The Onion Cell: Lab

MATERIALS

Whole white onion **soaked in water overnight*

Microscopes (2-3 students per scope)

Microscope slides

Water bottle

Cover slips

Eyedropper/pipette

Iodine

Tweezers

Worksheet

PROCEDURE

Preparing the wet mount slide of onion skin

1. Break an onion slice in two.

2. Carefully pull the slice apart.

3. Use tweezers to pull off a very thin piece of onion skin (the thinner, the better)

4. Place the skin in the center of the slide. Try to keep it from folding; get it as flat as possible.

5. Add a drop of water to the onion skin and cover with a cover slip.

6. Press the cover slip down carefully to remove any air bubbles.

7. Place the slide on the stage of the microscope, set it to low power, adjust the focus so the onion slice is clear. Draw four or five cells as seen. Label the cell walls.

9. Switch to higher power and try to identify the cell membrane, nucleus, and cytoplasm.

Staining the onion cells

1. Lift up the cover slip and add one or two drops of iodine to the slide.

2. Lower the cover slip and examine the cells on higher power.

3. Iodine stains different parts of the cells so that different organelles can be seen. Draw and label the cell wall, cell membrane, cytoplasm, and nucleus.

DISCUSSION QUESTIONS

1. What is the general shape of the onion cells?

2. Describe what you saw without the stain.

3. Why do you think there are many cells close together?

4. Is the onion skin composed of one cell or many cells?

5. Why is it easier to see the onion cells after they are stained?

6. All plant cells have cell walls. What is the function of the cell wall?

7. Count the number of cells that are seen in the field of view under low power

magnification and also under higher magnification. Compare the number of cells

observed in each field of view.

The Scientific Method: The Onion Cell

Objective/Purpose: What is it that you wantto find out?

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Hypothesis: What do you think will happen?

The ______

Materials: What exactly do you need to dothis experiment?

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______

______

______

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Method/Procedure: List all the steps that youtake to do this experiment.

______

Observations: What do you see? Record your data in a table or labelled diagram. Diagrams must be completed in pencil.

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Conclusions: Was your hypothesis correct? Explain. Answer questions here.

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The Onion Cell: Observations

Onion Cell: Low Power

Stained Onion Cell: ______Power

Lab Report: The Onion Cell Lab Report: The Onion Cell

Scientist: ______

Class: ______
1)
2)Overall
Title page includes name, date, title
Report is neat
Report was handed in on time
3)Purpose
Is complete
Hypothesis
Written in 3rd person
(no I, My, We or Our)
Materials
Written as a list
The list is complete
Procedure
Reference is made to the worksheet
Worksheet is attached for reference
Observations
2 diagrams neatly completed
2 diagrams in pencil
2 diagrams are accurately labelled
Observations are clear and detailed
Conclusion
Question 1 is correct
Question 2 is correct
Question 3 is correct
Question 4 is correct
Question 5 is correct
Question 6 is correct
Question 7 is correct
___
20 /

Scientist: ______

Class: ______
4)
5)Overall
Title page includes name, date, title
Report is neat
Report was handed in on time
6)Purpose
Is complete
Hypothesis
Written in 3rd person
(no I, My, We or Our)
Materials
Written as a list
The list is complete
Procedure
Reference is made to the worksheet
Worksheet is attached for reference
Observations
2 diagrams neatly completed
2 diagrams in pencil
2 diagrams are accurately labelled
Observations are clear and detailed
Conclusion
Question 1 is correct
Question 2 is correct
Question 3 is correct
Question 4 is correct
Question 5 is correct
Question 6 is correct
Question 7 is correct
___
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