A student wants to compare the amounts of CO2 given off by yeast provided with different amounts of sugar. The student places a balloon over each
container to catch the released CO2. How can the student make quantitative
observations of the CO2 collected in the balloons?
A. Describe the shape of each balloon.
B. Approximate the relative size of each balloon.
C. Measure the circumference of each balloon.
D. Count the individual CO2 molecules in each balloon.

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i.e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).