Q.Describe the process of fertilization in human with the help of four sequential diagrams.

Fertilisation: sperm reach and surround the oocyte → acrosome reaction digests the egg coverings → sperm-oocyte membrane fusion (blocking polyspermy via the zona reaction) → fusion of male and female pronuclei (karyog...

Fertilisation is a four-stage process — approach, acrosome reaction, membrane fusion, and nuclear fusion — that converts two haploid gametes into one diploid zygote.

Described with four sequential sketches: Diagram 1 — many sperm cells cluster around a single secondary oocyte in the ampulla of the fallopian tube, the oocyte still surrounded by its protective corona radiata (follicle cells) and the underlying zona pellucida. Diagram 2 — the acrosome reaction: the acrosomal cap of a sperm ruptures and releases hydrolytic enzymes (like hyaluronidase and acrosin) that digest a path through the corona radiata and zona pellucida, allowing one sperm to reach the oocyte's plasma membrane. Diagram 3 — plasma membrane fusion: the head of the successful sperm fuses with the oocyte's plasma membrane, and the sperm nucleus (and centriole) enters the ooplasm; this fusion also triggers the cortical reaction, releasing granules that harden the zona pellucida (the 'zona reaction'), blocking entry of any further sperm (preventing polyspermy) and completing meiosis II of the oo …