12.1 Respiration
- Syllabus
- 0610–2026–2027
- Topic
- 12.1
- Level
- —
Learning objectives
12.1.1Uses of energy in living organisms• State the uses of energy in living organisms, including: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature12.1.2Effect of temperature on respiration• Investigate and describe the effect of temperature on respiration in yeast
State how living organisms use energy
Respiration releases energy that cells transfer to processes that cannot proceed by passive movement alone.
| Required use | What the energy enables |
|---|---|
| muscle contraction | movement, posture, heartbeat and ventilation |
| protein synthesis | joining amino acids to make proteins |
| cell division | copying and separating cell contents to form new cells |
| active transport | moving substances against a concentration gradient |
| growth | making new cell material and increasing cell number or size |
| passage of nerve impulses | maintaining ion gradients and transmitting signals |
| constant body temperature | replacing heat lost to the surroundings |
Diffusion, osmosis and evaporation are passive processes; they do not directly use energy released by respiration.
Investigate temperature and respiration in yeast
Yeast respiration is enzyme-controlled, so its rate changes with temperature.
| Stage | Fair-test decision |
|---|---|
| prepare | use equal volumes and concentrations of yeast and glucose solution |
| vary temperature | place identical mixtures in water baths at a suitable range of temperatures and allow them to equilibrate |
| measure rate | collect carbon dioxide in a gas syringe, or count bubbles over the same timed interval |
| control | keep pH, yeast amount, glucose concentration, total volume and measurement time constant |
| reliability | repeat each temperature and calculate a mean rate |
| Temperature range | Expected respiration rate | Explanation |
|---|---|---|
| low to warmer | increases | particles have more kinetic energy, causing more successful enzyme–substrate collisions |
| optimum | highest | respiratory enzymes work at their fastest rate |
| above optimum | decreases | enzymes denature and active sites lose their complementary shape |
Temperature is the independent variable and carbon-dioxide production per unit time is the rate measure; comparing only final gas volume after unequal times is not a fair rate comparison.