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Biology is the study of living things. It deals with what all living things can do, how they do it and why they do it. In biology, there is always a relationship between the structure of an organism, its function and its adaptation to its function or environment. An individual living thing, such as an animal or a plant, is called an organism. The term ‘living organism’ is usually used to describe something which displays all the characteristics of living things.

Characteristics of living things There are seven activities which make organisms different from non-living things:
1. Nutrition: Living things take in materials from their surroundings that they use for growth or to provide energy. Nutrition is the process by which organisms obtain energy and raw materials from nutrients such as proteins, carbohydrates and fats.
2. Respiration: Respiration is the release of energy from food substances in all living cells. Living things break down food within their cells to release energy.
3. Movement: All organisms are able to move. Some, including most animals, are able to move their whole body from place to place, and this is called locomotion. But even seemingly non-moving organisms, such as plants, are able to move parts of themselves. If you look at some living plant cells under a microscope, you may be able to see the tiny structures within each cell moving around.
4. Excretion: All living things excrete. As a result of the many chemical reactions occurring in cells, they have to get rid of waste products which might poison the cells. Excretion is defined as the removal of toxic materials, the waste products of metabolism and substances in excess from the body of an organism.
5. Growth: Growth is seen in all living things. It involves using food to produce new cells. The permanent increase in cell number and size is called growth.
6. Reproduction: All living organisms have the ability to produce offspring of the same kind.
7. Sensitivity: All living things are able to sense and respond to stimuli around them such as light, temperature, water, gravity and chemical substances. Learn these characteristics of living organisms. They form the basis of the study of Biology. Classification of living organisms Classification can be defined as grouping organisms according to their features similarities. The science of classifying organisms is called Taxonomy. All organisms in the living world are classified and named according to an international system of criteria. The rules of classification apply only to formal scientific names, not to common names. The groups are arranged from the largest group of organisms to the smallest with an example for classification of human:

§Domain: Eukaryote
§ Kingdom: Animalia
§ Phylum: Chordata
§ Class: Mammalian
§ Order: Primate
§ Family: Hominidae
§ Genus: Homo
§ Species: sapiens

The domain is the broadest category, while species is the most specific category available. About 1.8 million species have been given scientific names. Thousands more are added to the list every year.

Tropical forests and deep ocean areas very likely hold the highest number of still unknown species.

Domains: The domains are organized based on the difference between eukaryotes and prokaryotes. The three domains are as follows: § Archea (Archeabacteria): consists of archeabacteria, bacteria which live in extreme environments.
The kingdom Archaea belongs to this domain. § Eubacteria: consists of more typical bacteria found in everyday life. The kingdom Eubacteria belongs to this domain. § Eukaryote: encompasses most of the world's visible living things. The kingdoms Protista, Fungi, Plantae and Animalia fall under this category.

Source/Further Reading: http://www.deltauniv.edu.eg/Pharmacy/PDF/Mo7adarat/General%20biology/General%20Biology%20-%20Chapter%20I.pdf .

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