Photosynthesis
carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. It is endothermic. Glucose is used in respiration, stored as starch, used to make cellulose, amino acids and lipids.
Limiting factors are light intensity, carbon dioxide concentration and temperature. A limiting factor is the one in shortest supply. Inverse square law: light intensity ∝ 1/distance².
Respiration
Respiration transfers energy from glucose for movement, warmth and chemical reactions. It is exothermic and happens continuously in living cells.
- Aerobic: glucose + oxygen → carbon dioxide + water. Transfers more energy.
- Anaerobic in animals: glucose → lactic acid. Oxygen debt is the extra oxygen needed afterwards to break down lactic acid.
- Anaerobic in plants/yeast: glucose → ethanol + carbon dioxide (fermentation).
Exercise increases heart rate, breathing rate and breath volume so more oxygen is delivered to muscles.
Taught with support from Joseph Danso, Science Lecturer in London. Book a session.