When living cells break down food molecules, energy is

A)stored as a phosphate group added to ADP.
B)stored as ATP.
C)released as heat.
D)all of the above

To answer this question, we need to have a basic understanding of cellular respiration, the process by which cells break down food molecules to obtain energy.

During cellular respiration, the food molecules (such as glucose) go through a series of chemical reactions. These reactions release energy in the form of ATP (adenosine triphosphate). ATP is a molecule that carries chemical energy within cells and is commonly referred to as the "energy currency" of cells.

So, the correct answer to the question is B) stored as ATP. When living cells break down food molecules, the released energy is converted and stored in ATP molecules for later use.

Option A states that energy is stored as a phosphate group added to ADP (adenosine diphosphate). This is an incorrect statement because ADP is actually converted to ATP by attaching a phosphate group, not the other way around. ATP is the fully charged molecule that stores energy, whereas ADP is the partially discharged form of ATP.

Option C states that energy is released as heat, which is partially correct. However, while the breakdown of food molecules does release some heat, the majority of the energy is captured in the form of ATP for the cell's immediate use. Heat is considered a waste product.

Therefore, the most comprehensive answer is D) all of the above, as energy is stored as ATP, while some energy is released as heat during cellular respiration.