Theme 6: REGULATION
Explanation: Everything from cells to organisms to ecosystems is in a state of dynamic balance that must be controlled by positive or negative feedback mechanisms.
Clarification: You would post here examples of how a dynamic equilibrium is maintained at different levels of life, from homesostatic control of cellular and body conditions to maintenance of population levels in ecosystems.
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Populations are always regulated by different factors. Competitors, prey, predators, parasites, and diseases are biotic factors which limit population growth. Abiotic factors include sunlight, temperature, water, and soil. Popualtion growth has a logistic rate of growth as pupulations reach their carrying capacity which is set by the limiting factors. Humans so far have had an exponential growth rate as we have very little limiting factors.
Keystone Species control population growth. Predators mostly act as Keystone species. An example of a keystone species is an otter. In the late eighteenth century Russian and Europeans hunted the otters to near extinction in North America.With the decline of sea otters there was a significant increase in the sea urchin population. The sea urchins feast on the kelp beds which were critical habitats for spawning fish. The spawning fish population declines and there was less catch for fishermen.An international treaty was finally enacted to protect sea otters.
When the otters recovered, urchin populationswent down, the kelp beds recovered, fish population recovered, and fish catches rose again.
Cell: The cell membrane is a selectively permeable membrane which allows certain materials in and out of a cell. This maintains homeostasis within the cell. The lipid bilayer separates the outer liquid of the body from the cytosol. The membrane also includes receptor proteins which identify materials and are marker molecules. Nutrients are allowed in as wastes are removed. Large molecules cannot fit so they are blocked. This maitains balance as the cell does not become poisoned or lack nutrients.
The Endocrine system regulates the release of hormones. These hormones regulate metabolism, growth and development. The Endocrine system affects every cell and with very quick responses. It is a very strong force of regulation in the body.
Homeostasis can be maintained through feedback. In negative feedback the body responds in such a way as to reverse the direction of change. In positive feedback a change occurs in some variable, the response is to change that variable even more in the same direction. This has a de-stabilizing effect. An example are the contractions during childbirth. Negative feedback is mostly seen in the body as in bloodpressure and hormones.
the management of water balance in cells is an example of regulation. In hypotonic solutions which are cells in fresh water, for example, paramecium. the cells gain water because it continuously enters the cell, which would be a problem if they were to swell or burst but too prevent this the cell contains a contractile vacuole which pumps the water out of the cell, regulating the amount of water inside the cell.
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