Local elementary school (5th graders) – plant cells and animal cells with Dr. Chris Sacchi (and me, of course!)

The 1st and 5th graders from the local elementary school visited Kutztown University to learn the difference betwee plant and animal cells using the Microscopic Digital Imaging Lab. 

The questions of the day were:
1) Are plants and animals really made of cells?
2) How do animal cells and plant cells differ?

The microscope we used had a digital camera attached to it so we could take photographs of the different cells for comparison.

We first looked at plant cells. 

elodia cellsThe image to the right shows plant cells from the elodia plant - a floating, flowering plant common in ponds that has leaves that are only two cells thick!  The green specks are chloroplasts, which are the little packets inside the cells containing chlorophyll (the molecule that allows plants to convert sunlight + carbon dioxide + water into sugar). 

The chloroplasts float around in the cell fluid (called cytoplasm) and try to orient themselves so that they are exposed to as much light as possible.  Click here to see a 6 Mb Quicktime®  movie of these elodia plant cells experiencing "cytoplasmic streaming." 
The cell is sort of like a vegetable stew, slowly convecting and churning.

salted elodia cellsMost of the cell parts (called organelles) are almost invisible because they are colorless.  Dr. Sacchi put a little salt water on the slide to see what would happen.  The insides of the cells squished up and the chloroplasts all bunched together because the water in the cytoplasm was "sucked out" of the cell by a phenomenon called "osmosis." 

onion cellsWe also looked at the cells of an onion bulb.  Since the onion bulb grows underground, it doesn't see any sunlight and so it doesn't have any chloroplasts for photosynthesis.  Not having all those chloroplasts in the way, we wanted to see the nucleus of the cell, which is where the DNA is stored.  We added a drop of iodine to the slide, which acted as a stain that made the nucleus visible.  The little circular dot inside each cell is the nucleus.

cheek cellsNow it was time to compare plant cells with animal cells, but where would we find an animal?
We found an animal by looking in the mirror!
Using a toothpick, we scaped some cells off the inside of our cheeks.  You can imagine how often the skin on the inside of your cheeks rubs against your teeth -- whenever you move your mouth!  Every time you move your mouth, a few cheek cells (called epithelial cells) rub off and you swallow them. 

That made me think.  The cells are very small, so we don't swallow very much each time, but if I were to add up all of the times that I have swallowed in my whole life, I wonder if all of those the swallowed cheek cells would add up to be as big as my whole body!

cheek cellsWe stained the cells using a chemical called methylene blue, which reacts with acids to turn purple.  Those parts of the cell that contained some acid turned purple.  The soft purple circles in each cell are the cell nucleus - why do you suppose the nucleus stained purple?  What molecules are acids that you would find there?  (Hint: the molecules are shaped like a double helix!)
You can also see little dark purple dots on the surface of the cells.  Those are bacteria!  Everyone has billions of bacteria growing in their mouths and all over their bodies!  It's natural.  Some of those bacteria are actually good for us - they help us in many ways and all they ask is for a little place to live!

So, do you see any differences between plant and animal cells? 
I'm a teacher, so you didn't think I was going to just tell you the answer right away, did you?  My job is to set people up learn things for themselves!
You have the pictures - study them and you can figure it out!

Everybody had a chance to use the microscopes - it was a fun day for all!

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