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Human Reproduction — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYHuman Reproduction4 Marks
Question
Read the following and answer any four questions from (i) to (v) given below:

During copulation, semen is released by the penis into the vagina. 'The motile sperms swim rapidly, fuse with ovum in the ampullary region, resulting in fertilisation. Haploid nucleus of sperm fuse with that of ovum to form diploid zygote.

  1. In female genital tract, sperms are made capable of fertilising the egg. This phenomenon of sperm activation is called:
  1. Amphimixis.
  2. Cortical reaction.
  3. Capacitation.
  4. Acrosomal reaction.
  1. Select the correct sequence of various physical and chemical events that take place during fertilisation.
  1. Fusion of cortical granules with plasma membrane of secondary oocyte.
  2. Formation of fertilisation cone to receive sperm.
  3. Release of sperm lysin from acrosome.
  4. Mixing up of chromosomes of a sperm and an ovum.
  1. R → Q → P → S
  2. Q → S → R → P
  3. Q → R → S → P
  4. R → P → Q → S
  1. Assertion: Only one sperm can fertilise an ovum.

Reason: The secretion of acrosome help the sperm to enter into cytoplasm of ovum through zona pellucida and plasma membrane.

  1. Both assertion and reason are true, and reason is the correct explanation of assertion.
  2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
  3. Assertion is true, but reason is false.
  4. Both assertion and reason are false
  1. What is the significance of fertilisation?
  1. It restores haploid number of chromosomes.
  2. It produces offspring genetically identical to parents.
  3. It initiates cleavage.
  4. Both (b) and (c).
  1. Site of fertilisation in humans is:
  1. Endometrium of uterine cavity.
  2. Ampullary isthmic junction of oviduct.
  3. Cervix of uterus.
  4. Infundibulum of fallopian tube.
✓

Answer

  1. (c) Capacitation.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

The secretions of female genital tract remove coating substances deposited on the surface of the sperms. This phenomenon of sperm activation is called capacitation.

  1. (d) R → P → Q → S
  2. (b) Both assertion and reason are true, but reason is not the correct explanation of assertion.

​​​​​​​Explanation:

Binding of sperm to the secondary oocyte induces depolarisation of the oocyte plasma membrane. Depolarisation prevents polyspermy and ensures monospermy.

  1. (c) It initiates cleavage.

​​​​​​​Explanation:

Fertilisation restores diploid number of chromosomes. It introduces variations as it combines characters of the two parents.

  1. (b) Ampullary isthmic junction of oviduct.

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