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Encyclopedia > Chloroplast

Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant. Chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis. It is derived from the Greek words chloros which means green and plast which means form ( in biological terms it can be more roughly translated as organelle or cell ). Schematic of typical animal cell, showing subcellular components. ... Plant cell structure Plant cells are quite different from the cells of the other eukaryotic kingdoms organisms. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... The leaf is the primary site of photosynthesis in plants. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength [citation needed]. The elementary particle that defines light is the photon. ... The Sun is the star of our solar system. ... The free energy is a measure of the amount of mechanical (or other) work that can be extracted from a system, and is helpful in engineering applications. ... Adenosine 5-triphosphate (ATP), discovered in 1929 by Karl Lohmann,[1] is a multifunctional nucleotide primarily known in biochemistry as the molecular currency of intracellular energy transfer. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... The leaf is the primary site of photosynthesis in plants. ...

Contents

Origins

Chloroplasts are one of the many unique cells in the body, and are generally considered to have originated as endosymbiotic cyanobacteria. In this respect they are similar to mitochondria, but are found only in plants and protista. Both organelles are surrounded by a double celled composite membrane with an intermembrane space; both have their own DNA and are involved in energy metabolism; and both have reticulations, or many infoldings, filling their inner spaces. The endosymbiotic theory, now generally accepted by biologists, concerns the origins of mitochondria and plastids (e. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) (from Greek μιτος or mitos, thread + κουδριον or khondrion, granule) is an organelle, variants of which are found in most eukaryotic cells. ... Divisions Green algae Chlorophyta Charophyta Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) †Rhyniophyta - rhyniophytes †Zosterophyllophyta - zosterophylls Lycopodiophyta - clubmosses †Trimerophytophyta - trimerophytes Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta... Typical phyla Protists (IPA: ) are a heterogeneous group of living things, comprising those eukaryotes that are not animals, plants, or fungi. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ...


In green plants, chloroplasts are surrounded by two lipid-bilayer membranes. The inner membrane is now thought to correspond to the outer membrane of the ancestral cyanobacterium. The chloroplast genome is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities. Many of the missing genes are encoded in the nuclear genome of the host. Drawing of a cell membrane A cell membrane, plasma membrane or plasmalemma is a selectively permeable lipid bilayer coated by proteins which comprises the outer layer of a cell. ... Genome reduction (Genome degradation) is the process by which a genome shrinks relative to its ancestor. ...


It is interesting to note that in some algae (such as the heterokonts and other protists such as Euglenozoa and Cercozoa), chloroplasts seem to have arisen through a secondary event of endosymbiosis, in which a eukaryotic cell engulfed a second eukaryotic cell containing chloroplasts, forming chloroplasts with three or four membrane layers. In some cases, such secondary endosymbionts have themselves been engulfed by still other eukaryotes, forming tertiary endosymbionts. Typical classes Colored groups Chrysophyceae (golden algae) Synurophyceae Actinochrysophyceae (axodines) Pelagophyceae Phaeothamniophyceae Bacillariophyceae (diatoms) Raphidophyceae Eustigmatophyceae Xanthophyceae (yellow-green algae) Phaeophyceae (brown algae) Colorless groups Oomycetes (water moulds) Hypochytridiomycetes Bicosoecea Labyrinthulomycetes (slime nets) Opalinea Proteromonadea The heterokonts or stramenopiles are a major line of eukaryotes. ... Typical phyla Protists (IPA: ) are a heterogeneous group of living things, comprising those eukaryotes that are not animals, plants, or fungi. ... Classes Euglenoidea Kinetoplastea Diplonemea Postgaardea The Euglenozoa are a large group of flagellate protozoa, dominated by the euglenids and kinetoplastids. ... The Cercozoa are a group of protists, including most amoeboids and flagellates that feed by means of filose pseudopods. ... An endosymbiont is any organism that lives within the body or cells of another organism, i. ...


Structure

The inside of a chloroplast with the granum circled.
Enlarge
The inside of a chloroplast with the granum circled.

Chloroplasts are flat discs usually 2-10 micrometer in diameter and 1 micrometer thick. The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the Intermembrane space. Image File history File links Chloroplast-new. ... Image File history File links Chloroplast-new. ...


The fluid within the chloroplast is called the stroma, corresponding to the cytoplasm of the bacterium, and contains tiny circular DNA and ribosomes, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products transported to the chloroplast. Stroma can refer to: The connective supportive framework of a biological cell, tissue, or organ. ... Organelles. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...


Within the stroma are stacks of thylakoids, the sub-organelles where photosynthesis actually takes place. A stack of thylakoids is called a granum (plural: grana). A thylakoid looks like a flattened disk, and inside is an empty area called the thylakoid space or lumen. The photosynthesis reaction takes place on the membrane of the thylakoid, and, as is also the case with mitochondria, involves the coupling of cross-membrane fluxes with biosynthesis. A thylakoid is a phospholipid bilayer membrane internal to chloroplasts. ... A granum (plural grana) is a stack of thylakoids in the chloroplast, an organelle found in plants and eukaryotic algae where photosynthesis takes place. ... In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks. ... This article or section does not cite its references or sources. ...


Embedded in the thylakoid membrane is a dish of chlorophyll molecules known as an antenna complex, this outer array helps to increase the surface area of light capture. The light photons are then funneled to the centre of this complex. Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre.


See also

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References

  • This article contains material from the Science Primer published by the NCBI, which, as a US government publication, is in the public domain

crapsqwfdvdwWED The National Center for Biotechnology Information (NCBI) is part of the US National Library of Medicine (NLM), which is a branch of the US National Institutes of Health. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...


External links

  • Chloroplasts and Photosynthesis: The Role of Light from Kimball's Biology Pages
  • Chloroplast, Botany
  • Use of chloroplast DNA in studying plant phylogeny and evolution
Organelles of the cell
Acrosome | Cell wall | Cell membrane | Chloroplast | Cilium/Flagellum | Centrosome | Cytoplasm | Endoplasmic reticulum | Endosome| Golgi apparatus | Lysosome | Melanosome | Mitochondrion | Myofibril | Nucleus | Nucleolus (sub-organelle, found within the nucleus) | Parenthesome | Peroxisome | Plastid | Ribosome | Vacuole | Vesicle

  Results from FactBites:
 
Chloroplast - Wikipedia, the free encyclopedia (491 words)
Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis.
Chloroplasts are one of the forms a plastid may take, and are generally considered to have originated as endosymbiotic cyanobacteria.
The fluid within the chloroplast is called the stroma, corresponding to the cytoplasm of the bacterium, and contains tiny circular DNA and ribosomes, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products trafficked to the chloroplast.
  More results at FactBites »

 
 

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