Which of the following four statements, if any, is true regarding essential elements and living organisms?
1. the elements carbon, hydrogen, nitrogen, and oxygen make up 20-25% of living mass.
2. given their low concentrations in nature, the toxicity of some elements is generally not a factor in the evolution of biological communities.
3. although all forms of life require iron, other elements are required only by certain species.
4. all organisms require 25 of the 92 naturally occurring elements to survive.
5. all of the listed responses are correct.