An investigator prepared a transverse section of a Camellia leaf to observe palisade mesophyll cells under an optical microscope.
Explain why preparing a specimen that is extremely thin (one or two cell layers thick) is essential for viewing under an optical microscope.
The investigator used an optical microscope with a magnification of ×400 \times 400\,×400 to view the leaf section. Using a metric ruler, they measured the height of five different palisade cells on a printed micrograph. The measured heights were: 18 mm, 16 mm, 21 mm, 17 mm, and 18 mm.
Calculate the mean actual height, in μm\mu\text{m}μm, of these palisade cells. Show your working.
State the absolute uncertainty associated with taking a measurement using a ruler with 1 mm graduations, assuming the uncertainty is equal to the resolution of 1 mm (due to two readings being taken).
Calculate the percentage error for a measurement of 18 mm using this ruler. Give your answer to three significant figures.
