2022-12-23 13:46:27
Human Reproduction Important Questions for CBSE Class 12 Biology Fertilisation, Pregnancy and Embryonic Development
Previous Year Examination Questions
1 Mark Questions
1.How is the entry of only one sperm ensured into an ovum during fertilisation in humans?[All India]
Ans.During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes (depolarisation) in the membrane that blocks the entry of additional sperms. This ensures that only one sperm can fertilise an ovum
2.Mention the function of trophoblast in human embryo.[Delhi 2011]
Ans.Trophoblast is the outer layer of blastocyst which helps in attachment of blastocyst to the endometrium of the uterus.
3.Name the embryonic stage that gets implanted in the uterine wall of a human female. [All India]
Ans.Blastocyst gets implanted in the uterine wall.
4.What stimulates pituitary to release the hormone responsible for parturition? Name the hormone.[All India ]
Ans.Foetal ejection reflex stimulates pituitary to release the oxytocin hormone, which is responsible for parturition.
5.How does colostrum provide initial protection against diseases to newborn infants? Give one reason. [Delhi 2009]
Ans.Colostrum contains necessary antibodies (IgA) that provide protection against diseases to newborn infants.
2 Marks Questions
6.Where does fertilisation occur in humans? Explain the events that occur during this process. [All India]
Ans.In humans, the fertilisation of ovum takes place in ampullary-isthmic junction of Fallopian tube.
The events that occur during the process of fertilisation are:
(i) The sperm reaches the junction of ampulla and isthmus and comes in contact with zona pellucida layer of ovum.
(ii) Acrosome of sperm head release sperm lysin enzymes that dissolves corona radiata and digests zona pellucida layer and enters cytoplasm.
(iii) Entry of sperm stimulates secondary oocyte to complete its suspended second meiotic division, thus producing haploid egg or ovum and second polar body.
(iv)Nucleus of sperm and of ovum fuses to form a diploid zygote.
7.Explain the events that occur during fertilisation of an ovum in humans. How is it that only one sperm enters the OVUm? [All India]
Ans.(i)In humans, the fertilisation of ovum takes place in ampullary-isthmic junction of Fallopian tube.
The events that occur during the process of fertilisation are:
(a) The sperm reaches the junction of ampulla and isthmus and comes in contact with zona pellucida layer of ovum.
(b) Acrosome of sperm head release sperm lysin enzymes that dissolves corona radiata and digests zona pellucida layer and enters cytoplasm.
(c) Entry of sperm stimulates secondary oocyte to complete its suspended second meiotic division, thus producing haploid egg or ovum and second polar body.
(d)Nucleus of sperm and of ovum fuses to form a diploid zygote.
(ii)During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes (depolarisation) in the membrane that blocks the entry of additional sperms. This ensures that only one sperm can fertilise an ovum
8.(i) Where do the signals for parturition originate in humans?
(ii) Why is it important to feed the newborn babies on colostrum? [All India 2012]
Ans.(i)The signals for parturition originate from the fully developed foetus and the placenta, which induce mild uterine contraction called foetal ejection reflex
(ii)Colostrum contains necessary antibodies (IgA) that provide protection against diseases to newborn infants.
9.Name the hormones produced only during pregnancy in human female. Mention their source organ.
Ans.The hormones produced only during pregnancy in human female are human Chorionic Gonadotropin (hCG), human Placental Lactogen (hPL) and relaxin. The source of hCG and hPL — Placenta, and Relaxin — Ovary.
10.Placenta acts as an endocrine tissue. Justify. [All India 2010]
Ans.Placenta acts as an endocrine tissue as it secretes hormones like
(i) hCG (human Chorionic Gonadotropin)
(ii) hPL
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