DIVERSITY OF LIVING THINGS INTRODUCTION

Scientists have found and described approximately 1.75 million species on Earth. Plus, new species are being discovered every day. From tiny bacteria to yeasts to starfish to blue whales, life's diversity is truly impressive! With such a diversity of life on Earth, how does one go about making sense of it all?

One way to make sense of it is by classification. Scientists put similar species into groups so that those millions of species do not seem so overwhelming. People rely on their knowledge of classification to understand what different species are like. You may have done this without even thinking about it! For instance, let’s say that a friend of yours tells you that he saw an egret last weekend. You have never heard of an egret before, but if he tells you that an egret is a type of bird, you should have some idea of what it is like.

Living things are divided into three groups based on their genetic similarity. The three groups are:

• Archaea: very primitive forms of bacteria.
• Eubacteria: More advanced forms of bacteria.
• Eukaryota: All life forms with eukaryotic cells including plants and animals

These three groups are called domains. The figure at the left shows the three domains of life. The distance between groups indicates how closely related they are. Groups that are close together, like plants and animals, are much more closely related than groups that are far apart, like plants and bacteria! Do you see how the two types of bacteria, Archaea and Eubacteria, are about as similar to one another as they are to animals? Recent studies have found that bacteria are far more diverse than anyone had suspected.

ARCHAEA BACTERIA

Archaea are microbes. Most live in extreme environments. These are called extremophyles. Other Archaea species are not extremophiles and live in ordinary temperatures and salinities. Some even live in your guts!

Some extremophile species love the heat! They like to live in boiling water, like the geysers of Yellowstone Park, and inside volcanoes. They like the heat so much that it has earned the nickname "thermophile", which means "loving heat", and it would probably freeze to death at ordinary room temperature. Other extremophile Archaea love to live in very salty, called hypersaline, environments. They are able to survive in these extreme places where other organisms cannot. These salt-loving Archaea are called halophyles.

Archaea was originally thought to be just like bacteria, but archaea is a much different and simpler form of life. It may also be the oldest form of life on Earth!

Archaea requires neither sunlight for photosynthesis as do plants, nor oxygen. Archaea absorbs CO₂, N₂, or H₂S and gives off methane gas as a waste product the same way humans breathe in oxygen and breathe out carbon dioxide.

Planets which contain an environment wherein archaea might survive include Venus, the past environment of Mars, Jupiter, Saturn, and Jupiter's moon Io.

Eubacteria

Eubacteria, also know as “true bacteria”, are microscopic prokaryotic cells.

Cyanobacteria, also called blue-green algae, are Eubacteria that have been living on our planet for over 3 billion years. Blue-green algae grow in the shallow parts of the ocean. Today it is only common in certain regions, but a few billion years ago, there was tons of it! Through photosynthesis, which produces oxygen, billions of tiny bacteria were able to add oxygen to Earth’s atmosphere. This allowed animals that breath oxygen to survive.

Some Eubacteria can cause health problems like strep throat and food poisoning. Bacteria such as E.coli and Salmonella are sometimes found in undercooked meat and eggs and can make people sick. Other bacteria are good to eat, such as those in yogurt.

People have found that some types of Eubacteria can be very useful. Some are used at wastewater treatment plants to help clean the water. Others are also used to make grapes into wine and milk into cheese.

this photo is of the bacteria that gives you strep-throat infection

The Domain Eukaryota

What do trees, monkeys, plankton and mushrooms have in common? They are all members of the Eukaryota domain! You are a member of the Eukaryota domain too! Plants, animals, protists, and fungi, are all members of the domain.

These groups might seem pretty different, and they are, but they all have a few key aspects in common including their unique cells that are called eukaryotic. All members of the domain Euraryota have eukaryotic cells. And it is the only domain whose members have this cell type. Eukaryotic cells contain a special part called a nucleus that contains genetic material within chromosomes.