Q10. What is introduced into the female reproductive tract during artificial insemination?
[UPSC CDS — 14 February 2016]
(A) An unfertilised egg alone
(B) A fully developed fetus
(C) Semen containing sperm
(D) A blastocyst and an egg together
Answer: (C) Semen containing sperm
Explanation: Artificial insemination introduces semen containing sperm into the female reproductive tract, commonly the cervix or uterus, without normal intercourse. Fertilisation may then occur inside the oviduct. It differs from in vitro fertilisation, where gamete fusion occurs in a laboratory.
Q9. Select the correct sequence of cell types during spermatogenesis.
[RPSC Second Grade Teacher (Science) — 2015]
(A) Spermatogonia → spermatocytes → spermatids → spermatozoa
(B) Spermatogonia → spermatids → spermatocytes → spermatozoa
(C) Spermatocytes → spermatogonia → spermatids → spermatozoa
(D) Spermatids → spermatogonia → spermatocytes → spermatozoa
Answer: (A) Spermatogonia → spermatocytes → spermatids → spermatozoa
Explanation: Diploid spermatogonia give rise to primary spermatocytes, which undergo meiosis to produce haploid spermatids through a secondary spermatocyte stage. Spermiogenesis then remodels spermatids into spermatozoa. The progression represents multiplication, maturation and differentiation within seminiferous tubules.
Q8. Which region of the human oviduct lies nearest the ovary?
[AIPMT Preliminary Examination — 2010]
(A) Infundibulum
(B) Isthmus
(C) Ampulla
(D) Uterine part
Answer: (A) Infundibulum
Explanation: The infundibulum is the funnel-shaped ovarian end of the fallopian tube, bearing fingerlike fimbriae that help collect the released oocyte. The wider ampulla follows, while the narrower isthmus approaches the uterus. Fertilisation commonly occurs near their junction.
Q7. What principally initiates the fetal ejection reflex at the end of pregnancy?
[AIPMT — 2009]
(A) A sudden fall in maternal blood glucose
(B) Signals from the fully developed fetus and placenta, together with cervical stretching
(C) Increased secretion of melatonin
(D) Disappearance of all placental hormones
Answer: (B) Signals from the fully developed fetus and placenta, together with cervical stretching
Explanation: Signals associated with the mature fetus and placenta initiate mild uterine contractions and cervical stretching. Neural feedback promotes maternal oxytocin release, which intensifies contractions through a positive-feedback mechanism. This cycle facilitates expulsion of the fetus during parturition.
Q6. Which extraembryonic membrane protects the developing human embryo within an enclosing fluid?
[AIPMT — 2008]
(A) Amnion
(B) Chorion
(C) Yolk sac
(D) Allantois
Answer: (A) Amnion
Explanation: The amnion forms an enclosing sac containing amniotic fluid. This fluid cushions the developing embryo and fetus, protects against mechanical shocks and helps prevent drying. The chorion contributes to placental structures; the other membranes perform different developmental roles.
Q5. Which ovarian structure functions as an endocrine gland after ovulation?
[AIPMT — 2007]
(A) Primary follicle
(B) Corpus luteum
(C) Zona pellucida
(D) Oogonium
Answer: (B) Corpus luteum
Explanation: After ovulation, cells of the ruptured Graafian follicle reorganise into the corpus luteum. This temporary endocrine structure secretes progesterone and some oestrogen, helping maintain the endometrium. Without pregnancy, it normally regresses and hormone concentrations fall.
Q4. Which anterior pituitary hormone chiefly acts on Sertoli cells?
[AIPMT — 2006]
(A) LH
(B) TSH
(C) FSH
(D) ACTH
Answer: (C) FSH
Explanation: Follicle-stimulating hormone acts on Sertoli cells to support spermatogenesis, including production of androgen-binding protein and inhibin. Luteinising hormone acts mainly on Leydig cells, stimulating testosterone secretion. Thyroid-stimulating hormone and ACTH target different endocrine glands.
Q3. Which hormone is NOT secreted by the human placenta?
[AIPMT — 2004]
(A) Oestrogens
(B) Progesterone
(C) Prolactin
(D) Human chorionic gonadotropin
Answer: (C) Prolactin
Explanation: Human placenta releases hCG, human placental lactogen, progesterone and oestrogens during pregnancy. Prolactin, which supports milk synthesis in mammary glands, is primarily secreted by the maternal anterior pituitary. Therefore, prolactin is not regarded as a placental secretion.
Q2. The establishment of anterior–posterior and dorsal–ventral polarity in an embryo is termed what?
[AIPMT — 2003]
(A) Organizer phenomenon
(B) Pattern formation
(C) Binary fission
(D) Spermiation
Answer: (B) Pattern formation
Explanation: Pattern formation establishes spatial identities and body axes in the developing embryo, enabling cells to adopt region-specific fates. Signalling gradients and regulatory genes coordinate this organisation. It differs from cleavage, which increases cell number, and from spermiation, which releases sperm.
Q1. What happens to individual cell size during early cleavage of a mammalian zygote?
[AIPMT — 2002]
(A) The whole embryo shrinks continuously
(B) The embryo greatly increases in total size
(C) Individual blastomeres increase steadily in size
(D) Individual blastomeres become progressively smaller
Answer: (D) Individual blastomeres become progressively smaller
Explanation: Cleavage consists of rapid mitotic divisions without substantial growth between divisions. Consequently, the original zygotic cytoplasm becomes distributed among increasingly numerous, smaller blastomeres. The embryo generally remains enclosed by the zona pellucida during these initial developmental stages.
