The regulation of gas exchange by the guard cells of stomata is an example of A.
a limiting factor.
B.
a feedback mechanism.
C.
natural selection.
D.
anaerobic respiration

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

light dependent reactions:

light independent reactions:

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c. heat from the poles back down towards the equator.