Natural selection is the process that result in the adaptation of an organism to environment by means of selectively reproducing changes in its genotype, or genetic constitution. It is the a key mechanism of evolution. Charles Darwin popularised the term "natural selection" contrasting it with artificial selection, which is intentional, whereas natural selection is not.
To make it simple, let's have a group of beetle composing of green and some are brown as an example. here, there is a variation in traits. Since the environment could not support continuous population growth, not all species can reproduce to their full potential. Green beetles can easily be eaten by other species like birds compared to brown beetles. The surviving brown beetles will then generate brown offsprings because their trait has a genetic basis. Since more brown beetles survive and becomes more common in the population, the process continues until all individuals will eventually be brown. so basically, if you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome.
The soles of people’s feet have a greater concentration of sensory receptors because more people are ticklish on the bottoms of their feet than the backs of their necks. There are more neurons in your appendages especially the ends of them because they are the furthest from the brain. Getting a tattoo on your feet vs. the back of your neck hurts more as well, making the soles of your feet have the greater concentration.
B - They both use protein channels (I think so at least) they differ because active transports use a pump to leave the cell and it uses atp (cell energy).
Facilitated diffusion therefore allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.
