IB Biology Topic B2.1: Membranes and Membrane Transport Key Definitions

Active transport is the movement of molecules or ions across a membrane against their concentration gradient (from low to high concentration), which requires energy.

Amphipathic: A molecule that has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

A molecule with both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions, such as a phospholipid.

Cell-adhesion molecules (CAMs) are proteins that span the phospholipid bilayer of the membrane.

A specialized protein embedded in the membrane, allowing specific ions or molecules to diffuse across.

A network of protein fibers, including microtubules, microfilaments, and intermediate filaments.

The process by which the plasma membrane pinches inward to form a vesicle that brings external materials into the cell.

The process by which a vesicle fuses with the plasma membrane to release its contents outside the cell.

A protein with carbohydrate chains attached, which are involved in cell recognition, signalling, and adhesion.

Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

The ability of a substance (e.g., oxygen, carbon dioxide, or water) to pass through a membrane or surface.

Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, down their concentration gradient, without requiring energy (ATP).

The sodium-glucose cotransporter is a protein that moves sodium ions (Na⁺) and glucose molecules together across a plasma membrane into a cell.

Vesicles are small, membrane-bound sacs composed of a phospholipid bilayer. They enclose a fluid-filled space and can carry various substances.