Motion is not the only indicator of the passage of time in art. use the changing properties of organic material to create a sense of time passing in their art

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus

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.