Suppose that the radius of a typical cell is $10 \mu \mathrm{m}$ and that inside it $10^6$ ATP molecules are hydrolyzed each second. What is the power density of the cell in watts per cubic meter ( $1 \mathrm{~W}=1 \mathrm{~J} \mathrm{~s}^{-1}$ )? A computer battery delivers about 15 W and has a volume of $100 \mathrm{~cm}^3$. Which has the greater power density, the cell or the battery? (For data, see Exercise 2.23.)