CAIE A Level Biology 9700 · Cell structure
A student makes a temporary preparation of onion epidermal cells for viewing with a light microscope. The eyepiece graticule has 100 divisions. The stage micrometer has 100 divisions per mm.
Describe how the student would calibrate the eyepiece graticule and use it to measure the actual length of an onion epidermal cell in micrometres. In your answer, include a definition of resolution and explain why light microscopes cannot resolve organelles such as ribosomes.
6 marks, so the mark scheme is looking for about 6 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.