Suppose a mutation greatly increases the affinity of a rod's sodium channels for cgmp, such that once cgmp binds to a channel, it remains bound for much longer than normal. what would be the effect of this mutation on the rod's sodium channels?

The effect of this mutation is a gain in function that will stimulate the sodium channel and allow more sodium to pass inside the cell.

There are two types of consequence of mutations on proteins, loss of function, gain of function or neutral.

Mutation gain of function (which is rare) is that the protein is gaining activity, this is the example shown with the sodium channel. This has negative consequences (toxic effect) if the protein works more than it should. This will affect the function of the cell and may destroy it. the rod cells are cells found at the level of the photoreceptor of the eye, this mutation can have serious consequences on the sight.

answer: decrease

a limiting factor is the one which decrease the abundance, distribution and causes extinction of the population of species in a ecosystem. here, predators including hawks, owls and snakes are the limiting factor for the population of mexican free tailed bat.   although bats are nocturnal animals as they forge for food at night these predators also may remain active during night which can decrease the population of the mexican free-tailed bats. also, these bats eat only one type of insects that are moths. the food can also be a limiting factor as all 400 members are dependent upon same type of food needs that are moths. the decrease in the moth population can cause decrease in population size of the mexican free-tailed bats.

therefore, the scenarios will most likely to decrease the population size of the mexican free-tailed bats.  

i think that it is plants