2.5 g of maggots take up 0.90 cm3 of oxygen in 30 minutes. Calculate the rate of respiration per gram per hour.
- 30 minutes is 0.5 hour, so uptake per hour = 0.90 ÷ 0.5 = 1.8 cm3 h−1.
- Per gram: 1.8 ÷ 2.5 = 0.72.
Answer: 0.72 cm3 g−1 h−1.
Cell respiration
Biology · C Interaction and interdependence. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The idea
ATP (adenosine triphosphate) is the molecule that carries energy around the cell. When ATP is hydrolysed to ADP and phosphate, energy is released for cell work such as active transport, building large molecules and movement. Making ATP again from ADP and phosphate needs energy.
Cell respiration is the controlled release of energy from carbon compounds, mainly glucose and fatty acids, to make ATP. It happens in every living cell. It is not the same as gas exchange, which is the diffusion of oxygen and carbon dioxide across a surface.
With oxygen, respiration is aerobic and gives a large yield of ATP. Without oxygen, it is anaerobic and gives a small yield.
Rules to remember
- ATP is a nucleotide: adenine + ribose + three phosphate groups.
- ATP → ADP + phosphate releases energy; ADP + phosphate → ATP needs energy from respiration.
- Aerobic (humans): glucose + oxygen → carbon dioxide + water; large ATP yield; needs mitochondria; can use glucose, fatty acids and other compounds.
- Anaerobic (humans): glucose → lactate; small ATP yield; in the cytoplasm only; no carbon dioxide produced; carbohydrates only.
- Ventilation moves air, gas exchange is diffusion of gases, cell respiration makes ATP.
- rate of respiration = oxygen taken up (or carbon dioxide released) ÷ time, often also ÷ mass of the organism.
- In a respirometer an alkali absorbs carbon dioxide, so the movement of the fluid measures oxygen uptake. Temperature must be kept constant.
Common mistake
Students say anaerobic respiration in humans makes carbon dioxide or ethanol. In humans the only product is lactate. Ethanol and carbon dioxide are made by yeast.
Worked example
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