Cell theory

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The Modern Cell Theory consists of three statements based on a large body of scientific research. The original work was done by Schleiden, Schwan, and Virchow.The cell is the fundamental unit of structure and function in living things. All living things are composed of cells. Cells come from preexisting cells. The CELL THEORY, or cell doctrine, states that all organisms are composed of similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden & Schwann and has remained as the foundation of modern biology. In 1838, Theodor Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann's lab to look at his slides. Schwann published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of acknowledgments of anyone else's contribution, including that of Schleiden (1838). He summarized his observations into three conclusions about cells The cell is the unit of structure, physiology, and organization in living things.

The cell retains a dual existence as a distinct entity and a building block in the 

construction of organisms. Cells form by free-cell formation. Cell theory says that all cells arise from previous cells. The problem is that even the simplest prokaryotic cells are amazingly complicated and finely structured organisms, and organization like that doesn't just pop up on its own. That means every new cell needs to be built by a previous cell. this can't be completely right because we know that life on earth had to start sometime in the past, and whatever the first cells were, they didn't come from previous cells. We now know that the building blocks of life were present in the oceans of the early earth, forming an organic mixture called the primordial soup. As time went on, the molecules of the primordial soup got more and more complex and they engaged in complex chemical reactions. In some of these reactions, big molecules like proteins and nucleic acids could actually copy themselves. Then, when the right kinds of self-copying molecules were trapped inside of the right kind of oil droplets, the first prokaryotic cells were formed! These first cells could reproduce themselves and were therefore subject to evolution by natural selection. They were also able to use the organic molecules floating around in the primordial soup as fuel and nutrients. To break down their fuel, they used anaerobic respiration. In biology, the cell is the basic structure of organisms. All cells come from pre existing 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.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. 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.