It is useful for an ecologist to identify the keystone species in an ecosystem because the keystone species is important to maintaining the stability of an ecosystem, and any changes in the keystone species population shows that there is changes in ecosystem health.
The answer should be proteins. Because the protein is consists of different kinds of amino acids(usually 20 in total). And our cell can not produce essential amino acids itself.
The answers are A and D
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No because bacteria multiplies at a very fast rate. Medicine can help destroying bacteria and white blood cells commonly known in term leukocytes eat the bacteria.
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