Question
Receptors for sperm binding in mammals are present on [NEET 2021]
(a) corona radiata
(b) vitelline membrane
(c) perivitelline space
(d) zona pellucida
Answer/Explanation
Question
Capacitation occurs in [NEET 2017]
(a) rete testis
(b) epididymis
(c) vas deferens
(d) female reproductive tract
Answer/Explanation
Ans. (d)
Capacitation is a process, where the spermatozoa acquire the capacity to fertilise the eggs. It occurs in female reproductive tract.
Concept Enhancer
Capacitation involves following changes
(i) Dilution of inhibitory factors of semen.
(ii) Removal of cholestrol vesicles covering sperm head and acrosome.
(iii) Increase in the permeability of acrosome.
Ans. (d)
Receptors for sperm binding are present on zona pellucida layer of ovum in mammals.
A sperm comes in contact with zona pellucida layer of ovum and induces changes that blocks further entry of other sperms.
It ensures entry of only one sperm inside the ovum for fertilisation.
Question
Fertilisation in humans is practically feasible only if [NEET 2016, Phase I]
(a) the ovum and sperms are transported simultaneously to ampullary – isthmic junction of the Fallopian tube
(b) the ovum and sperms are transported simultaneously to ampullary-isthmic junction of the cervix
(c) the sperms are transported into cervix within $48 \mathrm{hrs}$ of release of ovum in uterus
(d) the sperms are transported into vagina just after the release of ovum in Fallopian tube
Answer/Explanation
Ans. (a)
Fertilisation in humans, is practically feasible only if the sperms and ovum are transported simultaneously at ampullary-isthmic junction of Fallopian tube.
Question
Ectopic pregnancies are referred to as [CBSE AIPMT 2015]
(a) pregnancies with genetic abnormality
(b) implantation of embryo at site other than uterus
(c) implantation of defective embryo in the uterus
(d) pregnancies terminated due to the hormonal imbalance
Answer/Explanation
Ans. (b)
Ectopic pregnancy develops when an embryo implants somewhere other than the uterus, such as in one of Fallopian tube. It is also known as eccysis or tubal pregnancy.
Question
In human females, meiosis-ll is not completed until [CBSE AIPMT 2015]
(a) puberty
(b) fertilisation
(c) uterine implantation
(d) birth
Answer/Explanation
Ans. (b)
In human females, meiosis II is not completed until fertilisation. Secondary oocyte is arrested in metaphase ll stage until sperm cell contacts plasma membrane of the oocyte and completes meiosis $\|$ resulting in release of ovum.
Question
Select the correct option describing gonadotropin activity in a normal pregnant female [CBSE AIPMT 2014, 12]
(a) High level of FSH and LH stimulates the thickening of endometrium
(b) High level of FSH and LH facilitate implantation of the embryo
(c) High level of hCG stimulates the synthesis of estrogen and progesterone
(d) High level of hCG stimulates the thickening of endometrium
Answer/Explanation
Ans. (c)
hCG (human Chorionic Gonadotrophin) secretion occurs about 48-72 hours after implantation. Its level increases and excess of hCG leaks into urine which is the indication of pregnancy.
This hormone like LH stimulates the corpus luteum to secrete high levels of progesterone and some estrogen to maintain pregnancy. There steroids are required to maintain the development of placenta, initiate the development of mammary glands and inhibit ovulation.
Question
Which one of the following statements about morula in humans is correct? [CBSE AIPMT 2010]
(a) It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA
(b) It has far less cytoplasm as well as less DNA than in an uncleaved zygote
(c) It has more or less equal quantity of cytoplasm and DNA
(d) It has more cytoplasm and more DNA than an uchleaved zygote
Answer/Explanation
Ans. (a)
Cleavage divisions are mitotic division, in which the single-celled zygote is converted into a multicellular morula.
But during cleavage divisions, there is no growth of resultant daughter cells /blastomeres. So, the DNA content will increase, but there is no increase or insignificant increase in amount of protoplasm.
Question
A change in the amount of yolk and its distribution in the egg will affect. [CBSE AIPMT 2009, 95, 93]
(a) formation of zygote
(b) pattern of cleavage
(c) number of blastomeres produced
(d) fertilisation
Answer/Explanation
Ans. (b)
Patterns of cleavage are based on amount of yolk and its distribution in the eggs. Any change in amount and distribution of yolk directly affects the pattern of cleavage.
As holoblastic cleavage is found in microlecithal, mesolecithal or telolecithal types of eggs. Meroblastic cleavage is found in macrolecithal and highly telolecithal eggs of reptiles, birds and monotreme mammals.
Question
Gray crescent is the area [CBSE AIPMT 2005]
(a) at the point of entry of sperm into ovum
(b) just opposite to the site of entry of sperm into ovum
(c) at the animal pole
(d) at the vegetal pole
Answer/Explanation
Ans. (b)
The gray crescent area is the area just opposite to the entry of sperm into ovum.
Question
What is true for cleavage? [CBSE AIPMT 2002]
(a) Size of embryo increases
(b) Size of cells decreases
(c) Size of cells increases
(d) Size of embryo decreases
Answer/Explanation
Ans. (b)
Cleavage is a succession of rapid cell division during which the cells undergo the $S$ phase (DNA synthesis) and M-phase(mitosis) of the cell cycle but often virtually skip the $G_1$ and $G_2$-phases. Cleavage simply divides the cytoplasm of larger cells into smaller cells, called blastomeres.
Question
Cleavage in mammalian egg is [CBSE AIPMT 2000]
(a) equal holoblastic
(b) unequal holoblastic
(c) superficial meroblastic
(d) discoidal meroblastic
Answer/Explanation
Ans. (b)
The progressive division of cells during embryonic growth is called cleavage. it is not accompanied by increase in the overall size of embryo. The first cleavage occurs in human zygote about 30 hours after fertilisation. It is holoblastic (complete) and gives rise to the blastomeres-one of which is slightly larger than the other.
Question
Blastopore is [CBSE AIPMT 2000, 1992]
(a) opening of neural tube
(b) opening of gastrocoel
(c) future anterior end of embryo
(d) found in blastula
Answer/Explanation
Ans. (b)
Blastopore is the opening of gastrocoel. Gastrulation is a process of migration and rearrangement of cells which are already present in blastula, a new cavity is formed named archenteron or gastrocoel which open outside through blastopore.
Question
What is true about cleavage in fertilised egg of human? [CBSE AIPMT 1994]
(a) Meroblastic
(b) Starts when egg reaches uterus
(c) Starts in Fallopian tube
(d) It is identical to normal mitosis
Answer/Explanation
Ans. (c)
In human, cleavage occurs in the Fallopian tube (oviduct) during the movement of zygote towards uterus.
Question
Acrosome reaction in sperm is triggered by [CBSE AIPMT 1993]
(a) capacitation
(b) release of lysin
(c) influx of $\mathrm{Na}^{+}$
(d) release of fertilisin
Answer/Explanation
Ans. (d)
Ovum secretes a chemical substance, called fertilisin which has number of spermophilic sites on its surface where the sperm of species specific type can be bound by their antifertilisin site. This fertilisin-antifertilisin reaction triggers acrosome reaction The main aim of this reaction is to thin out the number of sperms to reduce the chances of polyspermy.
Question
Extrusion of second polar body from egg nucleus occurs [CBSE AIPMT 1993]
(a) after entry of sperm but before completion of fertilisation
(b) after completion of fertilisation
(c) before entry of sperm
(d) without any relation of sperm entry
Answer/Explanation
Ans. (a)
The sperm entry stimulates the secondary oocyte to undergo Meiotic II division, which produces the ovum and second polar body.
Question
Termination of gastrulation is indicated by [CBSE AIPMT 1993]
(a) obliteration of blastocoel
(b) obliteration of archenteron
(c) closure of blastopore
(d) closure of neural tube
Answer/Explanation
Ans. (a)
Termination of gastrulation is indicated by obliteration of blastocoel.
Question
Meroblastic cleavage is a type of division [CBSE AIPMT 1992]
(a) horizontal
(b) partial/parietal
(c) total
(d) spiral
Answer/Explanation
Ans. (b)
In meroblastic cleavage zygote divides partially. This type of cleavage is found in mesolecithal and centrolecithal eggs like eggs of reptiles, birds, insects and egg-laying mammals.
Question
During cleavage, what is true about cells? [CBSE AIPMT 1991]
(a) Nucleocytoplasmic ratio remains unchanged
(b) Size does not increase
(c) There is less consumption of oxygen
(d) The division is like meiosis
Answer/Explanation
Ans. (b)
Cleavage is the rapid mitotic cell division of the zygote upto the completion of blastula stage. Cleavage differs from the ordinary mitosis in following respects:
(a) Interphase are short and do not involve growth.
(b) Divisions are very rapid, nuclear cytoplasmic ratio increases with each division.
(c) There is a decrease in the size of blastomeres (cells resulting from cleavage), but size and shape of the embryo do not change.
Question
How many sperms are formed from a secondary spermatocyte? [CBSE AIPMT 1990]
(a) 4
(b) 8
(c) 2
(d) 1
Answer/Explanation
Ans. (c)
As it is clear from the figure that each secondary spermatocyte, after second meiosis give rise to two spermatids, each of which develops into sperm.
