Question

Which statement best characterizes the oxygen levels in the bottom layer of a water body?

1. Oxygen levels are highest due to active photosynthesis.
2. Oxygen levels are significantly reduced due to decomposition.
3. Oxygen levels are maintained by direct atmospheric diffusion.
4. Oxygen levels are comparable to the surface layer.

• A. 2 only
• B. 1, 2
• C. 1, 3
• D. 4 only

Answer 1

Answer:

A. 2 only

• The surface layer has the maximum oxygen content due to two main reasons.

• Being well lighted, maximum photosynthetic oxygen is produced here.

• Being in intimate contact with the atmosphere, it permits free diffusion of oxygen into it from the air.

• The oxygen content, beneath the surface water decreases, as both these oxygen sources disappear.

• At the bottom the oxygen content decreases further due to utilisation of oxygen by decomposers occurring here.