instruction:
Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.
question:
Question: Most food chains and webs have a maximum of how many trophic levels? Answer: 4
answer:
A trophic level is a feeding position in a food chain or food web. Most food chains and webs have a maximum of four trophic levels. There is less energy and biomass at higher trophic levels.

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Question: What type of tissue is made up of cells that have the unique ability to contract? Answer: muscle tissue
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Muscle tissue is made up of cells that have the unique ability to contract, or become shorter. Muscles attached to bones enable the body to move.

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Question: What word describes a molecule that repels polar water? Answer: hydrophobic
answer:
The other end of each phospholipid molecule is nonpolar and has no electric charge. This end of the phospholipid molecule repels polar water and is described as hydrophobic, or "water hating. ".