AQA Biology 4.4.2.3
Metabolism
Every reaction in your body counts. Sort them into building up and breaking down, and follow excess protein out.
Triple Science · Higher tier
Start here
Half a tonne a year.
You eat about half a tonne of food every year.
If you had to guess, does your body only break that food down, or does it also build new things from it?
Building up and breaking down
Small units, big molecules.
Metabolism is the sum of all the reactions in a cell or the body. The energy transferred by respiration is used for the continual, enzyme-controlled processes of metabolism that synthesise new molecules. Pick each reaction.
Building up: glucose is converted to starch, glycogen and cellulose.
Sugars, amino acids, fatty acids and glycerol are the small units: carbohydrates, proteins and lipids are built from them and broken back down to them. Why plants store starch: in Uses of glucose.
Thyroxine
Thyroxine from the thyroid gland stimulates the basal metabolic rate.
Excess protein
Protein out, as urea.
The body can’t store excess protein. Excess proteins are broken down to form urea for excretion. Urea is carried in the blood plasma to the kidneys.
The kidneys
The kidneys filter urea out of the blood, and it leaves the body in the urine.
In the liver
Excess amino acids are deaminated in the liver to form ammonia. Ammonia is toxic, so it is immediately converted to urea for safe excretion.
Think again · what makes a lipid?
“Fat is made of glycerol and one fatty acid.”
Your call
ChooseA lipid molecule is formed from…
Sort
Building up or breaking down?
Place each reaction.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Describe
- Metabolic reactions, with their small units.
- Explain
- How respiration and building-up are linked.
- Suggest
- Why a missing substance stops a reaction.
Key fact
Metabolism is the sum of all the reactions in a cell or the body. Energy from respiration drives the reactions that build new molecules.
Key note · AQA 4.4.2.3
Metabolism
- Metabolism is the sum of all the reactions in a cell or the body.
- Energy transferred by respiration drives the continual, enzyme-controlled reactions that synthesise new molecules.
- Building up: glucose to starch, glycogen and cellulose; glycerol + three fatty acids to a lipid; glucose + nitrate ions to amino acids, then proteins.
- Breaking down: respiration; excess proteins to urea for excretion.
- Higher: thyroxine stimulates the basal metabolic rate.
- Triple: the kidneys filter urea into the urine.
- Triple Higher: excess amino acids are deaminated in the liver to ammonia, then converted to urea.
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
Connects to
Ask MrBadmus
Not sure which reactions build up?
Molecule drawings are schematic.