Excretion notes
Excretion Notes 4.2.1
(a) Define the term excretion
(b) Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body.
Definitions:
Excretion: “The removal of waste products of metabolism from the body”.
Ingestion: “The intake of substances into the stomach”.
Digestion: “The breakdown of molecules that are ingested from large molecules into small molecules”.
Absorption: “The intake of those small molecules through the plasma membrane and into the cells”.
Egestion: “The removal of waste products not used in the metabolism e.g. Cellulose & faeces”.
Metabolism: “All ongoing chemical and biological reactions in the body”.
Organs of excretion:
Skin: Salt and water in sweat
Lungs: Removal of CO2 from respiration in every body cell. (CO2 lowers blood pH and can lead to death).
Kidneys: Removal of nitrogenous waste in urine. (Too much can lead to kidney stones and bone loss.) Urea is produced from excess amino acids.
Nitrogenous Excretion:
When proteins are metabolised they produce carbon dioxide and water, but also nitrogen-containing products. To metabolise amino acids containing the nitrogen, the amino group has to be removed (deamination), to form ammonia and a keto acid. The keto acid can be used in respiration, or converted to lipids or cholesterol and stored.
Fish can directly excrete ammonia. Ammonia is highly toxic and soluble in water, it takes a lot of water to flush out ammonia, but as fish have a plentiful supply, they can simply diffuse the ammonia out through cells.
Birds convert ammonia into uric acid. They do this as they cannot carry as much water as humans or fish, so they convert it into solid uric acid mixed with a little water.
Mammals convert ammonia into urea. Urea is formed in the liver by the ornithine cycle; it's less soluble than ammonia and less toxic. This means that less water is required for excretion. Urea is soluble in blood plasma and is transported to
(a) Define the term excretion
(b) Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body.
Definitions:
Excretion: “The removal of waste products of metabolism from the body”.
Ingestion: “The intake of substances into the stomach”.
Digestion: “The breakdown of molecules that are ingested from large molecules into small molecules”.
Absorption: “The intake of those small molecules through the plasma membrane and into the cells”.
Egestion: “The removal of waste products not used in the metabolism e.g. Cellulose & faeces”.
Metabolism: “All ongoing chemical and biological reactions in the body”.
Organs of excretion:
Skin: Salt and water in sweat
Lungs: Removal of CO2 from respiration in every body cell. (CO2 lowers blood pH and can lead to death).
Kidneys: Removal of nitrogenous waste in urine. (Too much can lead to kidney stones and bone loss.) Urea is produced from excess amino acids.
Nitrogenous Excretion:
When proteins are metabolised they produce carbon dioxide and water, but also nitrogen-containing products. To metabolise amino acids containing the nitrogen, the amino group has to be removed (deamination), to form ammonia and a keto acid. The keto acid can be used in respiration, or converted to lipids or cholesterol and stored.
Fish can directly excrete ammonia. Ammonia is highly toxic and soluble in water, it takes a lot of water to flush out ammonia, but as fish have a plentiful supply, they can simply diffuse the ammonia out through cells.
Birds convert ammonia into uric acid. They do this as they cannot carry as much water as humans or fish, so they convert it into solid uric acid mixed with a little water.
Mammals convert ammonia into urea. Urea is formed in the liver by the ornithine cycle; it's less soluble than ammonia and less toxic. This means that less water is required for excretion. Urea is soluble in blood plasma and is transported to