Name:______Block:______Date:______

Label the parts of the microscope image below: (use your textbook- in the back)

Background Information: Biologist frequently need to know the actual, or best approximate, size of the objects they are viewing. For example, Biologist might wish to know the size of various cells; however, even the smallest commonly used metric unit, the millimeter, would be too large to measure under these microscopic objects. Instead, another smaller unit, the micrometer (m) is used. One millimeter equal one thousand micrometers or microns.

Purpose: In the following laboratory activity, you will approximate the actual size of objects by comparison with a known field size

Procedure/Data:

  1. Locate the objectives, eyepiece and calculate total magnification (objective x eye piece = total magnification) and complete the chart:

Power / Objective / Eyepiece / Total Magnification / Field of Diameter/view
(mm) / Field of Diameter/view
(m)
Scan / 4x / 10x / 4.5 / 4500
low power / 10X / 100x / 1.8 / 1800
high power / 10x / .45 / 450
  1. Look at the chart and answer the following question:
  2. As the magnification increases the field of diameter increases or decreases(circle one)?

Which means we increase our detail of each object because we are looking at the object more closely.

  1. Practice: How many millimeters fit across the diameter of this circle?

______mm

  1. Now using the microscope: Adjust the light microscope for viewing under scan power (4X). Place the metric ruler across the stage so that the millimeter scale is centered across the circle on the stage. You should see the ruler lines through the eyepiece

(see image).

This circle represents the Field of View (what you see when you

look through the eyepiece)

  1. Focus on the edge of the ruler so that the markings are clearly visible across the field of view. Now, rotate the nosepiece until you are looking through low power (10X). Refocus the image using the course focus knob.
  1. Adjust the rulers so that one of the millimeter marks is visible at the left edge of the circle(remember you are view through glass that causes the image to move the opposite direction from your actual movement)
  1. The distance between each mark represents a millimeter. Count how many millimeters fit across the Field of View. If the millimeter marks does not reach each edge on the Field of View, estimate the fraction of the millimeter that is visible in the Field of View.

Example: 3.6 millimeter marks are visible across this Field of View

  1. a. Draw a picture of what the Field of View looks like under low power with the ruler:

b. How many millimeters fit across the

Field of view/diameter? ______mm

  1. What is the Field of View in microns for the above picture?

______mm (answer from number 8) multiply by 1000 = ______m

  1. Describe what happen to the amount of millimeter lines when you moved from scan to low power? ______
  1. Prepare a wet mount of a human hair:
  2. Place one strand of hair across the center of the glass slide
  3. Place a drop of water on top of the hair
  4. Place a plastic slide cover on top of the hair sample. Start by placing the cover at an angle and slowly lowering it (see picture) and remove any excess moisture with a paper towel.
  1. Place the slide on the stage and adjust the eyepiece under scan power (4X). Use the course focus to view the hair.
  2. Draw the image:
  1. Now, adjust the eyepiece to low power (10X) and use the course focus knob to clearly view the hair. Draw image:
  1. Estimate how many of your hairs would fit across the field of view : ______

Example: The 4 stands of hair fit across the Field of View.

  1. Now calculate the fraction of your hairs that would fit across the diameter: ______

Example: Image above ¼

  1. When using high power the magnification is smaller than one millimeter, so it is necessary to use known constants like, Field of Diameter to calculate the size of objects. Practice this skill by calculating the width of your strand of hair using the known field of diameter: ______mm

Example:

(MULTIPLICATION METHOD)

The chart tells me the field of diameter under low power is 1.8 mm

I know that 1 out of 4 strands fits across the field of view = ¼. The decimal of ¼ is 0.25.

SO…. 0.25x 1.8mm = .45mm

(DIVISIONMETHOD)

The chart tells me the field of diameter under low power is 1.8mm.

I know that 4 stands of hair would cover the width of the field of diameter.

SO…. 1.8mm/4 = .45mm. The width of one stand of my hair is 45mm

  1. Now, repeat the procedures g-h under high power and calculate the Field of Diameter in microns (m) = ______m

hint: (chart )high power field of diameter is 450 m and then estimate how many stands of hair (width) will fit across the field of diameter. Now, do the math (divide).

  1. Now, with out using the microscope practice your skills and calculate the size of the cell in the below image under High Power (40X)

Magnification (use chart) ______

Field of View (use chart) ______m

How many cells fit across the field of view ______

Size of the cell ______m (hint use math)

  1. Now, obtained a prepared slide. Practice finding the image using the scan power and then draw a DETAILED pictures of the object under low and high power and calculate the size of the image.

LOW POWERHIGH POWER

Magnification ______Magnification ______

Field of View ______mField of View ______m

How many cells fit How many cells fit across

across the field of view ______the field of view ______

Size of the cell ______m Size of the cell ______m

Be sure to wash and dry slides and cover slips and properly arrange your microscope before returning it to the cart!

Conclusion:

  1. Describe the process of calculating the size in microns of a cell under low power: ______.
  1. Using correct parts and detailed description, explain the procedure of preparing a wet mount and focusing under high power (40X): ______.