#Every organism is made up of one or more than one cells.The cell is the basic structural, functional and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently, and are often called the "building blocks of life". The study of cells is called cell biology. Cells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as [http://images.wisegeek.com/amoeba-diagram.jpg unicellular] (consisting of a single cell; including most bacteria) or [http://4.bp.blogspot.com/-RgT6bWtW1MY/T8em8BNV4xI/AAAAAAAAAWE/7DSwOORg1bQ/s400/article-new_ehow_images_a08_5r_lo_kingdoms-contain-multicellular-organisms-800x800.jpg multicellular] (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain about 100 trillion cells. Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres. | #Every organism is made up of one or more than one cells.The cell is the basic structural, functional and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently, and are often called the "building blocks of life". The study of cells is called cell biology. Cells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as [http://images.wisegeek.com/amoeba-diagram.jpg unicellular] (consisting of a single cell; including most bacteria) or [http://4.bp.blogspot.com/-RgT6bWtW1MY/T8em8BNV4xI/AAAAAAAAAWE/7DSwOORg1bQ/s400/article-new_ehow_images_a08_5r_lo_kingdoms-contain-multicellular-organisms-800x800.jpg multicellular] (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain about 100 trillion cells. Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres. |