Symbiosis:
A relationship in which two different organisms live in close association with each other is called symbiosis.The individuals in a symbiotic relationship can benefit from, be unaffected by, or be harmed by the relationship. Often one species lives in or on the other species. All the different symbiotic relationships are classified into three groups: mutualism, commensalism, and parasitism.
Mutualism:
A symbiotic relationship in which both organisms benefit is called mutualism. For example, you and a species of bacteria that live in your intestines benefit each other. The bacteria get food from you, and you get vitamins that the bacteria produce. It also occurs between some corals and the algae living inside those corals.
Example:
Bees fly from flower to flower gathering necter, which they make into food benifiting the bees. When they land in a flower pollen gets on them then when they land in the next flower some of the pollen from the first flower rubs off pollinating the plant, which benifits the flower.
Commensalism:
A symiotic relationship in which one organism benefits and the other is uneffected is called commensalism. For example a flatworm attaching to the horsecrab and eating the crabs food and the crab is uneffected.
Example:
The fish attached to the shark benefits from the relationship by being carried around from meal to meal feeding on scraps and the shark neither benefits nor is harmed.
Parasitism:
A symboitic association in which one organism benefits while the other is harmed is called parasitism. The organism that benefits is the parasite. The organism that is harmed is called the host. The parasite gets nourishment fro its host while the host is weakened. For example a female wasp laid tiny eggs on a caterpillar. When the eggs hatch, each young wasp will burrow into the caterpillars body. The young wasps will actually eat the caterpillar alive!
Example:
The parasite is the tick which is feeding off the dog. The tick takes blood from the dog which is harming the dog and benefiting the tick.