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Ragman
Junior Editor
A member of the Definitions.net vibrant community of passionate editors.
January 2015
9 years ago
Latest Entries: 3 total
| five kingdom 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. 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. Protists 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. Nutrien |
| back bone | In polymer science, the backbone chain or main chain of a polymer is the series of covalently bounded atoms that together create the continuous chain of the molecule. In polypeptides, the backbone consists of carbon and nitrogen atoms of the constituent amino acids. The backbone does not include the side chains |
| trilobites | Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago), and they flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian, all trilobite orders except Proetida died out. Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago. The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years. |
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