Unit 2: Cell structure and function

centrosome

Parts necessary for creating spindle fibers; contain centrioles.

centromere

The middle part of a chromosome through which sister chromatids attach.

simple diffusion

The movement of small, nonpolar molecules and lipids (fats and steroids) across a membrane.

facilitated diffusion

The process by which polar molecules (like glucose and amino acids) and ions pass through a membrane via channel proteins.

passive transport

Movement of substances down the concentration gradient without the use of energy.

active transport

Movement of substances up the concentration gradient that requires energy (ATP or electron flow).

endocytosis

The intake of molecules through the formation of vesicles from the cell membrane.

exocytosis

The process where molecules exit the cell through vesicles that become part of the cell membrane.

membrane potential

Electrical charge across a membrane created by pumping ions across their membranes.

hypotonic

A solution with relatively more water and less solute; cells shrink when placed in a hypotonic environment.

hypertonic

A solution with relatively less water and more solute; cells expand when placed in a hypertonic environment.

turgor pressure

The pressure of the cell contents against the cell wall, which is beneficial for plant cells.

contractile vacuole

An organelle in protists that pumps excessive water out of the cell to prevent it from exploding.

water potential (ψ)

A measurement of water’s tendency to move; calculated as ψ = ψs + ψp.

solute potential (ψs)

The contribution of solute concentration to the overall water potential; adding solute potential decreases overall water potential

pressure potential (ψp)

The contribution of pressure to the overall water potential; adding pressure increases water potential.

water diffusion (in context with water potential)

Water moves from areas of higher water potential to areas of lower water potential.