1. Links to GCSE: Structure of animal & plant cells Using a microscope

2. Hooke’s compound microscope

3. Hooke’s view of cork

4. Generalised (a) plant cell and (b) animal cell as seen under the light
Week 1
Generalised (a) plant cell and (b) animal cell as seen under the light
microscope
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5. Standard light microscope

6. Answers!

7. Using the light microscope
1: To carry the microscope grasp the microscopes arm with one hand. Place your other hand under the base.
2. Place the microscope on a table with the arm toward you.
3. Turn the coarse adjustment knob to raise the body tube.
4. Revolve the nosepiece until the low-power objective lens clicks into place.
5. Adjust the diaphragm. While looking through the eyepiece, also adjust the mirror until you see a bright white circle of light.
6. Place a slide on the stage. Center the specimen over the opening on the stage. Use the stage clips to hold the slide in place.
7. Look at the stage from the side. Carefully turn the coarse adjustment knob to lower the body tube until the low power objective almost touches the slide.
8. Looking through the eyepiece, VERY SLOWLY the coarse adjustment knob until the specimen comes into focus.
9. To switch to the high power objective lens, look at the microscope from the side. CAREFULLY revolve the nosepiece until the high-power objective lens clicks into place. Make sure the lens does not hit the slide.
10. Looking through the eyepiece, turn the fine adjustment knob until the specimen comes into focus.

8. Cross sectioning: Longitudinal: cut along
the long axis of a structure.
The opposite of a cross section.
Transverse: cut perpendicular
to the longitudinal axis

9. Images of specimens seen under the light microscope

10. Explain the difference between magnification and resolution.
Week 1
State the resolution and magnification that can be achieved by a light microscope.
Explain the difference between magnification and resolution.
Explain the need for staining samples in light microscopy.
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11. Key definitions
Magnification: the degree to which the size of an image is larger than the object itself. Numerically, it is the image size divided by the actual size of the object, measured using the same units. It is usually expressed as x10, x1.5.
Resolution: is the degree to which it is possible to distinguish between 2 objects that are very close together. The higher the resolution the greater the detail that can be seen

12. Low resolution image

13. High resolution image

14. Andromeda at low resolution

15. Andromeda at high resolution

16. Week 1
Calculate the linear magnification of an image such as a photomicrograph or electron micrograph.
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17. Units of measurement Unit Symbol Equivalent in metres
Fraction of a metre
Metre m 1
One
Decimetre dm
0.1
One tenth
Centimetre cm
0.01
One hundredth
Millimetre mm
0.001
One thousandth
Micrometre µm
One millionth
nanometre nm
One thousand millionth

18. Key definitions:
A micrometre is equal to one millionth of a metre (10ˉ6) and is the standard unit for measuring cell dimensions.
A nanometre is one thousandth of a micrometre (10ˉ3). It is therefore a thousand millionth of a metre (10ˉ9). It is useful for measuring the sizes of organelles within cells and large molecules

19. Limits of resolution Human eye: 100µm Light microscope 200nm
Electron microscope 0.20nm

20. Week 1
Eyepiece graticule and stage micrometer at (a) x40 magnification and (b) x100 magnification
Please note that magnification sizes are subject to variation on different screens
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21. Calibrating the eyepiece graticule
A microscopic ruler on a slide (stage micrometer) is placed on the microscope stage.
This ruler is 1mm long and divided into 100 divisions.
Each division is 0.01mm OR 10 µm.
With a x4 objective lens and x10 eyepiece (magnification x40),
40 epu (eyepiece units) = 1mm (1000 µm).
Therefore 1 epu = 1000/ 40 = 25µm.
With a x10 objective lens (magnification x100)
100 epu = 1000 µm.
So 1 epu = 10µm.

22. An amoeba seen under a light microscope; (a) with a x10 objective
Week 1
An amoeba seen under a light microscope; (a) with a x10 objective
(b) with a x40 objective
Please note that magnification sizes are subject to variation on different screens
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23. Magnification of
eyepiece lens
Magnification
of objective
lens
Total
magnification
Value of one eyepiece
division/µm
X 10
X 4
X 40 25
X 100 10
X 400
2.5
X 100 (oil immersion)
X 1000
1.0

24. Worked example In figure 1a the length on the nucleus is 3.2 epu
At X100 magnification, one epu = 10µm
We have 3.2 all worth 10µm
So the length of this nucleus is 32.0µm
In figure 1b the length of the nucleus is 13 epu
At X 400 magnification, one epu = 2.5 µm
So the length of this nucleus is 32.5 µm

25. IMA triangle Week 1 © Pearson Education Ltd 2008
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26. Calculations of actual size from magnification given
Week 1
Calculations of actual size from magnification given
Please note that magnification sizes are subject to variation on different screens
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27. Explain the need for staining samples for use in electron microscopy.
Week 1
State the resolution and magnification that can be achieved with the electron microscope.
Explain the need for staining samples for use in electron microscopy.
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28. Transmission electron micrograph

29. Electron microscope in outline
Week 1
Electron microscope in outline
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30. Electron Microscopes
Transmission
Scanning

31. Advantages & disadvantages of electron microscopes
Resolution is 0.1nm (2000x more than LM)
Produces detailed images of internal cell organelles
SEM produces 3D images
Electron beams are deflected by molecules in the air, samples are placed in a vacuum
Expensive
Operators are highly skilled and trained

32. Comparing LM to EM
Both allow us to see a magnified image of a small object
Both use a radiation beam focused using lenses to generate an image
LM are easier to use, portable and can be used to observe living specimens
EM need training and skill to prepare specimens, and it has to be placed in a vacuum. It is not possible to observe living specimens
It is not possible to see colours of an EM
EM has much greater resolution and give greater magnification with a clear image

33. Images of specimens seen under a scanning electron microscope

34. Topic outcomes revisited
State the resolution and magnification that can be achieved by a light microscope.
Explain the difference between magnification and resolution.
Explain the need for staining samples in light microscopy.
Calculate the linear magnification of an image such as a photomicrograph or electron micrograph.
State the resolution and magnification that can be achieved with the electron microscope.
Explain the need for staining samples for use in electron microscopy.