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In biology, an organ (Latin: organum, "instrument, tool", from Greek όργανον - organon, "organ, instrument, tool") is a group of tissues that perform a specific function or group of functions. Usually there is a main tissue and sporadic tissues. The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are the nerves, blood, connective etc.

[edit] Plant organs

The flower is the angiosperms reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamens and pistils.

Organs of plants can be divided into vegetative and reproductive. Vegetative plant organs are root, stem and leaf. The reproductive organs are variable. In angiosperms, they are represented with the flower, seed and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions of plants, the reproductive organs are called strobili (in Lycopodiophyta) or simply gametophores (in mosses).

The vegetative organs are essential for maintaining the life of a plant (they perform the vital functions, such as photosynthesis), while the reproductive organs are essential in reproduction. But, if there is asexual vegetative reproduction, the vegetative organs are those which create the new generation of plants (see clonal colony).

[edit] Organ systems

A group of related organs is an organ system. Organs within a system may be related in any number of ways, but relationships of function are most commonly used. For example the urinary system comprises organs that work together to produce, store, and carry urine.

The functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system. The same is true for the musculoskeletal system, which involves the relationship between the muscular and the skeletal system.

The two main organ systems in vascular plants are the root system and the shoot system.

[edit] Animal organs and organ systems

The organ level of organisation in animals can be first detected in flatworms and the more advanced phyla. The less-advanced taxons (like Placozoa, Porifera and Radiata) do not show consolidation of their tissues into organs.

[edit] Organs and organ systems in invertebrates

Freshwater bryozoan with lophophore extended.

The animals without backbone are known as invertebrates. They posses many specific organs which are not found in vertebrates.

[edit] List of major human organ systems

There are typically considered to be eleven major organ systems of the human body.

• Digestive system - Absorption of nutrients and excretion of waste.

• Skeletal system - Support, lymphocyte production

• Muscular system - Support and movement, production of heat.

• Nervous system - Integration, coordination and regulation through electrochemical signals.

• Endocrine system - Integration, coordination and regulation through hormones.

• Respiratory system - Elimination of CO₂ and absorption of O₂

• Circulatory system - The transporting of needed materials to the cells and the transporting of wastes away from the cells.

• Reproductive system - Production of offspring.

• Integumentary system - Body covering

• Lymphatic system - Regulate fluids and immunity

• Urinary system - Excretion of nitrogenous waste, and maintain homeostasis of electrolytes

[edit] See also

• Cloning
• Fascia
• Organ transplant
• Organelles, analogous sub-cellular structures

[edit] External links

• Could we clone our organs to be used in a transplant? at HowStuffWorks