Question

When a fresh-water protozoan possessing a
contractile vacuole, is placed in a glass containing
marine water, the vacuole will
(a) increase in number
(b) disappear
(c) increase in size
(d) decrease in size

Answer 1

When a fresh-water protozoan possessing a contractile vacuole, is placed in a glass containing marine water, the vacuole will:

(b) disappear

• Protozoans live in a hypotonic solution.

• To regulate the excess water coming in protoplasm due to the process of endosmosis, the development of vacuoles takes place in them.

• Marine water is hypertonic in nature and therefore when the protozoans are placed in them, the vacuole disappears.

• The disappearance of vacuole occurs because endosmosis doesn't take place and hence no water comes inside the protoplasm.

Answer 2

When a fresh-water protozoan possessing a  contractile vacuole, is placed in a glass containing  marine water, the vacuole will disappear.

Option (B) is correct.

Explanation:

• Protozoans live in a hypotonic environment.
• A hypotonic solution is any solution where osmotic pressure is low.
• In protoplasm endosmosis takes place.
• In order to regulate the extra water due to the process of endosmosis, the development of vacuoles takes place in them.
• When a fresh-water protozoan possessing a  contractile vacuole, is placed in a glass containing  marine water, the vacuole will disappear.

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