Question

What causes the decrease in oxygen content below the surface water layer?

1. Increased photosynthetic activity at greater depths.
2. Reduced penetration of sunlight, limiting photosynthesis.
3. Enhanced diffusion of oxygen from the atmosphere.
4. Decreased utilization of oxygen by decomposers.

• A. All
• B. None of these
• C. ii only
• D. iii only

Answer 1

Answer:

C. ii 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.