Calibrations and Preparing Slides

Question 1

What is the purpose of calibrating an eyepiece graticule?

Answer 1

Ensures accurate measurements of specimens

Allows conversion between eyepiece divisions (EPG) and micrometres (μm)

Question 2

How do you calibrate an eyepiece graticule?

Answer 2

1. Place a stage micrometer on the microscope stage
2. Focus so both the eyepiece graticule and stage micrometer are visible
3. Align the scales and count how many EPG divisions match a known micrometre scale
4. Calculate the value of 1 EPG in μm using:
   1 EPG = Stage micrometer units ÷ EPG divisions

Question 3

What is the formula to calculate the true size of a cell?

Answer 3

Mean length (EPG) × Size of 1 EPG (μm) = Length of cell (μm)

Question 4

How do you calculate the length of an organelle?

Answer 4

Example:
1. 100μm corresponds to 36 EPG divisions
2. 1 EPG = 100 ÷ 36 = 2.78μm
3. Organism = 20 EPG × 2.78 = 55.6μm

Question 5

What happens when increasing magnification?

Answer 5

• The image appears larger- the field of view decreases
• The stage micrometer divisions appear bigger

Question 6

How do you prepare an onion cell slide?

Answer 6

1. Peel a thin layer of onion cells
2. Place the sample onto a slide using a wet mount
3. Stain with iodine for contrast
4. Place a cover slip at an angle to avoid air bubbles

Question 7

How do you make a blood smear?

Answer 7

1. Pipette blood onto one side of the microscope slide
2. Add a fixative to preserve the sample
3. Add stain to highlight cell structures
4. Use a cover slip to spread the blood evenly.
   Leave to air dry

Question 8

How do you use a light microscope?

Answer 8

1. Clip the slide onto the stage
2. Select the lowest-powered objective lens
3. Use the coarse adjustment knob to focus
4. Look down the eyepiece and adjust with the fine adjustment knob
5. If higher magnification is needed u have to swap lenses and refocus
6. Fit an eyepiece graticule and calibrate if measuring specimens

Question 9

What are the key rules for scientific drawings?

Answer 9

• Use white and unlined paper
• Draw with a sharp pencil
• No shading or colour
• Include an informative title and magnification used
• Label structures with horizontal lines
• No arrows
• Ensure clear proportions
• No sketching

Question 10

Why is staining important in microscopy?

Answer 10

• Adds contrast
• Makes structures more visible.
• Differentiates organelles and cell components

Question 11

What is differential staining?

Answer 11

Uses multiple stains to distinguish between structures.

Example: Haematoxylin stains nuclei purple, eosin stains cytoplasm pink.