Microscope Skills: Magnification and Specimen Preparation Worksheet

Question 1

A compound light microscope has a 10x eyepiece and a 40x objective lens. What is the total magnification?

Accepted Answer

The total magnification is 400x because 10x multiplied by 40x equals 400x.

Question 2

A student views a specimen first under 100x total magnification and then under 400x total magnification. Describe two changes the student should notice in the image.

Accepted Answer

At 400x total magnification, the specimen should appear larger and the field of view should be smaller. The image may also appear dimmer and show less of the specimen at one time.

Question 3

A microscope has a 10x eyepiece. The available objective lenses are 4x, 10x, and 40x. List the total magnifications from lowest to highest.

Accepted Answer

The total magnifications from lowest to highest are 40x, 100x, and 400x. These come from multiplying the 10x eyepiece by each objective lens.

Question 4

A prepared slide label says the onion cells are stained with iodine. Explain why a stain is often used when viewing cells under a light microscope.

Accepted Answer

A stain is often used to increase contrast so cell structures are easier to see. Iodine can make parts of onion cells stand out more clearly against the background.

Question 5

Put these wet mount steps in the correct order: place the specimen on the slide, add a drop of water, lower the coverslip at an angle, place the slide on the stage.

Accepted Answer

The correct order is to place the specimen on the slide, add a drop of water, lower the coverslip at an angle, and place the slide on the stage.

Question 6

Why should a coverslip be lowered slowly at an angle when making a wet mount?

Accepted Answer

The coverslip should be lowered slowly at an angle to reduce trapped air bubbles. Air bubbles can block the view and may be mistaken for parts of the specimen.

Question 7

A student begins focusing a slide using the 40x high-power objective and the coarse adjustment knob. Explain the problem with this technique and describe the safer method.

Accepted Answer

Starting with the high-power objective and using the coarse adjustment knob can crash the lens into the slide and damage the microscope or specimen. The safer method is to begin with the lowest-power objective, use the coarse adjustment to find the image, then switch to higher power and use only fine adjustment.

Question 8

When a specimen moves left in the field of view, which direction did the student move the slide on the stage?

Accepted Answer

The student moved the slide to the right. In a compound microscope, the image appears to move in the opposite direction from the actual slide movement.

Question 9

A student estimates that the field of view is 4.0 millimeters wide at 40x total magnification. About how wide is the field of view at 400x total magnification?

Accepted Answer

The field of view at 400x is about 0.4 millimeters wide. The magnification increases by a factor of 10, so the field of view becomes 10 times smaller.

Question 10

A cell appears to take up about one-fourth of a 0.8 millimeter field of view. Estimate the cell's length in millimeters and micrometers.

Accepted Answer

The cell is about 0.2 millimeters long because one-fourth of 0.8 millimeters is 0.2 millimeters. This is equal to 200 micrometers because 1 millimeter equals 1000 micrometers.

Question 11

Explain why a very thick specimen may be difficult to observe clearly with a compound light microscope.

Accepted Answer

A very thick specimen may be difficult to observe because light may not pass through it evenly. Thick specimens can also have several layers in focus at different depths, making the image blurry or confusing.

Question 12

A student sees many dark circles with bright edges in a wet mount. The circles move when the coverslip is gently tapped. What are these circles most likely to be, and how could the student reduce them next time?

Accepted Answer

The circles are most likely air bubbles. The student can reduce them by using a small drop of water and lowering the coverslip slowly at an angle.

Question 13

What is the purpose of the diaphragm or iris on a compound light microscope?

Accepted Answer

The diaphragm or iris controls the amount of light passing through the specimen. Adjusting it can improve contrast and make details easier to see.

Question 14

A student switches from the 10x objective to the 40x objective. The image is almost in focus but slightly blurry. Which adjustment knob should the student use, and why?

Accepted Answer

The student should use the fine adjustment knob because it makes small focusing changes. At high power, the coarse adjustment knob can move the stage too much and may damage the slide or lens.

Question 15

Design a brief procedure for preparing and viewing a wet mount of cheek cells. Include specimen collection, slide preparation, staining, and focusing.

Accepted Answer

A good procedure would gently collect cheek cells with a clean swab, smear the cells in a drop of water on a slide, add a small drop of stain such as methylene blue, and lower a coverslip at an angle. The slide should be viewed first on low power using coarse adjustment, then on higher power using fine adjustment.

Microscope Skills: Magnification and Specimen Preparation

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