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Biology-Mr.Willets
Lab- Cells #2
All organisms are made of cells. Today, we will make slides from various plant parts looking for cells and in some cases structures within the cells. Plant cells are easier to get than animal cells.
Part One- Cells of the Potato
The potato is a part of the plant that is used mostly for storage. Cells in the potato contain structures called leucoplasts that store starch.
a) I will use a device called a microtome to cut a thin slice of potato. Bring a slide to the front of the room to get the slice. Add 2-3 drops of water and a cover glass. The cover glass may not lie flat if the potato slice is thick (which I hope it won't be.) Don't smush it down. Since this may be a thick specimen, you may not be able to use high power. Try anyway but be careful as you move the high power lens into place that it doesn't hit the cover glass. If it does, call me over.
b) Examine under scanning power and then switch to low power. You will have to move the slide to find as thin an area as possible. Usually near the edges of the specimen is the thinnest. Look for the cells. They may be hard to see. The small roundish structures are the leucoplasts. Most of the cells will have been broken open when we made the slide and the leucoplasts will be scattered about. Look for a cell that is still intact with the leucoplasts inside. The TV scope will show you what to look for.
c)Answer question #1
d) Remove the cover glass and add a drop of iodine. Replace the cover glass (make a new slide if necessary). Examine under low power. What color are the leucoplasts now? What does this color change tell you about leucoplasts?
e) Answer question #2
Part Two- Cells of the Tomato Skin
a) Bring a clean slide to the front of the room to get a small piece of tomato skin. Place it on a slide with the outside of the skin facing up.
b) Put 2-3 drops of water on the tomato skin and add a cover glass. Examine under low power. Switch to high power to get a better view
c) Note the thick cell walls. Note how tightly packed the cells are. Remember how this looks for comparison to the cells on the inside of the tomato (the tomato pulp)
d) Answer questions #3-4
Part Three- Cells of Tomato Pulp
The pulp cells of a tomato are used mostly for storage. Most of the inside of these cells is taken up by the water filled vacuole and appears empty. The cytoplasm is pushed to the edge and is barely visible.
a) Bring a clean slide to the front of the room and smear a small amount of tomato pulp on it. Avoid any seeds or large chunks on the slide. Add 2-3 drops of water and a cover glass.
b) Search under low power for a clear area where cells may be visible. The cells will be somewhat round and appear empty. Focus on one when you find it.
c) The vacuole is obvious (the empty looking area). The cytoplasm may be visible near the edges. A nucleus might be seen along the edge also.
d) Answer questions #5-6
Questions and Diagrams
1) In the circle below, draw several potato cells including the leucoplasts. Use low power. Estimate the size of the average cell and the size of an average leucoplast..
Specimen______________________ / ________X
Size of one cell _________________microns
Size of average leucoplast__________microns
2) What evidence tells us that leucoplasts contain starch? (be specific) ______________________
________________________________________________________________________
3) What is the general function of the skin of the tomato_______________________________ How are the tomato skin cells designed for this function? _______________________________________
___________________________________________________________________________
This represents an example of " _______________ follows _________________"
4) In the circle below, draw a group (6 or so) of tomato skin cells as seen under high power
Specimen_________________ / ________X
Size of one cell ____________microns
5) From your everyday experience, how would you describe what the inside of a tomato is like? _____________________________________ This is easily explained when we see that the insides of the pulp cells are mostly __________________________
6) In the circle below, make a diagram of one tomato pulp cell as seen under low power. Estimate the diameter of the cell.
Estimated diameter ________________