2. What structures or abilities are essential to the success of organisms who do not use photosynthesis?

Ability to perform locomotion with their legs

Explanation:

Plants and animals are two distinct species of organisms. Plants are capable of using photosynthesis to obtain their food due to the unique structures that can capture light energy in their cells (autotrophic). Animals, on the other hand, are heterotrophic i.e. cannot perform photosynthesis and therefore, rely on other organisms for food.

Since animals depends on eating other organisms to obtain food/energy, their possession of LEGS or ability to LOCOMOTE is very instrumental to their success as non-photosynthetic or heterotrophic organisms. This enables them leave one position in search for food and resources