CBSE Important Questions Class 10 Science Chapter 7 – How do Organisms Reproduce?

Class 10 Science Chapter 7 How do Organisms Reproduce? is part of the CBSE Class 10 Science syllabus. It explains why living things reproduce, the difference between asexual and sexual reproduction, how plants reproduce through pollination and double fertilisation, the human male and female reproductive systems, the menstrual cycle, and methods of family planning and reproductive health.

These CBSE important questions for Class 10 Science Chapter 7 cover variation and the survival of a species, artificial selection in cattle, the menstrual cycle, contraceptive methods, wind and insect pollination, undescended testes, cross-pollination experiments, external fertilisation in frogs, the placenta, double fertilisation and the human male reproductive system. Every question has a clear step-by-step answer in simple English with figures, so students can practise on their own, parents can check the answers, and teachers can use them for class tests.

Q1. Answer the following questions:
i. How does variation improve the fitness of a species?
ii. Why can variation in somatic cells not pass to the next generation?
iii. With the help of an example, explain how variation is beneficial for the survival of a species over time.

Answer: i. A population with many variations can adapt and survive when the surroundings change. This genetic diversity improves the biological fitness of the species.
ii. Variations in body (somatic) cells are called somatic mutations. They do not occur in the cells that make gametes, so they cannot be passed on. Only germ cells carry traits to the next generation.
iii. If the water temperature rises because of global warming, most bacteria living in cool water would die. But a few bacteria that happen to have a variation making them resistant to heat would survive and multiply. So variation helps a species survive over time.

Q2. Farmers crossed two breeds of cattle, the Jersey from Europe and the Sahiwal from Africa. For many generations, the farmers picked out the offspring with the highest milk yields to breed the next generation. Which phrase best describes this process?
(a) Evolution
(b) Natural selection
(c) Artificial selection
(d) Discontinuous variation

Answer: (c) Artificial selection
Here human beings, not nature, choose which animals will breed. When people deliberately select organisms with a desired trait (high milk yield) and breed them, it is called artificial selection or selective breeding.

Q3. In Shruti's case, her periods started on 10th April and her next period started on 9th May, with ovulation in the middle of the cycle. Estimate the length of her menstrual cycle and pick the incorrect statements.
I. The level of estrogen and progesterone will be high from 22nd April to 25th April.
II. Shruti's chances of getting pregnant are lowest from 11th to 14th April.
III. The level of LH will be highest on 23rd–24th April.
IV. If intercourse occurs from 23rd to 26th April, Shruti can conceive easily.
V. The uterus lining will start disintegrating from 30th April to 3rd May.
(a) I and II
(b) III and V
(c) I and V
(d) II and III

Answer: (c) I and V
From 10th April to 9th May is a 30-day cycle, so ovulation happens around 24th–25th April.
Statement I is wrong: just before ovulation, estrogen is high but progesterone is still low. Progesterone rises only after ovulation.
Statement V is wrong: the uterus lining breaks down only at the very end of the cycle, around 8th–9th May, not from 30th April.
Statements II, III and IV are correct.

Q4. Amita has three children and does not want any more babies. Rita has one child and wants another child, but not right now. Which of the given is correct in the case of Amita and Rita?
(a) Cervical cap to Rita and IUD to Amita
(b) Vasectomy to Amita and tubectomy to Rita
(c) IUD to Amita and diaphragm to Rita
(d) Tubectomy to Amita and IUD to Rita

Answer: (d) Tubectomy to Amita and insertion of an IUD to Rita.
Amita wants no more children, so she needs a permanent method. Tubectomy, in which the fallopian tubes are blocked, is a permanent method for women.
Rita wants a child later, so she needs a long-term but reversible method. An IUD (intra-uterine device) can be removed whenever she wants to conceive. Vasectomy is done on men, so option (b) is wrong for Amita.

Q5. The following data about two plant species was obtained after a study.

Which valid conclusion(s) can be drawn from the given data?
I. Plant A is more likely to be wind pollinated.
II. Plant B is more likely to be cross pollinated with plant A.
III. The stigma of plant A is likely to be more exposed than that of plant B.
IV. Plant B is likely to be pollinated by insects.
V. The rate of pollination will be higher in plant A.
(a) I, II and III
(b) IV and V
(c) II and III
(d) I and IV

Answer: (d) I and IV
Plant A has light, smooth, dry pollen and small, dull flowers. These are the features of wind-pollinated plants, so I is correct.
Plant B has heavy, spiny and sticky pollen and large, brightly coloured flowers that attract insects. Sticky, spiny pollen sticks to an insect's body, so IV is correct.
Plants of two different species cannot pollinate each other, so II is wrong.

Q6. A child was born with a congenital disorder in which his testes remained within the abdominal cavity and did not descend into the scrotum. Which of the following problems will he face in later years of his life?
(i) Abnormal secondary sexual characters
(ii) Reproductive sterility
(iii) Stunted growth
(iv) Enlargement of larynx
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i), (ii) and (iii)
(d) Only (ii)

Answer: (a) (i) and (ii)
The testes lie in the scrotum outside the body because sperm need a temperature slightly lower than body temperature. If the testes stay inside the abdomen, the higher temperature stops sperm from forming, which causes sterility. The testes also make less testosterone, so the secondary sexual characters such as a deep voice, beard and body hair do not develop properly. Height is controlled by other hormones, so growth is not stunted.

Q7. Rohit took two plants, 1 and 2, of the same species with bisexual flowers and performed the following activities.
I. He removed the petals from plant 1.
II. He removed the anther from plant 2.
III. He removed the stigma from plant 1.
IV. He removed the sepals from plant 2.
Which two listed activities would ensure cross-pollination in plants?
(a) I and II
(b) II and III
(c) III and IV
(d) I and IV

Answer: (b) II and III
Removing the anther (the male part) from plant 2 means plant 2 cannot pollinate itself, so it can only receive pollen from plant 1. Removing the stigma (the female part) from plant 1 means plant 1 cannot receive pollen, so it can only donate pollen. Together these two steps make sure that pollen travels from plant 1 to plant 2, which is cross-pollination.

Q8. Frogs produce a large number of eggs whereas humans produce a large number of sperms. Which of the following statements correctly applies to the stated facts?
(a) The number of sperms is fewer in frogs.
(b) This feature eliminates the disadvantages of external fertilisation.
(c) Frogs have less built-in population control mechanism.
(d) Production of more eggs allows equal distribution of males and females.

Answer: (b) This feature eliminates the disadvantages of external fertilisation.
In external fertilisation, the eggs and sperms are released into water, where many are washed away, eaten by other animals or never meet. By producing very large numbers of eggs and sperms, the chance that at least some will meet and develop successfully becomes much higher.

Q9. During pregnancy, a temporary connection forms between the tissues of the mother and the foetus. Which of the mentioned functions of this tissue is incorrect?
(a) It allows exchange of materials between the mother and the foetus.
(b) Antibodies cannot cross this tissue from mother to the foetus.
(c) The foetal part of this tissue consists of the cells of chorion which produce chorionic villi.
(d) It secretes pregnancy hormones required for supporting foetal growth.

Answer: (b) Antibodies cannot cross this tissue from mother to the foetus.
The tissue described is the placenta. This statement is incorrect, because antibodies (mainly IgG) do pass from the mother to the foetus through the placenta. These antibodies give the baby passive immunity, which protects it for the first few months after birth. The other three statements are correct functions of the placenta.

Q10. Higher organisms such as flowering plants and vertebrates have adapted to sexual means of reproduction. Identify the reason behind this adaptation.
(a) The sexual mode of reproduction produces a large number of individuals.
(b) The DNA-copying mechanism is inaccurate in case of asexual reproduction.
(c) Sexual reproduction speeds up the process of producing variants.
(d) These organisms lack the machinery required for asexual reproduction.

Answer: (c) Sexual reproduction speeds up the process of producing variants.
In sexual reproduction, genes from two different parents combine, so the offspring are all slightly different from each other and from their parents. This creates variation much faster than asexual reproduction, and variation helps the species survive when the environment changes.

Q11. The process of double fertilisation is a characteristic feature of a flowering plant. In this process, two male gametes enter the ovule for fertilisation. Identify the cell that fuses with the male gamete in triple fusion during the process of double fertilisation.
(a) I
(b) II
(c) III
(d) IV

Answer: (c) III
In double fertilisation, one male gamete fuses with the egg cell to form the zygote. The second male gamete fuses with the two polar nuclei of the central cell. Because three nuclei join, this is called triple fusion, and it forms the endosperm, which feeds the growing embryo. The central cell is the part marked III.

Q12. a. Mustard was growing in two fields, A and B. In field A, the offspring showed only the parental trait for several generations, whereas in field B most offspring showed variation. What is the probable reason for this?
b. Draw the human male reproductive system and label the parts. Mention the function of the vas deferens and the seminal vesicle.

Answer: a. In field A the plants were self-pollinated, so the same genes were passed on and the offspring looked just like the parents. In field B cross-pollination took place, so genes from two different plants combined (recombination) and the offspring showed variation.
b. The labelled diagram of the human male reproductive system is given below.
• Vas deferens (ductus deferens): carries mature sperm from the testis to the urethra.
• Seminal vesicle: produces the fluid that mixes with the sperm to form semen, which nourishes the sperm and helps them move.

Related Study Material on Extramarks

• CBSE Important Questions Class 10 Science Chapter 1
• CBSE Important Questions Class 10 Science Chapter 2
• CBSE Important Questions Class 10 Science Chapter 3
• CBSE Important Questions Class 10 Science Chapter 4
• CBSE Important Questions Class 10 Science Chapter 5
• CBSE Important Questions Class 10 Science Chapter 6
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