How do Organisms Reproduce CBQs — CBSE Class 10 (2027) with step-wise solutions

Sample How do Organisms Reproduce CBQs

1. Question 1MCQ1 mark
   "The biological sex of an individual only depends on the sperm cell." Which option correctly evaluates this statement?
   • False, as the egg may carry either an X or a Y chromosome
   • True, as every sperm carries a Y chromosome
   • True, as every egg carries an X chromosome while a sperm carries either X or Y
   • False, as sex in humans is decided by the environment
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   1. [1 mark] True, as every egg carries an X chromosome while a sperm carries either X or Y — the egg always contributes X; whether the sperm brings X or Y decides the sex of the child.

   Answer: True, as every egg carries an X chromosome while a sperm carries either X or Y

2. Question 2Assertion-Reason1 mark
   Two statements are given - one labelled Assertion (A) and the other labelled Reason (R). Read the statements carefully and choose the option that correctly describes statements A and R. Assertion (A): Oral contraceptive pills and copper-T do not prevent sexually transmitted diseases. Reason (R): Sexually transmitted disease are transmitted by contact with mucous membranes of infected organs.
   • Both A and R are true and R is the correct explanation of A.
   • Both A and R are true but R is not the correct explanation of A.
   • A is true but R is false.
   • A is false but R is true.
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   1. [1 mark] Correct option: (1) Both A and R are true and R is the correct explanation of A. Neither pills nor copper-T forms a barrier at the mucous membranes, and it is exactly that contact route named in R which explains why these methods cannot prevent transmission.

   Answer: Both A and R are true and R is the correct explanation of A.

3. Question 3Short answer2 marks
   A farmer bought some strawberries and liked the taste. He decided to grow his own strawberries that should have the same taste. (a) Which method of cultivation should the farmer adopt? (b) Why would the farmer choose this method?
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   1. [1 mark] (a) asexual reproduction / vegetative propagation
   2. [1 mark] (b) because fruit produced through vegetative propagation would carry conserved parental characteristics

   Answer: (a) vegetative propagation; (b) the offspring are genetically identical, so the taste is preserved.

4. Question 4Case study4 marks
   During the monsoon, Riya, a Class 10 student in Guwahati, recorded three observations in her science notebook. Observation 1: A slice of moist bread kept in a closed tin for four days was covered with white cottony threads. Tiny black, round structures were present at the tips of some of the threads. Observation 2: In a drop of pond water seen under a microscope, a single-celled organism split into two equal halves, each becoming a new organism. Observation 3: In a freshwater sample, a Hydra had a small outgrowth on one side of its body. A few days later the outgrowth separated from the parent and lived on its own. (i) Name the tiny black, round structures seen in Observation 1 and state what they contain. (ii) Name the mode of reproduction seen in Observation 2 and in Observation 3. (iii) The young Hydra of Observation 3 grew into an adult. Name the cells that Hydra uses for this mode of reproduction, and explain why the young Hydra is almost identical to its parent.
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   1. [1 mark] (i) The black, round structures are sporangia (blobs on the hyphae of bread mould, Rhizopus); they contain spores (cells that can develop into new Rhizopus individuals).
   2. [1 mark] (ii) Observation 2 — binary fission; Observation 3 — budding.
   3. [1 mark] (iii) Hydra uses regenerative cells for reproduction by budding; the bud develops as an outgrowth due to repeated cell division at one specific site.
   4. [1 mark] (iii) Budding is asexual — only one parent is involved and no gametes fuse, so the bud receives a copy of the parent's DNA; it is therefore almost identical to the parent (only minor variations arising from errors in DNA copying).

   Answer: (i) Sporangia containing spores; (ii) binary fission, budding; (iii) regenerative cells — single parent, copied DNA, so nearly identical.

5. Question 5Long answer5 marks
   Given below are certain situations. Analyse each one and describe its possible impact: (a) Both oviducts (fallopian tubes) of a woman are surgically blocked. (b) The inner lining of a pregnant woman's uterus fails to stay thick, spongy and blood-rich, so it cannot hold the embryo. (c) A copper-T is placed in the uterus of a woman. (d) A person has unprotected sexual contact with a partner infected with HIV. (e) The muscles of the uterus of a pregnant woman do not undergo rhythmic contractions at the end of nine months.
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   1. [1 mark] (a) Sperms cannot reach the egg (and the egg cannot reach the uterus) through the blocked oviducts, so fertilisation cannot take place — pregnancy is prevented (a surgical method of contraception).
   2. [1 mark] (b) The thick, spongy, blood-rich lining is needed to receive the embryo and nourish it; without it the embryo cannot be implanted and nourished, so the pregnancy cannot continue.
   3. [1 mark] (c) The copper-T placed in the uterus prevents pregnancy; it may cause side effects due to irritation of the uterus.
   4. [1 mark] (d) The person may get infected with HIV and develop HIV-AIDS, a viral disease transmitted through sexual contact; using a condom (barrier) helps prevent its transmission.
   5. [1 mark] (e) The child is born as a result of rhythmic contractions of the muscles of the uterus; without these contractions normal childbirth will not take place and medical help will be needed.

   Answer: (a) No fertilisation; (b) embryo not implanted/nourished; (c) pregnancy prevented, possible irritation of uterus; (d) risk of HIV-AIDS; (e) normal childbirth will not occur.

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