Blood moves into and then out of a heart chamber because 1. the veins and arteries constrict and dilate to propel and attract blood. 2. it moves along its pressure gradient, and that gradient depends on contraction and relaxation during the cardiac cycle. 3. it is under constant pressure, but its movement is dictated by the control of valve openings and closures. 4. All of the choices are correct.

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.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.