Subject: Does the rate-det. step depend on Ea from starting mat. or relative Ea?

Hi,
This may be a basic question, but when I asked my orgo prof. and TA, I 
still wasn't quite sure of their answer.  They said that the slow step of a 
reaction is the rate determining step, and that the step with the highest 
activation energy is slowest step, which all make sense to me.  However, I 
asked what about a graph where the Ea to get from the starting material to 
the intermediate is greater than the Ea from the intermediate to the 
product (like below), wouldn't the rate determining step (the slow one) be 
getting from the starting material to the intermediate?
                   _
            _     /|\
           /|\   / |(Ea2)          Ea1 > Ea2
          / | ---  |  \
         /  |          \
        /   |(Ea1)      \
       /    |            \
They said that the rate-det. step is the greatest Ea from the starting 
material only, but that doesn't make sense to me since it's faster to get 
from the intermediate to the prod.  If we said the starting is X, the 
intermediate is Y, and the prod is Z, then wouldn't it be like this?:
                  X->Y   slow
                  Y->Z   fast, so rate = k[Y] = k'[X]?
Thanks.

Ben

Re: Does the rate-det. step depend on Ea from starting mat. or relative Ea?