A student observes two types of cells under an electron microscope: a mesophyll cell from a plant leaf and a bacterium. Explain why the bacterium would not show membrane-bound organelles when viewed at the same magnification as the mesophyll cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Mesophyll cells are found in plant leaves and are the primary site of photosynthesis. Bacteria are unicellular organisms that can be found in a wide range of environments, including soil and living tissues.
Model answer (4 marks)
Bacteria are prokaryotic organisms, so they lack a nuclear envelope and other membrane‑bound organelles.
In contrast, a mesophyll cell is eukaryotic and therefore contains a nuclear envelope and organelles such as mitochondria and chloroplasts.
Thus, when viewed at the same magnification, the bacterium will not show any membrane‑bound structures, whereas the mesophyll cell will display them.
In contrast, a mesophyll cell is eukaryotic and therefore contains a nuclear envelope and organelles such as mitochondria and chloroplasts.
Thus, when viewed at the same magnification, the bacterium will not show any membrane‑bound structures, whereas the mesophyll cell will display them.
Examiner tips
- Use the term ‘prokaryotic’ to justify the absence of organelles. Mention the nuclear envelope or a specific organelle (e.g. mitochondrion) to show contrast. Keep the answer concise – 4 marks can be earned with two short sentences.
- common_mistakes
- :
- Confusing prokaryotes with eukaryotes and claiming bacteria have organelles. Failing to mention the nuclear envelope or a specific organelle as evidence of eukaryotic structure.
Mark scheme (4 marks)
- Bacteria are prokaryotic organisms
- Prokaryotic cells lack membrane-bound organelles
- The mesophyll cell is eukaryotic and does possess membrane-bound organelles
- Correct contrast linking the presence or absence of a nuclear envelope or named membrane-bound organelle to cell type
Key terms in this question
electron microscope · membrane-bound organelles · mesophyll cell · magnification
Related
- Revision notes: Cell structure →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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