Microscopy and magnification (RP1) – GCSE Biology exam questions with mark scheme

1Grade 4–54 marks

A student viewed a cheek cell with a light microscope and drew it. The width of the cell in the drawing is 30 mm. The real width of the cell is 60 µm.

(a) Calculate the magnification of the drawing. [2]

(b) An electron microscope was then used to look at the same type of cell. Give two advantages of using an electron microscope. [2]

(a) converts to the same units: 30 mm = 30 000 µm (or 60 µm = 0.06 mm) and uses magnification = image size ÷ real size, e.g. 30 000 ÷ 60(1)
(a) ×500 (allow 500 / 500 times; correct answer with no working scores 2 marks)(1)
(b) higher / greater magnification(1)
(b) higher resolution / resolving power; accept can see sub-cellular structures in more detail / can see smaller structures such as ribosomes; ignore 'clearer' alone(1)
Answer: (a) ×500 (b) higher magnification; higher resolution
Examiner tip: Convert both sizes to the same unit before dividing — 30 ÷ 60 = 0.5 is the most common wrong answer.

2Grade 6–73 marks

An electron micrograph shows a mitochondrion. The length of the mitochondrion in the micrograph is 24 mm. The magnification is ×12 000.

Calculate the real length of the mitochondrion in metres.

Give your answer in standard form. [3]

real size = image size ÷ magnification: 24 ÷ 12 000 (= 0.002 mm)(1)
converts correctly to metres: 0.002 mm = 0.000 002 m (allow 2 µm seen)(1)
$2 \times 10^{-6}$ m(1)
Answer: $2 \times 10^{-6}$ m
Examiner tip: Write the unit at every step — 1 mm = 10⁻³ m and 1 µm = 10⁻⁶ m; students often stop at 0.002 and forget the unit conversion.

3Grade 1–3Foundation4 marks

A student uses a light microscope to look at some cells. The microscope has a ×10 eyepiece lens and three objective lenses: ×4, ×10 and ×40.

(a) Which objective lens should the student use first?

Give one reason for your answer. [2]

(b) Calculate the total magnification when the student uses the ×40 objective lens. [1]

What is 1 µm in millimetres? Tick (✓) one box.

0.1 mm	☐
0.01 mm	☐
0.001 mm	☐
1000 mm	☐

[1]

(a) ×4 (allow the lowest power objective lens)(1)
(a) reason: largest field of view so the cells are easier to find (allow easier to focus / less chance of the lens hitting or breaking the slide); reason only creditable if ×4 chosen(1)
(b) ×400 (allow 400; total magnification = eyepiece × objective = 10 × 40)(1)
(c) 0.001 mm only; more than one box ticked = 0(1)
Answer: (a) ×4 – largest field of view / easiest to find cells (b) ×400 (c) 0.001 mm
Examiner tip: Total magnification is eyepiece × objective (10 × 40), not eyepiece + objective — 50 scores zero.

4Grade 4–55 marks

Human red blood cells have a real diameter of 7.5 µm.

A student looks at a blood smear using a light microscope at a magnification of ×400.

(a) Calculate the diameter of the image of one red blood cell.

Use the equation:

$$\text{magnification} = \frac{\text{size of image}}{\text{size of real object}}$$

Give your answer in millimetres (mm). [3]

(b) The diameter of the field of view at this magnification is 0.45 mm.

Calculate how many red blood cells would fit side by side across the diameter of the field of view. [2]

(a) size of image = magnification × size of real object or 400 × 7.5(1)
(a) 3000 (µm)(1)
(a) 3 (mm) (allow 3.0 mm); correct answer with no working scores 3 marks; 3000 with unit mm = 2 marks(1)
(b) 0.45 mm = 450 µm or 7.5 µm = 0.0075 mm(1)
(b) 60 (cells) (correct answer with no working scores 2 marks; 0.06 scores 0)(1)
Answer: (a) 3 mm (b) 60
Examiner tip: Rearrange first (image = magnification × real), then convert µm to mm by dividing by 1000 — many leave the answer as 3000 with the wrong unit.

5Grade 4–54 marks

The diagram shows a drawing of a single-celled organism seen with a light microscope. The drawing includes a scale bar.

When the diagram is printed, the scale bar is 20 mm long and the length of the organism from X to Y is 80 mm.

(a) The scale bar represents a real length of 50 µm.

Calculate the magnification of the drawing. [2]

(b) Calculate the real length of the organism from X to Y.

Give your answer in micrometres (µm). [2]

(a) 20 mm = 20 000 µm or 20 000 ÷ 50 (allow 20 ÷ 0.05)(1)
(a) ×400 (allow 400; correct answer with no working scores 2 marks)(1)
(b) 80 ÷ 400 = 0.2 (mm) or 80 000 ÷ 400 (allow ecf from (a))(1)
(b) 200 (µm) (correct answer with no working scores 2 marks); alternative method: X–Y is 4 times the scale bar so 4 × 50 = 200 µm scores 2 marks(1)
Answer: (a) ×400 (b) 200 µm
Examiner tip: Convert the scale bar length into the same unit as the real length (20 mm = 20 000 µm) before dividing.

6Grade 8–9Higher5 marks

The table shows the approximate sizes of some structures in a plant leaf cell.

Structure	Approximate size
Palisade cell	0.1 mm long
Chloroplast	5 µm long
Ribosome	25 nm in diameter

(a) Give the length of a chloroplast in metres.

Give your answer in standard form. [1]

(b) Calculate how many times longer a chloroplast is than the diameter of a ribosome. [2]

Calculate the magnification needed.

Give your answer in standard form. [2]

(a) 5 × 10⁻⁶ (m); allow 5.0 × 10⁻⁶; do not accept 0.000005 (not standard form)(1)
(b) converting to the same unit: 5 µm = 5000 nm or 25 nm = 0.025 µm (allow both in m: 5 × 10⁻⁶ ÷ 2.5 × 10⁻⁸)(1)
(b) 200 (correct answer with no working scores 2 marks)(1)
(c) 200 000 or 5 × 10⁻³ ÷ 2.5 × 10⁻⁸ (allow 5 000 000 nm ÷ 25)(1)
(c) 2 × 10⁵ (allow ×2 × 10⁵; correct answer in standard form with no working scores 2 marks; 200 000 not in standard form scores 1 mark)(1)
Answer: (a) $5 \times 10^{-6}$ m (b) 200 (c) $2 \times 10^{5}$
Examiner tip: 1 nm = 10⁻⁹ m and 1 µm = 10⁻⁶ m — put both sizes in the same unit before dividing, then write the final answer in standard form for the last mark.

7Grade 4–55 marks

Microscopes have developed over time. The table gives approximate data for three types of microscope.

Microscope	First used	Maximum magnification	Resolution in µm
Single-lens light microscope	1670s	×270	1
Modern light microscope	1900s	×2000	0.2
Transmission electron microscope	1930s	×2 000 000	0.0002

(a) How many times greater is the maximum magnification of the transmission electron microscope than the modern light microscope? [1]

(b) What is meant by the resolution of a microscope? [1]

Use the table to explain which type of microscope could be used to see individual ribosomes. [2]

(d) Suggest how the development of the electron microscope has increased scientists’ understanding of cells. [1]

(a) 1000 (times) (allow 10³)(1)
(b) the smallest distance between two points that can still be seen as separate (allow the ability to distinguish between two points that are close together); ignore ‘how clear the image is’ / ‘amount of detail’ alone(1)
(c) transmission electron microscope; allow electron microscope(1)
(c) because its resolution (0.0002 µm) is smaller than the ribosome (0.025 µm) or the light microscopes’ resolution (0.2 µm / 1 µm) is larger than the ribosome so they cannot distinguish / show it; ignore ‘higher magnification’ alone(1)
(d) sub-cellular structures can be seen in much more detail / smaller structures could be seen for the first time, e.g. ribosomes or the internal membranes of mitochondria / chloroplasts (allow so the functions of sub-cellular structures could be worked out)(1)
Answer: (a) 1000 (b) smallest distance between two points that can be seen as separate (c) TEM – its resolution (0.0002 µm) is smaller than the ribosome; light microscopes cannot resolve 0.025 µm (d) sub-cellular structures seen in more detail / new structures discovered
Examiner tip: Magnification alone does not let you see a ribosome — the mark goes for comparing the ribosome size with the resolution figures in the table.

8Grade 6–74 marks

A student looked at onion epidermis cells with a light microscope at a total magnification of ×100.

The diagram shows what the student saw. The diameter of the field of view is 1.6 mm.

There are 8 cells end to end along the dashed line across the diameter of the field of view.

(a) Estimate the mean length of one onion cell.

Give your answer in micrometres (µm). [2]

(b) The student changed the magnification to ×400. This made the diameter of the field of view 4 times smaller.

Calculate the new diameter of the field of view in mm. [1]

(a) 1.6 mm = 1600 µm or 1.6 ÷ 8 = 0.2 (mm)(1)
(a) 200 (µm) (correct answer with no working scores 2 marks; 0.2 µm scores 1 mark)(1)
(b) 0.4 (mm); allow 400 µm(1)
(c) any one from: cells are not all the same length; the cells may not lie exactly along the diameter / are not perfectly lined up; the cells at the edges may be partly outside the field of view / hard to count; only one row of cells was used; ignore ‘human error’ alone(1)
Answer: (a) 200 µm (b) 0.4 mm (c) e.g. cells are not all the same length
Examiner tip: Convert 1.6 mm to 1600 µm before dividing by 8 — leaving the answer as 0.2 with the unit µm loses a mark.

9Grade 6–76 marks

A student wants to observe onion epidermis cells with a light microscope and produce a labelled scientific drawing of the cells.

Describe how the student should:

prepare a slide of the onion cells
use the light microscope to view the cells
make a labelled drawing that includes the magnification.

[6]

peel a thin layer of epidermis from the inside of an onion scale leaf using forceps (one layer of cells so light can pass through)(1)
place the epidermis flat on a drop of water on a clean microscope slide, avoiding folds(1)
add a drop of iodine solution to stain the cells so the nucleus / cell wall can be seen(1)
lower a coverslip at an angle with a mounted needle to avoid trapping air bubbles(1)
place the slide on the stage and secure with the clips; switch on the lamp(1)
start with the lowest-power (×4) objective lens; use the coarse focusing knob to move the lens close to the slide while looking from the side(1)
look through the eyepiece and focus by moving the lens away from the slide, then use the fine focusing knob for a sharp image(1)
change to a higher-power objective lens and refocus using the fine focusing knob only(1)
draw with a sharp pencil using clear, continuous lines and no shading; draw cells in correct proportion(1)
label sub-cellular structures (e.g. cell wall, nucleus, cytoplasm) with ruled label lines that do not cross(1)
write the magnification: total magnification = eyepiece lens × objective lens (e.g. ×10 × ×40 = ×400) or add a scale bar(1)
safety: iodine is an irritant, so wear eye protection / avoid skin contact(1)

Level	Marks	What it looks like
Level 3	5–6	A clear, logically ordered description covering all three parts: slide prepared with a thin stained layer and a coverslip, the microscope used correctly from low to high power with coarse then fine focus, and a drawing that follows the conventions and states how the magnification is found. Someone else could follow it.
Level 2	3–4	A description covering at least two of the three parts with some correct detail, but steps may be out of order or key details (e.g. stain, starting lens, how magnification is worked out) are missing.
Level 1	1–2	Some relevant, isolated steps (e.g. put onion on a slide, look through the microscope, draw the cells) with little detail or logical order.
No relevant content	0	Nothing worthy of credit.

Answer: Thin epidermis on water on slide; iodine stain; coverslip lowered at an angle; lowest-power objective first, coarse then fine focus; higher power refocused with fine focus; pencil drawing, no shading, ruled labels; magnification = eyepiece × objective or a scale bar.
Examiner tip: Vague steps such as ‘focus the microscope’ stay in Level 1–2 — say which objective lens you start with and when you use the coarse and fine focusing knobs.

10Grade 6–7Higher6 marks

A student looked at a palisade cell from a leaf with a light microscope at a magnification of ×800.

In the student’s image, one chloroplast is 4.0 mm long.

(a) Calculate the real length of the chloroplast in micrometres (µm). [2]

(b) A scientist took an electron micrograph of a chloroplast of the same real length. In the electron micrograph the chloroplast is 75 mm long.

Calculate the magnification of the electron micrograph.

Give your answer in standard form. [2]

Give two disadvantages of electron microscopes compared with light microscopes. [2]

(a) 4.0 ÷ 800 = 0.005 (mm) or 4000 ÷ 800(1)
(a) 5 (µm) (correct answer with no working scores 2 marks)(1)
(b) 75 mm = 75 000 µm and 75 000 ÷ 5 or 15 000 (allow ecf from (a))(1)
(b) 1.5 × 10⁴ (allow ×1.5 × 10⁴; 15 000 not in standard form scores 1 mark)(1)
(c) any two from: cannot be used to view living cells / specimens must be dead (because they are viewed in a vacuum); very expensive (to buy / run); large so not portable / need a special room; preparation of specimens is complex / needs trained staff; images are black and white (allow colour has to be added artificially); preparation may damage the specimen / produce artefacts(1)
(c) second disadvantage from the list above; ignore ‘lower magnification / resolution’ (these are advantages of electron microscopes); ignore ‘harder to use’ alone(1)
Answer: (a) 5 µm (b) $1.5 \times 10^{4}$ (c) e.g. cannot view living cells; very expensive
Examiner tip: Electron microscopes have higher magnification and resolution — giving either as a disadvantage scores zero; think about cost, size and living specimens instead.

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