47 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

What are the principles in labelling of drawings from a microscope?

Answer 1

Label lines should be simple lines, not arrows or lines ending with a dot.

Lines should be drawn with a ruler.

Lines should end inside the structure to which they refer, rather than merely touching the outer edge.

The lines should be parallel, but if the diagram is circular, then radial lines are suitable.

The line should end well away from the drawing so that the label does not obscure what has been drawn.

Question 2

How does microscope calibration help?

Answer 2

Microscope calibration allows you to measure the lengths of structures in the microscope.

Question 3

What does microscope calibration require?

Answer 3

It requires:

1. An eyepiece graticule.
2. A stage micrometer.

Question 4

Why does calibration have to be done for each objective lens?

Answer 4

The eyepiece graticule looks the same in every objective lens because it is in the eyepiece.

So with objective lenses of different magnifications, the divisions on the graticule represent different lengths.

The higher the power of the objective lens, the smaller length each division of the graticule represents.

Calibrating, therefore, has to be done for each objective lens.

Question 5

What is a stage micrometer?

Answer 5

This is a microscope slide on which the object is a line 1 mm long.

It is ruled with markings for tenths and hundredths of a millimetre.

Question 6

What are the steps in calibrating the microscope?

Answer 6

Line up the zero of the eyepiece graticule with
a major division of the stage micrometer, making sure the graduation lines are parallel.

Look along the scales and see where they coincide again.

Question 7

What does this diagram show?

Answer 7

The diagram shows a x40 objective lens, with 20 stage micrometer divisions lining up exactly with 80 small eyepiece divisions.

Question 8

What is the length of the divisions on the micrometer vs the eyepiece graticule?

Answer 8

The length of the smallest divisions on the micrometer is 0.01 mm = 10 μm.

The length of the divisions on the eyepiece graticule depend on the objective lens with which you look at them.

Question 9

How do you calculate the size of the eyepiece measuring unit from this diagram?

Answer 9

Question 10

What does epu and smu stand for?

Answer 10

epu = eyepiece units
smu = stage micrometer units

Remember to give a key for these abbreviations