Mutualism is the symbiotic relationship is when two organism benefit from interacting with the other one. Lichen is an example of mutualistic relationship. Lichen is a composite organism or one organism that is made up of smaller organisms. In this case the lichen is made up of algae and fungi. The algae goes through photosynthesis and produces glucose which the fungi then uses to get energy from. In return the fungi protects the algae from harmful factors in the environment by shielding the algae.
Commmensalism (Crow and Tree)
Commensalism is the symbiotic relationship in which two organisms interact with one another with one benefiting and the other not being harmed or benefited by the relationship. An example of this type of relationship is between a crow and a tree. The branches of the trees provides a crow with a place to rest and build a nest when it needs to. The tree is neither harmed nor benefited from the presence of the crow on its branches.
Parasitism (Dog and Tick)
Parasitism is the symbiotic relationship in which one organism benefits at the expense of the other. An example of parasitism is a tick living within the fur of a dog. The tick benefits from living within the fur of the dog since the fur provides shelter for the tick and the tick can feed off the dog's blood and get nutrients from it. The dog is harmed by the relationship, because not only is the tick sucking up some of its blood the tick can also spread disease like Lyme Disease to the dog.