Which defines a codon? * a protein that begins transcription by breaking apart H bonds
three nucleotide bases on mRNA that specify one amino acid
O the strong bond between two complementary nitrogen bases
O a free-floating base that attaches to an open DNA strand

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

What is turgor pressure, what causes it, and what does it do for a plant?

What environmental cues and landmarks do the geese use to determine the timing and direction of their migration over the mountains? how do they find their way?