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6.5.1. Nutrition

Nutrition function

The function of nutrition consists of the set of processes through which living beings obtain the matter and energy necessary to be able to live.

There are several processes within the nutrition function:

En la función de nutrición se realizan los procesos de alimentación, respiración, circulación y excreción


Respiration is the process carried out by living beings to obtain oxygen. Oxygen is used to combine it with nutrients and to obtain simpler substances and energy.

Breathing has two phases:

  • The incorporation of air into the body. Humans do it through pulmonary ventilation performed by the respiratory system.
  • Cellular respiration.
    • It is produced in the mitochondria of eukaryotic animal and plant cells. Oxygen is used to break down nutrients for energy. Waste is also obtained, such as CO2 that is expelled through expiration and other substances that are carried by the blood.
    • Prokaryotic cells do not have mitochondria, so they have to do their breathing in a different way. They have adaptations in their membrane that allow them to breathe.

Circulation: distribution of substances

Unicellular beings are very simple and have the facility to exchange substances (nutritive and waste) with the external environment, so they do not need anything special to do so.

Multicellular beings are much more complex and need a circulatory system that carries nutrients from the digestive system to the cells, and waste substances from the cells to the outside.

En la nutrición intervienen los aparatos digestivo, respiratorio, circulatorio y excretor


In the function of nutrition, living beings take the necessary substances so that their cells can carry out cellular metabolism,  which consists of two phases:

  • Catabolism: Complex molecules are broken down and simple molecules are obtained, releasing energy.
  • Anabolism: Complex molecules are formed from simple molecules, requiring energy to do so.

Excretion is the set of processes by which organisms eliminate waste substances resulting from cellular respiration of metabolism.

The excretory system is responsible for eliminating these toxic substances (kidney) that the blood carries, but excretion is also carried out when the respiratory system expels CO2.