Either effect pedals, the knobs on the bass itself, of the bass-mid-treble controls on the amplifier

Actually, you can play both bass and guitar on any amplifier.

But to produce a better and lower sound for bass, you need a special amplifier for it.

I am not sure that there is an amplifier that can play bass and guitar with equal quality.

If this means you are using a guitar amplifier to power an electric bass, stop this immediately. Guitar amps are not designed to handle the low register of a bass, and you can blow out your speakers.

If this means you are using a guitar amplifier to power a guitar, but want a more bass-like tone, turn down the mids and highs and turn up the lows on your EQ. That should do the trick.

Electromagnets are not used on bass guitars, but guitar and bass guitar pickups use magnets in order to turn the string's vibration into an electrical signal to send to amplifier.

A bass guitar is a solid-bodied stringed instrument tuned to produce bass or low notes, with a fretted fingerboard and four thick strings, requiring use of an amplifier.