Protozoan vacuoles — what is the principal function of the contractile vacuole?
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AMaintain osmotic balance by continuous expulsion of water
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BCreate sites of intracellular food digestion
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CContain specific enzymes for assorted metabolic functions
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DServe as the site for photosynthesis
Answer
Correct Answer: Maintain osmotic balance by continuous expulsion of water
Explanation
Introduction:Vacuoles in protozoa are specialized compartments. Contractile vacuoles are especially important for osmoregulation in freshwater habitats where water influx is constant.
Given Data / Assumptions:
- We compare roles of different vacuole types.
- Organism is a freshwater protozoan unless otherwise stated.
Concept / Approach:Due to hypotonic surroundings, water enters cells by osmosis. A contractile vacuole collects excess water and expels it rhythmically to prevent lysis, thereby maintaining internal osmotic balance.
Step-by-Step Solution:
Identify contractile vacuole function: water expulsion ✔Differentiate from food vacuoles (digestion) ✘Differentiate from lysosomes or enzyme compartments ✘Note photosynthesis requires chloroplasts not present in typical protozoa ✘Verification / Alternative check:Observation of Paramecium shows periodic contraction cycles correlated with water management.
Why Other Options Are Wrong:
- Food digestion: that is the role of food vacuoles.
- Enzyme storage: generalized for lysosome-like bodies, not contractile vacuoles.
- Photosynthesis: protozoa lack chloroplasts (except in certain endosymbiotic or mixotrophic cases).
Common Pitfalls:Assuming all vacuoles serve digestion; overlooking osmoregulation in hypotonic environments.
Final Answer:Maintain osmotic balance by continuous expulsion of water