Which of these sentences is true with respect to species?

two organisms belong to the same species even if they are separated by a geographical barrier, as long as they can mate and produce sterile offspring.

two organisms belong to the same species even if they are separated by a geographical barrier, as long as they can mate and produce fertile offspring.

two organisms belong to different species if they are separated by a geographical barrier, even if they can reproduce and produce fertile offspring.

What have we learned from fossil evidence about evolution? a) it is an abrupt change. b)the process is observable. c) it takes place during one lifetime only. d)the most complex traits are always selected.

All living organisms are composed of a. only one cell. b. at least 100 cells. c. at least three cells. d. one or more cells.

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