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The deepest water of an ice-covered lake is oxygen poor because:
ADecomposition uses the oxygen up
BFish crowd into the deepest layer
COxygen freezes out of the water
DSunlight destroys dissolved oxygen
Answer & Solution
Correct answer: A. Decomposition uses the oxygen up
1. Oxygen normally enters a lake by diffusion at the surface.
2. A surface ice layer blocks that route.
3. The deepest water is oxygen poor because the decomposition of organic material at the bottom of the lake uses up available oxygen.
4. That oxygen cannot be replaced by diffusion into the water because of the surface ice layer.
_Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 35 'Ecology and the Biosphere', sections 35.1-35.5_
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