A deep-sea fish lives in very cold, oxygen-poor water at great depth. Explain why the fish must still carry out respiration continuously, referring to specific uses of energy in the fish's cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Deep-sea fish face extreme conditions including near-freezing temperatures, very low oxygen availability, and crushing pressures. Despite these challenges, their cells remain metabolically active.
Model answer (5 marks)
Respiration releases ATP from glucose, providing the energy required for all cellular processes.
1. Muscle contraction – ATP powers the actin–myosin cycle, enabling the fish to swim and maintain position in the water.
2. Active transport – ATP‑driven pumps (e.g. Na⁺/K⁺‑ATPase) move ions and nutrients against concentration gradients, keeping cells functional.
3. Thermoregulation – ATP is used to generate heat in mitochondria, helping the fish keep its body temperature close to the surrounding water.
4. Biosynthesis – ATP supplies the energy for peptide bond formation during protein synthesis and for building new cellular components.
5. Maintenance of cellular integrity – ATP fuels repair mechanisms and the synthesis of membrane lipids, ensuring cells remain viable in the high‑pressure, low‑oxygen environment.
1. Muscle contraction – ATP powers the actin–myosin cycle, enabling the fish to swim and maintain position in the water.
2. Active transport – ATP‑driven pumps (e.g. Na⁺/K⁺‑ATPase) move ions and nutrients against concentration gradients, keeping cells functional.
3. Thermoregulation – ATP is used to generate heat in mitochondria, helping the fish keep its body temperature close to the surrounding water.
4. Biosynthesis – ATP supplies the energy for peptide bond formation during protein synthesis and for building new cellular components.
5. Maintenance of cellular integrity – ATP fuels repair mechanisms and the synthesis of membrane lipids, ensuring cells remain viable in the high‑pressure, low‑oxygen environment.
Examiner tips
- Use the word ‘ATP’ to show the link between respiration and energy use.
- Mention at least two specific cellular functions (e.g. muscle contraction, active transport).
- Show that all functions rely on ATP produced by respiration.
- Keep each point brief but complete.
Common mistakes
- Confusing respiration with photosynthesis or omitting ATP as the energy currency.
- Listing only one cellular use of energy, e.g. only muscle movement.
- Using vague terms like ‘energy’ without specifying ATP or the process of respiration.
Mark scheme (5 marks)
- Respiration releases energy (from glucose/food) for use in the cell
- Energy is needed for movement / contraction of muscle fibres
- Energy is needed for active transport (to move substances across cell membranes / against a concentration gradient)
- Energy is needed to maintain body temperature / for warmth in the cold deep-sea environment
- Energy is needed for the synthesis of large molecules (e.g. proteins from amino acids / building new cells)
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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