Test : Previous Year - 3 - Class 12 MCQ

Eggs are of 4 types regarding the amount of yolk present in them :
(i) Alecithal Egg : Almost free of yolk eg. most mammals like man.
(ii) Microlecithal Egg : Very small amount of yolk eg. Branchiostoma.
(iii) Mesolecithal Egg : Moderate amount of yolk eg. Frog’s egg
(iv) Macrolecithal Egg : Large amount of yolk eg. Reptiles, birds and egglaying mammals.

Oogonia is the immature female reproductive cell which migrates to the ovary during development of the baby mature to forms a primary oocyte. The primart oocyte arrests at prophase -1 of meiosis till the child reaches puberty. At puberty meiosis -1 end and the primary converts to secondary oocyte which is liberated from the ovary. Meiosis -2 ends when it fuses with the sperm and that’s when the egg becomes a mature ovum.

Ectoderm produces – Liver, Epidermis, glands, hair, nervous system etc.
Endoderm produces – Pancreas, lining of urinary bladder etc.
Mesoderm produces – Dermis, most muscles, Kidneys, Gonads etc.

Primary spermatocyte (46) divides through meiosis to give two secondary spermatocytes (23). Each secondary spermatocyte divides through mitosis giving rise to two spermatids (23) which on spermatogenesis mature as sperms.

A glycoprotein fertilizin (composed of monosaccharides and amino acids) is secreted by a mature egg. Penetrating sperm also has some proteinaceous substance on its surface called antifertilizin. Due to the interaction between fertilizin & antifertilizin, the sperm adheres to the egg.

Human female has X X chromosomes. When eggs formed each egg carries 22 autosomes & one X chromosome. In human male each sperm carries 22 autosomes & either X or Y-chromosomes.

Interstitial cells = Leydig’s cells are present in testes and secrete male hormone testosterone.

The Entry of sperm stimulate the secondary oocyte to resume and complete the suspended meiosis II. This produces a haploid mature ovum and a second polar body. The second polar body and sperm tail immediately degenerate.

The activated spermatozoan on reaching the egg plasma membrane, undergoes a number of changes in its acrosomal region. All these changes are collectively described under acrosome reaction. Acrosome reaction is calcium-dependent involving massive uptake of calcium with an efflux of hydrogen generating high pH and osmotic pressure, producing negative surface charge, and partial or total release of the acrosomal enzymes Calcium influx may activate phospholipase resulting in accumulation of unsaturated fatty acids and fusiogenic lysophospholipids contributing to acrosome reaction.

Four extraembryonic membranes are present in mammals which originally arise from trophoblast viz. amnion, chorion, allantois and yolk sac. The trophoblast is the outermost layer of cells in morula.

After first meiotic division primary spermatocyte (diploid) gives rise to two secondary spermatocytes (haploid).

The 28 days human ovarian cycle is called menstrual cycle. On 14th day a mature ovarian follicle leaves ovary & comes into  the fallopian tube.

Estrous cycle is the characteristic of mammalian females other than primates. It is due to estrogen hormone. Estrous is the period during which ovulation occurs and the females mate with male.

In test tube baby, fertilization of the sperm and the ova  is carried out in lab conditions (in vitro) and when the embryos have reached the 32-celled stage, it is implanted back into the uterus of the mother.

Amniocentesis is the most widely used method for prenatal detection of many genetic disorders. It is also a technique used for determining the sex of the foetus.

After  ovulation ovarian follicle, undergo several stages of degeneration the follicular cells inlarge and fill with a yellow fluid to form corpus luteum.

Luteinizing hormone causes ovulation. The remaining cells of ovarian follicle are stimulated by LH to develop corpus luteum.

Embryo growth graph is 'J' shaped.

Urethra is a tube that connects the urinary bladder to the genitals for the removal of fluids from the body. The urethra travels through the penis, and carries semen as well as urine. 

All vertebrate eggs are strongly polar structures. The two opposite poles are differentiated as animal pole and vegetal pole. The imaginary axis passing through these two poles is called polar axis or animal-vegetal axis. It is the main axis of an egg. Polarity is usually expressed as a gradient in the ratio of cytoplasm and yolk from animal to vegetal pole. Polarity is responsible for the differentiation of egg as a bipolar structure.
So, the correct answer is option B.

Since corpus luteum degenerates so progesterone also decreases rapidly (progesterone is essential for maintenance of pregnancy). Also estrogen continues to curve growth of the endometrium which ultimately becomes thick enough to break down and cause menstruation. Hence choice (c) is incorrect as estrogen secretion does not decreases further. Primary follicles start developing.

On the surface of the egg opposite to  the point of sperm entry, the peripheral area of the egg becomes lighter in colour and assumes a grey appearance. This area is crescentic in shape and is known as the grey crescent.

Progesterone hormone which is secreted by the corpus luteum in the ovaries is responsible to stop ovulation (during pregnancy) and fixes the foetus to the uterine wall, facilitates placenta formation and controls the foetus development in uterus. If this hormone is withdrawn then fixation of foetus to uterine wall will not take place, formation of placenta will also not take place, ovulation starts from the ovaries and hence in human female menstruation starts.

When the production of progesterone and estrogen hormone stops in blood this leads to shed off the lying of uterine endometrium. Therefore, by supply of estrogen and progesterone the menstruation can be deferred.