Measuring Cells Activity

Objectives:

a) measuring the sizes of several different cells while viewing through the microscope

b) use an SI unit for measuring length (micrometer).

Materials:

microscope glass slide coverslip dropper prepared slide frog blood
Lugol's (iodine) stain Elodea onion skin water prepared slide of paramecium

Procedure:

1.  Look through the microscope using low power magnification. The circle of light you see is called the field of view. It has the diameter of about 4 mm. If you convert millimeters (mm) to micrometers (m), the diameter of the field view equals 4000 m.

2. Look through the microscope using high power magnification. The field of view is now about 0.3 mm (300 um) in diameter.

3. Convert the following measurements.

a) 1.5 mm = ____ m        b) 400 m = ____ mm

4. To estimate the size of a cell while looking through the microscope, follow this method.

a) locate the cell under low power and then under high power.

b) draw a circle that represents your field of view. Draw the cell to scale (same size as it appears) within the circle.

c) estimate the number of same-sized cells that could fit end-to-end or side-by-side across the diameter of the circle.

d) to determine cell size on low power, divide 1350 m by the total number of cells that would fit across the circle's diameter. The size of the original cell will be that quotient. (Example if 3.5 cells fit across the diameter, then 1350/3.5 = 385 m).

e) to determine the cell size on high power, divide 300 um by the number of cells lined up end-to-end or side-by-side . (Example 300/10 cells = 30 m).

5. Examine the prepared slide of frog red blood cells. Determine if this slide is best viewed under low or high power. Complete the data table (column 1).

6. Examine the prepared slide of Paramecium. Determine if this slide is best viewed under low or high power. Complete the data table (column 2).

7. Prepare a wet mount of an Elodea leaf and observe it through the microscope. Determine if this slide is best viewed under low or high power. Complete the data table (column 3).

8. Prepare a wet mount of onion skin (not the brown part) the clear peel between the sections and observe it through the microscope. Add a drop of Lugol's to stain the onion darker. Determine if this slide is best viewed under low or high power. Complete the data table (column 4).

Data Table (reproduce this table in your journal, make sure you leave enough room for drawing cells).

  Frog Red Blood Cell Paramecium Elodea Onion
Viewed under high or low power        
Diagram of 1 cell drawn to scale

 

 

 

       
Number of cells that fit side-by-side        
Diameter of field of view        
Calculated cell size (show work)

 

       

Conclusion Questions

Directions: Refer to your results and your text for aid in answering each of the following questions in your journal.

1. Convert each of the following cell measurements.

a) 0.25 mm = ___ m b) 0.06 mm = ____ m c) 10.7 m = _____ mm

2. A student observed the same cell under low power and then under high power. The number of cells that could fit across the field of view was estimated at 10 on low power and 2.2 on high power. Determine the cell size under each power.

3.  Determine the cell length and cell width in each diagram.

a) low power

b) high power

 

4. a) What structures are in the elodea cells that are missing in the onion?

b) Why do you think it was necessary to stain the onion specimen?

c) So approximately how many cells are in one elodea leaf?

Additional Activity

( 2000 Flinn Scientific, Inc. All Rights Reserved.)

Introduction:

What do your skin cells look like? It is easy to remove some and look at them with a microscope.

Biological Concepts:

Cell structure

Epidermis

Materials:

Clear tape, 1.0 cm 1.0 cm Microscope slide

Soap/water

Slide and cover slip

Methylene blue stain, 1% aqueous

Dissecting needle

Microscope Forceps

Caution:

This activity requires the use of hazardous components and/or has the potential for hazardous reactions. Please review the

Safety Precautions section on the following page and relevant Material Safety Data Sheets before beginning this activity.

Procedure:

1. Wash the underside of a wrist that will be sampled for epidermal cells with soap and water.

2. Stick a clean piece of clear tape on the underside of the washed wrist.

3. Gently remove the piece of tape from the wrist being careful to avoid getting fingerprints on the tape. A forceps might help

to remove the tape and avoid fingerprinting the tape.

4. Place the tape, sticky-side up, on a clean microscope slide.

5. Stain the top, sticky side of the tape with 2 or 3 drops of 1% methylene blue solution.

6. Use a dissecting needle to gently place a cover slip over the sticky tape. Lower the coverslip down onto the tape and then

remove the dissecting needle. This should help prevent staining your fingers. Caution: Use methylene blue carefully. It

will stain most items including skin, clothing, and table tops.

7. Examine the slide under a microscope. Look for cells with low power first, and then switch to high power for details.

8. Record your observations of epidermal cells by making drawings. Label your drawings with appropriate magnifications.

Use your knowledge of the size of the microscopic field to estimate the size of the cells.

Discussion:

There has been concern expressed about the classic activity in which students remove cheek cells from the inside of their

mouths. The procedure described in this activity eliminates the potential dangers inherent in collecting cheek cells from the

mouth. The cells secured from the wrist will be easy to find. Students may have to examine numerous cells before they find a

nice cell with nucleus, etc. Patience will yield good results. Students are likely to be amazed at how easy it is to remove cells

from the surface of the skin. The simple removal technique illustrates the fact that the skin is continually shed. Microbes and other

organisms are shed along with the skin thus helping in the fight against microbe invasion.

Safety Precautions:

Methylene blue is a vital stain, it stains nearly everything, and it is difficult to remove. Prevention is the key when working

with vital stains. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron.