Download OnionCellObservationLab-1

Name _____________________________________ Date ____________________ Per. ___________
Onion Cell Lab
Problem: What is an onion made out of?
Background: There are two main types of cells, plant cells and animal cells. Those that are found in
onions are plant cells. Plant cells have a rigid outer layer called a cell wall. This cell wall gives plant
cells a definite boxy shape, which is why Robert Hooke called them “cells” when he first observed
them in 1663. You will have the chance to become young Robert Hookes yourself and explore the
basic units of structure and function in living things…cells!
Hypothesis (a statement predicting the outcome of the problem being tested).
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Materials
microscope
onion (cut into sections)
microscope slide
cover slip
iodine
Procedure:
2 drops iodine
1. Add 2 drops of iodine to the center of a glass slide.
Be careful! Iodine can stain your clothes.
onion skin
2 drops iodine
2. Obtain a piece of onion. Bend the piece back so that
it breaks in two. Slowly pull the two halves apart. A
thin layer of onion tissue will peel off. With your
fingers, remove a piece of this thin tissue. Throw the
rest of the onion piece away.
glass slide
3. Carefully lay the onion skin flat in the center of the slide on top of the iodine.
4. Add 2 drops of iodine to the top of the onion skin.
cover slip
5. Slowly lower the side of the cover slip until it covers
the onion skin completely. If there are air bubbles,
gently tap on the glass to “chase” them out.
6. Make sure the lowest power objective (4X) is in place over the stage and the microscope light is
turned on. Place the slide onto the stage of the microscope.
7. Look through the eyepiece and turn the course adjustment knob until an image comes into focus. It
should look like a brick wall or like lizard skin.
8. Rotate the objective to the next highest power. If you need to, use the fine adjustment knob to get
the image into focus. You may see a small dot in the middle of each cell.
9. In your observations, draw a picture of what you see. Label the picture “Onion skin cells 100X.”
Label as many parts of the cell as you can see.
10. In your observations, draw a picture of what you see. Label the picture “Onion skin cells 400X.”
Label as many parts of the cell as you can see.
11. When finished, wipe your slide clean with a paper towel and place the onion skin and towel in the
trash. Set your clean slide and cover slip aside for the next class to use.
100X:
Approximate dimensions of an
onion cell: _________________
Qualitative Observations:
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400X:
Approximate dimensions of an
onion cell: _________________
Qualitative Observations:
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Conclusion (1. restate purpose, 2. was your hypothesis correct or incorrect, 3. give an example of what happened, 4.
why do you think it happened that way, 5. tell what you learned, 6. how would you do this differently?)
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