(a) While deriving Bernoulli’s equation, we say that, decrease in pressure energy per second = increase in K.E./sec. + increase in P.E./sec. Assume that viscous forces are absent. Thus as the fluid flows from lower to upper edge, there is a fall of pressure energy due to the fall of pressure. If dissipating forces are present, then a part of this pressure energy will be used in overcoming these forces during the flow of fluid. So there shall be greater drop of pressure as the fluid moves along the tube.
(b) Yes, the dissipative forces become more important as the fluidvelocity increases.
According to Newton’s law of viscous drag, we know that F=−ηA

dv

dx

Clearly as v increases, velocity gradient increases and hence viscous drag i.e. dissipative force also increases.