The cell is the basic unit of structure , function, and biology of all known organisms. The least unit of life is a cell. Cells are often referred to as "the building blocks of life" Cell study is termed cell biology, cell biology, or cytology.
Cells consist of cytoplasm containing many biomolecules such as proteins and nucleic acids within a membrane. Most plant and animal cells are visible only under a microscope, measuring between 1 and 100 micrometres. Organisms may be classified as single cells (such as bacteria) or multicells (including plants and animals). Most microorganisms are classified as unicellular organisms.
The number of cells in plants and animals varies from species to species, humans have been estimated to contain about 40 trillion (41013) cells somewhere. The human brain accounts for about 80 billion of these cells.
Cells consist of cytoplasm containing many biomolecules such as proteins and nucleic acids within a membrane. Most plant and animal cells are visible only under a microscope, measuring between 1 and 100 micrometres. Organisms may be classified as single cells (such as bacteria) or multicells (including plants and animals). Most microorganisms are classified as unicellular organisms.
The number of cells in plants and animals varies from species to species, humans have been estimated to contain about 40 trillion (41013) cells somewhere. The human brain accounts for about 80 billion of these cells.
Discovery of Cells
The first time a British scientist named Robert Hooke used the word cell to refer to those tiny units of life was in 1665. Hooke was one of the first scientists to microscope-study living things. His day's microscopes weren't very powerful but Hooke was still able to make a major discovery. When, beneath his microscope, he looked at a thin slice of cork, he was surprised to see what looked like a wafer. Hooke rendered the drawing for showing what he saw in the figure below. As you can see, there were many tiny units in the cork which Hooke called cells.
Soon after the discovery of cells in cork by Robert Hooke, Anton van Leeuwenhoek made further important discoveries using a microscope in Holland. Leeuwenhoek made his own lenses for a microscope, and he was so good at it that his microscope was stronger than other microscopes of his day. In fact the microscope of Leeuwenhoek was nearly as strong as modern light microscopes. Leeuwenhoek had been the first person to observe human cells and bacteria using his microscope.
Cell Theory
By the early 1800s the cells of several different species had been studied by scientists. These observations led two German scientists, named Theodor Schwann and Matthias Jakob Schleiden, to suggest that cells are all living things' basic building blocks. A German physician named Rudolf Virchow was studying cells under a microscope around 1850, when he saw them divide and form new cells. He realized that it is through division that living cells produce new cells. Based on that realization, Virchow suggested that living cells only originate from other living cells.
The ideas of all three scientists — Schwann, Schleiden, and Virchow — led to cell theory, which is one of the basic theories that unifies biology as a whole. Cell theory reads:
- All organisms are made of one or more cells.
- All the life functions of organisms occur within cells.
- All cells come from already existing cells.