Human nutrition:The cells of all organisms require nutrients to grow and function, heterotrophic organisms, like humans cannot produce their own nutrients so they obtain it from food. Multicellular organisms have many organs.These organs are grouped together and they form systems like digestive and respiratory systems.

Digestive process:As with all animals, human beings obtain proteins, fats and sugars from food. This is done by the digestive system. There are three phases in food processing: digestion, absorption and the expulsion of waste.The movement of food through the digestive tract is done thanks to what are known as peristaltic movements. These consist of the narrowing of the tube through the contraction of the muscles of the walls.Respiratory movements:There are two stages of respiration:

inspiration and expiration.Inspiration (inhalation): The air enters the lungs and these swell (expand). The muscles related with respiration broaden the thoracic cage. The diaphragm contracts and descends and the ribs lift.Expiration (exhalation): The air leaves the lungs. These relax and the thoracic cage contracts. The diaphragm relaxes, curves and moves up and the ribs move down and inRespiratory rhythm: is the number of inhalations per minute. Normally, we make 12 inhalations per minute. After heavy exercise, this number may increase to 40inhalations per minute. In normal conditions, around 8 litres of air are moved per minute, but this can increase to 100 litres during forced breathing.