Unit 1 Biology – Plasma Membrane & Transport

Vocabulary flashcards covering plasma membrane structure, components, and transport mechanisms including diffusion, osmosis, and active transport.

Plasma Membrane

The outer boundary of a cell that separates intracellular from extracellular environments and controls the movement of substances in and out.

Phospholipid

A lipid with a polar hydrophilic head and two non-polar hydrophobic tails; main structural molecule of cell membranes.

Hydrophilic Head

Water-loving, polar portion of a phospholipid that faces aqueous environments.

Hydrophobic Tail

Water-hating, non-polar fatty acid chains of a phospholipid that face inward in the bilayer.

Phospholipid Bilayer

Double layer of phospholipids with heads outward and tails inward, forming the basic structure of the plasma membrane.

Fluid Mosaic Model

Model describing the membrane as a fluid, moving phospholipid sea with proteins embedded like mosaic tiles.

Integral Protein

Membrane protein permanently attached and extending partway into the bilayer.

Transmembrane Protein

Integral protein that spans the entire membrane from one side to the other.

Peripheral Protein

Protein temporarily attached to the membrane surface or to integral proteins.

Channel Protein

Transmembrane protein forming an open pore for specific molecules or ions to diffuse through.

Carrier Protein

Membrane protein that changes shape to transport specific substances across the membrane.

Glycoprotein

Protein with attached carbohydrate chain; functions in cell recognition and signalling.

Glycolipid

Lipid with attached carbohydrate chain; involved in cell recognition and communication.

Cholesterol

Steroid molecule inserted between phospholipids that regulates membrane fluidity, especially in cold temperatures.

Selective Permeability

Property of membranes that allows some substances to cross more easily than others.

Polarity

Distribution of electrical charge within a molecule, leading to polar or non-polar character.

Polar Molecule

Molecule with unequal charge distribution (e.g., water); generally hydrophilic.

Non-polar Molecule

Molecule with even charge distribution (e.g., lipids); generally hydrophobic.

Hydrophilic

Having an affinity for water; dissolves or interacts with water.

Hydrophobic

Repelled by water; does not mix with or dissolve in water.

Like Dissolves Like

Principle that polar substances mix with polar, and non-polar with non-polar, but not with each other.

Passive Transport

Movement of substances across membranes without energy input, driven by concentration gradients.

Concentration Gradient

Difference in the concentration of a substance between two regions.

Simple Diffusion

Passive movement of small non-polar or weakly polar molecules directly through the phospholipid bilayer.

Facilitated Diffusion

Passive movement of larger or charged molecules via channel or carrier proteins.

Factors Affecting Diffusion Rate

Concentration gradient magnitude and temperature; steeper gradients and higher temperatures increase rate.

Osmosis

Passive diffusion of free water molecules across a semi-permeable membrane from high to low free-water concentration.

Free Water Molecule

Water molecule not bound to a solute and thus free to move across membranes.

Tonicity

Relative concentration of solutes (and thus free water) outside a cell compared to inside.

Isotonic Solution

External solution with equal solute concentration to the cell; no net water movement.

Hypotonic Solution

External solution with lower solute (higher free water) than the cell; water enters the cell.

Hypertonic Solution

External solution with higher solute (lower free water) than the cell; water leaves the cell.

Crenation

Shrivelling of animal cells in hypertonic solutions.

Lysis

Bursting of animal cells in extreme hypotonic solutions.

Turgor Pressure

Pressure of the plasma membrane against the cell wall in plant cells, produced by water uptake in hypotonic environments.

Active Transport

Energy-requiring movement of substances against their concentration gradient via transport proteins.

ATP (Adenosine Triphosphate)

Cellular energy currency used to power active transport and other processes.

Protein Pump

Membrane protein that uses ATP to move ions or molecules against their gradient.

Bulk Transport

Energy-dependent movement of large particles or many molecules via vesicles; includes endocytosis and exocytosis.

Endocytosis

Bulk transport process where the membrane folds inward to bring substances into the cell, forming a vesicle.

Exocytosis

Bulk transport process where vesicles fuse with the plasma membrane to release contents outside the cell.

Vesicle

Small membrane-bound sac used to transport substances within or into/out of the cell.

Semi-Permeable Membrane

Barrier that allows certain molecules to pass while restricting others, essential for osmosis and selective transport.