Symbiosis is a close relationship between organisms of different species. In a symbiosis, the relationship can prove to be beneficial or harmful to the organisms involved. Now, I want to take a look here at a great example of a beneficial symbiosis. What we're looking at are plant roots that have developed these nodes. These nodes contain bacteria that perform nitrogen fixation, which allows the plant to absorb nitrogen. Basically, these bacteria provide the plant with usable nitrogen. So their relationship is one of mutualism because both species benefit. The plant gets nitrogen, and it provides the bacteria with nutrition and a safe environment. Now, in this case, the plant is actually acting as a host because it's harboring the symbiont, the bacteria inside its roots. Now, it's worth noting that some relationships can be commensalism, where one organism benefits and the other is unaffected. It's also worth noting that some interactions can occur without a symbiotic relationship. For example, facilitation is an interaction where one or both species benefit. And getting back to nitrogen fixation by certain plants adding more nitrogen into the soil, they can facilitate the growth of other species later on. So those two different types of plants wouldn't have a symbiotic relationship, but one would be benefiting the other.
Now, let's talk about when these relationships sour a little. Things take a turn for the worst. Parasitism. This is a relationship where one species, the parasite, benefits at the expense of its host. Endoparasites are parasites that live in the body of their host, but some parasites live on the outside of their hosts, and they're called ectoparasites. Here is an example of a crazy fungal parasite, which in this case has completely taken over the body of a tarantula. This is called Cordyceps fungus. That's all I have for this lesson. I'll see you guys next time.