cell strucure and function for human physiology
he cell (from Latin cella, meaning "small room"[1]) is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, and cells are often called the "building blocks of life". The study of cells is called cell biology.
Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids.[2] Organisms can be classified as unicellular (consisting of a single cell; including bacteria) or multicellular (including plants and animals).[3] While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (1012) cells.[4] Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometres.[5]
The cell was discovered by Robert Hooke in 1665, who named the biological units for their resemblance to cells inhabited by Christian monks in a monastery.[6][7] 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, that all cells come from preexisting cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.[8] Cells emerged on Earth at least 3.5 billion years ago.[9][10][11]
In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells, also known as cell biology. Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. Cell theory was eventually formulated in 1839. This is usually credited to Matthias Schleiden and Theodor Schwann. However, many other scientists like Rudolf Virchow contributed to the theory. Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.
The three tenets to the cell theory are as described below:
All living organisms are composed of one or more cells. (However, this is considered a controversy because non-cellular life such as viruses are disputed as a life form.[1] See Non-cellular life.)
The cell is the basic unit of structure and organization in organisms.
Cells arise from pre-existing cells.
The generally accepted parts of modern cell theory include:
All known living things are made up of one or more cells[16]
All living cells arise from pre-existing cells by division.
The cell is the fundamental unit of structure and function in all living organisms.[17]
The activity of an organism depends on the total activity of independent cells.[citation needed]
Energy flow (metabolism and biochemistry) occurs within cells.[citation needed]
Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm.[18]
All cells are basically the same in chemical composition in organisms of similar species
The modern version of the cell theory
The modern version of the cell theory includes the ideas that:
Energy flow occurs within cells.[19]
Heredity information (DNA) is passed on from cell to cell.[19]
All cells have the same basic chemical composition
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