Lesson 25 - Microscope calibration and calculations

Question 1

Describe how you could make a temorary mount of a piece of plant tissue to observe the position of starch grains in cells when using an optical (light) microscope (4marks)

Answer 1

1. add adrop of water to a glass slide
2. obtain a thin section (of plant tissue) and place on slide/float on drop of water
3. stain with/add iodine in potassium iodide
4. lower cover slip using mounted needle

Question 2

What are the parts of a microscope/

Answer 2

eyepiece, objective lens, stage, lamp, base, coarse focusing knob, fine focusing knob, arm, slide with specimen, eyepiece graticule

Question 3

what is an eyepiece graticule used for?

Answer 3

to measure the size of cells

Question 4

what is the stage micrometre used for?

Answer 4

to calibrate the eyepiece graticule

Question 5

how can an eyepiece graticule move?

Answer 5

can rotate clockwise/anticlockwise

Question 6

How can you measure the size of an object viewed with an optical microscope?

Answer 6

1. work out which is the eyepiece graticule and which is the stage micrometer (eyepiece can rotate)
2. Line up the eyepiece graticule and the stage micrometer so that they’re parallel to each other
3. Work out how many eyepiece units there are in 1 mm or 0.1mm (decide based on how zoomed in you are)
4. Then convert mm into micrometers
5. Now work out how many micrometers in 1 epu

Question 7

Describe how you could measure the mean diameter of the starch grains present in cells viewed in a temporary mount of plant tissue.

Answer 7

1. Measure the diameter of a grain using the eyepiece graticule
2. Calibrate the eyepiece graticule using a stage micrometer at the same magnification.
3. Randomly sample 10+ grains and use to calculate the mean