Name: Date: Investigation: What Are the Different Types of Cells? All living organisms are made of cells. The smallest cells are about 0.001 millimeters in diameter and belong to one of two domains: Bacteria and Archaea. Organisms in these groups do not have a nucleus or membranebound organelles. These organisms were some of the first to live on the planet; archaea lived over 3.5 billion years ago. Organisms can belong to a third domain: Eukarya. Eukaryotic cells are larger (0.01 to 1 mm) and contain a nucleus and organelles, such as mitochondria and endoplasmic reticulum. Plants, animals, fungi and protists belong to this domain. In this investigation, you will view both preserved specimens and living specimens from the domain Eukarya and the domain Bacteria. Write all of your answers on the summary sheet. Exercise 1: Getting to Know the Domain Bacteria 1. Obtain prepared slides of bacterial cells and examine them under the 40x objective following proper microscope protocol. The cells are small and difficult to see even at 400x; look for small squiggles stained pink or purple. Bacteria come in three shapes: rods, spheres, and spirals. Sketch your cells to SCALE and label any structures you can identify at this magnification. 2. Estimate the size of a bacterium. Divide the diameter of your viewing field by the number of cells you estimate would fit across it. For example, if your field of view measures 5 mm, and you estimate that 25 cells would fit across it, then 5.0/25 = 0.2 mm. Sample 1: Sample 2:
Size Size Exercise 2: Getting to Know the Domain Eukarya 1. Create a wet mount of your own cheek cells. (Kingdom Animalia) a) Add a small drop of methylene blue to a clean slide. b) Gently scrape the inside of your cheek with a toothpick and then smear the sample in the dye. c) Place a cover slip over the dye/sample and view. d) Cells will appear as small light blue with a darker area in the center (nucleus) e) They will appear very small at 40x. f) When finished, throw the entire slide away. g) Sketch the cheek cells at each of the magnifications (to scale) and label the nucleus, plasma membrane and cytoplasm of the 400x sample (high power) h) Estimate the diameter of a cheek cell: 2. View Blood Cells (Kingdom Animalia) Obtain a prepared slide of blod and observe them with the 40x objective. These cells appear as faint pink blobs and may be difficult to see with the bright ligtht of the microscope, adjust the diaphragm to reduce the light. Be sure to return all prepared slides to their proper location! RBC's, 400x a) Sketch a few of the cells at 400x. b) Do red blood cells have a nucleus? c) Estimate the size of a red blood cell.
3. Create a Wet Mount of Onion Cells (Kingdom Plantae) a) Cut an onion and remove the thin skin-like membrane that lines the onion layers with tweezers. Onion Cells, 400x b) Place a tiny portion of this skin a slide and stain with iodine. c) Place a cover slip over the sample and view at 40x, 100x and 400x. d) Sketch the onion cells and label the cell wall and the nucleus of the sample at 400x. e) Estimate the length of a single onion cell. 4. View Prepared Onion Root Tip (Kingdom Plantae) a) Obtain a slide of onion root tip. This slide has been stained in such a way that chromosomes are visible. Onion Root Tip, 400x b) The root of an onion is an area that is growing quickly, so many of the cells are in various stages of mitosis. c) Sketch the onion root tip at 400x, label the cell wall, nucleus, and chromosomes d) Recall the four phases of mitosis: prophase, metaphase, anaphase, telophase. Locate cells on the slide in each of the four phases and sketch them below. You may need to reference other sources to determine what each phase looks like. 5. View Plant Cell Leaves (Kingdom Plantae) a) Prepare a wet mount of an elodea leaf by placing a single leaf on a slide with a drop of water. Elodea, 400x b) Place a cover slip over the sample and view at 400x.. c) You will notice many green blobs within your cells, these are chloroplasts. The nucleus will appear brownish-red in color, but it may be obscured by the many chloroplasts within the cell. d) You may also notice that the chloroplasts move around a large central vacuole. This movement is a result of cytoplasmic streaming. e) Sketch the elodea cells at 400x and label an structures you can see.
6. View Protozoa (Kingdom Protista) a) There are many preserved slides of protozoans available which include the ameba, paramecium, euglena and spirogyra. You can choose to focus on one or two of these samples. b) Sketch and label the protozoan(s) you chose to investigate. c) Choose one of your samples and estimate it's size. Exercise 3: Application 1. Compare and contrast prokaryotic cells and eukaryotic cells, listing at least 3 similarities and 3 differences. 2. Compare and contrast plant cells and animal cells, listing at least 3 similarities and 3 differences. 3. Much of this investigation asked you to estimate the sizes of cells you viewed. Create a list of cells, ranked in order from the smallest to the largest that includes at least 4 of the cells you observed in this investigation. 4. You looked at three samples of cells from different parts of the plant: the root tip of an onion, the bulb of an onion, and the leaf of an elodea. Why are the cells in each area of the plant different?
5. The Kingdom Protista traditionally contains microorganisms that are difficult to classify as plants or animals. In fact, one protist, called the euglena can switch from being a heterotroph to being an autotroph depending on food availability. The image below shows a euglena. Discuss why biologists might have a difficult time classifying this organism.