Edited by Luke Many of you who are reading this have probably heard the words 'parasites', and have heard the words 'symbiotic' or 'symbiosis'. (Most likely from some Spiderman movie.) The movie definition of these two words are actually quite different.
A real example of a symbiotic relationship between two different species is the bacteria in our stomach. They help us digest our food, and also get theirs! Overall, an accurate definition of a real symbiotic relationship is that both species part of the relationship benefit from it.
Parasitism on the other hand, is quite the opposite. Parasitic relationships are ones where only one species benefits and the other doesn't. For example, fleas and lice get their food and energy from their hosts, but the host gets nothing.
Sometimes, different species in a symbiotic relationship become so evolved and reliant on each other that they turn into composite organisms. For example, the Portuguese man of war. (I will simply refer to it as PMOW. Heh, "PMOW", never heard that before!) The PMOW often resembles a jellyfish but is actually different groups of different organisms working together in one whole, happy colony.
MY source for this post came from a book called "Sciencia".