Capacitation is the final change a sperm goes through inside the female reproductive tract, which makes it able to fertilise the ovum. Block to polyspermy is the change in the zona pellucida after one sperm enters, which stops any other sperm from getting in, so only ONE sperm fertilises the egg. Memory hook: "Capacitation = sperm gets its FINAL license inside the female; Block = ONE-sperm-only door shuts after the first guest."
Capacitation makes the sperm ready in the female tract. When one sperm binds the zona pellucida and enters, the zona changes (block to polyspermy) so all other sperms are stopped.
Your doubts, answered
Where exactly does capacitation take place?
Capacitation takes place in the FEMALE reproductive tract, NOT in the male body. This is the most tested point. Sperms first mature in the epididymis, but their final functional maturation (capacitation) happens only after they enter the female tract. So the correct NEET answer is 'female reproductive tract', not rete testis, epididymis or vas deferens.
Is capacitation the same as the acrosome reaction?
No. Capacitation happens FIRST and is the final maturation of the sperm inside the female tract that makes it capable of fertilising. The acrosome reaction happens LATER, at the ovum, when acrosomal enzymes are released to help the sperm cross the coverings of the egg. Simple order: capacitation -> reach ovum -> acrosome reaction -> zona reaction (block to polyspermy).
What is block to polyspermy in simple words?
After ONE sperm touches and enters the ovum, the zona pellucida changes. This change stops all other sperms from entering. 'Poly' means many and 'spermy' means sperm, so block to polyspermy means 'blocking many sperms'. It makes sure only one sperm fuses with the ovum, keeping the correct chromosome number (diploid zygote).
Why must only one sperm enter the egg?
If two or more sperms entered, the zygote would get extra sets of chromosomes and would not be a normal diploid (2n). The block to polyspermy at the zona pellucida guarantees a single sperm nucleus fuses with the ovum nucleus, so the zygote has the right chromosome number.
Which layer of the ovum carries the sperm-binding receptors?
The ZONA PELLUCIDA carries the receptors for sperm binding. The sperm first comes in contact with the zona pellucida, binds to it, and the changes in this same layer then block polyspermy. This was directly asked in NEET 2021 (answer: zona pellucida), not corona radiata or vitelline membrane.
⚠️ The NEET trap ✗ Capacitation occurs in the epididymis (because sperms mature there). ✓ Capacitation occurs in the FEMALE reproductive tract. Epididymis gives earlier maturation and motility, but the FINAL change (capacitation) needs the female tract. 🧠 Sperm gets its final 'license to fertilise' only inside the female. NEET 2017 answer = Female Reproductive tract.
Real NEET questions
2017
Capacitation occurs in
A · Rete testis
B · Epididymis
C · Vas deferens
D · Female Reproductive tract ✓
Solution: Capacitation is the final functional maturation of sperms that happens in the female reproductive tract, enabling them to fertilise the ovum. It does not occur in the rete testis, epididymis or vas deferens. NCERT describes the motile sperms swimming through the female tract to the ampulla where fertilisation occurs.
2021
Receptors for sperm binding in mammals are present on
A · Perivitelline space
B · Zona pellucida ✓
C · Corona radiata
D · Vitelline membrane
Solution: During fertilisation the sperm first contacts the zona pellucida, which carries the sperm-binding receptors. The same zona pellucida then changes to block polyspermy so that no other sperm can enter. Hence the receptors are on the zona pellucida, not on the corona radiata, perivitelline space or vitelline (plasma) membrane.
Solved Human Reproduction NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Capacitation is the final maturation change sperms undergo in the female reproductive tract that makes them able to fertilise the ovum.
What is the block to polyspermy?
It is the change in the zona pellucida after one sperm enters the ovum, which prevents entry of any other sperm so that only one sperm fertilises the egg.
Does capacitation happen in the male or female body?
In the female body. It occurs in the female reproductive tract, which is a very common NEET question (NEET 2017).
Which egg layer blocks polyspermy?
The zona pellucida. Its change after the first sperm enters blocks all other sperms.
Why is block to polyspermy important?
It keeps the chromosome number correct. Only one sperm fuses with the ovum, so the zygote stays diploid (2n).
