Microscopy and cell fractionationAQA A-Level Biology: Flashcards

Exam questions on Microscopy and cell fractionation

1. A student examines a transmission electron micrograph of a liver cell. On the micrograph one mitochondrion is 45 mm long, and the magnification of the micrograph is ×30 000. The same magnification is later used to photograph a chloroplast from a leaf cell, which is 6 μm long in life.
   Calculate the length of the image of the chloroplast on the micrograph at the same magnification. Give your answer in mm.2 marks
2. A student measures the length of an onion epidermal cell using an optical microscope fitted with an eyepiece graticule. The student places a stage micrometer on the stage. Ten divisions on the stage micrometer, which total 100 μm, line up exactly with 40 divisions on the eyepiece graticule. The onion cell is then measured as 18 eyepiece divisions long, using the same lenses.
   The student changes to an objective lens of higher power. Explain why the eyepiece graticule must be calibrated again before further measurements are made.2 marks
3. A research team wants to study three specimens: the surface of a pollen grain, the internal structure of a mitochondrion, and living single-celled algae in pond water.
   For each specimen, name the most suitable type of microscope and give a reason for your choice.3 marks