Taxonomy

Early Organization

There have been many different ideas about how to organize, or classify, living things.

A Greek philosopher was one of the first people to classify organisms.

His name was Aristotle (384 - 322 BC)

Aristotle placed all organisms into 2 large groups: Plants & Animals.

  • He classified animals based on 3 criteria:

    • The presence of “red blood”

    • The animal’s environment

    • Shape & size of animal

  • He classified animals according to:

    • The plant’s structure

    • Size

    • Whether they were trees, shrubs, or herbs.

Taxonomy is the branch of biology that identifies, names, & classifies SPECIES based on their natural relationships. The study of taxonomy developed as scientists looked more closely at organisms.

  • For centuries, people have examined the similarities & differences among organisms.

  • They have done this to classify the organism into different groups.

The first taxonomic system was developed by Carolus Linnaeus, a Swedish physician & botanist in the 1700s.

  • He proposed a TWO-KINGDOM SYSTEM to classify organisms based on similar structures.

  • He named his kingdoms:

    • Animals

    • Vegetable

    • Mineral

  • Keep in mind that he considered mineral to be ‘non-life’.

***Linnaeus placed all organisms into 2 main groups called Kingdomes.

Over the next 200 years, people learned more about & discovered new organisms.


In 1969, american biologist Robert H. Whittaker proposed a FIVE-KINGDOM SYSTEM for classifying organisms.

  • His system included the kingdom of:

    • Monera

    • Protists

    • Plants

    • Fungi

    • Animals

  • Keep in mind that we have a 6-kingdom system today! (Monera was eventually split into bacteria and archaea.)

  • Molecular analysis technology has changed taxonomy. Instead of just looking at the features of different organisms, scientists are able to look at genetic material. This helps to see more differences among organisms.

An American microbiologist, Carl Woese found differences in prokaryotes that split the Kingdom Monera into 2 kingdoms – the bacteria and the archaea.

***The 6-kingdom system has been used in taxonomy since the 1990s***

Modern Organization

The current classification method is called systematics.

***Systematics uses ALL THE EVIDENCE that is known about organisms to classify them.

  • This evidence includes an organism’s cell type, & habitat

  • It includes the way an organism obtains food & energy.

  • It includes the structure & function of the organism’s features & the common ancestry of organisms.

  • It also includes molecular analysis.

    • This is the study of genetic material within organisms.

***USing systematics, scientists identified 2 distinct groups in KINGDOM MONERA. They are BACTERIA & ARCHAEA.

  • This led to the development of another level of classification called DOMAINS. All organisms are now classified into 1 of 3 domains.

    • They are:

  1. Bacteria

  2. Archaea

  3. Eukarya

  • Then, they are classified into one of six kingdoms.

The Taxonomic Classification System

The modern taxonomic classification system has 8 levels.

  • It is arranged using hierarchical organization.

  • The DOMAIN level has the MOST DIFFERENCES in traits.

  • The SPECIES level has organisms with the MOST SIMILARITIES.

  • When an organism is discovered, it is classified into each taxonomic level by comparing the similarities & differences of its traits to other organisms.

***Organisms are grouped into 3 domains & 6 kingdoms based on:

  • Their cell type

  • Ability to make food

  • Number of cells that make up their bodies.

3 DOMAINS:

  • Bacteria

  • Archaea

  • Eubacteria

6 KINGDOMS:

  • Bacteria

  • Archaea

  • Protista

  • Plantae

  • Fungi

  • Animalia

8 Modern Systems

Domain

  • The highest level of the hierarchy of classification.

  • The domain is the taxonomic group of one or more kingdoms.

  • This is the broadest group.

  • It is the most complex with the largest species diversity.

  • The organisms in this group have the most differences in their traits in comparison to other levels.

Kingdom

  • The next level of classification is kingdom.

  • A kingdom is a taxonomic group of related phyla or divisions.

  • Classification is narrowed down to include organisms with certain traits.

Phylum

  • The next level is phylum

  • The phylum – singular phyla – is a taxonomic group of related classes.

Class

  • The next level is class

  • The class is a taxonomic group that contains one or more related orders.

Order

  • The next level of classification is order.

  • The order is the taxonomic group that contains related families.

Family

  • The next level of classification is family.

  • The family is a taxonomic group of similar, related genera.

Genus

  • The next level is genus.

  • The genus is a taxonomic group of similar, related species.

  • Genus is the first word – the first letter is capitalized – in the scientific name.

Species

  • The next & last level of classification is species.

  • A species is a group of organisms that have similar traits and are able to produce fertile offspring.

  • The second word in the scientific name, all lowercase.

Classification Tools

Suppose you go out into the forest. You see several trees. You want to learn more about them. But how do you figure out which trees you are observing? There are several tools that you can use to classify & identify organisms.

  • A dichotomous key is used to identify unknown organisms.

  • Phylogenetic trees, including cladograms are used to understand the evolutionary history of an organism.

  • These tools help us understand how organisms are similar or different.

Dichotomous Keys

A dichotomous key is a series of descriptions arranged in pairs.

***It leads the user to the identification of an unknown organism.

  • The chosen description leads to another pair of statements.

  • Or it leads to the identification of the organism.

  • Choices continue until the organism is identified.

Phylogenetic Trees

  • Recall that different organisms are grouped into different categories based on similarities or differences in their characteristics.

  • Scientists show these relationships using a phylogenetic tree. It is also called a phylogeny.

  • A phylogenetic tree is a branched diagram that shows the relationships among organisms.

    • It includes a common ancestor.

  • Parts of a phylogeny:

    • Learning to read a phylogenetic tree will allow you to understand how organisms are related to one another through evolutionary time.

    • The first step is learning the parts of the phylogenetic tree.

  • After learning the parts of the phylogenetic tree, you can observe how the branches of the tree relate.

  • Patterns of the branching indicate whether organisms are closely related or not.

  • For example, organisms that are separated by only one node, or common ancestor, are more closely related than those separated by several nodes.

👆 This is a cladogram.

  • A cladogram is a type of phylogenetic diagram.

  • It shows the relationships among organisms based on similar characteristics.

***A cladogram has a series of branches. Each branch follows a new characteristic or trait. Each trait is observed in all the species that come after it.

Kingdoms

There have been more than 2 million species identified & more than 8 million are estimated to be on this planet.

Currently, these organisms are organized into 6 different kingdoms. Each kingdom contains organisms with similar characteristics. The 6 kingdoms are:

  1. Bacteria

  2. Archaea

  3. Protists

  4. Fungi

  5. Plantae

  6. Animalia

Bacteria

Did you know that billions of tiny organisms too small to be seen surround you?

***These organisms are called bacteria.

They even live inside your body. Bacteria live in almost every habitat on Earth. This includes the air, glaciers, the ocean floor, & soil. A teaspoon os soil can contain between 100 million and 1 billion bacteria! There are almost 10,000 known species of bacteria with many more to be discovered.

Characteristics of Bacteria

Bacteria (singular, bacterium), are single-celled microorganisms.

***They are prokaryotes.

They do not have a nucleus or other membrane-bound organelles.

A typical bacterium consists of a jelly material called cytoplasm & genetic material surrounded by a cell membrane & a cell wall.

***The cell wall contains peptidoglycans. These are molecular chains of sugar. The cytoplasm also cains ribosomes. These are structures that make proteins in the cell. Most bacteria have genetic material that is one coiled, circular package.

All bacteria reproduce asexually.

That means only one parent organism or part of that organism produces a new organism.

Some types of bacteria are motile.

***This means they can move with the use of a structure called a FLAGELLUM. It helps people them forward. But some bacteria cannot move at all & lack any propulsive structure.

***They can be AUTOTROPHIC (produce their own food), or they can be HETEROTROPHIC (eat other organisms to survive).

Importance of Bacteria

When you hear about bacteria, you probably think about getting sick. However, only a fraction of all bacteria causes diseases. While some bacteria are harmful, most are beneficial. In fact, many organisms & ecosystems depend on bacteria to survive.

Digestion

In animals, bacteria are required to help break down food.

One type of bacteria lives in you intestine to prevent harmful bacteria from growing. Cows rely on bacteria to break down plant material in the stomach. Without it, they would not be able to break down cellulose found in the cell walls of grass.

*** Bacteria are commonly used to clean up areas that have been contaminated by metals, oils, or harmful plastics. Without using bacteria, the substance would take centuries to change form. They would contaminate the surrounding soils & water. For example, uranium is converted into a different form with bacteria.

Decomposition

The breaking down of dead organisms & organic waste is an important process in nature.

When a tree dies, bacteria & other decomposing organisms feed on the dead organic matter. As decomposers break down the tree, they release molecules such as carbon & phosphorus into the soil that other organisms can then take in and use for life processes.

Nitrogen Fixation

***Nitrogen is an important element that helps plants make protein.

Nitrogen is found in the atmosphere.

IT CANNOT BE ABSORBED BY THE PLANT WITHOUT THE HELP OF BACTERIA.

These special bacteria live on structures called nodules on the roots. Bacteria in the nodules can convert the nitrogen in the atmosphere to a form usable by the plant.

Archaea

Prokaryotes called archaea were once considered bacteria. This is because of their many similarities. However, they are not the same.

***These unique organisms are also known as extremophiles.

An extremophile is an organism that lives under extreme environmental conditions.

  • Kingdom Archaea is a small kingdom at just under 400 named species.

Characteristics of Archaea

Archaea are like bacteria. They share many characteristics. This includes having a cell wall, non-membrane-bound organelles & circular genetic material.

However, there are some important differences between archaea and bacteria.

  • Ribosomes (these make protein) of archaea more closely resemble the ribosomes of eukaryotes than those of bacteria.

  • Archaea are prokaryotes whose cell walls do not contain peptidoglycan.

*** Archaea can be motile using an appendage called an archaellum.

It rotates to move the organism forward. The appendage is like a flagellum found in a bacterium. However, it has different structural makeup.

Importance of Archaea

Archaea play an important role in ecosystems.

***They are one of a few types of organisms that can use energy form inorganic compounds such as sulfur & ammonia. Given this unique ability to produce energy from inorganic compounds, scientists are studying them. They hope to help engineer solutions to the world’s growing energy requirements.

Living in the Extremes

***Archaea are some of the only organisms that can survive in extreme environments where regular cells could not survive.

For example, some archaea live in hot temperatures. Two of those hot places are a hot springs pool or a thermal vent under the ocean. Others can live in the extreme cold of the Arctic.