Question

in the upper part of the photic zone, organisms carry out both photosynthesis and cellular respiration. deep in the aphotic zone, only cellular respiration occurs. which statement is the most likely reason photosynthesis does not occur in the deepest aphotic zone?

• not as much dissolved oxygen from the surface reaches the deepest aphotic zone.
• not enough soil is present to support plant growth in the deepest aphotic zone.
• water pressure limits the survival of animals in the deepest aphotic zone.
• sunlight for photosynthesis does not reach the deepest aphotic zone.

Explanation:

Photosynthesis requires sunlight as an energy source. The aphotic zone is defined as the part of a body of water where sunlight does not reach. So, in the deepest aphotic zone, the absence of sunlight (which is necessary for photosynthesis) is the key reason photosynthesis can't occur. The other options: dissolved oxygen relates to respiration, soil isn't a factor in aquatic aphotic zone plant growth, and water pressure affecting animals doesn't relate to photosynthesis's light requirement.

Answer:

D. Sunlight for photosynthesis does not reach the deepest aphotic zone.