Part 5: Fertilisation and Embryo Development up to Blastocyst Formation

Part 5: Fertilisation and Embryo Development up to Blastocyst Formation

Q1. Fertilisation in humans normally occurs in the:

a) Vagina
b) Uterus
c) Ampullary–isthmic junction of fallopian tube
d) Cervix

Answer: c) Ampullary–isthmic junction of fallopian tube
Explanation:

• (c) Correct. Site of fertilisation in humans.
• (a, b, d) — incorrect. Vagina = sperm deposition; uterus = implantation; cervix = sperm entry.

Q2. Capacitation of sperm occurs in:

a) Epididymis
b) Female genital tract
c) Testis
d) Prostate

Answer: b) Female genital tract
Explanation:

• (b) Correct. Capacitation = physiological changes enabling acrosome reaction; occurs in female tract.

Q3. The enzyme that helps sperm penetrate zona pellucida is:

a) Hyaluronidase
b) Acrosin
c) Lipase
d) Lysozyme

Answer: b) Acrosin
Explanation:

• (b) Correct. Acrosin digests zona pellucida (glycoprotein coat).
• Hyaluronidase → disperses cumulus cells.

Q4. Cortical reaction in oocyte prevents:

a) Polyspermy
b) Fertilisation
c) Ovulation
d) Menstruation

Answer: a) Polyspermy
Explanation:

• (a) Correct. Cortical granules modify zona pellucida → block additional sperm entry.

Q5. The sperm contributes to the zygote:

a) Mitochondria
b) Centrosome and haploid nucleus
c) Cytoplasm
d) Yolk

Answer: b) Centrosome and haploid nucleus
Explanation:

• (b) Correct. Sperm provides paternal DNA and centriole.
• Mitochondria from sperm are degraded.

Q6. The secondary oocyte completes meiosis II:

a) At ovulation
b) At fertilisation
c) At implantation
d) During menstruation

Answer: b) At fertilisation
Explanation:

• (b) Correct. Meiosis II resumes only after sperm entry.

Q7. The human zygote is:

a) Haploid
b) Diploid
c) Triploid
d) Polyploid

Answer: b) Diploid
Explanation:

• (b) Correct. Fusion of haploid gametes → diploid zygote.

Q8. First cleavage division of zygote produces:

a) Blastomeres
b) Morula
c) Blastocyst
d) Gastrula

Answer: a) Blastomeres
Explanation:

• (a) Correct. Zygote divides → 2 blastomeres → cleavage divisions.

Q9. Morula is a stage with:

a) 2 cells
b) 4 cells
c) 8–16 cells
d) Hundreds of cells

Answer: c) 8–16 cells
Explanation:

• (c) Correct. Solid ball of 8–16 cells = morula stage.

Q10. Blastocyst formation occurs:

a) In vagina
b) In fallopian tube
c) In uterus
d) In ovary

Answer: c) In uterus
Explanation:

• (c) Correct. Blastocyst formed in uterine cavity before implantation.

Q11. The outer layer of blastocyst is:

a) Inner cell mass
b) Trophoblast
c) Zona pellucida
d) Endometrium

Answer: b) Trophoblast
Explanation:

• (b) Correct. Trophoblast → placenta formation.

Q12. The inner cell mass of blastocyst forms:

a) Placenta
b) Embryo proper
c) Zona pellucida
d) Amniotic fluid

Answer: b) Embryo proper
Explanation:

• (b) Correct. Inner cell mass → embryo body.

Q13. Zona pellucida disappears at:

a) Ovulation
b) Fertilisation
c) Blastocyst implantation
d) Cleavage

Answer: c) Blastocyst implantation
Explanation:

• (c) Correct. Zona shed before implantation → “hatching.”

Q14. The first mitotic division of zygote occurs after:

a) 6 hours
b) 12 hours
c) 24 hours
d) 72 hours

Answer: c) 24 hours
Explanation:

• (c) Correct. Cleavage usually begins ~24 hours after fertilisation.

Q15. Human embryo reaches uterus after:

a) 12 hours
b) 24 hours
c) 2–4 days
d) 10 days

Answer: c) 2–4 days
Explanation:

• (c) Correct. Morula/blastocyst reaches uterus in ~3–4 days.

Q16. The process of repeated mitotic divisions of zygote is:

a) Fertilisation
b) Cleavage
c) Gastrulation
d) Ovulation

Answer: b) Cleavage
Explanation:

• (b) Correct. Cleavage produces blastomeres without growth.

Q17. Fertilisation restores:

a) Diploidy and species chromosome number
b) Haploidy
c) Polyploidy
d) Cytoplasmic inheritance

Answer: a) Diploidy and species chromosome number
Explanation:

• (a) Correct. Haploid gametes combine → diploid zygote.

Q18. The fertilisation membrane is formed by:

a) Acrosome
b) Zona reaction
c) Trophoblast
d) Polar body

Answer: b) Zona reaction
Explanation:

• (b) Correct. Zona hardens after cortical granule release → fertilisation membrane.

Q19. Which of the following is the first embryonic stage implanted in uterus?

a) Zygote
b) Morula
c) Blastocyst
d) Gastrula

Answer: c) Blastocyst
Explanation:

• (c) Correct. Blastocyst attaches to endometrium.

Q20. The cavity inside blastocyst is called:

a) Morula
b) Blastocoel
c) Archenteron
d) Amnion

Answer: b) Blastocoel
Explanation:

• (b) Correct. Blastocoel is fluid-filled cavity of blastocyst.

Q21. Which ensures monospermy in humans?

a) Acrosome reaction
b) Cortical reaction
c) Capacitation
d) Spermiation

Answer: b) Cortical reaction
Explanation:

• (b) Correct. Cortical granules alter zona pellucida → block polyspermy.

Q22. Fertilisation is essential for:

a) Restoration of diploidy
b) Activation of egg metabolism
c) Initiation of cleavage
d) All of the above

Answer: d) All of the above
Explanation:

• (d) Correct. Fertilisation triggers all these processes.

Q23. The phase between fertilisation and implantation is:

a) Gestation
b) Cleavage phase
c) Gastrulation
d) Luteal phase

Answer: b) Cleavage phase
Explanation:

• (b) Correct. Cleavage produces morula, blastocyst before implantation.

Q24. The fate of trophoblast in blastocyst is to:

a) Form embryo proper
b) Form placenta and extraembryonic tissues
c) Form yolk sac
d) Form germ layers

Answer: b) Form placenta and extraembryonic tissues
Explanation:

• (b) Correct. Trophoblast → chorion, placenta.

Q25. Assertion (A): Zona pellucida prevents implantation in fallopian tube.

Reason (R): Blastocyst must first “hatch” from zona before implantation in uterus.
a) Both A and R true; R correct explanation
b) Both A and R true; R not explanation
c) A true, R false
d) Both false

Answer: a) Both A and R true; R correct explanation

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