Concept:Fertilisation in mammals involves the fusion of a sperm cell (P) with an ovum (Q) to complete the process.
Explanation:P is the sperm cell and Q is the ovum.
In P, the part labelled III is the sperm head/nucleus region.
In Q, the part labelled I is the egg plasma membrane.
During fertilisation, the sperm head/nucleus part III attaches to and fuses with the egg plasma membrane part I.
This fusion allows the sperm nucleus and its contents to enter the egg cytoplasm.
Thus, the parts of P and Q that fuse are part III of P and part I of Q.
Answer:A. III and I
