Keywords

Active transport: Transport of molecules or ions against a concentration gradient. Requires additional energy, usually in the form of ATP.

Allostery: Where binding of a molecule at one site triggers a change in chape of the protein.

Cholesterol: Steroid that inserts between the fatty acid tails of the phospholipids and regulates the fluidity of a membrane.

Crenated: When an animal cell is placed in a solution of low water potential, water leaves the cell by osmosis down the water potential gradient, causing the cell to shrivel up.

Cytolysis: When an animal cell is place in a solution of high water potential, water enters the cell by osmosis down the water potential gradient, rupturing its cell surface membrane.

Endocytosis: The inward transport of large quantities of molecules through the cell surface membrane. This requires an input of energy in the form of ATP.

Exocytosis: The outward transport of large quantities of molecules through the cell surface membrane. This requires an input of energy in the form of ATP.

Facilitated diffusion: Transport of molecules or ions across a membrane down a concentration gradient that require a transport protein to cross the membrane.

Flaccid: Plant cell in an isotonic solution that has lost its turgidity or a plant tissue in which the plants cells are plasmolysed.

Fluid mosaic model: Current model for the structure of membranes.

Hormones: Chemicals released by endocrine glands which acts as chemical signaling molecules.

Hydrophilic: A molecule able to associate with water as it possesses a charge which interacts with the dipoles on water molecules.

Hydrophobic: A molecule not able to associate with water as it is uncharged. It repels water.

Incipient plasmolysis: The point at which water leaving a plant cell by osmosis shrinks the protoplast so much that it no longer exerts any pressure on the cell wall.

Osmosis: A specialised form of diffusion where water molecules move from an area of higher water potential to one of lower water potential, down the water potential gradient, through a partially permeable membrane.

Partially permeable: Able to let some molecules or ions pass through and not others.

Phagocytosis: ‘Cell eating’. Uptake of large quantities of sold materials by endocytosis.

Phospholipid: Specialised lipid molecule containing a phosphate group, two fatty acids and glycerol. Forms a bilayer that is the structural basis of membranes.

Pinocytosis: ‘Cell drinking’. Uptake of large quantities of solutes in solution by endocytosis.

Plasmolysis: When a plant cell is placed in a solution of low water potential, water leaves the cell by osmosis , causing the protoplast to shrink, pulling the plasma membrane away from the cell wall.

Protoplast: Cell contents inside plasma membrane.

Selectively permeable: Presence of transport proteins determines which molecules can be transported across.

Tonoplast: The membrane surrounding the vacuole in a plant cell.

Turgid: When a plant cells is placed in a solution of high water potential, water enters by osmosis and the protoplast pushes against the cell wall.

Water potential: Measure of the tendency of water molecules to move from one region to another. Affected by solute concentration and any external applied pressure. Always a negative value measured in KPa.