During the course of an action potential, the membrane potential rapidly rises and reaches a peak of about +40 mV before falling
to about -75 mV. What causes the fall in membrane potential? A) A decrease in Na+ permeability, and an increase in K+ permeability
B) A decrease in the permeability to both Na+ and K+
C) An increase in Na+ permeability, and a decrease in the K+ permeability
D) An increase in the permeability to both Na and K
A) A decrease in Na+ permeability, and an increase in K+ permeability.
Explanation:
When the potential action reaches a peak of about +40 mv Na+ channels are open and a high number of Na+ ions are entering the inside of the cell. Shortly after this happens the K+ channels will start to open their gates increasing the cell K+ permeability while the Na+ channels will start to close their gates, so the Na+ permeability will decrease. This happens in order to valance the positive charge on the inside of the cell. Normally the inside has a negative charge while the outside has a positive one, as the inside is more positive due to the increase in Na+ permeability at the beginning of the potential action, K+ cations (which are in abundance in the cell) will have to go out through the K+ channels so as to restore the charge valance, that means that there is an increase in K+ permeability.
To find the allele frequencies, we again look at each individual's genotype, count the number of copies of each allele, and divide by the total number of gene copies
The most likely cause of the beak variation is the food source of the finch, the break size and shape was adapted to most likely have easier and better access to food. <span />
