Abby+H.

** Cell theory ** refers to the idea that [|cells] are the basic unit of structure in every living thing. Development of this [|theory] during the mid 1600s was made possible by advances in [|microscopy]. This theory is one of the foundations of [|biology]. The theory says that new cells are formed from other existing cells, and that the cell is a fundamental unit of structure, function and organization in all living organisms. The cell was first discovered by [|Robert Hooke] in 1665. He examined very thin slices of cork and saw a multitude of tiny pores that he remarked looked like the walled compartments of a honeycomb. Hooke's description of these cells (which were actually non-living cell walls) was published in //[|Micrographia]//.[|[2]]. His cell observations gave no indication of the [|nucleus] and other [|organelles] found in most living cells. The first man to witness a live cell under a microscope was [|Antonie van Leeuwenhoek], who in 1674 described the [|algae] //[|Spirogyra]// and named the moving organisms animalcules, meaning "little animals".[|[3]]. Leeuwenhoek probably also saw [|bacteria] .[|[4]] Cell theory was in contrast to the [|vitalism] theories proposed before the discovery of cells. The idea that cells were separable into individual units was proposed by [|Ludolph Christian Treviranus][|[5]] and [|Johann Jacob Paul Moldenhawer][|[6]]. All of this finally led to [|Henri Dutrochet] formulating one of the fundamental tenets of modern cell theory by declaring that "The cell is the fundamental element of organization" .__ [7] __ The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things. The cell theory states: . 
 * Cell Theory**
 * 1) All living things are composed of one or more cells.
 * 2) Cells are the basic units of structure and function in living things.
 * 3) new cells are focused on other cells.



Photosynthesis

** Photosynthesis ** is a process that converts ** carbon dioxide  ** into ** organic compounds  ** especially ** sugars,  ** using the energy from sunlight. Photosynthesis occurs in ** plants **, ** algae , ** and many species of ** bacteria ** , but not in ** Archaea. ** Photosynthetic organisms are called ** photoautotrophs **, since it allows them to create their own food. In plants, algae, and ** cyanobacteria ** photosynthesis uses carbon dioxide and water, releasing ** oxygen ** as a waste product. Photosynthesis is vital for ** life on earth **. As well as maintaining the normal level of oxygen in the ** atmosphere, ** nearly all life either depends on directly as a source of energy, or indirectly as the ultimate source of the energy in their food, the amount of energy trapped by photosynthesis is immense, approximately 100 ** terawats : ** which is about six times larger than the ** power consumption of human civilization **. As well as energy, photosynthesis is also the source of carbon in all the organic compounds within organisms bodies. In all, photosynthetic organisms convert around 100,000,000,000 ** tonnes ** of carbon into ** biomass ** per year. Although photosynthesis can occur in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by ** proteins ** called ** photosynthetic reaction centers ** that contain ** chlorophylls **. In plants, these proteins are held inside ** organelles ** called ** chloroplasts **, while in bacteria they are embedded in the ** plasma brain **. Some of the light energy gathered by chlorophylls is stored in the form of ** adenosine triphosphate. ** The rest of the energy is used to remove **electrons** from A substance such as water. These electrons are then used in the reactions that turn Carbon Dioxide into organic compounds. In plants, these proteins are held inside ** organelles ** called ** chloroplasts, ** while in bacteria they are embedded in the ** Plasma Membrane **. Some of the light energy gathered by chlorophylls is stored in the form ** adenosine troposphere **. The rest of the energy is used to remove **electrons** from a substance such as water. These electrons are then used in the reactions that turn Carbon Dioxide into organic compounds. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis. Photosynthesis ** evolved ** early in the ** evolutionary history of life, ** when all forms of life on earth were ** microorganisms ** and the atmosphere had much more Carbon Dioxide. The first photosynthetic organisms probably evolved about ** 3,500 ** million years ago and used ** hydrogen ** and ** hydrogen sulfide ** as sources as electrons, other than water. ** Cyanobacteria ** appeared later, around ** 3,000 ** million years ago. This new atmosphere allowed the ** evolution of complex life ** such as ** protists. ** Eventually, no later than a billion years ago, one of these protists formed a ** symbiotic relationship ** with a cyanobacterium, producing the ancestor of the plants and ** algae. ** The chloroplasts in modern plants are the decedents of these ancient symbiotic cynobacteria.