We first looked at plantcells.
Theimage to theright shows plant cells from the elodiaplant - a floating, floweringplantcommon in ponds that has leaves that are only two cells thick!The green specks are chloroplasts, which are the little packets insidethe cells containing chlorophyll (the molecule that allows plants toconvert sunlight + carbon dioxide + water into sugar). Thechloroplasts float around in the cell fluid (called cytoplasm) and tryto orient themselves so that they are exposed to as much light aspossible. Clickhere to see a 6 Mb Quicktime® movie of these elodia plantcells experiencing "cytoplasmicstreaming." Thecell is sort of like a vegetable stew, slowly convecting and churning.
Most of the cell parts (calledorganelles) are almost invisible because they are colorless. Dr.Sacchi put a little salt water on the slide to see what wouldhappen. The insides of the cells squished up and the chloroplastsall bunched together because the water in the cytoplasm was "suckedout"of the cell by a phenomenon called "osmosis."
Wealso looked at the cells of an onion bulb. Since the onion bulbgrows underground, it doesn"t see any sunlight and so it doesn"t haveany chloroplasts for photosynthesis. Not having all thosechloroplasts 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 tothe slide, which acted as a stain that made the nucleus visible.The little circular dot inside each cell is the nucleus.
Now it was time to compare plantcells with animal cells, but wherewould we find an animal?We found an animal by looking in the mirror!Usinga toothpick, we scaped some cells off the inside of our cheeks.You can imagine how often the skin on the inside of your cheeks rubsagainst your teeth -- whenever you move your mouth! Every timeyou move your mouth, a few cheek cells (called epithelial cells) ruboff and you swallow them. That made me think. The cells are very small, so we don"t swallowvery much each time, but if I were to add up all of the times that Ihave swallowed in my whole life, I wonder if all of those the swallowedcheek cells would add up to be as big as my whole body!
Westained the cells using a chemical called methylene blue, which reactswith acids to turn purple. Those parts of the cell that containedsome acid turned purple. The soft purple circles in each cell arethe cell nucleus - why do you suppose the nucleus stained purple?What molecules are acids that you would find there? (Hint: themolecules are shaped like a double helix!)You can also see little dark purple dots on the surface of thecells.
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Those are bacteria! Everyone has billions ofbacteria growing in their mouths and all over their bodies! It"snatural. Some of those bacteria are actually good for us - theyhelp 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 theanswer right away, did you? My job is to set people up learnthings for themselves!You have the pictures - study them and you can figure it out!Everybody had a chance to use themicroscopes - it was a fun day for all!