Metabolism is a network of coupled reactions. This HL lesson covers C1.1 Enzymes & metabolism, C1.2 Cell respiration and C1.3 Photosynthesis in full.
You will study enzyme kinetics, glycolysis to oxidative phosphorylation, and the light-dependent and Calvin reactions, with RQ, ATP and Calvin calculations.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
C1.1 Enzymes
Enzyme kinetics (HL)
Enzymes lower activation energy by induced fit of the active site. Kinetics can be described by:
Vmax: maximum rate when the enzyme is saturated.
Km: substrate concentration giving half Vmax — a low Km means high affinity.
Competitive inhibitors raise apparent Km (same Vmax); non-competitive lower Vmax.
End-product (feedback) inhibition: the product binds an allosteric site on an early enzyme.
C1.2 Cell respiration
Aerobic respiration in stages (HL)
Aerobic respiration proceeds in stages:
Glycolysis (cytoplasm): glucose → 2 pyruvate; net gain 2 ATP and 2 reduced NAD.
Link reaction and Krebs cycle (matrix): CO2 released; NAD and FAD reduced.
Oxidative phosphorylation (inner membrane): electrons pass down the chain, pumping protons; ATP synthase makes most of the ATP by chemiosmosis, with oxygen as the final electron acceptor.
RQ = CO2 produced ÷ O2 consumed
Calculate
Your turn — calculate
1In an experiment a respiring organism released 1.6 units of CO2 and consumed 2.0 units of O2. Calculate its respiratory quotient (RQ).
RQ
Hint: RQ = CO2 ÷ O2 = 1.6 ÷ 2.0.
Calculate
Your turn — calculate
2Glycolysis produces 4 ATP but uses 2 ATP per glucose. Calculate the net ATP yield of glycolysis.
ATP
Hint: net = produced − used = 4 − 2.
C1.3 Photosynthesis
Light-dependent reactions and the Calvin cycle (HL)
Light-dependent reactions (thylakoid membranes): photosystems absorb light, photolysis of water releases O2, electrons flow to make ATP and NADPH.
Calvin cycle (stroma): rubisco fixes CO2 onto RuBP to form GP, which is reduced to triose phosphate (TP) using the ATP and NADPH. Each turn fixes one CO2; six turns build one 6-carbon sugar.
Calculate
Your turn — calculate
3The Calvin cycle fixes one CO2 per turn. Calculate how many turns are needed to build one molecule of glucose (a 6-carbon sugar).
turns
Hint: glucose has 6 carbons and each turn fixes 1 CO2.
Sort it
Sort each item into its group
Sort each statement into the correct metabolic stage.
Glycolysis
Krebs cycle
Light-dependent reactions
Quick check
Question
?In aerobic respiration, most ATP is produced during...
Quick check
Question
?The products of the light-dependent reactions that are used in the Calvin cycle are...
Quick check
Question
?A low Km value for an enzyme indicates that it has...
Match it
Match each item to its partner
Match each metabolic component to its role.
Item
Partner
Quick check
Question
?End-product (feedback) inhibition typically works by the product binding to...
Recap
The big ideas to take away
C1.1 (HL): Vmax and Km; competitive vs non-competitive inhibition; allosteric feedback