4.2.3: Metabolism
Not started yet — this one needs some love.
Metabolism is the sum of all the reactions in a cell or the body.
Energy transferred by respiration is used for enzyme-controlled processes of metabolism that synthesise new molecules.
Glucose can be converted to starch, glycogen and cellulose.
Lipids are formed from one molecule of glycerol and three molecules of fatty acids.
Glucose and nitrate ions are used to form amino acids, which are used to synthesise proteins.
Respiration is part of metabolism.
Excess proteins are broken down to form urea for excretion.
Common exam mistakes
Do not reduce metabolism to respiration only; it is the sum of all reactions in a cell or the body.
Do not say lipids are made from amino acids; they are formed from glycerol and fatty acids.
Do not miss nitrate ions when linking glucose to amino acids and protein synthesis.
Do not say excess carbohydrates or fats are broken down to form urea; this point specifies excess proteins.
Do not confuse urea formation with excretion; urea is formed from excess proteins and then excreted.