1.4 Membrane Transport Flashcards
What is passive transport?
e.g. diffusion, osmosis, facilitated diffusion
does not use energy as molecules move from a high gradient to a low concentration i.e. moving down the concentration gradient
What is active transport?
e.g. ion pumps and phagocytosis uses energy (ATP) as molecules move from a low concentration to a high concentration i.e. against the concentration gradient two main types: protein pumps and use of vesicles
What is diffusion?
passive transport
high conc to low conc
no energy required
consequence of the random motion of particles
the cell membrane is only semi-permeable so many substances are unable to diffuse due to their size or polarity
mostly gases and minerals
Factors that affect rate of diffusion
size of the molecules - smaller = faster
temperature - Ek
concentration gradient - big difference = faster
What is facilitated diffusion?
passive transport
molecules or ions
via specific transmembrane integral proteins
polar molecules cannot diffuse easily due to the hydrophobic nature of the fatty acid tails - hence all polar molecules are transported by proteins
e.g. glucose (too big), sodium ions, chloride ions etc.
Ion channels
are different type of facilitated diffusion
involves channel proteins which do not bind to the molecules
allow rapid transport
What is osmosis?
movement of water molecules from an area of high conc to low conc through semi - permeable membrane
passive transport
Hypertonic
high salt solution low water cell will lose water and shrink become flaccid if it is a plant cell - the cell membrane will pull away from the cell wall and may not recover (become plasmolysed)
Hypotonic
low salt solution
high water
cell will gain water and swell
become turgid
if it is a plant cell it will be constrained by the cell wall (this is ideal)
is an animal or protist cell it may burst (not good)
Isotonic
same concentration as the cell
cell remains unchanged
just right for animal cells
ok but not ideal for plant cells
What is osmolarity?
measure of the concentration of solutes in a solution
water has osmolarity of zero
process of controlling this is called osmoregulation
Why is isotonic solutions important in medicine?
tissues or organs to be used in medical procedures must be placed in isotonic solutions must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis
How do potassium ion channels works?
most common
they are used to move K ions through the membrane
in axons of neurons
the axons cells transmit electrical impulses to create voltage differences across the membrane this causes either the opening of closing of this pump
How do protein pumps work? (AT)
only transport specific substances in a specific direction
substance bind to protein and energy is used to move substance through
3 types:
- uniport - transports one substance in one direction
- symport - transports two different substances in the same direction
- antiport - transports two different substances in opposite directions
How do sodium - potassium pumps work?
nerve cells contain a pump that moves sodium and potassium ions across the membrane in opposite directions (antiport)
one ATP molecule is enough to move 3 Na out and 2 K in
ATP causes switch from one state to another
it helps establish a net charge across the plasma membrane
