Five Kingdom Classification System
Once upon a time, all living things were lumped together into two kingdoms, namely plants and animals (at least, that's how I learned it). Animals included every living thing that moved, ate, and grew to a certain size and stopped growing. Plants included every living thing that did not move or eat and that continued to grow throughout life. It became very difficult to group some living things into one or the other, so early in the past century the two kingdoms were expanded into five kingdoms: Protista (the single-celled eukaryotes); Fungi (fungus and related organisms); Plantae (the plants); Animalia (the animals); Monera (the prokaryotes). Many biologists now recognize six distinct kingdoms, dividing Monera into the Eubacteria and Archeobacteria.
All I can say is that the sytem holds true for this week, at least. It might even hold up for a century or two. Accepted systems of classification have changed at a far faster pace than the species have taken to evolve, that's for certain.
Kingdoms are divided into categories called phyla, each phylum is divided into classes, each class into orders, each order into families, each family into genera, and each genus into species. A species represents one type of organism, such as dog, tiger shark, Ameoba proteus (the common amoeba), Homo sapiens (us), or Acer palmatum (Japanese maple). Note that species names should be underlined or written in italics.
Classifying larger organisms into kingdoms is usually easy, but in a microenvironment it can be tricky. If you have had a little biology, a good exercise is to describe individual living things, and to try to classify them as to kingdom.
Monera (includes Eubacteria and Archeobacteria)Individuals are single-celled, may or may not move, have a cell wall, have no chloroplasts or other organelles, and have no nucleus. Monera are usually very tiny, although one type, namely the blue-green bacteria, look like algae. They are filamentous and quite long, green, but have no visible structure inside the cells. No visible feeding mechanism. They absorb nutrients through the cell wall or produce their own by photosynthesis.
ProtistaProtists are single-celled and usually move by cilia, flagella, or by amoeboid mechanisms. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus and may have chloroplasts, so some will be green and others won't be. They are small, although many are big enough to be recognized in a dissecting microscope or even with a magnifying glass. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both.
FungiFungi are multicellular,with a cell wall, organelles including a nucleus, but no chloroplasts. They have no mechanisms for locomotion. Fungi range in size from microscopic to very large ( such as mushrooms). Nutrients are acquired by absorption. For the most part, fungi acquire nutrients from decaying material.
PlantaePlants are multicellular and most don't move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present, and cell walls are present. Nutrients are acquired by photosynthesis (they all require sunlight).
Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion.
A "mini-key" to the five kingdomsSuppose you see something in freshwater that certainly appears to be living. How can you begin to determine what it is? Here is a key (not quite perfect) that you might use to help determine the kingdom to which it belongs.
- 1. Is it green or does it have green parts?
- Yes - go to 2
- No - go to 3
- 2. Could be a plant or a protist, or blue-green bacteria. Make sure that the green is really part of the organism, though. An animal might have eaten something green, for example.
- Single-celled? go to 6
- Multicellular? Plantae. Look for cell walls, internal structure. In the compound microscope you might be able to see chloroplasts.
- 3. Could be a moneran (bacteria), protist, fungus, or animal.
- Single-celled - go to 4
- Multicellular (Look for complex or branching structure, appendages) - go to 5
- 4. Could be a moneran or a protist. Can you see any detail inside the cell?
- Yes - Protista. You should be able to see at least a nucleus and/or contractile vacuole, and a definite shape. Movement should be present, using cilia, flagella, or amoeboid motion. Cilia or flagella may be difficult to see.
- No - Monera. Should be quite small. May be shaped like short dashes (rods), small dots (cocci), or curved or spiral shaped. The largest them that is commonly found in freshwater is called Spirillum volutans. It is spiral shaped, and can be nearly a millimeter long. Except for Spirillum, it is very difficult to see Monerans except in a compound microscope with special lighting.
- 5. Animalia or Fungi. Is it moving?
- Yes - Animalia. Movement can be by cilia, flagella, or complex, involving parts that contract. Structure should be complex. Feeding activity may be obvious.
- No - Fungus. Should be branched, colorless filaments. May have some kind of fruiting body (mushrooms are a fungus, don't forget). Usually attached to some piece of decaying matter - may form a fuzzy coating on or around an object. In water, some bacterial infections of fish and other animals may be mistaken for a fungus.
- 6. Most likely Protista. If it consists of long, unbranched greenish filaments with no apparent structure inside, it is blue-green bacteria (sometimes mistakenly called blue-green algae), a Moneran.
Remember, the more you observe the organism, the more sure you can be. Many living things have stages that make them resemble members of another kingdom.
All living things can be grouped into five categories. This is called the five kingdom proposal and was introduced by Robert Whittaker in 1968 as a way to categorise all organisms.
Living organisms are divided into five kingdoms:
- Unicellular and Microscopic.
- Non-membrane bound (no nuclear membrane, no ER, no mitochondia).
- Cell wall made of murein.
- Examples: Bacteria or Cyanobacteria (photosynthesising bacteria).
- Mainly small eukaryotic organisms.
- Many live in aquatic environments.
- This is usually the kingdom where organisms which aren’t animals, plants or fungi go.
- Examples: Algae, slime moulds and the malaria causing Plasmodium.
- Cell wall made of chitin.
- The members of this kingdom don’t possess photosynthetic pigments and are therefore heterotrophic.
- Examples: Mushroom, Mold, Puffball
- Cell wall made of cellulose.
- Members of the plantae group contain photosynthetic pigment and gain their energy through it and are therefore autotrophic.
- The members of this kingdom can be split into two groups, vertebrates and invertebrates. The diagram below shows the different subsections of the animalia
The vertebrate subsection of the animalia kingdom can be split again into five different sections:
|Kingdom||Number of Cells||Type of Cells||How they gain their energy?||Do they move?||Examples|
|Prokaryotae||Unicellular||Prokaryotic||Some Heterotrophic, Some Autotrophic||Some||Bacteria, Cyanobacteria|
|Protoctista||Mainly Unicellular||Eukaryotic||Some Heterotrophic, Some Autotrophic||Some||Amoeba|
|Fungi||Multicellular||Eukaryotic||Heterotrophic||Mainly not||Mushroom, Mold, Puffball|
|Plantae||Multicellular||Eukaryotic||Autotrophic||No||Trees, Flowering Plants|
|Animalia||Multicellular||Eukaryotic||Heterotrophic||Yes||Bird, Human, Cow|