6/2/2023 0 Comments Free download cell wallCells emerged on Earth about 4 billion years ago. Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from pre-existing cells. The study of cells and how they work has led to many other studies in related areas of biology, including: discovery of DNA, cancer systems biology, aging and developmental biology.Ĭell biology is the study of cells, which were discovered by Robert Hooke in 1665, who named them for their resemblance to cells inhabited by Christian monks in a monastery. The brain accounts for around 80 billion of these cells. The number of cells in plants and animals varies from species to species it has been approximated that the human body contains an estimated 37 trillion (3.72×10 13) cells. Most unicellular organisms are classed as microorganisms. Organisms can be classified as unicellular (consisting of a single cell such as bacteria) or multicellular (including plants and animals). Electron microscopy gives a much higher resolution showing greatly detailed cell structure. Most plant and animal cells are only visible under a light microscope, with dimensions between 1 and 100 micrometres. Most cells are measured in micrometers due to their small size. Cells are capable of specialization and mobility within the cell. Ĭells can acquire specified function and carry out various tasks within the cell such as replication, DNA repair, protein synthesis, and motility. The term comes from the Latin word cellula meaning 'small room'. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients and metabolites. The cell is the basic structural and functional unit of life forms.
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