Microscope measurements

Question 1

State the metric prefixes

Answer 1

Centi 1x10^-2
Milli 1x10^-3
Micro 1x10^-6
Nano 1x10^-9

Question 2

Describe how to calculate magnification

Answer 2

Image size/actual size

Question 3

What must be the same before you use the magnification equation

Answer 3

The units for image size and actual size

Question 4

Describe what an eyepiece graticule is used for

Answer 4

An eyepiece graticule has 100 divisions, and it’s used to measure cells.

Question 5

What does calibrate mean, and why do we need to calibrate the eyepiece graticule

Answer 5

• Calibrate means to work out how long each division is
• We need to do this because the eyepiece graticule’s divisions have no scale

Question 6

What is a stage graticule/micrometer, and what is it used for

Answer 6

• A tiny ruler of known length
• It’s used to calibrate the eyepiece graticule

Question 7

What’s the difference between the stage graticule/micrometer and the eyepiece graticule

Answer 7

The eyepiece graticule has divisions with an unknown length, and is used to measure cells, whereas the stage micrometer has a known length, and is used to calibrate the eyepiece graticule

Question 8

Describe how to calibrate an eyepiece graticule using a stage micrometer/graticule

Answer 8

• Line up the eyepiece graticule with the stage micrometer
• Work out the length of the stage micrometer that lines up with the eyepiece graticule
• Divide the length of the stage micrometer by the number of divisions on the eyepiece graticule

Question 9

What must be done to the graticule at each magnification

Answer 9

recalibrated

Question 10

How do you measure the cell once you have calibrated the eyepiece graticule

Answer 10

• line up the cell with the eyepiece graticule
• count the number of divisions that cover the part of the cell we want to measure
• multiply the number of divisions by the length of each division

Question 11

Describe what is meant by field of view

Answer 11

The visible area when using microscope

Question 12

Describe how to increase the reliability of the mean

Answer 12

• Measure a large number of cells, because the more you measure, the more representative your mean will be

Question 13

Describe how to estimate the average size of cells

Answer 13

• Calibrate eyepiece graticule
• Measure a large number of cells
• Calculate mean

Question 14

Describe how to estimate the number of cells

Answer 14

• Count cells in field of view
• Repeat several times with randomly selected fields of view
• Calculate mean

Question 15

Why do we count cells

Answer 15

Ensures that the counting is consistent. This makes our method more reproducible

Question 16

Why do we repeat several times

Answer 16

• To get a more representative sample, that gives us a more reliable mean

Question 17

Why do we use randomly selected fields of view

Answer 17

Reduces bias, which increases the validity of our estimation