cell membrane and movement

Plasma Membrane (Cell Membrane)

Selectively permeable barrier that regulates the passage of substances into and out of the cell.

Fluid Mosaic Model

Describes the plasma membrane as a mosaic of protein molecules drifting in a fluid bilayer of phospholipids.

Phospholipid Bilayer

The basic framework of the membrane, with hydrophilic heads facing outwards and hydrophobic tails facing inwards.

Cholesterol

Lipid found in animal cell membranes that helps maintain fluidity and stability.

Integral Protein

Proteins embedded within the lipid bilayer, often spanning the entire membrane (transmembrane proteins).

Peripheral Protein

Proteins loosely bound to the surface of the membrane.

Glycocalyx

The carbohydrate portion of glycoproteins and glycolipids on the outer surface of the plasma membrane; involved in cell-cell recognition.

Selective Permeability

The property of a membrane that allows some substances to pass through more easily than others.

Passive Transport

Movement of substances across a membrane without the input of metabolic energy.

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

Facilitated Diffusion

Diffusion aided by transport proteins (channel proteins or carrier proteins).

Channel Protein

Provides a channel for specific molecules or ions to cross the membrane.

Aquaporin

Channel protein specific for water.

Carrier Protein

Binds to molecules and changes shape to move them across the membrane.

Osmosis

The diffusion of water across a selectively permeable membrane.

Solute Potential (Ψs)

The effect of solute concentration on water potential.

Pressure Potential (Ψp)

The effect of pressure on water potential (e.g., turgor pressure).

Water Potential (Ψ)

The potential energy of water per unit volume relative to pure water in reference conditions. Water moves from higher to lower water potential.

Hypertonic Solution

Solution with a higher solute concentration than the cell; causes cell to lose water (shrivel).

Hypotonic Solution

Solution with a lower solute concentration than the cell; causes cell to gain water (swell/lyse).

Isotonic Solution

Solution with the same solute concentration as the

cell; no net movement of water.

Turgid (Plant Cell)

Swollen state of a plant cell due to water uptake in a hypotonic solution.

Flaccid (Plant Cell)

Limp state of a plant cell in an isotonic solution.

Plasmolysis (Plant Cell)

Shrinking of the protoplast away from the cell wall due to water loss in a hypertonic solution.

Active Transport

Movement of substances across a membrane against their concentration gradient, requiring energy (ATP).

Sodium-Potassium Pump

An important active transport pump that maintains ion gradients across animal cell membranes.

Electrochemical Gradient

A gradient of electrochemical potential, usually for an ion, that consists of two parts

Cotransport (Secondary Active Transport)

The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.

Bulk Transport

Movement of large molecules or large quantities of substances across the membrane.

Endocytosis

Process by which cells take in substances from outside the cell by engulfing them in a vesicle.

Phagocytosis

"Cell eating"; engulfment of solid particles.

Pinocytosis

"Cell drinking"; engulfment of extracellular fluid and dissolved solutes.

Receptor-Mediated Endocytosis

Specific uptake of molecules bound to receptors on the cell surface.

Exocytosis

Process by which cells release substances from inside the cell to the outside by fusing vesicles with the plasma membrane.