Question

there are many species of jellyfish, and they inhabit all parts of the ocean. the food web below shows how jellyfish interact with other organisms
a team of scientists measures the biomass of jellyfish in a certain section of the ocean. they find that there are about 1,000 kg of jellyfish within 30 m of the surface. however, there are only about 200 kg of jellyfish between 30 m and 60 m of the surface. what best explains this difference?
a. there is more sunlight closer to the surface, so there are more photosynthetic organisms there for the jellyfish to eat.
b. the water near the surface is denser, so the water there contains more carbon dioxide for organisms to use.
c. the water near the surface is warmer, so dead organisms there decompose more quickly.
d. there is more oxygen dissolved in the water at lower depths, so jellyfish there are better able to carry out respiration.

Explanation:

To solve this, we analyze each option:

• Option A: Jellyfish eat plankton (from the food web). Photosynthetic organisms (like plankton's food source) need sunlight. Near the surface, more sunlight means more photosynthetic organisms, so more plankton, and thus more jellyfish. This makes sense.
• Option B: Surface water is less dense, and carbon dioxide is not the main factor for jellyfish biomass here. Eliminate.
• Option C: Decomposition speed of dead organisms doesn't directly explain jellyfish biomass difference. Eliminate.
• Option D: Lower depths (30 - 60m) having more oxygen would imply more jellyfish there, but the data shows less. Contradicts. Eliminate.

Answer:

A. There is more sunlight closer to the surface, so there are more photosynthetic organisms there for the jellyfish to eat.