The internal environment of multicellular organisms is called tissue fluid.Cells exchange substances with tissue fluid.
Molecules needed are obtained from the surrounding tissue fluid and waste products are released into tissue fluid to be taken away and excreted.Most cells are far away from the exchange surfaces. Materials diffuse across the exchange surfaces into the tissue fluid and are carried by a mass transport system to all cells where they diffuse into the cells. Waste products are returned to the exchange surfaces and removed by diffusion.The rate and amount of substances that need to be exchanged will depend on the size and metabolic rate of the organism.Substances exchanged with the environment include oxygen, glucose, carbon dioxide, fatty acids, amino acids, minerals and vitamins.
Molecules needed are obtained from the surrounding tissue fluid and waste products are released into tissue fluid to be taken away and excreted.Most cells are far away from the exchange surfaces. Materials diffuse across the exchange surfaces into the tissue fluid and are carried by a mass transport system to all cells where they diffuse into the cells. Waste products are returned to the exchange surfaces and removed by diffusion.The rate and amount of substances that need to be exchanged will depend on the size and metabolic rate of the organism.Substances exchanged with the environment include oxygen, glucose, carbon dioxide, fatty acids, amino acids, minerals and vitamins.