CBSE Class 10 Science How Do Organisms Reproduce VBQs Set 06

Question. What is placenta? Describe its structure. State its functions in case of a pregnant human female.
Answer: Placenta is a disc-like special tissue connection established between the mother's uterine wall and the developing embryo. Structure: It contains villi on the embryo's side of the tissue. On the mother's side are blood spaces, which surround the villi. Functions: (i) It provides a large surface area for glucose and oxygen to pass from the mother to the embryo. (ii) It also serves to remove waste substances like carbon dioxide and urea generated by the developing embryo by transferring them into the mother's blood.

Question. (a) State in brief the functions of the following organs in the human female reproductive system. Ovary, Fallopian tube, Uterus (b) What is menstruation? Why does it occur?
Answer: (a) Ovary: It produces the female germ cells (eggs) and secretes hormones like estrogen and progesterone. Fallopian tube: It is the site where fertilization of the egg by sperm takes place and it carries the egg or zygote to the uterus. Uterus: It is the site where the embryo gets implanted and develops into a fetus. (b) Menstruation is the periodic discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. It occurs every month if the egg released by the ovary is not fertilized, as the thickened uterine lining breaks down and is shed.

Question. Write the functions of the following in human female reproductive system. Ovary, oviduct, uterus How does the embryo get nourishment inside the mother’s body? Explain in brief.
Answer: (i) Ovary: Produces eggs and female sex hormones. (ii) Oviduct (Fallopian tube): Acts as the site of fertilization and conveys the egg from the ovary to the uterus. (iii) Uterus: Supports the growth and development of the embryo. Nourishment: The embryo gets nourishment from the mother's blood with the help of a special tissue called the placenta. Nutrients like glucose and oxygen diffuse from the mother's blood into the embryo's blood across the placenta.

Question. (a) Name the human male reproductive organ that produce sperms and also secretes a hormone. Write the functions of the secreted hormone. (b) Name the parts of the human female reproductive system where, (i) fertilisation takes place (ii) implantation of the fertilised egg occurs. Explain how the embryo gets nourishment inside the mother’s body. OR (a) Write the name of the human male reproductive organ that produces sperms and secretes a hormone. Name the hormone secreted and state its functions. (b) Write the site of fertilisation and the part where the zygote gets implanted in the human female. (c) State, in brief, how an embryo gets its nourishment inside the mother’s body.
Answer: (a) The organ is the Testis. The hormone secreted is Testosterone. Functions: (i) It regulates the production of sperms. (ii) It brings about changes in appearance seen in boys at the time of puberty (secondary sexual characters). (b) (i) Fertilization takes place in the Fallopian tube (Oviduct). (ii) Implantation occurs in the Uterus. (c) The embryo gets nourishment from the mother's blood through the placenta. The placenta contains villi which provide a large surface area for the transfer of glucose, oxygen, and other nutrients from the mother to the developing embryo.

Question. (a) Name the respective part of human female reproductive system : (i) that produces egg (ii) where fusion of egg and sperm takes place, and (iii) where zygote gets implanted. (b) Describe in brief what happens to the zygote after it gets implanted.
Answer: (a) (i) Ovary, (ii) Fallopian tube (Oviduct), (iii) Uterus. (b) After implantation, the zygote (which has now become an embryo) continues to divide and grow. A special tissue called the placenta develops to provide nourishment and oxygen from the mother's blood and to remove wastes. The embryo gradually develops body parts and becomes a fetus.

Reproductive Health

Question. The bacterial and the viral infections that may be caused due to unsafe sex respectively are
(a) Warts and HIV-AIDS
(b) HIV-AIDS and Warts
(c) Gonorrhoea and Syphilis
(d) Syphilis and Warts.
Answer: (d) Syphilis and Warts.

Question. Which of the following techniques is used as a contraceptive method in males only ?
(a) Copper-T
(b) Oral pills
(c) Blockage of fallopian tube
(d) Blockage of vas deferens
Answer: (d) Blockage of vas deferens

Question. Name two infections which can be sexually transmitted in human beings.
Answer: Two sexually transmitted infections are Gonorrhoea (bacterial) and HIV-AIDS (viral).

Question. Name the part/organ of the human female reproductive system
(a) where contraceptive devices such as loop or copper-T are placed to prevent pregnancy.
(b) which is blocked to prevent the transfer of eggs.
(c) where formation of germ cells as ova takes place.
(d) from where the embryo gets nutrition from the mother’s blood.
Answer: (a) Uterus, (b) Fallopian tube (Oviduct), (c) Ovary, (d) Placenta.

Question. (a) Explain the surgical method of contraception used by (i) males, and (ii) females to prevent fertilisation. (b) Write the role of oral pills taken by women as a contraceptive.
Answer: (a) (i) In males, a small portion of the vas deferens is removed or tied up (Vasectomy) to prevent sperm transfer. (ii) In females, the fallopian tubes are blocked or tied (Tubectomy) so that the egg cannot reach the uterus and meet the sperm. (b) Oral pills contain hormones that change the hormonal balance of the body so that eggs are not released (ovulation is prevented), thereby preventing fertilization.

Question. What are sexually transmitted diseases? List two examples each of diseases caused due to (i) bacterial infection and (ii) viral infection. Which device or devices may be used to prevent the spread of such diseases?
Answer: Sexually Transmitted Diseases (STDs) are infectious diseases that are spread from one person to another through sexual contact. (i) Bacterial infections: Gonorrhoea and Syphilis. (ii) Viral infections: Warts and HIV-AIDS. The use of mechanical barriers like condoms during sexual acts can help prevent the spread of such diseases.

Question. List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males?
Answer: Three techniques to prevent pregnancy are: (i) Barrier methods (e.g., use of condoms), (ii) Chemical methods (e.g., oral pills), and (iii) Surgical methods (e.g., vasectomy or tubectomy). The chemical method (oral pills) and IUCDs like Copper-T are not meant for males.

Question. How does the use of these techniques have a direct impact on the health and prosperity of a family?
Answer: The use of contraceptive techniques helps in family planning by limiting the number of children and providing adequate time gaps between consecutive births. This ensures better health for the mother and child, reduces the financial burden on the family, and allows for better resources, education, and nutrition for each child, thereby improving the overall prosperity of the family.

Question. Suggest three contraceptive methods to control the size of human population which is essential for the health and prosperity of a country. State the basic principle involved in each.
Answer: Three contraceptive methods are:

• Mechanical Barrier Method: Use of condoms or diaphragms. Principle: They prevent the physical meeting of sperm and egg.
• Chemical Method: Use of oral pills or vaginal pills. Principle: They change the hormonal balance of the body so that eggs are not released and fertilisation cannot occur.
• Surgical Method: Vasectomy in males and Tubectomy in females. Principle: They block the gamete transport by removing or tying a small part of the vas deferens or fallopian tube respectively.

Question. List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over the past 50 years in our country.
Answer: Four points of significance of reproductive health:

• Prevents the spread of sexually transmitted diseases (STDs).
• Helps in controlling the population by limiting family size.
• Ensures better maternal and child health by providing proper gaps between births.
• Empowers individuals to make informed choices about reproduction.

Two areas of improvement: (i) Increased awareness and use of contraceptives. (ii) Improved healthcare facilities for institutional deliveries and immunization.

Question. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? OR List four methods of contraception used by humans. Justify the following statement. “The use of contraceptive methods has a direct effect on the health and prosperity of a family.”
Answer: Four methods are: (i) Mechanical barriers (condoms), (ii) Chemical methods (oral pills), (iii) IUCDs (Copper-T), and (iv) Surgical methods (Vasectomy/Tubectomy). Justification: Contraception allows for smaller families, which leads to better financial stability and resource allocation. It prevents frequent pregnancies, which can deteriorate a mother's health, and ensures that every child receives better nutrition, education, and medical care, thus leading to the prosperity of the family.

Question. On the notice board of ultrasound clinics it is generally stated. “Here prenatal sex determination and disclosure of sex (boy or girl before birth) of fetus is not done. It is prohibited and punishable under law.” (a) List two advantages of imposing ban on prenatal sex determination. (b) What can students do to educate the society about the following? (i) The ill-effects of indiscriminate female feticide. (ii) Adopting small family norms.
Answer: (a) Two advantages: (i) It helps in maintaining a balanced male-to-female sex ratio in society. (ii) It prevents the practice of female feticide and protects the right to life of the girl child. (b) (i) Students can organize awareness rallies, perform street plays, and create posters highlighting the importance of gender equality. (ii) Students can talk to community members about the benefits of small families for better education and quality of life.

LA 

Question. (i) Where are testes located in the human males and why? State two functions of the testes. (ii) In the human female, one of the ovaries releases an egg every month. State the changes that take place if (1) the egg is fertilized (2) the egg is not fertilized (iii) What is done during the surgical method in males and females to prevent pregnancy?
Answer: (i) Testes are located in the scrotum, outside the abdominal cavity, because sperm formation requires a temperature lower than the normal body temperature. Functions: (1) Production of sperms. (2) Secretion of testosterone. (ii) (1) If fertilized: The zygote is formed, gets implanted in the uterine wall, and develops into an embryo. The uterus develops a thick, spongy lining with blood vessels for nourishment. (2) If not fertilized: The thickened uterine lining is not needed, so it breaks down and is shed along with blood as menstruation. (iii) In males, vasectomy is performed (vas deferens is tied/cut). In females, tubectomy is performed (fallopian tubes are tied/cut).

Question. The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population. (i) List two common signs of sexual maturation in boys and girls. (ii) What is the result of reckless female feticide? (iii) Which contraceptive method changes the hormonal balance of the body? (iv) Write two factors that determine the size of a population.
Answer: (i) Common signs: Growth of hair in armpits and pubic area, and skin becoming oily. (ii) Reckless female feticide leads to a skewed sex ratio where males significantly outnumber females, causing social instability. (iii) Chemical methods (oral contraceptive pills) change the hormonal balance. (iv) Two factors: Birth rate and Death rate.

Question. (a) List three different categories of contraceptive methods. (b) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run. (c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
Answer: (a) (i) Barrier methods, (ii) Chemical methods, (iii) Surgical methods. (b) It is prohibited to stop female feticide. Long-term benefits include a balanced sex ratio and the social empowerment of women. (c) Bacterial: Syphilis and Gonorrhoea. Viral: Warts and HIV-AIDS.

Question. (a) Suggest any two categories of contraceptive methods to control the size of human population which is essential for the prosperity of a country. Also explain about each method briefly. (b) Name two bacterial and two viral infections each that can get sexually transmitted. (c) List two advantages of using condom during sexual act.
Answer: (a) (i) Barrier Method: Use of physical blocks like condoms to prevent sperm from reaching the egg. (ii) IUCD: Devices like Copper-T are placed in the uterus to prevent implantation. (b) Bacterial: Gonorrhoea, Syphilis. Viral: HIV-AIDS, Warts. (c) (i) Prevents pregnancy. (ii) Protects against sexually transmitted diseases.

Question. (b) What is contraception? List three advantages of adopting contraceptive measures.
Answer: Contraception is the intentional prevention of pregnancy through various devices, drugs, or surgical procedures. Advantages: (i) Population control. (ii) Maintenance of mother's health. (iii) Prevention of STDs (if barrier methods are used).

Modes of Reproduction Used by Single Organisms

SA I

Question. Rajesh observed a patch of greenish black powdery mass on a stale piece of bread. (a) Name the organism responsible for this and its specific mode of asexual reproduction. (b) Name its vegetative and reproductive parts.
Answer: (a) The organism is Rhizopus (Bread Mold). Its mode of asexual reproduction is Spore Formation. (b) Vegetative parts: Hyphae (thread-like structures). Reproductive parts: Sporangia (blobs on sticks containing spores).

Sexual Reproduction

Sexual Reproduction in Flowering Plants

SA I

Question. Mustard was growing in two fields - A and B. While field A produced brown coloured seeds, field B produced yellow coloured seeds. It was observed that in field A, the offsprings showed only the parental trait for consecutive generations, whereas in field B, majority of the offsprings showed a variation in the progeny. What are the probable reasons for these?
Answer: In field A, the probable reason is self-pollination, which leads to less variation and maintains parental traits. In field B, the reason is cross-pollination, which combines genetic material from different plants, leading to variations in the progeny.

LA 

Question. Trace the changes that take place in a flower from gamete formation to fruit formation.
Answer:

• Formation of male gametes in pollen grains (anther) and female gamete in the ovule (ovary).
• Pollination: Transfer of pollen grains from anther to stigma.
• Pollen germination: Pollen tube grows through the style to reach the ovary.
• Fertilisation: Fusion of male and female germ cells in the ovule to form a zygote.
• Post-fertilisation: Zygote divides into an embryo; ovule develops a coat and becomes a seed; ovary ripens and turns into fruit.

Sexual Reproduction in Human Beings

SA I

Question. (a) Trace the path a male gamete takes to fertilise a female gamete after being released from the penis. (b) State the number of sets of chromosomes present in a zygote.
Answer: (a) Vagina
\( \implies \) Cervix
\( \implies \) Uterus
\( \implies \) Fallopian tube (site of fertilisation). (b) A zygote contains two sets of chromosomes (diploid, 2n).

LA 

Question. (a) Why is it not possible to reconstruct the whole organism from a fragment in complex multicellular organisms? (b) Sexual maturation of reproductive tissues and organs are necessary link for reproduction. Elucidate.
Answer: (a) Complex multicellular organisms have highly specialized cells organized into tissues, organs, and organ systems. They do not have a large mass of undifferentiated "stem cells" everywhere that can regenerate all body parts from a small fragment. (b) Sexual maturation ensures that the body is physiologically and hormonally capable of producing viable gametes, supporting fertilisation, and in females, sustaining pregnancy and development of the fetus.

Question. (a) How are variations useful for species if there is drastic alteration in the niches? (b) Explain how the uterus and placenta provide necessary conditions for proper growth and development of the embryo after implantation.
Answer: (a) If a niche changes drastically, some individuals with specific variations might survive the change while others die. This prevents the total extinction of the species. (b) The uterus thickens its lining and increases blood flow to support the embryo. The placenta acts as a physiological bridge for nutrient and oxygen transfer and waste removal, ensuring the embryo grows in a controlled and nourished environment.

Case Based Questions

Read the passage given below and answer the following questions : Overpopulation causes many socio-economic problems not only at the national level but also at the family level. The only possible way to mitigate the ill-effects of increasing population is to reduce the birth rate through family planning programme and practising birth control measures. The various methods are A, B, C and D. A method involves the use of various physical devices to prevent pregnancy and fertilisation. B method involves insertion of contraceptive device into uterus to prevent pregnancy. C method uses chemicals and hormonal preparations. D are the permanent methods of birth control.

Question. How does method 'A' prevent pregnancy?
Answer: Method A (Barrier) prevent pregnancy by preventing release of sperms in the vagina, e.g., condom.

Question. Name two devices that are used in method 'B'.
Answer: Method B is intrauterine contraceptive (IUD) method. E.g., Copper-T and loops

Question. Give the mechanism of action of method 'C'.
Answer: Method C is chemical method. Foam tablets, jellies, pastes, creams and spermicides are some common chemicals used by females. These are placed in vagina. These chemicals adhere to the mucous membrane and immobilise and kill the sperms. Oral pills are also used to check release of ovum.

Question. OR Give a short note on method 'D'.
Answer: Method D is permanent method or surgical method. In males, small portion of vas deferens are removed surgically to prevent the sperms from coming out. In females, a small portion of fallopian tubes are removed surgically to prevent the entry of ovum into the uterus.

A & R Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : In human male, testes are extra abdominal and lie in scrotal sacs. Reason : Scrotum acts as a thermoregulator and keeps testicular temperature lower by \( 2-2.5^\circ\text{C} \) for normal spermatogenesis.
(a) A
(b) B
(c) C
(d) D
Answer: (a) In males, testes are present outside the body (extra abdominal) in the scrotal sacs. Spermatogenesis (sperm formation) takes place in testes. This process needs temperature \( 2 - 2.5^\circ\text{C} \) lower than the normal body temperature. The low temperature is maintained by the scrotal sacs. The scrotal sacs have muscles which constantly contract and relax the loose scrotal skin. The loose scrotal skin helps to keep the ideal testicular temperature for developing sperm. So scrotum acts as a thermoregulator and helps in spermatogenesis.

Question. Assertion : Female germ cells are larger than male germ cells. Reason : Female germ cells contain the food reserves.
(a) A
(b) B
(c) C
(d) D
Answer: (b) In humans, the female gametes are large as they contain the food reserves and the male gametes are small and motile so that they can easily travel inside the female reproductive system and reach the site of fertilisation. Male gametes are haploid cells.

Multiple Choice Questions

Question. During gamete formation chromosome number becomes half, so that
(a) offsprings get half set of chromosomes
(b) further meiosis does not takes place in zygote.
(c) chromosome number in parents and offsprings remains constant always
(d) zygote remain haploid.
Answer: (c) Gamete formation involves meiosis or reduction division. The gamete mother cell is diploid (2n), i.e., it has two sets of chromosomes. This single diploid cell divides by meiosis to form 4 haploid (n) daughter cells. Each daughter cell becomes a gamete, either male or female. Each gamete possesses single set of chromosomes. Fusion of these gametes results in the formation of a zygote having a double set of chromosomes i.e., diploid (2n) (one set of paternal and the other set of maternal). Thus, the number of chromosomes in parents and offsprings of a particular species remains constant.

Question. Select the correct match. Organism - Mode of reproduction
(a) Bryophyllum – Leaf bud
(b) Hydra – Binary fission
(c) Paramecium – Multiple fission
(d) Spirogyra – Vegetative propagation
Answer: (a) Buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.

Question. Which of the following parts of a plant cannot take part in vegetative propagation?
(a) Root
(b) Stem
(c) Leaves
(d) Fruits
Answer: (d) Vegetative propagation is a type of asexual reproduction in which parts of plant like the root, stem and leaves develop into new plants under appropriate conditions.

Question. Select the incorrect statement regarding seeds.
(a) Seeds have tough seed coat that protect them from external environment.
(b) Cotyledons store food.
(c) Plumule develops into the root system.
(d) Seeds contain the future plant called embryo.
Answer: (c) Plumule develops into the shoot system.

Question. Which of the following is a mechanical barrier method of birth control?
(a) Copper-T
(b) Oral pills
(c) Condoms
(d) Both (a) and (c)
Answer: (d) Both copper-T and condoms provide mechanical barrier for the sperms so that they cannot reach to the uterus.