Learn: Cell Membranes, Transport, and Osmosis: Biology Terms

Surface Area (SA)

The total area of the outside surfaces of an object or cell.

Volume

The amount of space an object or cell occupies.

SA to V Ratio

The surface area divided by volume; a higher ratio allows more efficient exchange of materials.

Cube

A three-dimensional shape with six square faces; useful for studying surface area and volume.

Sphere

A round, three-dimensional shape; its surface area-to-volume ratio decreases as it grows.

Cylinder

A three-dimensional shape with two circular bases and one curved surface.

Cell Size

Cells are generally small because smaller cells have a higher surface area-to-volume ratio and exchange materials more efficiently.

Phospholipid

A molecule with a hydrophilic phosphate head and two hydrophobic fatty acid tails; the main component of cell membranes.

Hydrophilic

Attracted to water; usually polar or charged.

Hydrophobic

Repelled by water; usually nonpolar.

Amphipathic

A molecule that contains both hydrophilic and hydrophobic regions.

Fatty Acid Tails

The hydrophobic, nonpolar portions of phospholipids that face inward in the membrane.

Phosphate Head

The hydrophilic, polar portion of a phospholipid that faces the watery environments inside and outside the cell.

Polar Molecule

A molecule with an uneven distribution of electrical charge.

Nonpolar Molecule

A molecule with an even distribution of electrical charge.

Aqueous

Containing or consisting of water.

Phospholipid Bilayer

A double layer of phospholipids that forms the basic structure of the plasma membrane.

Fluid Mosaic Model

The model describing the membrane as a flexible phospholipid bilayer containing proteins and other molecules that move within it.

Cholesterol

A steroid in animal cell membranes that helps maintain membrane fluidity and stability as temperature changes.

Steroid

A lipid characterized by four fused carbon rings; cholesterol is an example.

Glycolipid

A lipid with a carbohydrate attached that helps with cell recognition and communication.

Glycoprotein

A protein with a carbohydrate attached that helps with cell recognition and communication.

Integral Protein

A membrane protein embedded in the phospholipid bilayer; may function as a channel, carrier, or pump.

Peripheral Protein

A protein attached to the surface of a membrane that can help with signaling, support, or other functions.

Protein Channel

A membrane protein that forms a passageway for specific substances to cross the membrane.

Aquaporin

A channel protein that allows water to cross the cell membrane rapidly.

Selective Permeability

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

Intracellular

Located inside a cell.

Extracellular

Located outside a cell.

Simple Diffusion

The passive movement of molecules from high to low concentration directly through the membrane, without transport proteins.

Facilitated Diffusion

The passive movement of substances from high to low concentration through membrane transport proteins.

Passive Transport

Movement of substances down their concentration gradient without requiring cellular energy (ATP).

Active Transport

Movement of substances against their concentration gradient using energy, usually ATP.

Concentration Gradient

A difference in the concentration of a substance between two areas.

Equilibrium

A state in which concentrations are balanced and there is no net movement of a substance.

Membrane Permeability

How easily a substance can cross a membrane.

Ion

An atom or molecule with a positive or negative electrical charge.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Osmosis

The net movement of water across a selectively permeable membrane toward the side with the higher effective solute concentration.

Water Potential

A measure of the tendency of water to move; water moves from higher water potential to lower water potential.

Solute Potential

The component of water potential affected by dissolved substances; adding solute lowers water potential.

Pressure Potential

The component of water potential caused by physical pressure, such as pressure against a plant cell wall.

Tonicity

The ability of a solution to cause a cell to gain or lose water based on effective solute concentrations.

Hypertonic

A solution with a higher effective solute concentration than the cell; water moves out of the cell, causing it to shrink.

Hypotonic

A solution with a lower effective solute concentration than the cell; water moves into the cell, causing it to swell.

Isotonic

A solution with the same effective solute concentration as the cell; there is no net movement of water.

Osmoregulation

The process of controlling water balance and solute concentrations in an organism or cell.

Osmolarity

The total concentration of dissolved solute particles in a solution.

Plasmolysis

The shrinking of a plant cell's membrane away from its cell wall as water leaves the cell.

Turgid

A firm plant cell swollen with water; the cell wall prevents it from bursting.

Flaccid

A limp plant cell that has lost turgor pressure.

Lysis

The bursting or breakdown of a cell.

Na+/K+ Pump

A membrane protein that uses ATP to move three sodium ions out of a cell and two potassium ions into it against their concentration gradients.

Endocytosis

A process in which a cell takes in substances by forming vesicles from its plasma membrane; requires energy.

Exocytosis

A process in which a vesicle fuses with the plasma membrane to release substances outside the cell; requires energy.

Vesicle

A small membrane-bound sac that transports or stores substances inside a cell.

Vacuole

A membrane-bound compartment used for storage, water balance, or other functions; plant cells often have a large central vacuole.

Contractile Vacuole

An organelle that collects and expels excess water from certain freshwater organisms.

Endomembrane System

A group of connected or interacting membranes and organelles that modify, package, and transport proteins and lipids.

Rough Endoplasmic Reticulum (RER)

Membrane network covered with ribosomes; makes and begins processing proteins destined for membranes, organelles, or secretion.

Smooth Endoplasmic Reticulum (SER)

Membrane network without ribosomes that synthesizes lipids, detoxifies substances, and stores calcium ions.

Golgi Body (Golgi Apparatus)

Organelle that modifies, sorts, and packages proteins and lipids for transport.

Lysosome

An organelle containing digestive enzymes that break down waste, food particles, and damaged cell components.

Hydrolytic Enzymes

Enzymes that break chemical bonds by adding water; lysosomes use them to digest substances.

Ribosome

A structure made of rRNA and proteins that carries out protein synthesis.

Ribosomal RNA (rRNA)

RNA that forms part of ribosomes and helps them build proteins.

Mitochondrion

An organelle that carries out most cellular respiration in eukaryotic cells and produces ATP.

Chloroplast

An organelle in plants and algae that carries out photosynthesis to produce sugars.

Plastid

A plant or algal organelle, including chloroplasts, that can perform photosynthesis or store substances.

ATP

A molecule that provides usable energy for many cellular processes.

Cellular Respiration

The process that extracts energy from organic molecules to produce ATP.

Photosynthesis

The process of converting light energy into chemical energy stored in sugars.

Apoptosis

Programmed cell death that helps organisms remove damaged, unnecessary, or unwanted cells.

Prokaryote

An organism whose cells lack a nucleus and other membrane-bound organelles; includes bacteria and archaea.

Eukaryote

An organism whose cells have a nucleus and membrane-bound organelles.

Cell Compartmentalization

The separation of cellular functions into distinct organelles or membrane-bound regions, increasing efficiency.

Extracellular Matrix (ECM)

A network of substances outside animal cells that provides structural support and helps cells communicate and attach.

Endosymbiosis

A relationship in which one organism lives inside another; explains the origin of mitochondria and chloroplasts from ancient prokaryotes.

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or other cells.

Binary Fission

A process in which a prokaryotic cell copies its DNA and divides into two cells.

Kelvin (K)

The SI unit of temperature; 0°C equals 273.15 K.

Cell Wall

A rigid outer layer in plants, fungi, and bacteria that provides support and protection; plant cell walls also help prevent bursting from water uptake.

Internal Membranes

Membranes within cells that create compartments and increase the surface area available for cellular reactions.