PAG 1: Microscopy

Question 1

What is an eyepiece graticule, and what is its function? (3)

Answer 1

Measuring scale fitted onto a microscope

That acts as a ‘ruler’

Allowing structures to be measured under the microscope

Question 2

What is the purpose of calibrating an eyepiece graticule? (2)

Answer 2

Ensures accurate measurements of structures under a microscope

By determining the actual length represented by each division at different magnifications

Question 3

Describe the method for calibrating an eyepiece graticule. (5)

Answer 3

1. Set up the microscope to the required magnification to view the sample
2. Place a stage graticule on the stage of the microscope
3. Line up the two scales (the stage and eyepiece graticules) so they are aligned
4. Count the number of divisions on the eyepiece graticule that match each division on the stage micrometer
5. Use the known length of each division on the stage micrometer to calculate the length of one eyepiece division

Question 4

What is the formula for calculating the actual size of a specimen using an eyepiece graticule? (1)

Answer 4

Actual size = Measured size ÷ Magnification

Question 5

How do you calculate the length of one eyepiece graticule division? (1)

Answer 5

Stage micrometer length ÷ Number of eyepiece divisions

Question 6

What is the formula for magnification in microscopy? (1)

Answer 6

Magnification = Image size ÷ Actual size

Question 7

How can you determine the size of a specimen using a graticule and micrometer? (3)

Answer 7

1. Calibrate the eyepiece graticule using a stage micrometer to find the length of one division
2. Measure the specimen using the number of eyepiece graticule divisions it covers
3. Multiply the number of divisions by the calibrated length of one division to find the actual size

Question 8

What is the formula for total magnification?

Answer 8

Eyepiece lens magnification × Objective lens magnification

Question 9

How do you convert micrometers (µm) to millimeters (mm)? (1)

Answer 9

1 mm = 1000 µm

Convert by:
Micrometers ÷ 1000 = Millimeters

Question 10

What is the purpose of staining samples with methylene blue or eosin? (2)

Answer 10

Staining adds contrast to the specimen

Making it easier to identify different parts of the cell under a microscope

Question 11

Why are specimens stained with lead when using an electron microscope? (1)

Answer 11

Used in electron microscopy to enhance contrast by increasing the electron density of cellular structures

Question 12

Describe the method for preparing a dry mount. (3)

Answer 12

1. Thinly slice the specimen to allow light to pass through
2. Use tweezers to place the specimen in the middle of a clean microscope slide
3. Place a coverslip gently over the specimen to protect it and hold it in place

Question 13

Describe the method for preparing a wet mount. (6)

Answer 13

1. Pipette a small drop of water onto the center of the slide
2. Use tweezers to place the specimen on top of the water droplet
3. Hold the coverslip upright next to the water droplet
4. Carefully tilt and lower the coverslip over the specimen to prevent air bubbles
5. Ensure the coverslip completely covers the specimen for clear viewing
6. Add a drop of stain next to the coverslip to enhance contrast in the specimen

Question 14

Why is it important to avoid air bubbles when preparing a wet mount? (2)

Answer 14

Air bubbles can obstruct the view of the specimen under the microscope

Making it difficult to observe details clearly

Question 15

What is the formula for magnification? (1)

Answer 15

Image size ÷ Actual size