What is the term for the body's immediate response to a perceived threat?

For a reaction $2{\mathrm{H}}_2{\mathrm{O}}_2$

$2{\mathrm{H}}_2{\mathrm{O}}_2\underset{\mathrm{Alkaline} \mathrm{medium}}{\overset{{\mathrm{I}}^{-}}{\to }}2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$

The proposed mechanism is as given below:

1. ${\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{I}}^{-}\to {\mathrm{H}}_2\mathrm{O}+{\mathrm{IO}}^{-}$ (slow)

2. ${\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{IO}}^{-}\to {\mathrm{H}}_2\mathrm{O}+{\mathrm{I}}^{-}+{\mathrm{O}}_2$ (fast)

Out of steps (1) and (2), which one is rate-determining step?

For the reaction 

$2{\mathrm{N}}_2{\mathrm{O}}_5\left(\mathrm{g}\right)\to 4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$,

the rate of formation of ${\mathrm{NO}}_2\left(\mathrm{g}\right)$ is $2.8\times {10}^{-3} {\mathrm{Ms}}^{-1}$. Calculate the rate of disappearance of ${\mathrm{N}}_2{\mathrm{O}}_5\left(\mathrm{g}\right)$.