Homeostasis may be defined as a self-regulating process whereby equilibrium is achieved between various organs or segments of an organic system, such as the human body. The term "homeostasis" was first coined in 1932 by American physiologist Walter Cannon (Freeman, n.d.), who observed that organisms have mechanisms in place to maintain a constant state of equilibrium or balance. The term has subsequently been utilized to describe this process of maintaining equilibrium in many different situations. Homeostasis has also been formally defined by many scientists in different ways, perhaps most accurately as the "maintenance of a stable internal environment" whether in a cell or in the organism as a whole (MSNucleus, 2004). Homeostasis is in essence equivalent to a state of equilibrium. Much like balanced scales, homeostasis ensures that too much nor too little exists at any point in time within organisms. When a state of imbalance occurs, the scale tips unfavorably to one side or the other. Homeostasis works via establishment and maintenance of the internal chemical balance of cells, whether they are in a human life form or a botanical one. Homeostasis is crucial to maintenance of the complex sequence of biochemical activities that occur within organisms, traditionally during the process of energy utilization (MSNucleus, 2004).

BASIC MECHANISMS

Cell membranes are critical to establishing and maintaining the homeostasis of any object; membranes control what substances enter or leave cells through a variety of means (Sirinet, 2004). One mechanism in which membranes control movement through cells is via passive transport a process through which substances are able to cross cell membranes without any added energy input by the cell (Sirinet, 2004). Cells require an exchange of food (including water) and waste in order to survive in any environment; materials such as food and waste cross through cells via the cell membrane (Sirinet, 2004).

All organisms that are "alive" need to be able to take in oxygen and subsequently release waste materials. This is true of humans as much as it is true of plant matter and cellular life forms. Optimal hydration levels are critical to the sustainment of life processes; the mechanisms controlling homeostasis enable this balance. Life sustaining organisms are enabled entry into cells, and waste products are subsequently excreted.

The human body is one example of organic life that must constantly adapt in order to maintain a state of "biological equilibrium." Under ordinary conditions, when a person is healthy, the body has natural mechanisms in place that adequately control this process.

All species, whether plant or animal in nature have certain characteristics in common related to homeostasis, whether biological, chemical or physiological in nature (MSNucleus, 2004). Organisms have special abilities to adapt to changes in their internal and external environment in order to survive (MSNucleus, 2004). These abilities are often described as mechanisms.

Homeostasis has also been defined as a "steady state" (Buckley, 2003). Traditionally changes in the environment are detected among all organisms at a cellular level. Mechanisms are in place that detect minute changes and trigger a sequence of reactions to restore normal functioning. There are several different types of homeostatic mechanisms, the majority of which are triggered by changes in extra cellular fluid (Freeman, n.d.). Homeostatic mechanisms are varied in their functions, but as a whole all work to produce a continual "steady state." Mechanisms work in general by restoring an equilibrium state and producing change in the opposite direction of an imbalance.

Feedback mechanisms act as mechanisms that help maintain a homeostatic state; in a human being a feedback mechanism might include an increase in heart rate or respiratory rate that occurs in response to increased muscular or cellular activity (Buckley, 2003). Sweating also acts as a regulator or feedback mechanism, allowing the body to dissipate and release heat instead of store it. If the human body were to store heat unconditionally, the equilibrium or homeostatic state would be disrupted, resulting in possible death or stroke.

BLOOD CALCIUM CONTROL IN HUMANS

Calcium is an important structural component of bone necessary...

There are many hormones that are responsible for regulating a homeostatic blood calcium level, including the following: parathyroid hormone (PTH), Calcitonin (CT) 1, 25-diydroxyvitamin D3 and a PTH related peptide called PTHrP (Rutgers, 2004).
Each of these hormones is essential to survival, and assists in mineral metabolism among other processes. Among the functions influenced by each of these hormones include parathyroid function and mammary gland production. When the homeostatic blood calcium level is disrupted, a variety of problems ensue; some are quite severe and might even lead to death. Hypoparathyroidism is an example of this; this disease is caused by low blood calcium levels and can result in convulsions (Rutgers, 2004). Alternatively, hyperparathyroidism is caused by elevated blood calcium levels, and may result in bone pain and kidney stones (Rutgers, 2004).

Paget's disease is another example of disease that results from a disruption of blood calcium levels. Paget's disease results in brittle bones and excessive bone pain (Rutgers, 2004). Blood calcium levels in patients with this disease are continually low; therefore a constant state of dis-equilibrium exists.

From a homeostatic perspective, when blood calcium levels rise the thyroid gland should be stimulated, resulting in a release of calcitonoin; calcium release from bone then occurs and calcium levels generally return to normal (Freeman, n.d.). At this point the homeostatic mechanism is generally switched off. Alternatively, when blood calcium levels fall, generally the Parathyroids are stimulated, causing calcium release from bone and release of parathyroid hormone that causes a re-asbsorption of calcium from the kidney (Freeman, n.d.). This also activates Vitamin D and causes an increased calcium absorption for the gut (Freeman, n.d.).

WATER BALANCE IN PLANTS

Plants require water as an "essential ingredient of photolysis" (N.A., 2000), the process through which photosynthesis results. Plants generally absorb water through their roots, and then transfer this water throughout all other areas of the plan, a process referred to as the "transpiration stream" (N.A., 2000). If water concentration in the roots is low, water is absorbed in greater quantities from the ground for transference through cells.

Plants maintain a state of homeostasis by maintaining a water balance. Plants utilize water to manage carbon dioxide intake and photosynthesis. Plants need to keep an appropriate amount of water within their cells to prevent wilting and eventual death (Buckley, 2003). Plants utilize two different mechanisms to help manage the equilibrium of water: stomata and guard cells. Stomata are microscopic holes in the plant leaf which enable entry of gases and evaporation of water vapor (Buckley, 2003). Guard cells are responsible for opening and closing each stomata. Guard cells must be able to close when water supply is limited or during times of drought in order to help a plant maintain the water it has, thus maintaining a state of homeostasis (Buckley, 2003).

Water is transpired in plants through the stomata (N.A., 2000). When water concentration in areas is low, water rushes into various areas to even out distribution throughout the plant so that osmosis can occur. There are several other mechanisms present within the plant structure that help maintain a plants water balance. This includes a curvature of leaves, which often occurs when water transpired remains in "close contact with the leaf" (N.A., 2000). Stomata may also be "hairy" meaning that they allow water molecules to stick to hairs in an adhesive fashion, in order again to maintain an equilibrium.

Plants will generally wilt in the absence of adequate water equilibrium, ultimately dying if the state of homeostasis is disrupted for extensive periods of time.

CONCLUSIONS

Cell membranes are responsible for helping organisms maintain Homeostasis (Sirinet, 2004). Cell membranes allow substances to enter and leave cells. Generally smaller molecules such as water and carbon dioxide can pass easily in and out of cells via the cell membrane; larger molecules such as proteins and carbohydrates are not able to (Sirinet, 2004).

Substances…