ⓘ Organisms - Organism, Unicellular organism, Multicellular organism, Model organism, Anaerobic organism, Microorganism ..


An organism is an individual living thing. It is easy to recognize a living thing, but not so easy to define it. Animals and plants are organisms, obviously. Organisms are a biotic, or living, part of the environment. Rocks and sunshine are parts of the non-living environment. Organisms usually have five basic needs to continue their metabolism. They need air, water, nutrient food, energy, and a place to live. However, not all living things need all these at the same time. Many organisms do not need access to air at all. A little thought is needed about viruses. There is no agreement as to ...

Unicellular organism

Unicellular organisms are organisms that have one cell. They are divided into two quite different types, from different classification kingdoms. Eukaryotes have a nucleus, and a more complex cell structure. The prokaryotes, bacteria and archaea, have cells with no nucleus and a simple cell structure. The differences between the prokaryota and eukaryota are significant. Eukaryotes possess a nucleus and various subcellular organs called organelles, and prokaryotes do not.

Multicellular organism

Multi-cellular organisms are organisms with more than one cell. This is the case for animals, plants and most fungi. In such organisms, cells are usually specialised. All the cells with the same function work together. Such a group of cells is then called a tissue. Multi-cellular organisms have a set of cells that specialize in reproduction. Reproduction in such organisms is usually sexual. The sex cells are either sperm or ovum also named "egg" cells. If they are sperm cells, the organism is male, if they are egg cells it is female. If both are present, the organism is a hermaphrodite.

Model organism

A model organism is a non-human species that is studied over many years, building up a lot of knowledge about it in order to understand fundamental biological phenomena. The hope is that discoveries made in the model will give insight into how other organisms work. In particular, model organisms are widely used in animal testing to explore potential causes and treatments for human disease when experimenting on humans would be impossible or less ethical. This strategy is made possible by the similarities of all living organisms. They are similar because of their common descent and the conse ...

Anaerobic organism

An anaerobic organism is any living thing that does not need oxygen for growth. Facultative anaerobes can use oxygen when it is present. Aerotolerant organisms can survive in the presence of oxygen, but they are anaerobic because they do not use oxygen as a terminal electron acceptor. Obligate anaerobes will die when exposed to atmospheric levels of oxygen. Microaerophiles are organisms that may use oxygen, but only at low concentrations low micromolar range; their growth is inhibited by normal oxygen concentrations approximately 200 micromolar. Nanaerobes are organisms that cannot grow in ...


A micro-organism or microbe is an organism which is microscopic, which means so small that people cannot see them with naked eye. The study of microorganisms is called microbiology. Micro-organisms include bacteria, fungi, archaea, protists and viruses, and are among the earliest known life forms. The first of these four types of micro-organisms may either be free-living or parasitic. Viruses can only be parasitic, since they always reproduce inside other living things. Most micro-organisms are unicellular organism with only one cell, but there are unicellular protists that are visible to ...

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