My Biology textbook says that there are either five or six kingdoms in the scientific classification system. The five-kingdom scheme is Monera (Bacteria), Plantae (Plants), Fungi (Mushrooms, etc.), Animalia (Animals), and Protista (Single-Celled Eukaryotes). However, in the six-kingdom scheme, Monera is divided into Archaebacteria and Eubacteria.

My question is: Which scheme of kingdoms is correct? Is there a definate answer to the latter? Or is it not decided yet? I'd also like to know the differences between Archaebacteria and Eubacteria, and reasons why some scientists think Monera should be divided into thoise groups.

Have a look here for lots of info

but the bottom line is that "Kingdoms" are really human constructs more than biologically defined entities so it's not so much a question of how many are there really, more of who's classification scheme do you prefer to use for "organising" biodiversity! I expect someone will shoot me down for saying this (and they may well be correct to do so) but I think these days Kingdoms are used more for organising teaching or classifying textbooks (e.g. zoology vs botany) than anything else.

How many colours are there in the spectrum? Six is one obvious answer (red, orange, yellow, green, blue, purple) but Isaac Newton thought seven was a more perfect number so he invented indigo so there could be seven colours. But you could equally argue for eight (turquoise is different from both green and blue), and so on. These are arbitrary distinctions; and so are those between biological kingdoms.