However you can practice engineering if you know the concepts of engineering. Logical thinking, up to date knowledge in the field and creativity are the key components. But with out a certificate, you cant call yourself an engineer. However you can practice. I have seen many good self-taught engineers (informal) who know what they are doing very well.
The training is quite different, but there are scenarios where you might be hired, more likely, if you are self trained in engineering.
i am an antennas engineer , can i work as a biologist ?
definately
