Lab 2: Using the Microscope: The Elodea Cell

Problem: What are the basic parts of a plant cell?

 

Background Information:

The cell you are going to look at in this lab is from the aquatic plant Elodea. Like any complex cell, it has the basic organelles. You will not see the nucleus with the DNA in this lab, but the cell wall and chloroplasts will be very obvious. The chloroplasts are the site for photosynthesis in the cell; they contain chlorophyll, which traps sunlight and thus enables the cell to combine carbon dioxide and water to make glucose (a simple carbohydrate with the formula C6H12O6). You will be:

  • looking at a cell under a microscope at both low (100X) and high power (400X).
  • drawing a diagram of the cell at each magnification.
  • labeling (with names and arrows) the high power diagram with the parts you see (cell wall and chloroplast).
  • adding to each drawing a title and the magnification.
  • measuring the diameter of the field of the low power magnification with a ruler and converting to microns (1 mm = 1000 microns).
  • estimating the length and width of the plant cell.

After answering the pre-lab questions, have your group give the teacher a small slip of paper with your group number and the name of the microscope part that you use to adjust light. Then begin the procedure.

 

Book Reference:
Plant Cell -
page 301 in the new light green version
Microscope Parts and Use page 831 in the light green version

 

Safety Considerations:

  • Always carry the microscope with 2 hands.
  • When in high power, only use the fine adjustment knob.
  • Never sit the microscope near the edge of the table.
  • Never pull out an electrical plug by the cord.

 

Pre-lab Questions:

  1. Why do plant cells need a cell wall?
  2. In high power, we use the long high power objective to view the slide. How much does this lens magnify the object? How much does it magnify when combined with the eyepiece?
  3. How many microns wide is your pencil?
  4. Fill in the blank: When the microscope is in high power, only use the _______ to focus the slide.

 

Materials: (per group)

Sprig of Elodea

Microscope

Textbook

Slide

Cover Slip

Transparent ruler

 


Procedure:

  1. Always begin with your microscope in the lowest magnification.
  2. Make a wet mount of an Elodea leaf on a microscope slide. (See page 831.)
  3. Place on the microscope stage with the leaf centered over the hole in the stage.
  4. Focus with the course adjustment knob. If in 40X (with the 4X objective down), increase to low power. (Revolve the 10X objective in place over the leaf until it clicks into place. Focus again.)
  5. In the data section of your lab, draw a circle with a 12 cm diameter.
  6. Diagram 2 3 cells in the circle such that the cells you draw are in the same proportion to the circle as the actual cells are to the lit up field you are looking at.
  7. Next rotate the high power objective into place, and then focus using ONLY the fine adjustment knob.
  8. Diagram 2-3 cells under this magnification in a similar circle, and label the cell parts that you see.
  9. Return to low power (100X), and remove and clean up the slide and cover slip.
  10. Place a transparent or translucent ruler on the stage, and focus on the millimeter marks.
  11. Estimate in millimeters the diameter of the visible field (the lit-up circle area).
  12. Convert the diameter to microns using the formula above.
  13. Estimate the length and width of a plant cell in microns from the known diameter.
  14. Return Microscope to the lowest power, turn off the light, and cover it.

 

Data: (This section should include the 2 circular field diagrams, the measurement, and the estimates.)

 

Title:

Title:

Magnification:

Magnification:

 

 

 

 

 

 

 

 

 

 

 

 

 

    [______________________________]

Field Diameter Estimate

______ mm            ________ microns

 

 

 

Estimated Cell Length  _______________  Estimated Cell Width ________________

 

What you should see:

 

Chloroplasts in the Cytoplasm Cell Wall around each cell

Post-Lab Questions: (Answer each in a 1-paragraph answer.)

 

1. How big is a plant cell?

2. How would humans be different if we had cell walls around our cells?

3. How many molecules of C02 does it take to make 1 molecule of glucose in the chloroplast? Explain how you got this answer.

4. Bonus Questions: How many plant cells placed end to end would be 1 cm long?

Conclusion:

(In your conclusion, you should briefly summarize the problem and what you did. Then answer the problem referring to the data.)

 



" because the Forest will always be there, and anybody who is Friendly with Bears can find it."
- A.A. Milne

George M. Radcliffe 
Centreville Middle School 
231 Ruthsburg Rd.
Centreville, MD 21617 
1-410-758-0883
radclifg@qacps.k12.md.us