Which of the following provides chemical energy for living organisms?

• A. Heat from a heater
• B. Light
• C. Food
• D. Movement

Answer: (C)

The main idea is that living cells rely on chemical energy stored in the bonds of molecules, which is obtained by consuming food. When we digest food and then run cellular respiration, those chemical bonds release energy that the cell captures as ATP, the fuel that powers everything from building molecules to moving and maintaining order in the cell. Heat from a heater is external thermal energy and isn’t stored in a form the cells can use to do work. Light is energy in the form of radiation; some organisms can convert light into chemical energy (through photosynthesis), but for most living things the directly usable chemical energy comes from the energy already stored in food. Movement itself is the expenditure of energy, not the source supplying chemical energy.