PermeabilityPermeabilityPermeability refers to the permeability of a porous barrier for substances. The passage of substances through cell walls and membranes is of crucial importance for biological systems. The permeability of a membrane is characterized by the permeability coefficient P in cms and is inversely proportional to its layer thickness dx and directly dependent on the diffusion coefficient D: P = Ddx First Fick's law J = −Ddcdx initially only applies to single-phase systems.
Example: Volume of a sphere We are looking for the volume V of a sphere around the origin with the radius a. The three-dimensional integration area is B: x2 + y2 + z2≤a2. Then V = ∭Bdxdydz = ∫-aadx∫-a2-x2a2-x2dy∫-a2-x2-y2a2-x2-y2dz. However, the integral is much easier to calculate in spherical coordinates: V = ∭B & 39; r2sinθdrdφdθ = ∫0ar2dr∫ 02πdφ∫0πsinθdθ = r330aφ02π-cosθ0π = a33⋅2π⋅2V = 4πa33.
Hess's Theorem One is often interested in the enthalpy of reaction of a reaction that cannot or has not yet been measured. For the chemist it is often of particular interest whether a reaction is exothermic or endothermic. For such questions, one uses Hess's theorem: Theorem For reactions that can be written as the sum of partial reactions, the reaction enthalpy is equal to the sum of the reaction enthalpies of the partial reactions.
Determined by an AB-oriented segment, it is the set of all AB-oriented segments. If we indicate with this set, symbolically we can write: where XY is any segment of the set. The vector determined by AB is indicated by either B - A or. The same vector is determined by an infinity of oriented segments, called representatives of this vector, which are all equipolent with each other.
Hormones bind to receptors located in the cell membrane, in the cytoplasm or in the nucleus of the target cell. In addition to the presence of a receptor, the physiological state of the cell (e.g. degree of differentiation) also decides what effect the hormone has on this cell. Hormone-receptor complexes either act directly as transcription factors (e.g.
The relative atomic mass Most elements consist of several isotopes that occur with different frequencies. Since this composition of isotopes is constant in nature, the isotope abundance can be given for the naturally occurring elements. The relative atomic mass is therefore calculated taking into account the isotope abundance.