CELL THEORY In biology, cell theory 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, 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. 1839. This is usually credited to Matthias Schleiden and Schleiden and Theodor Schwann. Schwann. However, many other scientists like Rudolf Virchow contributed 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 Cell Theory states:
All living organisms are composed of cells. They may be unicellular or multicellular.
The cell is the basic unit of life.
Cells arise from pre-existing cells. (They are not derived from spontaneous generation.)
The modern version of the Cell Theory includes the ideas that:
Energy flow occurs within cells.
Heredity information (DNA) is passed on from cell to cell.
All cells have the same basic chemical composition.
The generally accepted parts of modern cell theory include:
All known living things are made up of one or more cells.
All living cells arise from pre-existing cells by division.
The cell is the fundamental unit of structure and function in all living organisms.
The activity of an organism depends on the total activity of independent cells.
Energy flow (metabolism and biochemistry) occurs within cells.
Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm.
All cells are basically the same in c hemical composition in organisms of similar species.
In addition to the cell theory, the gene theory, evolution, homeostasis, and the laws of thermodynamics form the basic principles that are the foundation for the study of life.
CELL THEORY Credit for developing cell theory is usually given to two scientists: Theodor Schwann and Matthias Jakob Schleiden. While Rudolf Virchow contributed to the theory, he is not as credited for his attributions toward it. In 1839, Schleiden suggested that every structural part of a plant was made up of cells or the result of cells. He also suggested that cells were made by a crystallization process either within other cells or from the outside. However, this was not an original idea of Schleiden. He claimed this theory as his own, though Barthelemy Dumortier had stated it years before him. This crystallization process is no longer accepted with modern cell theory. In 1839, Theodor Schwann states that along with
plants, animals are composed of cells or the product of cells in their structures. This was a major advancement in the field of biology since little was known about animal structure up to this point compared to plants. From these conclusions about plants and animals, two of the three tenets of cell theory were postulated. 1.
All living organisms are composed of one or more cells
2.
The cell is the most basic unit of life
Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. In 1855, Rudolf Virchow added the third tenet to cell theory. In Latin, this tenet states Omnis cellula e cellula. This translated to: 3.
All cells arise only from pre-existing cells
However, the idea that all cells come from pre-existing cells had in fact already been proposed by Robert Remak; it has been suggested that Virchow plagiarized Remak and did not give him credit. Remak published observations in 1852 on cell division, claiming Schleiden and Schawnn were incorrect about generation schemes. He instead said that binary fission, which was first introduced by Dumortier, was how reproduction of new animal cells were made. Once this tenet was added, the classical cell theory was complete.
CELL BASICS All living organisms in the kingdoms of life are composed of and depend on cells to function normally. Not all cells however are alike. There are two primary types of cells: eukaryotic and prokaryotic cells. Examples of eukaryotic cells include animal cells, plant cells, and fungal cells. Prokaryotic cells include bacter ia and archaeans. Cells contain organelles, or tiny cellular structures, that carry out specific functions necessary for normal cellular operation. Cells also contain DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), the genetic information necessary for directing cellular activities.
TYPES OF CELLS Cells can be subdivided into the following subcategories: 1.
Prokaryotes: Prokaryotes are relatively small cells surrounded by the plasma membrane, with a characteristic cell wall that may differ in composition depending on the particular organism.[22] Prokaryotes lack a nucleus (although they do have circular or linear DNA) and other membrane-bound organelles (though they do contain ribosomes). The protoplasm of a prokaryote contains the chromosomal region that appears as fibrous deposits under the microscope, and the cyt oplasm.[22] Bacteria and Archaea are the two domains of prokaryotes.
2.
Eukaryotes: Eukaryotic cells are also surrounded by the plasma membrane, but on the other hand, they have distinct nuclei bound by a nuclear membrane or envelope. Eukaryotic cells also contain membrane-bound organelles, such as (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles).[23] In addition, they possess organized chromosomes which store genetic material.[citation needed]
Animals have evolved a greater diversity of cell types in a multicellular body (100 –150 different cell types), compared with 10 –20 in plants, fungi, and protoctista.
CELL REPRODUCTION Eukaryotic cells grow and reproduce through a complex sequence of events called the cell cycle. At the end of the cycle, cells will divide either through the processes of mitosis or meiosis. Somatic cells replicate through mitosis and sex cells reproduce via meiosis. Prokaryotic cells reproduce commonly through a type of asexual reproduction called binary fission. Higher organisms are also capable of asexual reproduction. Plants, algae, and fungi reproduce through the formation of reproductive cells called spores. Animal organisms can reproduce asexually through processes such as budding, fragmentation, regeneration, and parthenogenesis.
CELL PROCESSES - CELLULAR RESPIRATION AND PHOTOSYNTHESIS Cells perform a number of important processes that are necessary for the survival of an organism. Cells undergo the complex process of cellular respiration in order to obtain energy stored in the nutrients consumed. Photosynthetic organisms including plants, algae, and c yanobacteria are capable of photosynthesis. In photosynthesis, light energy from the sun is converted to glucose. Glucose is the energy source used by photosynthetic organisms and other organisms that consume photosynthetic organisms.
CELL PROCESSES - ENDOCYTOSIS AND EXOCYTOSIS Cells also perform the active transport processes of endocytosis and exocytosis. Endocytosis is the process of internalizing and digesting substances, such as seen with macrophages and bacteria. The digested substances are expelled through exocytosis. These processes also allow for molecule transportation between c ells.
CELL PROCESSES - CELL MIGRATION Cell migration is a process that is vital for the development of tissues and organs. Cell movement is also required for mitosis and cytokinesis to occur. Cell migration is made possible by interactions between motor enzymes and cytoskeleton microtubules.
CELL PROCESSES - DNA REPLICATION AND PROTEIN SYNTHESIS The cell process of DNA replication is an important function that is needed for several processes including chromosome synthesis and cell division to occur. DNA transcription and RNA translation make the process of protein synthesis possible.
