Doctors use the radioactive isotope chromium-51 to label red blood cells in the human body. Chromium-51 gives off relatively alpha particles that can be stopped by . A) energetic; lead
B) weak; a sheet of paper.
C) weak; a thin sheet of copper.
D) energetic; a thick sheet of copper.

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

Freckles are a dominant trait in humans. both of the girls have the genotype ff for freckles. if either one marries a man with no freckles, what are the chances that their children will have freckles?

What is one way intensive agriculture can contribute to climate change? a. tree loss to agriculture increases earth's albedo b. livestock manure absorbs greenhouse gases c. large herds of livestock release greenhouse gases d. fewer trees are available to replenish petroleum stores appex