<span>A change in a organism's surroundings that causes the organism to react is called a stimulus</span>
Answer:
C. A concentration gradient must exist.
During chemical reactions, the chemical bonds between atoms are altered. ... Enzymes make chemical reactions take less time by decreasing the activation energy of the chemical reaction. The role of the enzyme-substrate complex is to provide the energy to break or form bonds in chemical bonds.
Positive feedback is when you say something positive to someone. Example if someone says what do you think about my shirt? And you reply i love it! Its positive feedback. I hope this is what you here talking about