Organelle

organelle [¦ȯr·gə¦nel]

(cell and molecular biology)

A specialized subcellular structure, such as a mitochondrion, having a special function; a condensed system showing a high degree of internal order and definite limits of size and shape.

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Organelle 

a part of the body of a unicellular organism, or protozoan, that performs any one of various functions. Organelles are especially diverse and complex in Infusoria and Flagellata. There are several types of organelles. Skeletal and support organelles protect the organism from mechanical, chemical, and other harmful effects (for example, the shells of Sarcodina and Infusoria). There also are locomotor and contractile organelles (for example, flagella, cilia, and myonemes); sensory, or receptor, organelles (for example, photosensitive ocelli); and attack and defense organelles (for example, in Infusoria, the rod-shaped formations known as trichocysts, which are discharged from the body). Digestive organelles capture, conduct, and digest the food (for example, the digestive vacuoles of Infusoria). There are also excretory and secretory organelles (for example, the pulsating vacuoles of Infusoria). The term “organelle” is often used as a synonym for “organoid.”