The heart has four valves that control the flow of blood. Two of the valves (the AV valves) normally prevent blood fromflowing upwards. The other two valves (semilunar valves) normally prevent blood from flowing downwards. The AV valvesand semilunar valves have different shapes. Which principle of anatomy and physiology does this example represent?
1. Organ systems are interconnected.
2. Organ systems contribute to homeostasis.
3. There is a hierarchy of anatomical organization in an organism.
4. Structure is linked to function.

Match the following terms describing electrical events with the correct phases of the cardiac cycle. the ventricular muscle cells depolarize at the start of this phase. during this phase, na+ entry through the funny channels causes the pacemaker potential of sa nodal cells to gradually become less negative until it reaches threshold. the ventricular muscle cells repolarize right before this phase. the cytosolic concentration of calcium in the contractile cells of the ventricle is highest during this phase. a. isovolumetric relaxation b. ventricular ejection c. isovolumetric contraction d. ventricular filling

Asmall population of chimpanzees lives in a habitat thant undergoes no change for a long period of time. how will genetic drift affect this population

Why did mendel use pea plants in his experiments? a. they have no alleles. b. they are haploid organisms. c. they reproduce quickly. d. they are all male.