A scientist is investigating molecules found in cell membranes and in the adipose tissue of a deep-diving whale. Describe the structure of a lipid molecule and explain why the same type of molecule can serve two very different functions in the whale's body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Lipids are found throughout living organisms. In whales, lipids are a major component of cell membranes and are also stored in thick layers of adipose tissue beneath the skin.
Model answer (5 marks)
A lipid is a molecule composed of one glycerol backbone joined to three fatty‑acid chains.
The glycerol and fatty acids are rich in carbon, hydrogen and oxygen.
In adipose tissue the lipids are stored as triglycerides, which are hydrolysed to release energy.
The thick adipose layer also provides insulation, reducing heat loss to the cold deep‑water environment.
In cell membranes the same lipids form phospholipid bilayers, giving membranes their structure and fluidity.
The glycerol and fatty acids are rich in carbon, hydrogen and oxygen.
In adipose tissue the lipids are stored as triglycerides, which are hydrolysed to release energy.
The thick adipose layer also provides insulation, reducing heat loss to the cold deep‑water environment.
In cell membranes the same lipids form phospholipid bilayers, giving membranes their structure and fluidity.
Examiner tips
- Use the exact definition of a lipid (glycerol + three fatty acids).
- Mention the key elements (C, H, O).
- Explain energy storage and insulation for adipose tissue.
- State the phospholipid bilayer role in membranes.
Common mistakes
- Confusing triglycerides with phospholipids; not specifying the glycerol + three fatty acids.
- Omitting the insulation function of adipose tissue.
Mark scheme (5 marks)
- A lipid is made from one glycerol molecule joined to three fatty acid molecules
- Lipids contain carbon, hydrogen, and oxygen
- The adipose tissue stores lipids as an energy reserve / lipids release energy when broken down
- The layer of adipose tissue also acts as insulation, reducing heat loss to the cold water
- Lipids are a component of cell membranes / form the phospholipid bilayer of membranes
Key terms in this question
lipid · adipose tissue · cell membrane
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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