Download Observing Plant and Animal Cells

Observing Plant and Animal Cells
Date: _________________
Name: __________________
Introduction:
 Purpose: To observe plant and animal cells in a light microscope. To observe the different organelles
plant and animal cells contain. Why are these differences necessary?
 Hypothesis:
o What will onion cells look like? Which organelles will be seen in onion cells? Why do you think so?
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What will cheek cells look like? Which organelles will be seen in cheek cells? Why do you think so?
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Identify and explain at least two parts of the cell theory.
Research the history of the discovery of at least four organelles.
o Why do cells require so many different types of organelles?
Research the history of the discovery of dying agents, such as iodine and methylene blue.
o Why are dying agents used for viewing cells under the microscope?
Materials:
 Cover slips
 Eye dropper
 Iodine solution – Caution: will stain clothing
 Methylene blue solution – Caution: will stain
clothing
 Microscope
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Microscope slides
Onion
Tissue
Toothpick
Water
Procedure:
Onion Cells
1. Obtain a 1cm2 thin piece of onion skin and place it on a microscope slide.
2. Prepare a “wet-mount” by adding two drops of water and cover with a cover slip.
3. Observe at low power.
4. Use the diaphragm to adjust the intensity of light.
5. Observe at medium and high power.
6. Add a drop of the iodine solution to one side of the cover slip. Use a piece of tissue on the opposite
side to draw the solution across the onion.
7. Observe at low, medium and high power.
8. Clean slide and leave to dry.
Cheek Cells
1. Place 1 drop of the iodine solution on a microscope slide.
2. Use the flat end of a toothpick to gently scrape the inside of your cheek.
3. Stir the end of the toothpick in the iodine solution and cover with a cover slip.
4. Throw the toothpick away immediately.
5. Observe at low, medium and high power.
6. Clean slide and leave to dry.
7. Place 1 drop of the methylene blue solution on a microscope slide.
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Use the flat end of a toothpick to gently scrape the inside of your cheek.
Stir the end of the toothpick in the iodine solution and cover with a cover slip.
Throw the toothpick away immediately.
Observe at low, medium and high power.
Clean slide and leave to dry.
Observations:
Onion Cells
i. On 8½ x 11 paper, complete a scientific drawing of a few onion cells, stained with iodine, at high-power.
Identify any organelles that are visible. For organelles that can be seen but are too small to be
identified, label them as “unknown organelles”.
ii. Choose one onion cell that you have drawn. Calculate its estimated size at high power.
iii. Calculate the diagram magnification of the scientific drawing of the same onion cell.
Cheek Cells
iv. On 8½ x 11 paper, complete a scientific drawing of a few check cells, stained with methylene blue, at
high-power. Identify any organelles that are visible.
v. Choose one cheek cell that you have drawn. Calculate its estimated size at high power.
vi. Calculate the diagram magnification of the scientific drawing of the same check cell.
Discussion Questions:
Onion Cells
a. Which intensity of light allows the better view of the onion cell? Explain.
b. How did the iodine solution change what you viewed?
c. Why do the onion cells, which are from a plant, lack chloroplasts?
Cheek Cells
d. Which stain, iodine or methylene blue, stained the cheek cells better? Explain.
e. Which organelle do you think would be most numerous inside the cells in your mouth? Explain.
Hint: your salvia is the first site of chemical digestion, which starts the break down of carbohydrates.
f. How did the cheek cell differ from the onion cell? Give at least 2 ways.
General
g. If given an unknown specimen to observe under the microscope, how would
you be able to tell if it is a eukaryotic or prokaryotic cell?
h. Cells are able to divide their nucleus to make new cells through the process
of mitosis and meiosis. They must also divide their cytoplasm, through the
process of cytokinesis. When animal cells go through cytokinesis they simply
‘pinch in’ to create two new cells (see figure to the right). Why can plants
cells not do the same?
Conclusion:
 Answer the “Purpose”.
 Briefly describe your observations. Describe the structure and function of the organelles identified.
 Discuss whether your observations confirmed your hypothesis or not. If the results do not support
your hypothesis, try to explain why.
 Why will all organelles not be visible?
 Include if there were any specific errors that may have affected your observations.
Formal Lab due: Friday, February 24th