(a)[1]
State the type of nuclear division taking place at X and at Y.
(b)[2]
State what is meant by the term reduction division and explain why this division is needed in a life cycle such as the one shown in Fig. 5.1.
(c)[3]
The amoeboid cells of D. discoideum feed on protein-rich material and break it down to produce ammonium ions ($\text{NH}_4^+$). The cell membranes of D. discoideum contain transporter proteins that carry out the excretion of ammonium ions. Describe what happens to the ammonium ions excreted by D. discoideum into the soil.
(d)[2]
Suggest why a transporter protein is needed for the removal of ammonium ions from D. discoideum.