Transport across membranes - MZH Flashcards
Definition of osmosis
The net movement of water from a solution of higher to lower water potential through a partially permeable membrane.
Definition of water potential
The pressure exerted by water molecules as they collide with a membrane or container.
Why do solutes lower water potential?
- Solutes decrease the concentration of water molecules.
- The molecules are polar and cluster around the solute.
- Therefore, there is less ‘free’ molecules that can diffuse into other areas.
Will a more concentrated solution have a higher or lower water potential?
Lower (more negative) as the highest water potential (pure water) is 0 kPa
Definition of diffusion
The net movement of particles from where they are at a higher to where they are at a lower concentration.
Simple diffusion key points
- Passive process (No ATP required)
- Occurs down a concentration gradient
- Movement of small, non-polar, uncharged particles through a bilayer.
Facilitated diffusion key points
- Passive process (No ATP required) as substances pass using carrier protein (No cell energy)
- Occurs down a concentration gradient
- Movement of large molecules by carried proteins e.g. Glucose
- Movement of charged or polar particles through channel/pore proteins.
Osmosis key points
- Passive process (No ATP required)
- Occurs down a concentration gradient (higher to lower water potential)
- H2O molecules move through Aquaporins (channels)
Active transport
- Active process (ATP required)
- Occurs against a concentration gradient
- Occurs with the aid of carrier proteins; each one specific and has a binding site with a complementary fit with a particular molecule.
Cytosis key points
- Active process (ATP required)
- The bulk transport of large molecules by vesicles e.g. Bacteria, proteins
Definition of Exocytosis
An active transportation of large materials in bulk by vesicles from INSIDE the cell to the OUTSIDE.
Example:
Secretion of amylase from salivary glands
Definition of Endocytosis (Importing)
An active transportation of large materials in bulk by vesicles from OUTSIDE the cell to the INSIDE.
Definition of Phagocytosis
The uptake of SOLIDS by vesicle formation.
Example:
Ingestion of bacteria by white blood cells
Definition of Pinocytosis
The uptake of FLUIDS by vesicle formation.
Example:
Lipid absorption by epithelial cells of small intestine
Definition of equilibrium in relation to membranes
When the particle distributions on each side of the partially permeable membrane are equal.
