1.3: Cell membranes and transport

Proteins and phospholipids

What the cell membrane is made of.

Bilayers

Sheets of phospholipids facing each other.

Extrinsic

Proteins that can be embedded in either surface of the phospholipid bilayer, and provide structural support, form recognition sites, identify cells and form receptor sites for hormone attachment.

Intrinsic

Proteins that extend across both layers of the phospholipid bilayer, includes transport proteins.

Transport

Proteins that allow molecules or ions to pass through during active transport or facilitated diffusion.

Fluid-mosaic

Structural model of the plasma membrane where molecules are free to move within the bilayer.

Glycoproteins

A protein with one or more covalently attached carbohydrates. Used for cell-to-cell recognition.

Glycolipids

Membrane carbohydrates that are covalently bonded to lipids. Used for cell-to-cell communication and maintaining stability of the membrane.

Glycocalyx

A carbohydrate coat that covers the cell surface, used in hormone receptors and cell-to-cell recognition and adhesion.

Diffusion

Passive transport that occurs when ions and molecules move from a high to low concentration area.

Facilitated diffusion

Allows water-soluble molecules through the membrane via transport proteins.

Carrier

A transport protein that works with molecules binding to the protein, which reshapes to allow them through. Less efficient.

Channel

Transport protein that works by opening to allow molecules through and closing to stop them. More efficient.

Active transport

Diffusion that occurs against a concentration gradient - requires ATP.

Osmosis

Water diffusion, where an area of high water potential will move down a gradient to an area of low water potential.

Water potential

The measure of free water molecules and the tendency of water to move.

Solute potential

The meaure of how easily water molecules can leave a solution.

Kilopascals

How water, solute and pressure potential are measured.

Osmotic pull

The pull of a solution with a low water potential on neighbouring water molecules.

Pressure potential

The pressure exerted by the cell wall on the cell contents.

Turgid

When a plant cell can take in no more water, supporting the cell structure.

Hypotonic

A solution with a higher water potential than the cell it surrounds.

Hypertonic

A solution with a lower water potential than the cell it surrounds.

Incipient plasmolysis

The start of plasmolysis - when the cytoplasm begins to move away from the cell wall.

Plasmolysis

A process where the vacuole shrinks, causing the cytoplasm to move away from the cell wall.

Isotonic

A solution with the same water potential as the cell it surrounds.

Haemolysis

When an animal cell bursts due to being surrounded by a hypotonic solution.

Crenated

When an animal cell shrinks due to being surrounded by a hypertonic solution.

Endocytosis

When materials are absorbed by extensions of the cell membrane or cytoplasm and converted into vesicles, requiring ATP.

Phagocytosis

A form of endocytosis, occurs when solid material is too big to be taken up by other methods.

Pinocytosis

A form of endocytosis, occurs when liquids are unable to be taken up by other methods.

Exocytosis

How substances leave the cell - turning into vesicles and fusing with the cell membrane.

Respiratory inhibitors

Inhibit the production of ATP, therefore limiting active transport.

Co-transport

Occurs when molecules that use facilitated diffusion bond to other molecules to move them against a concentration gradient.

Co-transporters

Special carrier proteins used in co-transport.

Cholesterol

Sterol in animal cell membranes. Inbetween the phospholipid molecules, maintaining stability at higher temperatures and fluidity at lower temperatures.

Flaccid

When a plant has completed plasmolysis, so the cell has no structural support.