A multicellular organism that can easily move around its environment. This organism must consume other organisms in order to receive energy.

If you're looking for a term, I believe the answer is heterotrophic.

Explanation:

Heterotrophs consume other organisms (be it plants or animals) to get their energy.

Autotrophs are organisms that make their own food (plants use sunlight in a process called photosynthesis to make glucose, which they use for energy).

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.