Fig. 1.1 is a drawing of a single onion epidermal cell, made from a stained peel viewed with a light microscope. The drawing was prepared at a magnification...
Question 1 Report
Fig. 1.1 is a drawing of a single onion epidermal cell, made from a stained peel viewed with a light microscope. The drawing was prepared at a magnification of x300.
Fig. 1.1
(a) State the function of the cell wall. [1]
(b) The drawing of the cell measured 60 mm in length. Calculate the actual length of the cell in micrometres. Show your working. [3]
(c) Convert your answer to (b) into millimetres. [1]
(d) State the unit that is most suitable for expressing the size of a single cell. [1]
Answer Details
This tests magnification calculations and cell structure. Because a drawing is larger than the real cell, magnification is greater than 1, so to find the real (actual) size you divide the drawn size by the magnification.
- (a) The cell wall supports the cell and gives it a fixed, regular shape, and stops the cell bursting when it takes in water by osmosis. It is made of cellulose and is fully permeable. [1]
- (b) Use \( \text{actual} = \dfrac{\text{image}}{\text{magnification}} \). The drawing measured 60 mm at x300, so \( \dfrac{60}{300}=0.2\ \text{mm} \) [1]. Convert mm to micrometres by multiplying by 1000: \( 0.2 \times 1000 \) [1] \( = 200\ \mu\text{m} \) [1].
- (c) Convert back to millimetres by dividing by 1000: \( \dfrac{200}{1000}=0.2\ \text{mm} \) [1] (a useful check: this equals the actual size found in (b)).
- (d) The micrometre (\( \mu\text{m} \)) is the most suitable unit for a single cell, because most cells are only a few tens of micrometres across, so millimetres would give awkward small decimals. [1]
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