Form/Class
Biology Term 1, Lesson 1
Name
Making scale drawings using a microscope Introduction In Biology Unit 1 of the Smart Science Student’s Book, you learn that all living things are made of tiny cells. Many living things are very small, often consisting of just a single cell. Larger living things are made of millions of cells. Cells are so small that we need to use a microscope to see them. This practical will teach you how to use a microscope and record what you see.
Objectives During this activity, you will: plan how you are going to carry out your practical describe the steps you take to stay safe make a slide of one of your own cells from inside your cheek lining view the slide using a light microscope at low, medium and high magnifications make a drawing of a few cells and of a single cell measure the cell image you see and use your measurement to put a scale on your drawing.
Planning This practical contains five parts after the planning stage. You need to plan each part before carrying it out. Because the practical involves taking a sample of human cheek cells, the first part is a risk assessment. This is to make sure you and others stay safe. Here are all the parts you need to plan: 1. Carrying out a risk assessment. 2. Taking a sample of cells from inside your cheek and preparing a slide. 3. Viewing the slide using the light microscope. 4. Drawing the image. 5. Adding a scale.
Resources you will be given You will be provided with: sterilised cotton swabs disposable gloves a light microscope microscope slides and cover slips a dropper bottle containing some stain (methylene blue) some plain drawing paper a sharp pencil a ruler guidance on the magnifications of your microscope a shared large container of alcohol or disinfectant to put your used swabs and slides in safely. You will also need an exercise book or sheets of paper to carry out a risk assessment.
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SMART SCIENCE
1
Biology Term 1 – Practicals and Investigations
Practicals and Investigations
Biology Term 1 – Practicals and Investigations
Practicals and Investigations
Form/Class
Biology Term 1, Lesson 1
Name
Carrying out a risk assessment It is very important that you, your classmates and your teacher all stay safe in the laboratory. This means you need to think about how to carry out practicals safely. You also need to follow all the instructions your teacher gives you. Your teacher will give you some paper and some guidance on how your school wants you to stay safe. This will include assessing risks. Pay close attention; this is the most important part of any science lesson! You will need to fill in a table that will probably look something like this. The first row is filled in for you. What am I going to do? What could go wrong? What can I do to reduce the risk? Use a swab to gather some cells from inside the cheek.
The swab could be dirty or contain bacteria.
Always use a new, sterilised swab. Never reuse a swab.
Taking a sample and preparing a slide 1. Put on disposable gloves. 2. Gently move a new cotton bud over the inside of your cheek and along the gums to get some cells. 3. Transfer the cells onto a clean microscope slide by smearing the bud over a small area in the centre of the slide. 4. Immediately place the used end of the cotton bud into the alcohol or disinfectant provided by your teacher. 5. Add as small a drop as you can of methylene blue stain. 6. Add a cover slip without causing air bubbles. Look at the diagram below.
7. Once your slide is ready, follow the instructions for ‘Using the light microscope’ and ‘Drawing the image and adding a scale’, below. 8. When you have finished looking at it, put the whole slide into the disinfectant.
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TEACHER’S HANDBOOK 1
© Smart Learning Ltd 2014 – Copying permitted for purchasing institution only.
Form/Class
Biology Term 1, Lesson 1
Name
Using the light microscope Remind yourself about the main parts of a light microscope. You can read about this on page 12 of the Smart Science Student’s Book. Make sure you understand where to find the controls on the light microscope you are going to use. Every type of light microscope is slightly different. Here is an example:
You may find that your microscope has two different focus knobs. One will be ‘coarse’ – changing this makes the focus change quickly but not very precisely. One will be ‘fine’ – changing this makes much smaller adjustments. You will need to use both.
© Smart Learning Ltd 2014 – Copying permitted for purchasing institution only.
SMART SCIENCE
3
Biology Term 1 – Practicals and Investigations
Practicals and Investigations
Biology Term 1 – Practicals and Investigations
Practicals and Investigations
Form/Class
Biology Term 1, Lesson 1
Name
1. Place your slide on the stage of the microscope. 2. Different microscopes may use battery, electric lights or a mirror to light the sample. Check with your teacher how to switch on and adjust the light. 3. Once you have light coming through the slide and into your eye, you can start to look at it. 4. Look down the eyepiece with the low-power objective lens in place. Find some cheek cells. 5. Adjust the coarse focus knob until the cells are sharp and focused. At this magnification they will look something like this:
6. Have a look at these and then move on to medium and high power magnifications. When focusing at high power, you must use the fine focus knob. You should see something like this:
Drawing the image Now that you have a clear view of some of your own cheek cells, it's time to make a good scale drawing.
A good drawing will show all of the main structures labelled and at the correct sizes. The labelling lines should be straight but not cross each other. The label lines should point clearly at the structure they label. There should be no shading on the drawing. A scale bar or magnification number should be shown. (See the next sheet for how to show scale.)
4
TEACHER’S HANDBOOK 1
© Smart Learning Ltd 2014 – Copying permitted for purchasing institution only.
Form/Class
Biology Term 1, Lesson 1
Name
Biology Term 1 – Practicals and Investigations
Practicals and Investigations
Adding a scale How you do this depends on what equipment you have. Some microscopes have a distance scale marked in the view; ask your teacher how to use this correctly. Some microscopes do not have a distance scale in the view, so you will need to use this method. The following table shows the distance across the image, using a variety of different magnifications. Check with your teacher whether your microscope produces the same sizes of images.
Eyepiece lens
Total Objective magnification Distance across whole image lens (eyepiece x (approximate) objective)
Low power
10 x
4x
40 x
5 mm
Medium power
10 x
10 x
100 x
2 mm
High power
10 x
40 x
400 x
0.5 mm
You can use this table, or something similar that your teacher will provide, to estimate the size of the whole image. Then you can work out how big your cells are, by deciding how much of the image they stretch across. For example, if you are using x 400 total magnification, and the cell stretches halfway across the image: The image is about 0.5 mm across, using the table. This means the whole cell is about 0.25 mm across. To make your scale easier to work out, we can use the unit called the micrometre. There are 1000 μm in 1 mm. So the width of the cell in this example is 250 μm. You could choose, on your diagram, to use a scale of 1 cm : 50 μm. This means that 1 cm in your drawing represents 50 μm of the cell seen under the microscope. The finished drawing of the cell could look something like this:
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SMART SCIENCE
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