$A$ bear that eats a fish that further ate bugs that ate algae is a

Which of the following types of organisms occupies more than one trophic level in an aquatic ecosystem?

The following chart shows the phosphorus cycle in a terrestrial ecosystem. Select the correct option for the four labels $a, b, c$ and $d$ shown in the diagram.
$a$ - $b$ - $c$ - $d$

Which one of the following is not a gaseous biogeochemical cycle in ecosystem?

The 'Reed-swamp' stage refers to which of the following?

They are not included in decomposers.