Describe the structure of the ovule and the formation of embryo sac​

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.

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.