Lesson 8: Prokaryotic Power

Think back. Do you remember, from our very first lessons, the difference between a prokaryotic cell and a eukaryotic cell?

The plant and animal cells we have been studying are all eukaryotic, because they contain membrane-bound organelles. Now it is time to change our focus and take a look at prokaryotic cells – the cells that make up kingdom MONERA.

Remember from our first lesson that all living things are sorted into one of five kingdoms. Kingdom Monera is the classification home for all sorts of organisms that consist of only one prokaryotic cell. We call such organisms unicellular.

If a living thing is made of only one cell, it must be very tiny, right? And indeed, Monerans are microscopic. You could line up over three thousand members of kingdom Monera side by side across the eraser of a pencil. Even with a good microscope, it is hard to see much detail within these organisms. So in a few minutes we’ll look at and color a big diagram of a typical Moneran so we can see what kinds of structures they have inside.

First, though, what sorts of living things ARE these unicellular Monerans? Mostly, they are bacteria.

You probably already know alot about bacteria. You know, for example, that bacteria can cause diseases. We wash our hands to keep them bacteria free. We cover our mouths when we sneeze to keep our bacteria from being inhaled by our neighbors. We keep potato salad in the refrigerator and we cook our chicken until it’s well done to keep bacteria in the food from causing food poisoning. But did you know that not all bacteria are pathogenic? Most bacteria aren’t dangerous at all. Bacteria grows naturally in our stomachs to help us digest our food. Scientists use bacteria to make live-saving medicines. Dairy farmers use bacteria to produce yogurt and cheese from milk. So bacteria, as you may suspect, are everywhere. They can live in harsher climates than any other life form – in hot sulfur springs, in the bottom of the ocean, and, like I said before, even in your intestines. But they best love to live in moist warm, dark areas where there is plenty of food available. Most bacteria, aerobic bacteria, also need oxygen to live, but some types can even survive without it – we call these types anaerobic bacteria.

Think about the food you eat. Besides refrigerating it, can you think of some other ways we protect the food we eat from breeding bacteria? Sometimes we pickle or salt food to keep it fresh. Let’s start an experiment to help us see what kinds of environment best protects our foods from excessive bacterial growth:

You can use clear glasses instead of jars if you want. Make sure to leave them uncovered while you wait for bacteria to grow.

Have you heard of the bacteria E. coli? Some E. coli is harmless, but some strains can cause serious food poisoning in humans. Where does the name E. coli come from? Well, it is short for Escherichia coli, which are the genus and species names for that particular bacteria. All bacteria, like all other living things, have a two-name genus-species name assigned by the rules of binomial nomenclature. Here is a picture of some actual E. coli:

Do you see how each is rod-shaped, like a long grain of rice? This is a common bacterial shape and has a special name: bacillus. All rod-shaped bacteria are said to be bacilli.

What kind of symmetry do bacilli have? Well, think back. You could theoretically cut one from end to end along any plane down the center and get mirror image halves. Do you remember what kind of symmetry that is? Look back to your glossary to help you.

These bacteria, as you can see, are spherical.

The name used to identify sphere shaped bacteria is coccus (plural cocci). Cocci have, obviously, spherical symmetry. Any plane down the center, in any direction, will result in mirror image halves.

These bacteria are called spirillum, because they are spiral shaped.

Cocci, bacilli, and spirilli are the three most common shapes of bacteria. Look at these pictures and see if you can classify the bacteria by shape:

Bacteria can also be classified by how they cluster together. If bacteria line up together in a long string, we use the prefix “strepto” in front of the shape. So, streptococcus bacteria are spherical and tend to line up end to end like this:

If the bacteria don’t form lines but instead clump together in clusters like grapes, we use the prefix “staphylo“. Staphylococci, therefore, look like this:

What would we call a cluster of rod-shaped bacteria then?

How about a long line of rod-shaped bacteria?

Email me your answers and I’ll let you know if you are right :o)

One more last word before we look up close and personal at a typical bacteria: nutrition. We know that all living things must either make their own food or obtain food from an outside source. How do bacteria get the food they need to power their bodies? Well, some bacteria are autotrophic and some are heterotrophic. Do you remember what these words mean? Autotrophs make their own food. Some bacteria make their own food by photosynthesis, just like plants do. Heterotrophs cannot make their own food. Heterotrophic bacteria usually obtain their nutrients by decomposing, or breaking down, some other organism. We call such heterotrophs decomposers. Organisms like this, that feed on dead or decaying organic matter, are called saprophytes. Another type of heterotrophic bacteria is parasitic bacteria, which takes its nutrition from a living organism and harms the organism in the process.

Okay, ready to look inside? Print off a copy of this diagram and we’ll see exactly what makes up a typical prokaryote. CLICK HERE for the instructions and complete the coloring project for homework: