According to the cell theory where do all new cells come from

They come from pre-existing cells that divide (either by mitosis or meiosis).

(hope this helps!)

cells can only come from other, pre-existing cells

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

i believe the answer is snake.