Chapter 3: Cells and Membrane Transport

Vocabulary practice flashcards covering cell structure, cell membrane composition, passive mechanisms (diffusion, facilitated diffusion, osmosis, filtration), and active mechanisms (active transport, endocytosis, exocytosis) from Chapter 3: Cells.

Three Major Parts of a Cell

The three primary components that make up a cell: the nucleus, the cytoplasm, and the cell membrane (plasma membrane).

Cell Membrane (Plasma Membrane)

An actively functioning living boundary that regulates the movement of substances into and out of the cell while maintaining cellular integrity.

Selectively Permeable

A membrane characteristic describing the ability to regulate movement by allowing only certain substances to enter or exit while restricting others.

Phospholipid Bilayer

A double layer of phospholipid molecules forming the cell membrane framework, with polar hydrophilic heads facing outward and nonpolar fatty acid tails facing inward toward the center.

Membrane Readily Diffusing Molecules

Small molecules that move easily through the cell membrane lipid bilayer without transport assistance, specifically $O_2$, $H_2O$, and $CO_2$.

Membrane Proteins

Proteins appearing as globs, rods, or fibers embedded in or attached to the membrane; includes channel proteins that allow water-soluble substances (such as amino acids, sugars, proteins, nucleic acids, and various ions) to cross.

Membrane Carbohydrates

Surface molecules (such as glycoproteins and glycolipids) attached to membrane lipids or proteins that function in cell recognition and cellular adhesion.

Cholesterol (Membrane Structure)

A lipid constituent dispersed within the plasma membrane that functions to stabilize the membrane structure.

Passive Mechanisms

Transport processes across the cell membrane that move substances without requiring the expenditure of cellular energy, including diffusion, facilitated diffusion, osmosis, and filtration.

Active Mechanisms

Cellular transport processes that require metabolic cellular energy ($\text{ATP}$) to transport substances across or into/out of the cell.

Diffusion (Simple Diffusion)

The passive net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached (e.g., sugar or food dye spreading in water).

Facilitated Diffusion

A form of passive transport where molecules move from higher to lower concentration across a selectively permeable membrane with the assistance of a specific carrier helper protein (e.g., glucose transport).

Carrier Protein

A specialized membrane helper protein that binds specific molecules and facilitates their transport across the cell membrane down or against their concentration gradient.

Osmosis

A special case of diffusion referring to the movement of solvent molecules (water) across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Isotonic Solution

Any solution having the same osmotic pressure as body fluids, resulting in no net gain or loss of water by the cell.

Hypertonic Solution

A solution that has a higher osmotic pressure than body fluids, causing a net loss of water from the cell so that the cell shrinks.

Hypotonic Solution

A solution that has a lower osmotic pressure than body fluids, resulting in net water gain that causes the cell to swell.

Filtration

A passive movement mechanism that forces molecules across membranes using hydrostatic pressure, commonly separating solids from liquids (e.g., blood pressure driving glomerular filtration in the kidneys or coffee brewing).

Hydrostatic Pressure

The pressure exerted by a fluid (such as blood pressure) that forces smaller molecules through a membrane during filtration.

Active Transport

The energy-requiring transport mechanism that moves particles against their concentration gradient from an area of low concentration to an area of higher concentration using carrier proteins and $\text{ATP}$.

ATP (in Active Transport)

The cellular energy molecule that powers active transport; up to $40\%$ of a cell's total energy supply may be utilized to transport particles via this mechanism.

Pumps

A term used for active transport carrier proteins that utilize cellular energy ($\text{ATP}$) to move molecules such as sodium, potassium, calcium, sugars, and amino acids across the cell membrane.

Endocytosis

An active vesicular transport process in which a cell takes in substances from the outside without them directly passing through the membrane bilayer by enclosing them in vesicles.

Pinocytosis

A specific type of endocytosis commonly known as 'cell drinking' in which the cell takes in droplets of extracellular fluid containing dissolved particles.

Phagocytosis

A type of endocytosis known as 'cell eating' where the cell engulfs solid particles instead of liquids.

Receptor-Mediated Endocytosis

A highly selective type of endocytosis where only substances specific to membrane surface receptors can bind and enter the cell inside coated vesicles.

Exocytosis

An active vesicular process where an intracellular vesicle fuses with the cell membrane to expel or secrete substances out of the cell (e.g., secretion of certain hormones).