unicellular living organisms: perfomr the nutrition by exchaging substances directly with their sorrounding environment. Nutrients and oxygen enter the cell through a plasma membrane, through wich wastw is also expelled multicellular living organisms: such as human beings, most cellls don't come into contact with the outside world and cannot exchange substances with it directly.The nutrition function is performed through the join action of different systems that act as intermediaries between the outside world and cells.
the digestive system: transforme the food into simpler substances, which are abserbed into the blood stream.
the respiratory system: takes oxigen and ttransfers it to the blood. It also takes carbon dioxide from the blood and expels it out of the body.
the circulatory systen; uses tehblood to carry nutrients and oxygen to cells
the lymphatic system: works with the circulatory system to transport substances.
the excretory syten: extracts waste substances produced by celllular activity of the bloodbefore expeling them from the body.
the digestive system is a set of organs that perform the task of digestion. It transforms food into simpler substances, wich are then passed into the blood stream, meanwhile eliminating any non-digested material. digestive enzymes:are a type of proteins that accelarate the brakdown of complex food substances into their simplest components.
mouth: theeth chew and grind- mevhanicals digestive, taste buds-percive the teste, saliva-chemical digestion, tongue-push the nows in deglutition
pharynx: tube belonging both to digestive and respiratory system, epiglotis-prevents food from blocking the respiratory system, this comunicates the mouth with the oesophagus
oesophagus:conect the faringe to the stomach, the food goes cloun the oesophagus as a emet of peristatic movements
stomach:connected to the oesophagus through the cardia and to the intestine through the pilorus, gastric gland which digest food, the food mixed with juices is called the chyme, gastric juices. Vhemical, muscles of the stomavh- mechanical