Which term refers to the structure that forms the surface of a cell, seperating it's contents from the outside world? a. endoplasmic reticulum b. plasma membrane c. mitochondria d. capsule asap! quick! now!

1. beginning with all chambers of the heart in the "relaxed" phase, describe the cardiac cycle in mammals, with systole and diastole of the atria and ventricles. for each time point in the cycle you select, state the following: • whether the atria and ventricles are contracting or relaxing • whether the av valves and semilunar valves are closed or open • whether the pressure in the atria and ventricles is high or low