Scientists have observed and studied cells for over 300 years. Click the image below to watch a video and see how it all got started.

*Note* The video will open in a new window. Close the window to return to the resource.

This resource is about cell comparisons. The document in the image above is meant to help you track your learning as you proceed through the lesson. Click "Cell Comparison Graphic Organizer"  to access a copy of the document. If you have a science notebook, feel free to use that instead. After you've determined your tracking method, watch the video below to get started on your own cell discoveries.

*Note* Click the play arrow, then locate and click the full screen icon to improve the view of the video.

Prokaryotes, commonly known as bacteria, don't have a "good reputation." Have you ever heard anyone saying, "I'm so happy I have this bacterial infection?" No! Instead you see people whipping out the hand sanitizer, wiping down grocery cart handles, and sterilizing their kitchen counters. While it is true that some bacteria are bad, it is also true that some are good, and others are extremists and live in outrageous and ugly conditions.

The Good

First, let's take a look at bacteria we could think of as "good." Click the image below to view a slideshow that describes ways these prokaryotes are helpful. (In order to access the slideshow, use Microssoft Internet Explorer as your browser.)

The Bad

These are the prokaryotes we know and don't love; the ones that give us cavities, cause infection, and make us sick. We call these  prokaryotes "bacteria" or "germs." Fortunately for us, we have an immune system that helps fight infection. Plus, if we need help, we can treat bacterial infections or illnesses with antibiotics. However, the overuse of antibiotics and sanitizers is creating additional problems.

To see for yourself, click on the picture below. It opens in a new window and links to a microbial clock activity and slideshow. (This activity requires Microsoft Internet Explorer to open.) Read through the information and then start the microbial clock activity. Not only will you learn about how fast bacteria reproduce but also how they become disease resistant.

The Microbial Clock activity was created by WGBH Educational Foundation Clear Blue Sky Productions, Inc. ©2001 All Rights Reserved.

The Ugly

These prokaryotes aren't really ugly, but they may live in some extreme and unsavory or "ugly" conditions: places that are too salty, too hot, or filled with noxious gases. The archaebacteria are also called extremophiles and are actually classified differently than the bacteria we discussed earlier. In fact, they have their own domain name, Archea, which comes from the Greek word meaning "ancient." They are still prokaryotes, but you can think of them as the bacteria living off the edge.

Click on the image below to read more information about archaebacteria.

This image of Morning Glory Hole in Yellowstone Park is in the public domain.

This section focuses on the basic characteristics of Eubacteria. Eubacteria is the domain name for the prokaryotic organisms we are most familiar with, i.e., Escherichia coli, Lactobacillus acidophilus, Staphylococcus aureus, etc. To gain an understanding of these basic characteristics, play the brief tutorial below. Once the video begins, click the "full screen" icon for a better view. Press the Esc key on your keyboard when the tutorial has finished playing.

You may have heard the saying "Variety is the spice of life!" Is that statement valid? If we look at ourselves as humans, we look amazingly different, even though we are all the same species, Homo sapiens. We are also amazingly the same. Our body parts are arranged the same, and for the most part we function the same way.

Variety among organisms made of eukaryotic cells is even greater. Even the cells themselves look amazingly different from one another and have specialized functions, yet they have many structures and functions that are the same.

Scientists use these similarities and differences to describe cell characteristics and then classify organisms according to those characteristics. When you study cell structure, it is easy to compare similarities and differences between eukaryotic cells using diagrams created from scientists' observations. Since it would be too difficult to represent everything scientists have learned, only the most obvious similarities and differences are represented in the drawn models.

Take a close look at the images above. These are two cells from different organisms. Can you see the similarities and differences? One represents a typical animal cell and the other a typical plant cell. Can you determine which is which? If you don't have a photographic memory, and most people don't, sketch both cells in your science notebook, on plain paper, or on the graphic organizer provided for you in the "Related Items" section below. Label them now if you know the names of the organelles, but if you don't, you can refer to the video tutorials or do your own web search.

Looking at drawings and micrographs of cells can be really interesting. The images in the graphic below are all representative eukaryotic cells. Five of the six images are from multi-cellular organisms.

PictureBone Cell ©Gopal Murti/Phototake, Epithelial Cell ©ISM/ Phototake, Neuron ©Dr. David Scott/Phototake, Liver Cells ©Carolina Biological Supply Company/Phototake, Paramecium and Muscle Cells ©Dennis Kunkel/Phototake.

Open "Eukaryote Variety" to view more images and read about other representative cells from the Domain Eukarya. You may also download the document to your computer.

Next, watch the video referred to in Slide 2 of the slideshow. In it you will see a single-celled protist swimming around in a fluid environment while managing its internal fluid levels by pumping water out with a vacuole that contracts. It's the organelle that resembles a star.

Are you ready to "read the fine print" about the cell structure of eukaryotes? If you made sketches of the cells during the Explore 2 section of this resource, this would be a good time to label the cells' organelles and make notes about their function.

Click to watch the video tutorial below. Once it begins, click the "full screen" icon for a better view. Press the Esc key on your keyboard when the tutorial has finished playing.

Before you move on to the last section, take a moment to check your understanding of the similarities and differences between prokaryotic and eukaryotic cells. Follow the directions in the TruthSeeker activity below.

By now you are getting the idea that what seems like clear lines drawn between eukaryotic cells and prokaryotic cells may be not quite as clear as you previously thought. For example, let's think about cell walls. The prokaryotes and some eukaryotes have cell walls, but they aren't made of the same material. The cell membranes of archaebacteria and eubacteria are structured differently, but they both have cell membranes, as do eukaryotes. It's this variation on a theme that people interested in life science find fascinating. The fascination grows as scientists manipulate prokaryotes and eukaryotes through the cells' genes.

In this last section, you can choose an area of interest to explore. There are three sections with one or more topics and links below it.

Health

Insulin—This site shows the steps in the recombinant DNA process.                    

//www.iptv.org/exploremore/ge/what/recombinant.cfm

Eukaryotic Stem Cells—Click the "Stem Cells Home" tab to view Stem Cells 101 and two or three other movies in the series.  

//stemcell.childrenshospital.org/?videold=1

Environment

Bioremediation—Bacteria and other microbes are used to clean up toxic waste.   

//www.youtube.com/embed/XB3p39wS87M

GMO—The first link describes what GMOs are and how they are used in our society. The second and third links are slide shows about how one specific bacteria is used in GMO process.

//www.ornl.gov/sci/techresources/Human_Genome/elsi/gmfood.shtml

//www.bt.ucsd.edu/bt_history.html

//www.bt.ucsd.edu/movies/movies.html

Daily Life

The Human Microbiome—This article explores our complex human ecosystem.   

//www.nytimes.com/2012/06/19/science/studies-of-human-microbiome-yield-new-insights.html?pagewanted=all&_r=0