Sally is a middle aged woman who has been experiencing strange pain in her abdomen. When she visits her doctor, the doctor discovers that Sally has a cancerous mass in her large intestine (colon). Upon further testing, it is discovered that Sally’s tumor is contained in her colon

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.

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.