Ch 4 Flashcards
T/F: The plasma membrane is permeable to any type of molecule.
False! The plasma membrane is selectively permeable.
Random molecular movement of substances through the membrane either through a channel or pore.
Passive transport
What is the energy source for diffusion?
Kinetic energy of matter; substances tend to move along the gradient from greater concentration to areas of lesser concentration
Define active transport.
Transport across a cell membrane that occurs against its electrochemical or concentration gradient and requires the use of ATP.
What is the difference between diffusion and osmosis?
Diffusion is the random motion of particles and their tendency to move from areas of higher concentration to lower; osmosis is the movement of water through a semipermeable membrane in the presence of a concentration difference
Define osmolarity.
Total concentration of all solute particles in a solution.
Hydrostatic pressure
Pressure exerted by water against its surrounding membrane
A hypertonic solution will cause a cell to:
lose water and shrink
A hypotonic solution will cause a cell to:
swell
How is filtration different from diffusion?
Filtration: water and solutes forced through membrane by hydrostatic pressure, rather than by the kinetic forces of molecular motion and the effects of concentration gradients.
What types of substances most easily diffuse through the cell membrane?
Lipid soluble molecules, such as oxygen, nitrogen, carbon dioxide, alcohols
T/F: thicker cell membrane=slower rate of diffusion
TRUE!
How does temperature effect rate of diffusion?
Higher temp=greater rate of diffusion
How does molecular weight effect rate of diffusion?
Greater molecular weight=greater resistance, i.e. slower diffusion
T/F: protein pores are selectively permeable to certain substances
FALSE! Well, unless a molecule is too big to pass through. Otherwise, they are open for passage. Protein channels, on the other hand, are selectively permeable and/or gated, regulated by electrical signals or chemical binding.
What type of gate is activated by a change in electrical potential across cell membrane?
Voltage gated protein channel
Define a ligand gated protein channel
Protein channel opened by the binding of a chemical substance (a ligand) with the protein.
Give an example of ligand gating in the propagation of nerve signals.
Acetylcholine: ACh opens gate of this channel, allows positively charged ions (Na+, K+, Ca2+) to enter to elicit further APs or trigger muscle contraction.
Sodium-Potassium Pump: List substances transported, direction of transport, and amount of each
3 Na+ ions out of cell; 2 K+ ions into cell
Major function(s) of Na+K+ pump
Maintains concentration differences across the cell membrane; establishes a negative electrical voltage inside the cell (electrogenic); basis for nerve function and nerve signal transmission; controlling cell volume (preventing too much water from entering the cell when there is a high presence of solute in the cell)
Calcium Pump: type of transport, function
Primary active transport; pumps calcium out of the cell; homeostatic function (maintain low intracellular Ca2+ level)
Coupling mechanism in which more than one substance are carried across the cell membrane
co-transport
Which secondary active transport method involves 1 ion entering and 1 ion leaving the cell simultaneously?
Counter-transport
Name the secondary active transport method by which glucose can enter a cell utilizing the transport of ANOTHER ion.
Co-transport: transport carrier protein has 2 binding sites, one for sodium and one for glucose; concentration of Na+ outside the cell provides a gradient/energy for transport to occur
What are 2 examples of substances that co-transport with Na+?
Amino acids and glucose
What is a general rule for predicting the behavior or water in the presence of solutes across a semi permeable membrane (osmosis)
“water follows salt”
Explain osmotic pressure
The exact amount of pressure required to stop osmosis. “Resistance” to the flow of water through a semi permeable membrane that is sufficient to stop the movement of water.
What are 3 types of gradient that can exist across a cell membrane?
Concentration difference of molecules, electrical (charge) difference, and pressure difference across a cell membrane may contribute to an electrochemical gradient.
