Microscopy
We can use microscopes to look at objects too small to be seen by the naked eye.
The microscope in the picture is a light microscope. It uses focused light passed through the object and two lenses to magnify an image of the object.
Lenses
If looking at an object under the ×4 objective lens, light will have passed through the object, the ×4 objective lens, and the ×10 eyepiece lens before it gets to your eye. This makes the image 4 × 10 = 40 times bigger.
Stage
It has a hole in the centre which light can be focused up through the object.
Using light microscopy it is possible to magnify using a ×40 objective lens which magnifies the image 400 times. Using an objective lens with higher magnification than this will make the image bigger but will not improve image clarity, this means the image will look bigger but less detailed. To see things at a higher magnification, and with a higher level of detail, then Using electrons to form images of dead organic matter. can be used.
Question
Using a ×10 eyepiece lens and a ×10 objective lens, by how much is the image magnified?
×10 eyepiece ×10 objective lens = ×100 overall magnification.
Making a glass slide
The easiest cells to look at in the lab are animal cells, from your own cheek. To look at the cells under the microscope you must first prepare a slide of the cells to place on the microscope stage.
- Rub a clean cotton bud gently on the inside of your cheek.
- Smear the sample across a clean glass slide.
- Cells are transparent, place a few drops of a dye called methylene blue onto the smear so the cells will be visible under the microscope.
- Use a mounted needle to gently lower a glass coverslip onto the sample on the slide, take care not to form air bubbles under the coverslip.
Carrying out a risk assessment
A risk assessment for the example above could look like this:
| Hazard | Risk | Control measure |
| Name the chemical or apparatus in the experiment and give a reason it is a hazard. Methylene blue. It is an irritant. | Give a step in the method where there is a risk of this hazard causing harm. If methylene blue comes into contact with the skin or eyes during the procedure, then it could cause irritation. | What you can do to minimise the risk? Wear laboratory gloves. Wear safety glasses. Use low concentrations of the chemical. |
| Hazard | Name the chemical or apparatus in the experiment and give a reason it is a hazard. Methylene blue. It is an irritant. |
|---|---|
| Risk | Give a step in the method where there is a risk of this hazard causing harm. If methylene blue comes into contact with the skin or eyes during the procedure, then it could cause irritation. |
| Control measure | What you can do to minimise the risk? Wear laboratory gloves. Wear safety glasses. Use low concentrations of the chemical. |
Question
Another hazard associated with the experiment is the thin glass coverslips. Complete the risk assessment for these.
| Hazard | Risk | Control measure |
| Name the chemical or apparatus in the experiment and give a reason it is a hazard: | Give a step in the method where there is a risk of this hazard causing harm: | What you can do to minimise the risk? |
| Hazard | Name the chemical or apparatus in the experiment and give a reason it is a hazard: |
|---|---|
| Risk | Give a step in the method where there is a risk of this hazard causing harm: |
| Control measure | What you can do to minimise the risk? |
| Hazard | Risk | Control measure |
| Name the chemical or apparatus in the experiment and give a reason it is a hazard: Glass is easily broken and is sharp. | Give a step in the method where there is a risk of this hazard causing harm: It can cut the skin when trying to lower onto the slide. | What you can do to minimise the risk? Handle carefully, report breakages. |
| Hazard | Name the chemical or apparatus in the experiment and give a reason it is a hazard: Glass is easily broken and is sharp. |
|---|---|
| Risk | Give a step in the method where there is a risk of this hazard causing harm: It can cut the skin when trying to lower onto the slide. |
| Control measure | What you can do to minimise the risk? Handle carefully, report breakages. |
Magnification
Katie drew an image of some onion cells she observed under a microscope. Her teacher told her that the cells were 0.4 mm in length. Her drawing was 40 mm in length.
Using this equation, she worked out the magnification of her drawing to be ×100.
\(\text{magnification}~=~\frac{\text{image size}}{\text{actual size}}\)
Question
Terry drew a bigger picture of the same cells. His image was 60 mm in length. What was the magnification of the image he drew?
Magnification = 60 ÷ 0.4 = ×150
