Required Practical Activity 1 - Use a light microscope to observe, draw and label biological specimens

Question 1

Stage:

Answer 1

• In the centre of the microscope
• Where we place the microscope slide

Question 2

Stage Clips:

Answer 2

To hold the slide in place

Question 3

Lamp:

Answer 3

• Light from the lamp passes up through the microscope slide and illuminates the specimen
• Sometimes optical microscopes have a mirror beneath the stage instead of a lamp
• The mirror is used to reflect the light up through the microscope slide and illuminate the specimen

Question 4

Objective Lenses:

Answer 4

• Most microscopes usually have three different objective lenses (high power objective lens, medium power objective lens and low power objective lens)
• These usually have a magnification of 4x, 10x or 40x
  You can change how magnified the specimen is
  This is the 2nd stage of magnification

Question 5

Eyepiece Lens:

Answer 5

• What we look through to see the specimen
• 1st stage of magnification. Usually has a magnification of 10x

Question 6

Coarse and Fine Focusing Knob:

Answer 6

For rough focusing and to see fine details

Question 7

Arm:

Answer 7

To hold, along with the base, when carrying the microscope

Question 8

What is the method for how to use an optical microscope to view a prepared slide?

Answer 8

1. Put the slide on the microscope stage.
2. Select the lowest power objective lens (this is usually ×4 objective lens). The end of the objective lens needs toalmosttouch the slide.
3. Turn the coarse adjustment knob to move the lens towards the slide. Look from the side (not through the eyepiece) when you are adjusting the lens.
4. Now look through the eyepiece. Slowly turn the coarse adjustment knob in the direction to increase the distance between the objective lens and the slide. Do this until the cells come into focus.
5. Slightly turn the fine adjustment knob to bring the cells into a clear focus. Use the low power objective lens (totalling ×40 magnification) to look at the cells.
6. When you have found some cells, turn the nose piece to switch to a higher power lens (×100 or ×400 magnification).
7. You will have to use the fine adjustment knob again to bring the cells back into focus.
8. Make a clear, labelled drawing of some of the cells. Make sure that you draw and label any component parts of the cell. Use a pencil to draw the cells.
9. Write the magnification underneath your drawing. Remember to multiply the objective magnification by the eyepiece magnification.

Question 9

What must you include when sketching the cells?

Answer 9

• labels
• magnification scale

Question 10

Why would you start of with the lowest powered objective lens when looking at something under a microscope?

Answer 10

• easier to focus
• gives a larger field of view

Question 11

What is the apparatus used for using a light microscope to observe, draw and label biological specimens?

Answer 11

• Microscope
• Prepared slides of plant and animal cells

Question 12

Why might mitochondria look different in different slides?

Answer 12

• the angle at which it is looked at or cut through is different
• different stage of mitochondria growth
• might have a mutation

Question 13

Method for using light microscope:

Answer 13

Preparing your slides:
1. Collect a sample of the tissue you want to observe
2. Remove the inner skin of a layer of onion using forceps / a thin layer of filament / algae using the scalpel
3. Place the thin slice (thin layer is used to help be able to see individual cells)onto a clean glass slide - use your forceps to keep the onion skin flat on the glass slide
4. Using a pipette add 1 or 2 drops of dilute iodine solution in top of the onion skin/slice of algae/plant (to stain/see parts of the cell)
5. Hold the coverslip by its side and lay one edge of the cover slip onto the microscope slide near the specimen
6. Lower the cover slip slowly over the specimen so that the liquid spreads out (to prevent/reduce any air bubbles

Setting up the Microscope
1. Move the stage to its lowest position
2. Place the prepared slide on the centre of the stage and fix it in place using the clips
3. Select the objective lens with the lowest magnification
4. Look through the eyepiece and turn the coarse focus adjustment until the cells on the slide come into view
5. Turn the fine focus adjustment knob to sharpen the focus so that the cells can be seen clear,y
6. If you wish to view the above at greater magnification to see more detail repeat the above steps using a higher magnification lens