In a PNP the charge carriers are positive (holes), so the conventional current arrow may be more intuitive.
A key fact about BJTs that's usually omitted in elementary descriptions is the doping levels.
In an NPN the emitter will be extremely heavily doped n-type, perhaps 100 times more than the p-type
base. The n-type collector is extremely lightly doped, perhaps 100 times less than the base.
This is why the emitter and collector are not interchangable.
When the base is biased positive about 0.6V or so compared to the emitter (for NPN) then electrons are
injected across the pn-junction into the base in huge concentrations, which diffuse through the base and
to the base-collector junction before much else happens. If the collector-base junction is reverse biased
then those electrons are immediatelly accelerated through the junction to the collector.
The base current is small only because the electrons don't have time to recombine in the base before
finding the collector junction. The base voltage controls the flow, but the base current and voltage are
strongly related and it turns out that controlling the base current (to control its voltage and thus the
whole device), is usually the way to operate the device. Its common to think of it as a current controlled
device, yet the base voltage is what pulls electrons to it from the emitter.
(lets say arduino 5V to Base)
That would burn out the device, the base-emitter
junction voltage cannot be increased much before huge currents flow. Its very common to have a series
resistor on the base so the current is limited.