With so many organisms on Earth, living things are bound to interact with one another. Symbiosis is a close relationship between two species.
One type of interaction between two species is called mutualism. An example of mutualism exists between honey bees and flowers. Flowers provide nectar to the bees. The bees use the sugar rich liquid to make honey. As the bees fly from flower to flower tiny grains of pollen get stuck to the bee. The bee moves the pollen without even knowing it. The pollination is necessary for flowers to reproduce. In this relationship both species benefit. The bee gets nectar and the flower gets pollinated.
Another relationship is called commensalism. This interaction takes place when sharks and remora live together. The remora use sucking disks on their heads to attach themselves to sharks. The sharks are powerful swimmers and do not even notice the remora and are neither helped nor harmed. However the remora benefit from this relationship. The fish get a free ride and protection. They also feed on scraps left over by the shark. In commensalism one species benefits and the other is neither helped nor harmed.
The last type of symbiotic relationship is called parasitism. An example of this relationship exists between humans and mosquitoes. The insects land on and take the blood from humans. The mosquito benefits as it uses the blood for energy. The human or host is harmed in this relationship as blood is needed and the human could become infected with disease. In parasitism one species benefits and the other is harmed.
Hank talks about the last major way humans are impacting the environment in this penultimate episode of Crash Course Ecology. Pollution takes many forms - from the simplest piece of litter to the more complex endocrine distruptors - and ultimately, humans are responsible for it all.