IB Diploma Biology SL · Theme C: Interaction & Interdependence — Metabolism, Respiration & Photosynthesis
Mini-Lesson
Interaction: Metabolism, Respiration & Photosynthesis
Metabolism is a web of interacting reactions. This SL lesson covers C1.1 Enzymes & metabolism, C1.2 Cell respiration and C1.3 Photosynthesis.
You will explore enzyme action, aerobic and anaerobic respiration, photosynthesis and its limiting factors, with RQ and rate 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
Enzymes and metabolism
Enzymes are biological catalysts that lower the activation energy of reactions. A substrate binds the active site (a good fit — specificity).
Activity depends on temperature, pH and substrate concentration; extreme conditions denature the enzyme.
Metabolism is all the reactions in a cell: anabolism builds up molecules; catabolism breaks them down.
Quick check
Question
?Enzymes increase the rate of reactions by...
C1.2 Cell respiration
Cell respiration
Cell respiration releases energy from glucose to make ATP.
- Aerobic (needs oxygen, in mitochondria): glucose → CO2 + water, with a large ATP yield.
- Anaerobic (no oxygen): in humans, glucose → lactate; in yeast, glucose → ethanol + CO2. Small ATP yield.
RQ = CO2 produced ÷ O2 consumedcarbohydrate ≈ 1.0, protein ≈ 0.9, lipid ≈ 0.7
Calculate
Your turn — calculate
1A germinating seed released 1.34 units of CO2 while consuming 1.96 units of O2. Calculate its respiratory quotient (RQ) to 2 decimal places.
RQ
Hint: RQ = CO2 ÷ O2 = 1.34 ÷ 1.96 (a value near 0.7 suggests lipid respiration).
C1.3 Photosynthesis
Photosynthesis
Photosynthesis converts light energy into chemical energy in glucose.
- Light-dependent reactions: light splits water (photolysis), releasing O2 and making ATP and reduced carriers.
- Light-independent (Calvin) reactions: CO2 is fixed into sugars using that ATP.
Limiting factors — light intensity, CO2 concentration and temperature — each can cap the rate.
Calculate
Your turn — calculate
2A pondweed released 24 cm³ of oxygen in 8 minutes of steady illumination. Calculate the mean rate of photosynthesis.
cm³/min
Hint: rate = volume ÷ time = 24 ÷ 8.
Sort it
Sort each item into its group
Sort each statement into the correct process.
Quick check
Question
?Anaerobic respiration in human muscle produces...
Quick check
Question
?In the light-dependent reactions, oxygen is produced by the splitting of...
Match it
Match each item to its partner
Match each enzyme concept to its correct description.
Quick check
Question
?On a warm, bright summer day, the factor most likely to limit photosynthesis in a crop is...
Recap
The big ideas to take away
C1.1: enzymes lower activation energy; affected by temperature, pH, substrate; inhibitors
C1.2: aerobic (O2, high ATP) vs anaerobic (lactate or ethanol); RQ = CO2/O2
C1.3: light-dependent (photolysis, O2) and Calvin reactions; limiting factors
Interaction: respiration and photosynthesis interlink the carbon and energy of life
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