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The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been identified.
History and terminology
In biology, organsare defined as confined functional units within anorganism. The analogy of bodily organs to microscopic cellular substructures is obvious, as from even early works, authors of respective textbooks rarely elaborate on the distinction between the two.
Credited as the first to use a diminutive of organ (i.e. little organ) for cellular structures was German zoologist Karl August MÃ¶bius (1884), who used the term "organula" (plural form of organulum, the diminutive of latinorganum). From the context, it is clear that he referred to reproduction related structures of protists. In a footnote, which was published as a correction in the next issue of the journal, he justified his suggestion to call organs of unicellular organisms "organella" since they are only differently formed parts of one cell, in contrast to multicellular organs of multicellular organisms. Thus, the original definition was limited to structures of unicellular organisms.
It would take several years before organulum, or the later term organelle, became accepted and expanded in meaning to include subcellular structures in multicellular organisms. Books around 1900 from Valentin HÃ¤cker, Edmund Wilson and Oscar Hertwig still referred to cellular organs. Later, both terms came to be used side by side: Bengt Lidforss wrote 1915 (in German) about "Organs or Organells".
Around 1920, the term organelle was used to describe propulsion structures ("motor organelle complex", i.e., flagella and their anchoring) and other protist structures, such as ciliates. Alfred KÃ¼hn wrote about centrioles as division organelles, although he stated that, for Vahlkampfias, the alternative 'organelle' or 'product of structural build-up' had not yet been decided, without explaining the difference between the alternatives.
In his 1953 textbook, Max Hartmann used the term for extracellular (pellicula, shells, cell walls) and intracellular skeletons of protists.
Later, the now-widely-used definition of organelle emerged, after which only cellular structures with surrounding membrane had been considered organelles. However, the more original definition of subcellular functional unit in general still coexists.
In 1978, Albert Frey-Wyssling suggested that the term organelle should refer only to structures that convert energy, such as centrosomes, ribosomes, and nucleoli. This new definition, however, did not win wide recognition.
While most cell biologists consider the term organelle to be synonymous with "cell compartment", other cell biologists choose to limit the term organelle to include only those that are DNA-containing, having originated from formerly-autonomous microscopic organisms acquired via endosymbiosis.
Other organelles are also suggested to have endosymbiotic origins, (notably the flagellum - see evolution of flagella).
Under the more restricted definition of membrane-bound structures, some parts of the cell do not qualify as organelles. Nevertheless, the use of organelle to refer to non-membrane bound structures such as ribosomes is common. This has led some texts to delineate between membrane-bound and non-membrane bound organelles. These structures are large assemblies of macromolecules that carry out particular and specialized functions, but they lack membrane boundaries. Such cell structures include:
Eukaryotes are one of the structurally complex cell type, and by definition are in part organized by smaller interior compartments, that are themselves enclosed by lipid membranes that resemble the outermost cell membrane. The larger organelles, such as
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Answers:Lysosomes are organelles that carry the cell's digestive enzymes. Lysosomes have to be membrane bound. This is because of the enzymes. The digestive enzymes in the cell break down and "recycle" the unneeded materials in the cell. If the enzymes were allowed to float freely within the cytoplasm, the digestive enzymes would "break down" and recycle the entire cell- they're that strong. When the lysosomes are membrane bound, they can only break down something that comes into it. This protects the cell from being digested by their own enzymes.
Answers:the cell membrane: - cell-cell recognition - separate cyctoplasm from outside enviroment - absorbtion of ions - maintain different conc of ions in and out of the cell by diffusion, facilitated diffusion, osmosis, endocytosis and active transport. - prevent viruses and bacteria from entering cell - enables phagocytosis (cell "eating") and pinocytosis (cell "drinking") - allows disposal of waste material (when secretory vesicles fuse with membrane to secrete material) - attaches cell to other cells through desosomes, gap junctions, and tight junctions - Increase surface area for exchange of substances using microvilli golgi body or golgi apparatus: - receives protiens from endoplasmic reticulum at the 'cis' face - packages and modifies proteins for export froom the 'trans' face - synthesis of secretory polysaccharides - formation of lysosomes - addition of material to cell membrane (enlargement) Lysosomes: - digestion of ingested particles (taken in by endocytosis) - disposal of defunct or surplus organelles (autophagy) - cell death (autolysis) Endoplasmic Reticulum: - provide large surface area for chemical reactions - form intracellular transport system - post-translational modifications of proteins synthesised at the ribosomes - synthesis of lipids and steroids - detoxication - storage and release of calcium ions Mitochondria - synthesis of ATP (Adenosine triphosphate) - Heat production (55% of energy released from the reactions in the mitochondria is given off as heat) Hope i helped you. that's to my knowledge, i'm a bio student =))
Answers:1. Centrosome 2. Ribosome 3. Rough Endoplasmic Reticulum 4. Plasma Membrane 5. Mitochondria 6. Lysosome 7. Smooth Endoplasmic Reticulum 8. Cell Wall 9. Golgi Apparatus (and Secretory Vacuoles) 10. Vacuole 11. Nucleus