Commensalism is a relationship between two organisms where one organism benefits but the other is not harmed and does not benefit at the same time.
Mutualism is a relationship between two organisms where both of them benefit.
Parasitism is a relationship between two organisms where one benefits and the other is harmed. The organism that is harmed is called a host where the benefitting organism lives in or on.
Crocodile bird and crocodile
The Egyptian plover is also known as the crocodile bird. The relationship between the two is called mutualism. The crocodile bird benefits by eating the food that is stuck in between the teeth of the crocodile. This benefits the crocodile because food that gets stuck in its teeth can actually cause infection.
Remora and shark
Remora and shark have a relationship called commensalism. The remora is a fish that swims under the shark or attaches itself to the shark. It benefits from the shark because it uses the shark as a means of transportation and at the same time, it gets to eat the left overs of the shark. The shark also serves as a bodyguard for these remoras. The shark is not harmed in this process but it does not benefit either.
Flea and dog
A flea and a dog have a relationship called parasitism. The dog is somewhat harmed by the flea, as it sucks its blood to feed itself and injects saliva into the skin of the dog which causes discomfort to the dog. The dog is the host on which the flea lives on.
Barnacle and whale
Barnacles and whales have a relationship that is called commensalism. The barnacle benefits from the whale by sticking to a whale. As the whale travels through plankton-rich waters, the barnacles get to feed on them through filter feeding. They also benefit because the whale acts as a mode of transportation and protection as they go to one feeding site to another.
Tapeworm and human
The tapeworm and human relationship is an example of parasitism. The tapeworm is a parasite that feeds off the human host. They enter the human host and reside in the intestines. They benefit from their host by eating the partly digested food that goes through the digestive tract. The host is harmed because it deprives the host from getting the nutrients it needs from the digested food.
Algae and fungus
Algae and fungus share a mutualistic relationship. The fungus benefits by growing around the algae which provides it a constant supply of food through photosynthesis of the algae. The algae benefits from the water and nutrients the fungus absorbs.
Clown fish and sea anemone
The clown fish and sea anemone both benefit from their relationship, which makes this mutualism. The clownfish makes the sea anemone its home because anemone have stinging tentacles which provide the clownfish protection. At the same time, the clownfish protects the sea anemone from other fishes that eat anemone.
Termite and digestive tract microorganisms
Termites and the microorganisms that live in their digestive tract share a mutualistic relationship. The termites rely on these microorganisms to help them breakdown the sugars they ingest from wood into something that they can digest. The microorganisms live off what the termites ingest.
Dwarf mistletoe and pine tree
The dwarf mistletoe and pine tree have a relationship called parasitism. The dwarf mistletoe extends fibers into the bark of the tree and taps into it, absorbing the nutrients and water from the tree. This causes harm to the tree because the lack of nutrients and water makes it more vulnerable to diseases, drought and the like.
Spanish moss and oak tree
The Spanish moss benefits from the oak tree but the oak tree does not benefit from it nor is it harmed. The Spanish moss grow on the branches of the oak tree keeping itself out of the reach of herbivores. They are capable of making their own food so they do not feed on the oak tree’s nutrients. This makes their relationship commensalism.