Answer: This is because amoeba cannot make their own food but algae can.
Step-by-step explanation:
Endocytosis is the method by which the amoeba engulf food by their podocytes also known as pseudo feet.
Red algae is capable of performing photosynthesis. It can trap sunlight and perform and synthesize food which can be used as a source of energy.
This is the reason why amoeba use endocytosis and algae perform photosynthesis.