Topic 1.3 - Membrane transport Flashcards
Give the two key properties of a membrane
Semi-permeable (only certain things can cross)
Selective (membranes can regulate material passage)
Give the two types of membrane transport
Passive (along concentration gradient, no ATP expenditure)
Active (against concentration gradient, ATP is required)
Describe simple diffusion
The net movement of particles from a region of higher
concentration to a region of lower concentration (i.e. along the gradient) until equilibrium is reached
Describe facilitated diffusion
The passive movement of molecules across a cell membrane via the aid of a membrane protein (carrier / channel protein)
What is osmosis ?
The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of higher solute concentration (diffusion of free water molecules)
What is osmolarity ?
Osmolarity is a measure of solute concentration
How can a solution’s osmolarity be measured ?
Solutions can be measured as:
* Hypertonic: High solute concentration (gains water)
* Hypotonic: Low solute concentration (loses water)
* Isotonic: Same solute concentration (no net flow)
What is Active transport ?
Active transport uses energy (ATP) to move molecules
against a concentration gradient (i.e. from low to high)
Molecule binds to a transmembrane protein pump
Hydrolysis of ATP causes a conformational change,
translocating the molecule across the membrane
Give example of active transport
Sodium-potassium pumps move ions in neuron
Give the two types of co-transport
- Symport: Both molecules move the same direction
- Antiport: Molecules move in opposite directions
What is vesicular transport ?
The fluidity of the plasma membrane allows it to break and reform around certain materials (this process requires ATP)
* Exocytosis: Materials released from a cell via vesicles
* Endocytosis: Materials internalised within a vesicle
What is the difference between exocytosis and endocytosis ?
Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell. Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
