  This paper studies the impact of a transmitter's molecule generation process
on the capacity of a concentration based Molecular Communication (MC) system.
Constraints caused by the molecule generation process affect the availability
of the molecules at the transmitter. The transmitter has a storage of
molecules, and should decide whether to release or save the currently produced
molecules. As a result, the MC system has conceptual connections with energy
harvesting systems. In this paper, we consider two scenarios on the propagation
channel. The first scenario assumes a channel with no Inter-symbol Interference
(ISI), \emph{i.e.,} a memoryless channel. We derive bounds on the capacity of
the MC system in this scenario. The second scenario assumes the MC network with
ISI, in which the output of the channel depends on the history of released
molecules in the previous time-slots. Based on the assumptions that either the
transmitter or the receiver knows the channel statistics, we compute a lower
bound on the channel capacity.
