A student uses a light microscope to view a sample of plant cells. Explain why the student needs to use a stain before viewing the cells, and describe how increasing the magnification of the microscope would affect what the student can see.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student prepares a slide of onion cells to observe under a light microscope. The cells appear almost transparent at first, so the student adds a stain before placing the coverslip.
Model answer (4 marks)
Stains are used because plant cells and their organelles are almost transparent and colourless, so they are difficult to see without a contrasting colour.
The stain is absorbed by particular cell structures, such as the cell wall or nucleus, giving them a coloured appearance that contrasts with the background.
Increasing the magnification makes the image of the cell appear larger, so the cell looks bigger.
However, higher magnification reduces the field of view, so fewer cells fit into the view at one time.
The stain is absorbed by particular cell structures, such as the cell wall or nucleus, giving them a coloured appearance that contrasts with the background.
Increasing the magnification makes the image of the cell appear larger, so the cell looks bigger.
However, higher magnification reduces the field of view, so fewer cells fit into the view at one time.
Examiner tips
- Use the word ‘stain’ and explain it makes cells visible by colour contrast.
- Mention that the stain is absorbed by specific structures.
- State that higher magnification enlarges the image but reduces the field of view.
- Keep each point brief and to the point.
Common mistakes
- Saying the stain is ‘necessary’ without explaining the contrast mechanism.
- Forgetting that higher magnification reduces the field of view.
- Using vague terms like ‘makes it clearer’ instead of ‘makes it visible by colour’.
Mark scheme (4 marks)
- Stains are used because cells/cell components are (almost) transparent / colourless / difficult to see without a stain
- The stain is absorbed by (certain) cell structures / organelles, making them show up in contrasting colour / making them easier to distinguish
- Increasing magnification makes the image of the cell appear larger / the cell looks bigger
- Increasing magnification means fewer cells fit into the field of view / the field of view becomes smaller
Key terms in this question
stain · magnification · light microscope
Related
- All Edexcel GCSE Biology (1BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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