What is generally true about essential elements and living organisms?
a. Although all forms of life require iron, other elements are required only by certain species
b. All organisms require 25 of the 92 naturally occuring elements to survive
c. Given their low concentration in nature, the toxicity of some elements is generally not a factor in the evolution of biological communities
d. The elements carbon, hydrogen, nitrogren and and oxygen make of 20-25% of living mass.
Answer: Although all forms of life require iron, other elements are required only by certain species
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