AQA GCSE Metabolism (Biology)
Metabolism
Metabolism is defined as the sum of all of the chemical reactions in a cell or body of an organism.
Metabolic reactions occur all the time, they are controlled by enzymes. Metabolic reactions include both building up (synthesis/anabolism) and breaking down (breakdown/catabolism).
Source of molecules for metabolism
Organisms need a source of molecules for metabolism
Source of molecules for animals.
Animals feed on other organisms such as animals or plants. These ingested molecules are then digested into simple molecules which can be used in metabolism.
During digestion:
Starch is broken down into sugars uses carbohydrases
Proteins are broken down into amino acids uses proteases
Lipids are broken down into fatty acids and glycerol using lipases.
Each of these simple molecules are absorbed in small intestine, transported by blood to cells, where they are used to make other molecules.
Source of molecules for plants
Plants carry out photosynthesis to synthesise glucose. They absorb nitrate ions from the soil. The glucose formed during photosynthesis can be convered into other molecules.
Below is a summary of the uses of glucose in plants.
Metabolism needs energy
Respiration occurs in living cells and transfers energy.
This energy is used to
1.Build larger molecules from smaller ones
2.Maintain body processes
3.Drive enzyme controlled reactions
Importance of sugars (mostly glucose)
Glucose is an important molecule for metabolism.
There are several uses for glucose
1.Glucose is used in respiration in all living cells to release energy.
2.Glucose is converted into starch for storage in plants.
3. Glucose is converted into cellulose for plant cell walls
4. Glucose is converted into glycogen for storage in animals. Glycogen is stored in both liver and muscle cells.
Importance of amino acids
Amino acids are the building blocks of proteins.
Proteins in animals are made by joining amino acids together.
Plants use glucose and nitrate ions to make amino acids, which are then used to synthesise proteins.
Importance of Fatty acids and glycerol
Lipids (fats and oils) are made from:
1 glycerol
3 fatty acids
Lipids are used for:
Energy storage
Insulation
Protection
Breakdown of sugars (glucose)
Respiration is a metabolic reaction that releases energy from glucose
Breakdown of excess protein
Excess amino acids in the body cannot be stored. The liver will break them down to form urea. Urea is then excreted by the kidneys.
Summary for metabolic pathways in plants
Summary of metabolic reactions in animals.
Practice Questions
1.Define the term metabolism
2. Give examples of molecules that glucose can be converted into
3. Outline how plants produce proteins.
Factors affecting the rate of photosynthesis
Measuring & calculating rates of photosynthesis
Inverse square law and photosynthesis
Economics of enhancing the conditions in greenhouses
Investigating the effect of light intensity on the rate of photosynthesis