1.4 Membrane Transport Flashcards
What are 2 key qualities that cellular membranes posses?
they are
- semi-permeable
- selective
What does it mean that a membrane is semi-permeable?
They are semi-permeable (only certain materials may freely cross – large and charged substances are typically blocked)
WHat does it mean that a membrane is selective?
They are selective (membrane proteins may regulate the passage of material that cannot freely cross)
In what 2 ways can movement of material occur across a membrane?
Movement of materials across a biological membrane may occur either ACTIVELY or PASSIVELY
What does passive transport involve?
Passive transport involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)
Does passive transport require energy? why?
NO
Because materials are moving down a concentration gradient, it does not require the expenditure of energy (ATP hydrolysis)
What are the 3 main types of passive transport?
- simple diffusion
- facilitated diffusion
- osmosis
What molecules are moved in simple diffusion?
movement of small or lipophilic molecules (e.g. O2, CO2, etc.)
What molecules are moved in osmosis? What is osmosis dependent on?
movement of water molecules (dependent on solute concentrations)
What molecules are moved in facilitated diffusion? What helps?
movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.)
What does active transport involve?
Active transport involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)
Does active transport require energy? why?
Because materials are moving against the gradient, it requires the expenditure of energy (e.g. ATP hydrolysis)
What are the 2 main types of active transport?
primary (direct)
secondary (indirect)
What does primary active transport involve?
Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport
What does secondary active transport involve?
Involves coupling the molecule with another moving along an electrochemical gradient
What is diffusion?
Diffusion is the (random) net movement of molecules from a region of high concentration to a region of low concentration
When will diffusion stop?
This directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium)
What 3 factors can influence diffusion?
- temperature
- molecular size
- steepness of gradient
How does temperature affect diffusion?
affects kinetic energy of particles in solution
How does molecular size affect diffusion?
larger particles are subjected to greater resistance within a fluid medium
How does the steepness of gradient affect diffusion?
rate of diffusion will be greater with a higher concentration gradient
What is osmosis?
Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
What type of solvent is water? What does this mean?
Water is considered the universal solvent – it will associate with, and dissolve, polar or charged molecules (solutes)
How does water help solute transport?
Because solutes cannot cross a cell membrane unaided, water will move to equalise the two solutions
How is the water concentration affected by a high solute concentration?
At a higher solute concentration there are less free water molecules in solution as water is associated with the solute
Where does osmosis occur and why?
Osmosis is essentially the diffusion of free water molecules and hence occurs from regions of low solute concentration (not associated with other molecules)
What is osmolarity?
Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)
Relating to osmolarity, what 3 categories can solutions be put into?
- hypertonic
- hypotonic
- isotonic
What does it mean if a solution is hypertonic?
Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water)
What does it mean if a solution is hypotonic?
Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water)
What does it mean if a solution is isotonic?
Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow)
How can the osmolarity of a tissue be tested?
by bathing the sample in solutions with known osmolarities
What will happen if the tissue is placed in a hypertonic solution?
The tissue will lose water when placed in hypertonic solutions
What will happen when a tissue is placed in a hypotonic solution?
gain water when placed in hypotonic solutions
How can the change in weight of a tissue be measured?
Water loss or gain may be determined by weighing the sample before and after bathing in solution
How can tissue osmolarity be inferred?
Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)