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 diffustion

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.