What occurs inside of a cell while it is performing the process of respiration? Light reactive chemicals combine carbon dioxide (CO2) and water to form glucose molecules that are stored as food. The cell membrane forms around air bubbles to create a vacuole that is used to separate the oxygen from the rest of the air. The negative charge inside of the cell is used to increase the concentration chemicals inside of the cell. Sugar is broken down to generate adenosine triphosphate (ATP) molecules that are used for energy.

All living organisms (unicellular and multicellular) need energy to carry out daily life processes. Respiration is considered to be the key process during which several reactions take place in a series and lead to the synthesis of energy rich molecules called ATP. These molecules serve as potential source of energy and are used by organism upon need.

Now, the respiration can be of two types, Aerobic or An-aerobic. They simply mean the process that take place in the presence or absence of oxygen.

Let's go though the equations of Aerobic and An-aerobic respiration.

Aerobic respiration:

Normally happens in all organisms including humans.

glucose + oxygen → carbon dioxide + water (+ ATP made)

An-aerobic respiration:

That occurs human muscle cells during stressful exorcise

glucose → lactic acid (+ ATP made)

Type of respiration in Yeast cells

glucose → ethanol + carbon dioxide (+ ATP made)

Now what is clear in all forms of respiration (no matter in humans or small organism like yeast) that sugars like glucose are broken down to generate energy rich Adenosine tri-phosphate (ATP) molecules. So option D is best option.

Hope it helps! :)