The graph shows the percentage of the cell that mitochondria fill by volume. the greater the percentage, the more mitochondria. what is the function of mitochondria? why do heart cells have a higher percentage of mitochondria than liver and pituitary gland cells?

The correct answer is -

Mitochondria produce energy from food, while chloroplasts produce food from the Sun’s energy.

Mitochondria is a specialised membrane bound organelle that is present in the eukaryotes (such as plant and animals) and it is considered as the power house of the cells. It helps in the generation of large amount of energy in the form of ATP (adenosine triphosphate) through cellular respiration (that depicts complete oxidation of food, such as glucose).

Chloroplast is a membrane bound organelle, which is present in the photosynthetic organsisms such as green plants and algae. It is the site for photosynthesis, which is a process of formation of food using sunlight in the presence of carbon dioxide and water.

Thus, second option is the right answer.