A globular protein that speeds up a reaction by lowering activation energy.
Active site
Region where the substrate binds; its shape and chemistry match the substrate.
Induced fit
Substrate binding changes the active site shape slightly, stressing bonds.
Anabolism / catabolism
Building larger molecules (condensation) / breaking them down (hydrolysis).
Inhibitor (HL)
Molecule that reduces enzyme activity: competitive (active site) or non-competitive (allosteric site).
Metabolism is the complex network of enzyme-catalysed reactions in a cell.
The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.
Exam tip: When describing an enzyme graph, quote values: give the optimum, explain the rise (more kinetic energy, more collisions) and the fall (denaturation of the active site).
C1.2Cell respiration
Key terms
ATP
Adenosine triphosphate: the cell's immediate energy currency.
Aerobic respiration
Uses oxygen; produces CO₂, water and a large yield of ATP.
Anaerobic respiration
No oxygen; small ATP yield. Lactate in humans; ethanol and CO₂ in yeast.
Respirometer
Apparatus measuring oxygen uptake to estimate respiration rate.
Chemiosmosis (HL)
ATP synthesis driven by protons flowing through ATP synthase.
ATP releases energy when hydrolysed to ADP + Pi; it's used for active transport, muscle contraction, synthesis of macromolecules.
The full notes, worked example and check questions for this subtopic are in the app.
C1.3Photosynthesis
Key terms
Limiting factor
The factor in shortest supply that limits the rate.
Absorption spectrum
Wavelengths absorbed by a pigment.
Action spectrum
Rate of photosynthesis at each wavelength.
Rf value
Distance moved by pigment ÷ distance moved by solvent in chromatography.
Photolysis (HL)
Splitting of water by light energy, releasing O₂, H⁺ and electrons.
RuBisCO (HL)
Enzyme that fixes CO₂ to RuBP in the Calvin cycle.
Photosynthesis converts light energy into chemical energy in carbon compounds; O₂ is a by-product from splitting water.
The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.
C2.1Chemical signalling HL
Key terms
Ligand
Signalling molecule that binds a receptor.
Quorum sensing
Bacteria detect population density by signal concentration, e.g. bioluminescence in <i>Vibrio fischeri</i>.
Second messenger
Molecule inside the cell that relays a signal, e.g. cAMP.
Intracellular receptor
Receptor inside the cell, used by steroid hormones.
Signal types: hormones, neurotransmitters, cytokines, calcium ions.
The full notes, worked example and check questions for this subtopic are in the app.
C2.2Neural signalling
Key terms
Resting potential
About −70 mV inside the axon, maintained by Na⁺/K⁺ pumps and K⁺ leak.
Action potential
Rapid depolarisation (Na⁺ in) then repolarisation (K⁺ out).
Myelin sheath
Insulating layer allowing saltatory conduction between nodes of Ranvier.
Synapse
Junction between neurons where neurotransmitter carries the signal.
Threshold potential (HL)
About −55 mV; depolarisation beyond this triggers an action potential.
Neurons carry electrical impulses; myelination speeds conduction by making impulses jump between nodes.
The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.
C3.1Integration of body systems
Key terms
Emergent property
A property of a system that its parts alone don't have.