Which material would be best to use for heating up food

What do you mean? are there any answers or like things you have? like paper plate or microwave?

A microwave is the fastest way to heat up food. But it's not the healthiest way to eat food. It's better to heat up food in the oven. The microwave contains too much radiation. Hope this helps! =)

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.

It really doesn't matter for any of the questions that you've listed.