Cell Membranes and Transport

These flashcards cover key vocabulary and concepts related to cell membranes, transport mechanisms, and their functions.

Plasma Membrane

A thin, fluid entity that is flexible yet stable, managing the movement of substances in and out of the cell.

Phospholipid Bilayer

A double layer of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails pointing inward.

Glycocalyx

A layer of short carbohydrate chains on the cell surface that functions in cell adhesion, identification, and binding sites on proteins.

Hydrophilic

A property of molecules that are attracted to water; they readily bond with water.

Hydrophobic

A property of molecules that repel water; they avoid contact with water.

Amphipathic

Describes molecules that have both hydrophilic and hydrophobic regions.

Diffusion

The movement of molecules from a region of higher concentration to a region of lower concentration.

Concentration Gradient

The difference in concentration of a solute between two regions.

Osmosis

The net movement of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Active Transport

The movement of molecules across a cell membrane that requires energy expenditure.

Passive Transport

The movement of molecules across a cell membrane without the expenditure of energy.

Exocytosis

The process by which a transport vesicle moves to the plasma membrane and releases its contents outside the cell.

Endocytosis

The process of taking in large materials into the cell by forming vesicles from the plasma membrane.

Pinocytosis

A form of endocytosis where moderate-sized molecules are brought into the cell by transport vesicles.

Phagocytosis

A form of endocytosis where cells use pseudopodia to engulf large particles or cells.

Plasma Membrane

A thin, fluid entity that is flexible yet stable, managing the movement of substances in and out of the cell. It consists mainly of lipids and proteins.

Phospholipid Bilayer

A double layer of phospholipid molecules. Each molecule is amphipathic, with hydrophilic heads facing outward toward the water and hydrophobic tails pointing inward, away from water.

Cholesterol

A lipid molecule interspersed within the phospholipid bilayer that helps regulate membrane fluidity and stability across different temperatures.

Glycocalyx

A sugar coating on the cell surface made of short carbohydrate chains (glycolipids and glycoproteins). It functions in cell adhesion, identification, and as receptor binding sites.

Fluid Mosaic Model

The model describing the cell membrane as a dynamic, flexible structure where lipids and proteins can move laterally within the plane of the membrane.

Membrane Proteins

Proteins associated with the membrane, categorized as Integral (spanning the bilayer) or Peripheral (attached to the surface). Their functions include transport, enzymatic activity, signal transduction, and cell-cell recognition.

Hydrophilic vs. Hydrophobic Interactions

Hydrophilic (water-loving) molecules are polar and interact with the phosphate heads; Hydrophobic (water-fearing) molecules are non-polar and interact with the lipid tails, often requiring transport proteins to cross the membrane.

Amphipathic

Molecules, such as phospholipids, that possess both a hydrophilic (polar) region and a hydrophobic (non-polar) region.

Concentration Gradient

The difference in the concentration of a solute between two regions. Substances naturally move "down" their gradient from high to low concentration.

Diffusion

The spontaneous movement of molecules from a region of higher concentration to a region of lower concentration until equilibrium is reached.

Semipermeable Membrane

A membrane that allows certain molecules or ions to pass through it by diffusion or specialized transport while blocking others.

Osmosis

The net movement of water across a semipermeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic).

Isotonic Solution

A solution with the same solute concentration as the cell. There is no net movement of water; animal cells remain stable, and plant cells become flaccid.

Hypotonic Solution

A solution with a lower solute concentration than the cell. Water enters the cell, causing animal cells to swell and potentially burst (lysis), while plant cells become firm (turgid) due to Turgor Pressure.

Hypertonic Solution

A solution with a higher solute concentration than the cell. Water leaves the cell, causing animal cells to shrivel and plant cells to undergo plasmolysis (the plasma membrane pulls away from the cell wall).

Passive Transport

The movement of substances across a cell membrane without the expenditure of energy (ATP). It includes simple diffusion and facilitated diffusion.

Simple Diffusion

A type of passive transport where small, non-polar molecules (like O{2} or CO{2}) pass directly through the phospholipid bilayer down their concentration gradient.

Facilitated Diffusion

A type of passive transport where ions or polar molecules cross the membrane through specific transport proteins (channels or carriers) down their concentration gradient.

Active Transport

The movement of molecules across a cell membrane against their concentration gradient (from low to high concentration), requiring energy expenditure.

Primary Active Transport

Directly uses energy from the hydrolysis of ATP to move molecules against their concentration gradient (e.g., the Sodium-Potassium pump).

Secondary Active Transport

Uses the energy from an electrochemical gradient created by primary active transport to move another substance against its own gradient.

Exocytosis

A form of bulk transport where materials are exported out of the cell via the fusion of a transport vesicle with the plasma membrane.

Endocytosis

The process of taking large materials into the cell by folding the plasma membrane inward to form a vesicle.

Pinocytosis

A type of endocytosis often called "cell drinking," where the cell engulfs extracellular fluid and dissolved solutes.

Phagocytosis

A type of endocytosis often called "cell eating," where the cell uses pseudopodia to engulf large particles, such as bacteria or food debris.

Receptor-Mediated Endocytosis

A highly specific type of endocytosis where extracellular ligands bind to specific receptors on the membrane surface, triggering vesicle formation.