21. Which discovery would challenge the validity of this cladogram? A. A large aquatic vascular plant about 200 million years old
B. A species of algae that has existed for less than one million years
C. A moss species that has existed for less than 380 million years
D. A fossil of a fern more than 425 million years old

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