Question

Marine protozoans do not have contractile vacuole because

• A. their body cannot accommodate it
• B. they are hypo-osmotic to their environment
• C. they are isotonic to their environment
• D. osmoregulation is done by the cell membrane

Answer 1

The correct option is B they are hypo-osmotic to their environment

Contractile vacuole helps to remove excess water and thus performs osmoregulation. It is helpful for organisms living in hypotonic conditions such as ponds. The marine protozoans are hypoosmotic to their environment. When one solution has a lower osmotic concentration than another, it is said to be hypoosmotic. As marine protozoans live in a hypertonic environment, they lose water due to exosmosis. In order to prevent water loss and conserve water in the body, marine protozoans lack contractile vacuole.