The Six Kingdoms
On Earth, there have been more than two million species successfully identified, with more than eight million estimated to be on this planet. Currently, these organisms are organized into six different kingdoms. 

Each kingdom contains organisms with similar characteristics. The six kingdoms include: Bacteria, Archaea, Protists, Fungi, Plants, and Animals. We will explore the unique characteristics and importance of each kingdom within Earth's ecosystems in this lesson.

Bacteria

Did you know that billions of tiny organisms too small to be seen surround you? These organisms, called bacteria, even live inside your body. Bacteria live in almost every habitat on Earth, including the air, glaciers, the ocean floor, and soil. A teaspoon of 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 that do not have a nucleus or other membrane-bound organelles. A typical bacterium consists of a jelly material called cytoplasm and genetic material surrounded by a cell membrane and a cell wall. The cell wall contains peptidoglycans, which are molecular  chains of sugar. The cytoplasm also contains ribosomes, which are structures that make proteins in the cell. Most bacteria have genetic material that is one coiled, circular
Package.

All bacteria reproduce asexually, which is when only one parent organism or part of that organism produces a new organism. Some types of bacteria are motile, meaning they can move with the use of a structure, called a flagellum, to propel them forward. Some bacteria, however, cannot move at all and lack any
propulsive structure. They can be either autotrophic (produce their own food) or 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 cause diseases. While some bacteria are harmful, most are beneficial. In fact, many organisms and ecosystems depend on bacteria to survive.

Digestion
In animals, bacteria are required to help break down food. One type of bacteria lives in your 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 substances would take centuries to change form, contaminating the surrounding soils and water. For example, uranium is converted into a different form with bacteria.

Decomposition
The breaking down of dead organisms and organic waste is an important process in nature. When a tree dies, bacteria and other decomposing organisms feed on the dead organic matter. As decomposers break down the tree, they release molecules such as carbon and 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 and cannot be absorbed by the plant without the use 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 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 currently one of the smallest kingdoms with just under 400 named species. 

Characteristics of Archaea
Archaea (singular, archaean) are like bacteria and share many characteristics. This includes having a cell wall, non-membrane-bound organelles, and circular genetic material. However, there are some important differences between archaea and bacteria. The ribosomes 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, with a 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 from inorganic compounds such as sulfur and ammonia. Given this unique ability to produce energy from inorganic compounds, scientists are studying them 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, such as a hot springs pool or a thermal vent under the ocean. Others can live in the extreme cold of the Arctic.

Protists
Most of the time, it is not difficult to identify plants from animals, and vice versa. Some organisms are easier to identify, such as a tree or polar bear, while other organisms, such as a protist, are not as easy to classify. A protist is a unicellular, multicellular, or colonial eukaryote whose cell walls may contain cellulose; can be plantlike, animal-like, or funguslike. Cellulose is a protein that makes up the structure of the plant's cell wall. Colonial means they can exist in colonies or large groups.

Characteristics of Protists
Protists are a unique and diverse classification of organisms. Typically, a protist is any eukaryote that cannot be classified as a plant, an animal, or a fungus. However, protists might look and act very much like these other types of organisms. Scientists classify protists as plantlike, funguslike, or animal-like based on which group they most resemble.

Plantlike Protists
You might have seen green or red seaweed at the beach or in an aquarium. These seaweeds are algae (AL jee; singular, alga), one type of plantlike protist. Algae are plantlike protists that produce food through photosynthesis using light energy and carbon dioxide. 

Most plantiike protists, however, are much smaller than multicellular algae. You cannot see most algae without a microscope. Dinoflagellates, euglena, and diatoms are other types of plantlike protists that require a microscope to view.

Funguslike Protists
In addition to plantlike and animal-like protists, there are funguslike protists. These are also called molds. Molds feed on decaying organic matter through absorption. These protists share many characteristics with fungi such as reproducing with spores. However, because of their differences from fungi, they are
classified as protists. Examples of funguslike protists include slime mold and water molds.

Animal-like Protists
Some protists are like plants, but others are more like animals. Protozoans are protists that resemble a tiny animal. Animal-like protists share several characteristics. They do not have chloroplasts or make their own food. Protozoans are usually microscopic, and all are unicellular eukaryotes. Most protozoans live in wet environments, such as ponds or lakes. Examples include amoebas, ciliates, flagellates, and sporozoans.

Importance of Protists 

Given the wide diversity of protists, they have many very important roles in ecosystems throughout the world. Plantiike, funguslike, and animal-ike protists have important roles in different ecosystems. 

Plantlike Protists
Did you know that you regularly use materials that contain algae or plantlike protists? You might be eating algae if you snack on ice cream, marshmallows, or pudding. Algae also provide food and shelter for animals and animal-like protists. It makes up thick groups of tall brown algae, called kelp forests. Sea otters and seals come to the kelp forests to eat smaller animals. Plantlike protists form the energy base of most freshwater and marine food chains. Without them, other organisms would not be able to get the energy they need to survive in these ecosystems.

Animal-like Protists
Imagine living in a world without decomposers. Plant material and dead animals would build up until the surface of Earth became covered. Many protozoans are beneficial to an environment because they break down dead plant and animal matter. This is important for nutrient cycling, which is an important process in all ecosystems. 

Funguslike Protists
Funguslike protists play a valuable role in the ecosystem. They break down dead plant and animal matter, making the nutrients from these dead organisms available for living organisms. While some slime molds and water molds are beneficial, many others can be very harmful. Many funguslike protists attack and consume living plants.

Fungi

What would you guess is the world’s largest organism? A fungus in Oregon is the largest organism ever measured by scientists. It stretches almost 9 km?. Fungi are a unicellular or multicelluar organism that absorbs nutrients from organic materials in its environment.  They are also eukaryotes. Scientists estimate more than 1.5 million species of fungi exist in the world, with just over 14,000 named species.

Characteristics of Fungi
Fungi differ from the other kingdoms in their characteristics. Most fungi are multicellular, but they can also be unicellular, like yeast. Some fungi form unique structures. This includes parts like the hyphae and mycelium. Hyphae are long, threadilike structures that make up the body of fungi and form an underground
structure that absorbs minerals and water. An underground network of hyphae is called the mycelium. The fruiting body of the mushroom, the part aboveground, is made of hyphae.
 

Fungi are heterotrophs, meaning they cannot make their own food. They obtain their nutrients from living organisms and dissolve their food by releasing chemicals that decompose organic matter. Then they absorb the nutrients.

Reproduction

Although fungi can reproduce sexually or asexually, almost all reproduce asexually by producing spores. Spores are small reproductive cells with a strong, protective outer covering. The spores can grow into new individuals. Classified by their reproductive structures, scientists currently recognize four groups: club fungi, sac fungi, zygote fungi,  and imperfect fungi. 

Importance of Fungi
Fungi have many applications in human society. They are used to make carbonated drinks, cheese, and bread. Some fungi are used as a meat substitute because they are high in protein and low in cholesterol. Other fungi are used to make antibiotics which fight bacterial infections. Fungi are essential for many processes in nature. They have roles as decomposers, plant helpers, and can impact the health of other organisms, including humans.

Decomposers
Fungi are an important part of the environment because they break down dead plant and animal matter. Fungi also help break down pollution, including pesticides, in soil. Living things need nutrients. The nutrients available in the soil would eventually be used up if they were not replaced by decomposing plant and animal matter. Fungi help put these nutrients back into the soil for plants to use.

Health and Medicine
For health reasons and medicinal uses, fungi can be both harmful and helpful. A small number of people die every year after eating poisonous mushrooms or spoiled food containing harmful fungi. Some fungi cause allergies, pneumonia, and rashes. Fungi are helpful because they can be used to make important medicines. Antibiotics are among the valuable medications made from fungi.

Plant Helpers
Many types of fungi and plants grow together, benefiting each other. Fungi take in minerals and water through the hyphae. The roots of the plants and the hyphae of the fungi weave together to form a structure called mycorrhiza (mi kuh Rl zuh; plural, micorthizae). 

As fungi break down decaying matter in the soil, nutrients are made available to the plants. Fungi help to increase water absorption by increasing the surface area on the roots of the plants. The plants benefit by receiving more nutrients and water. The fungi benefit and continue to grow by using sugars produced by the plants. This is an example of a symbiotic relationship.

Plants

Plants are an incredibly diverse group with over 350,000 described species. Historically, the plant kingdom used to contain all living species that were not algae, including protists and fungi. Now it is divided into its own kingdom. Plants are the foundation for all ecosystems. Many organisms would not be able to obtain energy or breathe the gases in the atmosphere without them.

Characteristics of Plants

Plants are easier to characterize than other kingdoms. All members of the plant kingdom have similar characteristics. Plants are made of eukaryotic cells that contain chloroplasts, a cell wall, and a central vacuole. Chloroplasts convert light energy to chemical energy. The cell wall provides support and protection. Plants are producers that make their own sugar. They are Multicellular.

Plants are grouped into two main categories—non-vascular and vascular plants. Nonvascular plants lack any tissue that transports nutrients and water and are considered the earliest living plants. Vascular plants have the tissues to transport nutrients and water and have true leaves, stems, and roots. A tree and a tulip are examples of vascular Plants.

Importance of Plants

Plants provide energy, habitat, and resources for different organisms. They are photosynthetic, which means they are producers. All other organisms rely on producers, either directly or indirectly, for sources of food. As a photosynthetic organism, plants capture carbon from the atmosphere and release oxygen, which builds an atmosphere that other organisms can breathe. 

Plants also have a wide variety of adaptations which help them live in difficult environments, like dry deserts. The presence of plants in these environments creates a strong foundation for each ecosystem. The science of how these adaptations work is also of interest to scientists in developing new technology.

Animals
As humans, we are a part of the animal kingdom, and it is probably the one you are most familiar with. Although animals have many traits that make them unique, all animals have certain characteristics in common. This is the most diverse kingdom with the greatest number of species documented so far.

Characteristics of Animals
Members of the animal kingdom have the following characteristics. They are multicellular eukaryotes with animal cells. They do not have cell walls or chloroplasts. Animals have a protein, called collagen (KAHL uh juhn), that surrounds the cells and helps them keep their shape. Animals get energy for life processes by eating other organisms. Animals digest their food. Most animals reproduce sexually and are capable of movement at some point in their life cycle.