Chapter 8 of NCERT Class 10 Science is How do Organisms Reproduce. This chapter provides an understanding of the entire process of Reproduction for multi-celled organisms and single-celled organisms. The chapter has eleven questions in which you will be asked to draw a diagram of a longitudinal section of flower and label it.
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NCERT Solution for Class 10 Science Chapter 8: How do Organisms Reproduce PDF
Explain the importance of DNA copying in reproduction?
DNA (Deoxyribonucleic acid) is the genetic material found in the chromosomes, which are present in the nucleus of a cell that carries the genes responsible for all the characters of the individual including physiological processes. A child inherits two copies of DNA, one from the mother and the other from the father. This is the reason why offspring look similar to their parents and also inherit some of the mannerisms from their parents. So, DNA copying during reproduction is an important phenomenon through which characters are passed over generations. DNA copying during reproduction is very accurate. If there is an error during
DNA copying (mutation), the offspring can have a faulty gene which might lead to some disease. So, DNA copying is very important during reproduction. DNA copying in sexually reproducing organisms also produces variations, which give a better survival advantage to species.
Why is variation beneficial for some species while not necessarily for any
Variations are beneficial to the species rather than individuals because sometimes for a species, their survival becomes difficult as the environmental conditions change drastically,
For example, if the temperature of water suddenly increased, then most of the bacteria that re living in that water would probably die. Only a few variants who are resistant to heat and high temperature would be able to survive, however, if these variants were not there, then the entire population of bacteria would have been destroyed. Thus, variants help in the survival of the species; however, all variations are not necessarily beneficial for individual organisms.
How does binary fission differ from multiple fission?
In binary fission, a single cell divides itself into two equal cells. For ex: The species like Amoeba and Bacteria divide by binary fission. In binary fission in Amoeba, in multiple fission, a single cell divides into many daughter cells simultaneously. Parent cell nucleus divides cytoplasm divides two daughter cells Binary fission in Amoeba Plasmodium and Amoeba divide by multiple fission.
Multiple fission in Plasmodium
How will an organism be benefited if it reproduces through spores?
Advantages of spore formation:
(i) Large numbers of spores are produced in one sporangium.
(ii) Spores are distributed by air to far-off places easily to avoid competition in one place.
(iii) Spores are covered by thick walls to safeguard itself and prevent dehydration under unfavourable conditions.
Can you think of any reasons that why more complex organisms does not
give rise to new individuals through regeneration?
Some simple organisms like Hydra are capable of producing new individuals from their own body parts and is called the process of regeneration, which results in the formation of new organisms. Simple organisms can utilize this method of reproduction since their entire body is made up of fewer and similar kinds of cells in which any part of their body can be formed by growth and development; on the other hand, complex organisms have an organ-system level of organization. All the organ systems of the bodywork together as an interconnected unit. They can regenerate their lost body parts such as blood, muscles, skin, etc. However,
they cannot give rise to new individuals through regeneration as a specific cell or tissue cannot form a complete organ. Therefore, it would not be possible to completely regenerate an entirely new organism. Organisms like lizards and starfish can regenerate broken parts of the body through the process of regeneration.
Explain why vegetative propagation is practiced for growing some types of
Asexual reproduction carried out by vegetative parts of the plant (leaf, stem, roots) is called vegetative propagation. This kind of propagation occurs independently of seeds. It has many advantages such as:
(i) Propagation of plants with no seeds or no viable seeds such as orchids, banana, etc can be done.
(ii) Propagation of a selected superior variety of a plant. This is because the plants produced will be genetically identical to the parent plant.
(iii) A quicker propagation method to obtain a large number of plants in much lesser time.
(iv) Due to unfavorable soil or environmental conditions, the seeds may not germinate. In that case vegetative propagation introduce and propagates plants in newer areas.
Why is DNA copying an essential part of the process of reproduction?
As DNA passes genetic information from parents to offspring, so DNA copying is an essential part of reproduction. It determines the body’s design of an individual. The DNA copying always takes place along with the additional cellular structure creation. This process is then followed by cell division to form two cells.
How is the process of pollination different from fertilization?
Pollination is the process of transfer of pollen from an anther to the stigma of a flower. Pollination is carried out with the help of pollinating agents such as air, water, birds, or insects. Fertilization happens after pollination. It is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of a zygote.
What is the role of the seminal vesicles and the prostate gland?
The secretions from seminal vesicles and prostate glands lubricate the sperms and thus provide a fluid medium for easy transport of sperms. Their secretion also provides nutrition to the flowing sperm in the form of fructose, calcium, and some enzymes to enable the sperm to survive for a few days until they can fertilize the egg.
What are the changes seen in girls at the time of puberty?
Secondary sexual characteristics in girls:
(i) Increase in size of breast and darkening of the nipples skin present at the tips of the breasts.
(ii) Hair appearance in genital area.
(iii) Hair appearance in other areas of skin like legs, underarms, hands, and face.
(iv) Size increase of uterus and ovary.
(v) Beginning of menstrual cycle.
(vi) Appearance of pimples in some of the cases due to more secretion of oil from the skin.
(vii) Hips widening.
How does the embryo get nourishment inside the mother’s body?
The embryo develops inside the body of mother for about 280 days or nine months. Inside the uterus, the outer tissue surrounding the embryo develops villi, a finger-like projections. These villi are surrounded by maternal blood and uterine tissue. They provide a large surface area for oxygen and nutrients exchange. Placenta, a special tissue is embedded in the uterine wall. The embryo receives nutrients and oxygen from the blood of mother via the placenta. The
waste materials produced by the embryo are also removed through the placenta.
If a woman is using a copper−T, will it help in protecting her from sexually
No. Using a copper-T will not provide protection from STD (sexually transmitted diseases), as it does not prevent the semen entry. It only prevents the embryo implantation in the uterus.
Exercise Chapter 8
Asexual reproduction takes place through budding in
Which one of the given below options is not a part of the female
reproductive system in human?
(c) Vas deferens
(d) Fallopian tube
(c) Vas deferens
The anther contains
(d) Pollen grains.
(d) The anther contains pollen grains.
Write some of the advantages of sexual reproduction over asexual
reproduction in organisms?
Advantages of sexual reproduction:
In sexual reproduction, more variations are produced. Thus, it ensures the survival of species.
(i) The newly formed individuals gain the characteristics of both the parents.
(ii) More viable variations because, in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
(iii) Progeny produced as a result of sexual reproduction are less than those produced byasexual reproduction.
Question 5: Mention the functions that are performed by the testis in human beings?
The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called the scrotum. Functions of testes:
(i) Produce sperms
(ii) Secrete testosterone, a hormone which is responsible for about secondary sexual characters in boys.
Why does menstruation occur?
All females, after reaching their puberty produce a mature egg cell every month during a process called the menstrual cycle.
(i) During this period, an ovary releases a mature egg.
(ii) If the egg is not fertilized, the uterine lining is shed and a new cycle begins.
(iii) Overall a menstrual cycle lasts for 28 days.
Draw a labelled diagram of the longitudinal section of a flower.
Solution 7: Refer pdf.
What are the different methods of contraception?
Contraception is the method employed to prevent pregnancy. The contraceptive methods is divided into the following types:
(i) Natural method → it involves avoiding the chances of sperm and ovum meeting. In this method, the sexual act is avoided from 10th to 17th day of the menstrual cycle because, during this period, ovulation is expected and therefore, the fertilization chances are very high.
(ii) Barrier method → in this method, the ovum and sperm fertilization is prevented with the help of barriers. Barriers are available for both females and males. Condoms are barriers made of thin rubber that are used to cover the penis in males and vagina in females.
(iii) Oral contraceptives → In this method, drugs or tablets are taken orally. These contain small hormones doses that prevent the release of eggs and thus fertilization cannot occur.
(iv) Implants and surgical methods → Contraceptive devices such as Copper-T are placed in the uterus to prevent pregnancy. Some surgical methods can also be used to block or stop the transfer of gametes. It includes the blocking of vas deferens to prevent the sperms transfer known as vasectomy. Similarly, fallopian tubes of female can be blocked so that the egg will not reach the uterus known as Tubectomy.
How the modes for reproduction are different in multicellular than those in
(i) In unicellular organisms, reproduction occurs by the division of the entire cell.
(ii) The modes of reproduction in unicellular organisms can be fission, budding, etc.
(i) Specialized reproductive organs are present.
(ii) They can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc.
(iii)More complex multicellular organisms like human beings and plants, the mode of reproduction is sexual reproduction.
How reproduction does contribute in providing the stability of populations
For the continuation of a particular species, living organisms chooses to reproduce. Reproduction provides stability to populations of species by producing a new individual that resembles the parents. Therefore, In addition due to the presence of variants, the species is also better equipped to handle environmental changes and survive in the long run.
What could be the reasons for adopting contraceptive methods?
Contraceptive methods are mainly adopted because of the following reasons:
(i) To prevent unwanted pregnancies.
(ii) To control population rise or birth rate.
(iii) To prevent the transfer of sexually transmitted diseases.