Cell
From Wikipedia, a free encyclopedia written in simple English for easy reading.
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For other uses, see Cell (disambiguation).
In biology, the cell is the basic structure of organisms. All cells come from pre exsisting cells. The outside of the cell is a cell membrane. Inside some cells, some parts of the cell stay separate from other parts by membranes. These separate parts are called organelles (like small organs.) They have different functions in the cell (do different work.) Some of these are ribosomes, nucleus (where DNA is), and mitochondria.
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[edit] Kinds of cells
There are two basic kinds of cells: prokaryotic cells and eukaryotic cells. Prokaryotes are simple cells, also known as bacteria. Eukaryotes are less simple cells. All eukaryotic cells have a nucleus. Both kinds of cells have DNA. In the prokaryote it is not separated from the rest of the cell by a membrane. In the eukaryote DNA is separate from the rest of the cell.
All prokaryotic organisms are made of just one cell.
[edit] Kinds of prokaryotic organisms
The only kinds of prokaryotic organisms that survived to the present are bacteria. Prokaryotic organisms evolved before eukaryotic organisms, so at one point the world consisted of nothing but prokaryotic organisms. However, eukaryotic cells could become bigger, so prokaryotic cells were largely gotten rid of.
[edit] Kinds of eukaryotic organisms
There are two kinds of organisms: multicellular and unicellular. they are two things without nucleus
There are also 2 kinds of cells with no nucleus.
[edit] Unicellular
Unicellular organisms are made up of one cell. Examples of unicellular organisms are:
- Amoeba
- Paramecium
Unicellular organisms live without other cells to help them. So the cell does all things that it needs to live. Each cell:
- eats
- moves
- respires (uses oxygen to make sugar into energy)
- gets rid of waste
- reproduce (make more of itself)
- senses its environment
[edit] Multicellular
Multicellular organisms are made from many cells. They are complex organisms. This can be a small number of cells, or millions of cells. All plants and animals are multicellular organisms. The cells of a multicellular organism are not all the same. They have different shapes and sizes, and do different work in the organism. The cells are specialised. This means they do only some kinds of work. By themselves, they cannot do everything that the organism needs to live. They need other cells to do other work. They live together, but cannot live alone.
[edit] Cell history
Cells were discovered by Robert Hooke. He used a microscope to look at organisms in 1665. He named cells after the Latin word cella, meaning room. He did this because he thought cells looked like small rooms.
Three German biologists - Schleiden, Schwann and Virchov - figured out three rules about all cells:
- All living things are made of cells
- The cell is the basic unit of structure and function in all organisms.
- Every cell comes from another cell that lived before it.
These ideas still are the basic ideas of cell theory.
[edit] Cell reproduction
Eukaryotic cells reproduce differently than prokaryotic cells, but both go through the same general process. Most eukaryotic cells undergo mitosis, creating exact genetic copies of themselves. Exceptions to this rule are nerve cells, which never split, and sex cells, which go through a separate process called meiosis. Prokaryotic cells reproduce using binary fission, where the cell simply splits in half without the complex steps of mitosis.
