Explain how the structure of the smooth endoplasmic reticulum (sER) is related to its functions in eukaryotic cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The smooth endoplasmic reticulum (sER) is an interconnected network of membrane‑bound tubules and cisternae, giving it a large surface area for enzyme attachment and metabolic reactions.
It lacks ribosomes on its surface, which distinguishes it from the rough ER and allows it to specialise in lipid and phospholipid synthesis rather than protein production.
The sER is continuous with the nuclear envelope and the rough ER, forming a connected membrane system that permits the transport of lipids and other molecules through the cell.
In liver and muscle cells the sER contains specific transmembrane proteins such as glucose‑6‑phosphatase and calcium pumps, which enable functions like detoxification of drugs/toxins and calcium ion storage and release for muscle contraction.
It lacks ribosomes on its surface, which distinguishes it from the rough ER and allows it to specialise in lipid and phospholipid synthesis rather than protein production.
The sER is continuous with the nuclear envelope and the rough ER, forming a connected membrane system that permits the transport of lipids and other molecules through the cell.
In liver and muscle cells the sER contains specific transmembrane proteins such as glucose‑6‑phosphatase and calcium pumps, which enable functions like detoxification of drugs/toxins and calcium ion storage and release for muscle contraction.
Examiner tips
- Use the word ‘smooth’ to contrast with rER; mention ribosome absence. Include the continuous membrane system with nuclear envelope. Give a specific example of a transmembrane protein and its function. Show the link between structure (tubules, large surface area) and function (enzyme attachment).
Common mistakes
- Confusing the sER with the rough ER or omitting ribosome absence. Failing to mention the continuity with the nuclear envelope. Not giving a specific example of a transmembrane protein or its role.
Mark scheme (4 marks)
- The sER is an interconnected network of membrane-bound tubules/cisternae, providing a large surface area for enzyme attachment and metabolic reactions.
- The sER lacks ribosomes on its membrane, distinguishing it structurally from the rER and allowing it to specialise in lipid/phospholipid synthesis rather than protein production.
- The sER is continuous with the nuclear envelope and rER, forming a connected membrane system that allows transport of lipids and other molecules through the cell.
- In liver/muscle cells, the sER contains transmembrane proteins (e.g. glucose-6-phosphatase / calcium pumps) embedded in its membrane, enabling specific functions such as detoxification of drugs/toxins or calcium ion storage and release for muscle contraction.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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