The Five Kingdoms and Classifying Organisms Study Guide (page 2)
Life began as very simple molecules that were bound by membranes. Eventually, these membrane-bound molecules were assembled into more complex structures we call cells. These cells evolved into many forms and even became multicelled collections, leading to organisms such as ourselves. All these organisms adapted to their environment and have characteristics that distinguish them from each other. Scientists have developed systems to organize and classify all of Earth's organisms.
Life first appeared on Earth as very simple, very tiny microorganisms. These creatures were mostly groups of organic molecules surrounded by a membrane. However, they could feed themselves in some fashion and were able to grow and reproduce. Gradually, over time and through the process of evolution, organisms assumed new forms. Eventually, life on Earth developed into many diverse forms and formed complex relationships. We have been able to organize life into five large groupings called Kingdoms. Each Kingdom contains organisms that share significant characteristics that distinguish them from organisms in the other Kingdoms. The five Kingdoms are Animals, Plants, Fungi, Protists, and Bacteria.
The Animal Kingdom
The organisms classified into this Kingdom are multicellular and, because they do not have chlorophyll, are unable to photosynthesize. We call them heterotrophs, meaning "eater of others," because they must eat preexisting organic matter (either plants or other animals) to sustain themselves. Animals have tissues that are more complexly constructed than plants and one-celled organisms. Animals also possess nervous tissue, which has reached high stages of development into nervous systems and brains. Animals are able to move from place to place (locomote) using their muscular systems. We usually divide the Animal Kingdom into two large groups, the vertebrates (animals with backbones) and the invertebrates (animals without backbones).
The Plant Kingdom
Plants are multicellular organisms that use chlorophyll in specialized cellular structures called chloroplasts to capture sunlight energy and convert it into organic matter. We refer to plants as autotrophs (self-feeders). Also included in the Plant Kingdom are algae that are not multicellular, but are cells with a nucleus (unlike bacteria).
Besides the algae, most plants are divided into one of two groups, the nonvascular plants (such as mosses) and the vascular plants (such as most crops, trees, and flowering plants). Vascular plants have specialized tissue that allows them to transport water and nutrients from their roots to their leaves and back again, even when the plant is several hundred feet tall. Nonvascular plants cannot do this and remain very small in size. Vascular plants are able to inhabit moist as well as dry environments, whereas nonvascular plants are mostly found in moist, marshy areas because they have no vascular tissue to transport water.
The Fungi Kingdom
Organisms in this Kingdom share some similarities with plants yet maintain other characteristics that make them more animal-like. They lack chlorophyll and cannot perform photosynthesis, so they don't produce their own food and are called heterotrophs. However, they reproduce by spores like plants do. They also resemble plants in appearance. The most common representative organisms in this Kingdom are mushrooms, yeasts, and molds. Fungi are very common and are a major benefit to other organisms, including humans. The bodies of fungi are made of filaments called hyphae. In large fungi, the hyphae interconnect to form tissue called mycelium. The largest organism in the world is believed to be a soil fungus whose mycelium tissue extends for many acres.
The Protist Kingdom
This Kingdom includes single-celled organisms that contain a nucleus as part of their structure. They are a relatively simple cell, but still contain many structures and perform many functions. This Kingdom includes organisms such as paramecium, euglena, amoeba, and slime molds. They often move around using cilia or flagellums.
The Moneran Kingdom
This Kingdom contains bacteria. All these organisms are single celled and do not contain a nucleus. They have only one chromosome for carrying genetic information, although sometimes they also transmit genetic information using small structures called plasmids. They also use flagella to move, like the protists, but their flagella has a different and simpler structure than the protists. They usually reproduce asexually. The bacteria E. coli (Escherichia coli) is a member of this Kingdom.
Levels of Classification
A grouping as large as a Kingdom is not very specific and contains organisms defined by broad characteristics. Other levels of classification become gradually more specific until we define an actual specific organism. To classify organisms, we generally start out by grouping them into the appropriate Kingdom. Within each Kingdom, we further subdivide organisms into other groupings. As an example, let's take the wolf:
|Phylum:||Chordates (This means the wolf had a notochord that developed into its backbone.)|
|Class:||Mammals (This means the wolf has hair, bears live young, and nurses them with mammary glands.)|
|Order:||Carnivores (This means the wolf is a meat eater.)|
|Family:||Canids (This means the wolf has nonretractable claws, a long muzzle, and separate toes.)|
|Genus:||Canis (This means the wolf is a member of the dog family.)|
|Species:||lupus (This refers to a particular type of wolf known as the European wolf.)|
The previous categories form the most common scheme for classifying organisms, although other groupings and other categories are often used. The reason for developing a classifying system is so that we have consistency in how we refer to an organism. If we didn't have this system, then the European wolf described previously would be called wolf in English, lobo in Spanish, and loup in French. This leads to confusion and a loss of scientific accuracy.
The system illustrated here is based on a system developed by Carlos Linneaus. It is called binomial nomenclature because in this system, any organism can be positively identified by two Latin words. The other words used previously illustrate where the named organism fits into the whole scheme, but it is only the last two, the Genus and species words, that specifically name an organism. The Genus name is always capitalized and written in italics, whereas the species name is written lowercase but also in italics. Thus, the European wolf is Canis lupus, Canis familiaris is the common dog, Felis tigrina is a tiger, Felis domesticus is a common cat, and humans are Homo sapiens.
|How to Remember the Classification Scheme
Here is an easy way to remember the terms used in this classification scheme:
Kings Play Cards On Friday, Generally Speaking.
If you take the first letter of each word in the sentence and apply it to the proper term in the classification scheme, you will get the following:
Kingdom, Phylum, Class, Order, Family, Genus, Species
Biologists classify organisms based on shared characteristics among groups. The largest level of groupings is the Kingdoms, which consist of Animal, Plant, Fungi, Protist, and Moneran. The Kingdoms are further subdivided into Phylum, Class, Order, Family, Genus, and species. The Genus and species designations form a two-name system, called binomial nomenclature, that specifically identifies a particular organism (for example, humans are designated Homo sapiens).
Practice problems of this concept can be found at: The Five Kingdoms and Classifying Organisms Practice Questions