Changing environments or major historical events.
B.cell
<span>thats what i wold say cause the cell is the main start of an organism</span>
This statement is true.
When a hormone binds to a hormone receptor it activates cell enzymes that start a cell cascade. This means that this enzyme makes changes in the activity other proteins or alters the expression of specific genes that change the cells activity.
I wanna add one more thing to his answer for the function of enzymes. Enzymes also help speed up chemical reactions by lowering the activation energy needed for the reaction to start.
