Bioenergetics
What's covered
Key facts
Chlorophyll is the green pigment in chloroplasts that absorbs light energy for photosynthesis.
Balanced symbol equation for aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Photosynthesis takes place inside chloroplasts, organelles found in the cells of green plant tissue (mainly leaves), not in root cells.
Aerobic respiration releases more energy per glucose molecule than anaerobic respiration.
Rate increases with CO₂ concentration up to a point where another factor becomes limiting and the rate plateaus.
Aerobic respiration uses oxygen and releases much more energy per glucose molecule than anaerobic respiration.
Above approximately 40–45°C the enzymes catalysing photosynthesis begin to denature, so the rate falls sharply.
Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy released).
Light intensity falls with the square of distance from the source (inverse square law) — so doubling the distance quarters the intensity.
Anaerobic respiration releases less energy because glucose is only partially broken down without oxygen.
Sample questions
A taste of the 24 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
What is the word equation for photosynthesis?
- •Carbon dioxide + glucose → water + oxygen
- ✓Carbon dioxide + water → glucose + oxygen
- •Glucose + oxygen → carbon dioxide + water
- •Water + oxygen → glucose + carbon dioxide
What is the word equation for aerobic respiration?
- •Carbon dioxide + water → glucose + oxygen
- •Glucose → lactic acid (+ energy released)
- ✓Glucose + oxygen → carbon dioxide + water (+ energy released)
- •Glucose + water → carbon dioxide + ethanol
Which three factors can limit the rate of photosynthesis?
- ✓Light intensity, carbon dioxide concentration, and temperature
- •Light intensity, glucose concentration, and chlorophyll amount
- •Oxygen concentration, nitrogen levels, and water pH
- •Temperature, nitrogen supply, and water availability
Which balanced symbol equation correctly represents aerobic respiration?
- •6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- •C₆H₁₂O₆ + 6H₂O → 6CO₂ + 6O₂
- ✓C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
- •C₆H₁₂O₆ + O₂ → 2C₃H₆O₃
In which organelle does photosynthesis occur?
- ✓Chloroplast
- •Mitochondria
- •Nucleus
- •Vacuole
What is a key difference between aerobic and anaerobic respiration in animals?
- •Aerobic happens only in plants; anaerobic only in animals.
- ✓Aerobic uses oxygen and releases much more energy.
- •Anaerobic uses more oxygen and produces more ATP per glucose.
- •Both produce lactic acid, but aerobic also makes CO₂.
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