Explain why the digestive system, the respiratory system and the circulatory system must work together in order for respiration in body cells to occur.

In order for respiration to occur in cells it needs ATP/ energy that is produced from the digestive system via the breakdown of glucose. The respiratory system inhales oxygen that is needed and the circulatory system enables the transport of oxygen to the other parts of the body.

Holozoic nutrition refers to the regular animal nutrition mode whereas saprophytic nutrition refers to the nutrition mode of fungi and bacteria.