PHUMA-SALUD key terms

Water chemical potential expressed relative to a defined pure-water reference, often in pressure units. Pure water at reference conditions is assigned zero; positive pressure can raise potential, and water moves toward lower potential.

The net movement of water across a partially permeable membrane from a region of higher water potential to one of lower water potential. It is passive and driven by the water potential gradient.

The component of water potential caused by dissolved solutes, always negative or zero. More concentrated solutions have more negative solute potentials and so attract water.

Shrinking of the protoplast away from the plant cell wall when a cell loses water in a hypertonic solution. It occurs because the protoplast contracts while the rigid wall stays in place.

Passive movement through membrane channels or carriers down an electrochemical gradient. The transport step does not directly hydrolyze ATP, although other processes may use energy to establish the gradient.

Energy-coupled movement against an electrochemical gradient. Primary transport can use ATP directly; secondary transport uses a gradient established by another energy-dependent process.

The description of membranes as a phospholipid bilayer with proteins and other molecules embedded in or attached to it, able to move laterally. It explains selective permeability and membrane flexibility.

The first stage of mitosis, when chromosomes condense, the nuclear envelope breaks down and spindle fibres begin to form. Each chromosome is already duplicated into two sister chromatids.

The number of protons in the nucleus of an atom, which uniquely identifies the element. In a neutral atom it also equals the number of electrons.

The total count of protons plus neutrons in one atom's nucleus. It is a whole number written as a superscript beside the element symbol and differs between isotopes.

One of two or more atoms of the same element that have equal proton counts but different neutron counts, so they differ in mass while sharing nearly identical chemical behaviour.

The weighted average mass of an element's atoms compared with one-twelfth the mass of a carbon-12 atom, taking natural isotopic abundance into account. It is dimensionless and rarely a whole number.

The rule that electrons occupy the lowest-energy available orbitals first when an atom is built up, giving the familiar 1s 2s 2p 3s filling order and the ground-state configuration.

The arrangement of an atom's electrons among its shells, subshells and orbitals, usually written with superscripts such as 1s2 2s2 2p6. It governs chemical behaviour and position in the periodic table.

The statement that electrons fill degenerate orbitals singly, with parallel spins, before any pairing occurs. It explains the unpaired electrons in nitrogen and the paramagnetism of many transition-metal ions.

The electrons in an atom's outermost occupied shell that are chiefly responsible for bonding and chemical reactivity. Their count determines group behaviour and typical ion charge.

The straight-line distance and direction of a point from its starting position, treated as a vector quantity. It differs from distance travelled, which is a scalar and ignores direction.

The rate of change of displacement with respect to time, a vector quantity with both magnitude and direction. Average velocity divides total displacement by total time taken.

The rate at which velocity changes with time, including changes in speed, direction, or both. It is measured in metres per second squared and is a vector.

The resultant force on a body equals the rate of change of its momentum; for constant mass this reduces to force equals mass times acceleration, measured in newtons.

The product of a body's mass and its velocity, a vector measured in kilogram metre per second. For a chosen system, total momentum is conserved when the net external impulse is zero; closure to matter alone does not establish isolation from force.

The time integral of resultant force, or average resultant force times duration, equal to the change in momentum of the chosen body or system. It is measured in newton seconds and explains why airbags reduce injury.

The inward radial component of the resultant force for circular motion; in nonuniform motion a tangential resultant component can also be present. It has magnitude mv squared divided by radius r.

The rate of change of angular displacement, measured in radians per second. It links linear speed to circular motion through the relation speed equals radius times angular velocity.