NCERT Solutions for Class 10 Science Chapter 7 - How Do Organisms Reproduce?

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Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should also be similar. Thus, DNA copying during reproduction involves making copies of the blueprints of body design.

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The DNA copies generated in reproducing cells are similar but may not be exactly identical to the original. Thus, the cells will be subtly different from each other. This inbuilt tendency for variation to occur during reproduction is the main cause of formation of new species. Hence, variations are beneficial to the species but not necessarily for the individual.

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The spores are covered with thick walls that protect them until they come into contact with another moist surface and begin to grow. Thus, it is beneficial for the organisms such as Rhizopus to reproduce through spores.

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More complex organisms have a very high degree of organization in their body, that is, specialized cells make up tissues, tissues make up organs, organs make up organ systems and organ systems make up organisms. Hence, they cannot be reproduced from their cut body parts by the process of regeneration. Organisms such as Hydra, Planaria can reproduce through regeneration as they have relatively simple body organization consisting of only a few specialized cells.

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(a) DNA copying provides cellular apparatus in the daughter cells. (b) DNA in daughter cells will be able to control the functioning of daughter cells. (c) DNA copies will retain the traits.

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Pollination is the process in which pollen grains are transferred from anther to the stigma of a flower. Fertilisation is the process in which fusion of male gamete with female gamete takes place to form zygote.

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Seminal vesicles secrete a viscous secretion containing fructose and prostaglandins. The fructose is source of energy for sperm and prostaglandins stimulate uterine contraction and thus help the sperm to move towards the female’s oviduct.

Prostate gland secretes an alkaline and milky fluid that aids in sperm motility. The fluid contains small amount of citric acid, some lipids and a few enzymes. It also contains bicarbonate ions which makes the semen alkaline.

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The following changes are seen in girls at the time of puberty:
(a) Growth of breast and external genitalia. (b) Darkening of nipple skin.
(c) Broadening of pelvis. (d) Growth of pubic and axillary hair.
(e) Increase in subcutaneous fat. (f ) Initiation of menstruation and ovulation. Changes at puberty occur under the influence of FSH (Follicle stimulating hormone) and estrogen hormone.

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Embryo gets nourishment through placenta inside the mother’s body. Placenta is a disc-like special tissue embedded in the wall of uterus. It contains villi on the embryo side of tissue. On the mother side are blood spaces which surround villi. Placenta brings the foetal and maternal blood close enough to permit exchange of materials between the two.

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Copper-T can prevent unwanted pregnancy but cannot protect women from acquiring sexually transmitted diseases (if her partner has such a disease).

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(b) Yeast

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(c) Vas deferens

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(d) Pollen grains

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The advantages of sexual reproduction over asexual reproduction are:
(a) Sexual reproduction introduces variations in offspring, hence it is of evolutionary significance.
(b) As a result of new character combination, better offspring are produced which results in the formation of better varieties.

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The following functions are performed by the testis in human beings:
(a) Testis produce haploid and motile male gametes called sperms.
(b) Leydig’s cells which lie scattered in interstitial spaces between seminiferous tubules secrete male sex hormone called testosterone which controls the development of secondary sexual characters in males.

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If a sperm is not available at the time of ovulation, then fertilization of ovum does not take place. As a result, the thick and soft uterus lining having a lot of blood capillaries in it is not required. The unfertilized ovum dies within a day and the uterus lining also breaks down. Since the thick and soft uterus lining contains a lot of blood vessels, the breaking of the uterus lining produces blood alongwith other tissues. The blood comes and other tissues come out of the vagina in the form of menstrual flow.

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Unicellular organisms mostly reproduce by asexual reproduction. The multicellular organisms reproduce mostly by sexual reproduction.

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Reproduction gives rise to more organisms with the same basic characteristics as their parents. If however, some species of the living organism cannot reproduce due to certain reasons, then the organisms of this species will gradually die out and disappear from the earth. Hence, reproduction is the only method which helps in providing stability to population of species.

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Some of the reasons for adopting contraceptive methods are:
(a) These methods prevent pregnancy in women.
(b) These methods also prevent transmission of sexually transmitted diseases.