|Levels of organization
||Matter in living beings is organized in a series of levels of increasing complexity, ranging from the atomic level to the multicellular level with tissues and organs. Only plants and animals reach the highest one, whereas bacteria stay at the unicellular level.
||The most abundant chemical elements in a livig being, which are not much the same ones that you can find in a rock. The top six are C, H, O, N, P, S, and they're called the primary bioelements.
||The most abundant types of molecules in living beings are always the same ones, no matter if it is a bacterium or a human. They may be organic (with a skeleton of carbon atoms: carbohydrates, lipids, proteins, nucleic acids) or inorganic (without it: water, mineral salts).
||The basic unit of Life. If something is not made up of cells, then it is not a living being. Cells can reproduce and interact with their environment (exchanginng matter and energy, and being able to notice its features). All cells have a plasma membrane, some organelles and genetic material.
|Prokaryotic / Eukaryotic
||Cells without a real nucleus (no nuclear membrane) are the first type. Cells with a real nucleus (genetic material enclosed in a nuclear membrane) are the second type. Bacteria and Archaea are prokayotes; Algae, Protozoa, Fungi, Plants and Animals are eukaryotes.
||In multicellular beings there may be different types of cells, each type being specialized in an specific function, and having the specific shape that allows them to fulfill that function the best. Each of those types is called a cellular tissue; examples are the vascular tissue (plants) or the blood tissue (animals). One tissue may have several subtypes of cells (e.g. white blood cells and red blood cells).
|Organs / Organ Systems
||There are some tasks in a multicellular being that must be achieved by cells of different kinds working together (such as pumping blood throughout the human body). In this case, cells of different tissues gather and make up an organ (epithelial, connective, muscle and adipose cells make up the heart). Several organs working together in a common general task make up an organ system (the heart and the blood vessels make up the circulatory system).
|Autotrophs / Heterotrophs
||Or Producers and Consumers. The former don't feed off other living beings: they transform inorganic substances to produce the organic substances they need; plants and algae are autotrophs. The latter need to feed on other beings and then transform the organic substances they have eaten into their own organic substances (i.e.: your proteins come partly from the proteins in that beef-steak you ate yesterday); animals, fungi and protozoa are heterotrophs.
Differences between Prokaryotic and Eukaryotic Cells
|Size (diameter)||1-10 µm||10-100 µm|
|Number of organelles||Few||Many|
|Occurrence||Bacteria||Protozoa, Algae, Fungi, Plants, Animals|
The Five Kingdoms
This is not the most modern way of classification of living beings, but still proves to be quite useful to understand and organise the huge diversity of the living beings:
| ||Groups of organisms||Type of cells||Organization||Nutrition|
|Monera||Bacteria and archaea||Prokaryotic||Unicellular||Both|
| ||Algae||Eukaryotic||Unicellular to multicellular||Autotrophic|
|Fungi||Yeasts, moulds, mushrooms||Eukaryotic||Unicellular to multicellular||Heterotrophic|
|Plant||Mosses, ferns, flowering plants||Eukaryotic||Multicellular||Autotrophic|