A student prepared a thin smear of human blood on a glass slide, added a stain and examined it under a light microscope. Fig. 1.1 is an accurate drawing of ...
Question 1 Report
A student prepared a thin smear of human blood on a glass slide, added a stain and examined it under a light microscope. Fig. 1.1 is an accurate drawing of one cell that the student saw when using a magnification of ×4000. A single straight measuring line, marked with a short tick at each end, has been drawn beneath the cell to show its widest part. The student was asked to work out the real size of the cell from the drawing.
(a) Measure the width of the image of the cell in Fig. 1.1, in mm. [1]
(b) Using your answer to (a) and the magnification of ×4000, calculate the real width of the cell. Give your answer in mm and then in micrometres (µm). Show your working. [2]
(c) State the function of this type of cell. [1]
(d) State one feature visible in Fig. 1.1 that shows this cell is a red blood cell. [1]
Answer Details
This question tests measuring an image, calculating real size from magnification, converting units, and identifying a red blood cell.
(a) Measure the width of the image between the tick marks with a ruler; a typical honest reading is 28 mm (accept 26 to 30 mm) [1].
(b) Real width = image width divided by magnification: \[\text{real width} = \frac{28\ \text{mm}}{4000} = 0.007\ \text{mm}\] [1]. Convert to micrometres by multiplying by 1000: \[0.007\times 1000 = 7\ \mu\text{m}\] so the cell is 0.007 mm = 7 µm wide [1]. [2]
(c) This type of cell transports / carries oxygen from the lungs to the tissues [1].
(d) Any one feature in the drawing that identifies a red blood cell: circular / disc shape; no nucleus; a paler centre (biconcave); no organelles shown [1].
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