MicroscopyEdexcel International A Level Biology: Mind map

Exam questions on Microscopy

1. A scientist photographs a human liver cell using a transmission electron microscope (TEM). The micrograph is printed at a magnification of ×15 000. On the micrograph the diameter of the cell measures 300 mm and the length of one mitochondrion measures 45 mm.
   Calculate the actual length of the mitochondrion. Give your answer in micrometres (µm).2 marks
2. A student prepares temporary mounts of onion epidermis and of potato tissue to view with a light microscope. In an unstained mount the cells are almost transparent and few structures can be seen.
   Explain why a stain is added to the onion epidermis before it is viewed.2 marks
3. A student calibrates an eyepiece graticule using a stage micrometer, which is a slide marked in divisions of 10 µm. With the ×40 objective lens, 80 divisions on the eyepiece graticule line up exactly with 40 divisions on the stage micrometer. The student then measures the length of a stained onion epidermis cell as 14 graticule divisions.
   Calculate the actual length of the onion cell. Show your working.3 marks