Answer: When the plant has enough water in its cells the guard cells swell up and open the stomata. When the plant isn't getting enough water the guard cells can't swell and the stomata stay closed, so the plant doen's lose water. But if the stomata are closed photosynthesis can't happen and eventually the plant might starve.
Explanation:
The answer would be the muscle fiber because it's the small part of the contracting unit.
I don't really get your question sorry :(
Answer: Thermal energy refers to the energy contained within an object that changes its temperature. Heat is the energy of thermal energy. A chemical change happens when one substance and another substance form into two or more different substances.