Question

How do protozoans expel excretory substances?

• A. By absorption
• B. By expulsion
• C. By osmosis
• D. By diffusion

Hint:

Small unicellular organisms rely on diffusion for respiration and excretion as they lack specialized organs.

Answer 1

The Correct Option is D

Step 1: Protozoans and Excretion:
Protozoans like Amoeba are unicellular organisms without specialized excretory organs. Step 2: Mechanism:
Nitrogenous wastes like ammonia are soluble in water.
They are removed from the body by simple diffusion across the cell membrane.
Sometimes contractile vacuoles also help in regulating excess water and excretion.
Step 3: Why Not Other Options?
Absorption → Brings substances in, not excretion.
Expulsion → Active removal, not suitable for unicellular organisms.
Osmosis → Refers to water movement, not excretion of wastes.
Diffusion → Correct, since waste moves from high to low concentration.
Step 4: Final Answer:
Protozoans expel excretory substances by diffusion.