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 membrane-bound 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.
Exercise 1: Getting to Know the Domain Bacteria
Refer to your text or other resources to review the structures found in bacteria to label the image.
Light microscopes in the lab are not powerful enough to clearly see bacteria to make observations. While some slides may be available
to you for viewing, complete the Bacteria exercise by going to "A Survery of Bacteria" at http://bit.ly/bactypes.
1. Sketch streptococcus and estimate its size.
2. Sketch Bacillus subtilis and estimate its size.
3. Sketch Spirillum volutans and estimate its size.
4. Watch the video showing Spirillum volutans. Based on the images, make an inference about the purpose of the flagella in these organisms.
5. Based on your observations in this investigation, rank each of the bacteria cells in order from smallest to largest.
6. This exercise included a sample from each of the three known shapes of bacteria. Match the shape with the organism:
- Spiral -shaped
- Rod - shaped
- Sphere - shaped
Exercise 2: Getting to Know the Domain Eukarya
1. Create a wet mount of your own cheek cells. (Kingdom Animalia)
- Add a small drop of methylene blue to a clean slide.
- Gently scrape the inside of your cheek with a toothpick and then smear the sample in the dye.
- Place a cover slip over the dye/sample and view.
- Cells will appear as small light blue with a darker area in the center (nucleus)
- They will appear very small at 40x.
- When finished, throw the entire slide away.
- 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)
- Estimate the diameter of a cheek cell: _______________________
2. Create a Wet Mount of Onion Cells (Kingdom Plantae)
- Cut an onion and remove the thin skin-like membrane that lines the onion layers with tweezers.
- Place a tiny portion of this skin a slide and stain with iodine.
- Place a cover slip over the sample and view at 40x, 100x and 400x.
- Sketch the onion cells and label the cell wall and the nucleus of the sample at 400x.
- Estimate the length of a single onion cell.
3. View Plant Cell Leaves (Kingdom Plantae)
- Prepare a wet mount of an elodea leaf by placing a single leaf on a slide with a drop of water.
- Place a cover slip over the sample and view at 400x.
- 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.
- You may also notice that the chloroplasts move around a large central vacuole. This movement is a result of cytoplasmic streaming.
- Sketch the elodea cells at 400x and label any structures you can see.
4. View Protozoa (Kingdom Protista)
- 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.
- Sketch and label the protozoan(s) you chose to investigate.
- Choose one of your samples and estimate its size. ____________
Exercise 3: Application
- Compare and contrast prokaryotic cells and eukaryotic cells, listing at least 3 similarities and 3 differences.
- Compare and contrast plant cells and animal cells, listing at least 3 similarities and 3 differences.
- 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.
- 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.