must be maintained. Because of reckless female foeticides, the child-sex ratio is declining at an alarming rate in some sections of our society, although prenatal sex determination has been prohibited by law.

• The rates of birth and death in a given population will determine its size. The size of the human population is a cause for concern for many people. This is because an expanding population makes it harder to improve everybody’s standard of living. However, if inequality in society is the main reason for poor standards of living for many people, the size of the population is relatively unimportant.

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NCERT Solutions Class 10 Science Chapter 8 How Do Organisms Reproduce?

In this section of NCERT Solutions Class 10 Science Chapter 8, let us now look at the solutions to the questions: 

1. Asexual reproduction takes place through budding in

(a) Amoeba

(b) Yeast

(c) Plasmodium

(d) Leishmania

Solution: (b) Yeast

Yeast is an example of asexual reproduction that takes place through budding. A small protuberance is produced on the parent cell and that grows in full size forming a bud. In the parent cell, the daughter nucleus splits and migrates to the daughter cell. The bud detaches from the mother’s body at the base by forming a constriction. This process of budding continues to form a chain of bud cells. Note that the mother cell is smaller than the daughter cell.

2. Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary

(b) Uterus

(c) Vas deferens

(d) Fallopian tube

Solution: (c) Vas deferens

Vas deferens- part of the male reproductive system. A long, muscular tube travelling into the pelvic cavity from the epididymis. It is behind the bladder. Its function is to transport the mature sperm to the urethra. It also carries urine to the outside of the body.

3. The anther contains

(a) Sepals

(b) Ovules

(c) Pistil

(d) Pollen grains

Solution: (d) Pollen grains.

Pollen grains are the microscopic particles that occur in the pollen and contain male germ cells.

4. What are the advantages of sexual reproduction over asexual reproduction?

Solution: The following are the advantages of sexual reproduction:

• The offspring has the characters of both the parents.
• Improves the health of humans.
• The survival of the species is ensured as there are more variations.
• Becomes easy for offspring to adapt to environmental changes.

5. What are the functions performed by the testis in human beings?

Solution: The Following are the functions performed by the testes in human beings:

• It produces sperm. 
• It also produces the male hormone known as androgens.
• They also produce a hormone known as testosterone, which is responsible for the development of secondary sexual characteristics in boys.

6. Why does menstruation occur?

Solution: Menstruation is the normal bleeding of the vaginal line, which starts at puberty and lasts till menopause. During this period, the body of the female prepares itself for pregnancy.

Every month an egg is released from one of the ovaries at the same time when the uterus prepares itself for the fertilized egg. The inner endometrial lining of the uterus becomes thick and is supplied with a rich amount of blood for the embryo. Now, when there is no interaction between the egg and the sperm, the fertilization of the egg doesn’t occur, egg is removed from the body with the thick endometrial lining from the uterus along with blood and mucous through the vagina. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

7. Draw a labelled diagram of the longitudinal section of a flower.

Solution:

8. What are the different methods of contraception?

Solution: The following are the different methods of contraception:

• Natural method: The main focus of this method is to avoid physical contact with sperm and ovum. This can be achieved by avoiding the mating from 10th to 17th day of the menstrual cycle. During this period, there are high chances of fertilization as ovulation is expected.
• Oral contraceptives: In this method, pills are taken orally. These pills contain a small portion of hormones that block the eggs so that fertilization doesn’t take place.
• Barrier method: In this method, the meeting of sperms and ovum is avoided by using a barrier. These barriers are available for males as well as for females. Condoms for both males and females, cervical cap, diaphragms for females, and contraceptive sponge for females.
• Implants and surgical method: In this method, certain contraceptive devices like a loop or a copper-T can be used to block the meeting of sperm and ovum. In the surgical methods, the fallopian tubes are blocked in females to stop the flow of eggs and vas deference is blocked in men to stop the flow of sperm.

9. How are the modes of reproduction different in unicellular and multicellular organisms?

Solution: The different modes of reproduction in unicellular organisms include fission, budding, regeneration,  etc. Here, the cell divides into two daughter cells and this process of cell division continues.

Whereas, in multicellular organisms, there is a different organ system for reproduction. The different modes of reproduction in multicellular organisms are vegetative propagation, spore formation, etc.

In more complex organisms like humans and animals, reproduction is through sexual reproduction.

10. How does reproduction help in providing stability to populations of species?

Solution: Reproduction is the process of producing the same species by the existing species. This is done to maintain the population of that species and also to take forward their species to the next generations. Stability is maintained by keeping a check on the rate of births and rate of deaths.

11. What could be the reason for adopting contraceptive methods?

Solution: The following are the reasons for adopting contraceptive methods:

• To control population
• To avoid unplanned pregnancy
• To avoid the transfer of sexually transmitted diseases

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