Consider the four spheres. as illustrated by the diagram, we would expect spheres a - c to be attracted to sphere d. sphere d has the greatest gravitational force because as represented here, it

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.