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Water activity (a w) is the partial vapor pressure of water in a solution divided by the standard state partial vapor pressure of water. In the field of food science, the standard state is most often defined as pure water at the same temperature. Using this particular definition, pure distilled water has a water activity of exactly one.
Mass flow of liquid water from the roots to the leaves is driven in part by capillary action, but primarily driven by water potential differences. If the water potential in the ambient air is lower than that in the leaf airspace of the stomatal pore, water vapor will travel down the gradient and move from the leaf airspace to the atmosphere.
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation.
One explanation for the effect is a cold-induced malfunction of the hypothalamus, the part of the brain that regulates body temperature. Another explanation is that the muscles contracting peripheral blood vessels become exhausted (known as a loss of vasomotor tone ) and relax, leading to a sudden surge of blood (and heat) to the extremities ...
In a scientific notion, the relative humidity (or ) of an air-water mixture is defined as the ratio of the partial pressure of water vapor in air to the saturation vapor pressure of water at the same temperature, usually expressed as a percentage: [11] [12] [5] = % /
The dew point of a given body of air is the temperature to which it must be cooled to become saturated with water vapor. This temperature depends on the pressure and water content of the air. When the air is cooled below the dew point, its moisture capacity is reduced and airborne water vapor will condense to form liquid water known as dew. [1]
The metabolic rate of a heterotroph is defined as the rate of respiration in which energy is obtained by oxidation of a carbon compound. The rate of photosynthesis on the other hand, indicates the metabolic rate of an autotroph. [6] According to MTE, both body size and temperature affect the metabolic rate of an organism.
A thermocline (also known as the thermal layer or the metalimnion in lakes) is a distinct layer based on temperature within a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) with a high gradient of distinct temperature differences associated with depth.