Taq polymerase is an enzyme used in the polymerase chain reaction (PCR) to replicate fragments of DNA, A study published in 1976 examined the properties of Taq polymerase
after the enzyme was isolated from Thermus aquaticus, a thermophilic bacterium that lives in
the hot springs of Yellowstone National Park. The graph shows one of the results of the study
Enzyme Activity
0 20 40 60 80 100
Temperature (°C)
Source: Chien et al., "Deoxyribonudeic Acid
Polymerase from the Extreme Thermophile
Thermus aquaticus," Journal of Biology
1976
Which statement about enzyme activity is best supported by this graph?
F An enzyme must be composed of multiple polypeptides, or subunits, to be active.
An enzyme's rate of activity increases with time until it becomes inactive.
HAn enzyme functions best under specific temperature conditions.
) An enzyme works equally well in bacteria that are adapted to high temperatures and in
eukaryotic cells such as human cells.

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).