Human Fertilisation

Sperm have special features that make them well adapted: flagella/streamline, acrosome, haploid nucleus and mitochondria for energy.
The egg is large and unable to move independently. The cytoplasm contains protein and lipid food reserves.
• Sperm reaches the ovum
• Chemicals are released from the cell surrounding the ovum, triggering the acrosome reaction
• The acrosome swells, fusing with the sperm cell surface membrane.
• Digestive enzymes in the acrosome are released The enzymes digest through the follicle cells and the zona pellucida surrounding the ovum
• The sperm fuses with the ovum membrane
• The sperm nucleus enters the ovum
• Enzymes released from lysosomes in the ovum thicken the jelly-like layer, preventing entry from other sperm. This is called the cortical reaction.
• Nuclei of the ovum and sperm fuse