Classify real relationships between organisms as mutualism, commensalism, or parasitism based on whether each partner benefits, is unaffected, or is harmed.
Symbiosis means two different species living in a close, long-term relationship. There are three main types, and the difference comes down to who benefits and who is harmed. In mutualism, both species benefit -- a bee gets nectar from a flower while carrying pollen to the next flower, helping it reproduce. In commensalism, one species benefits while the other is essentially unaffected -- a barnacle attached to a whale gets a free ride to food-rich waters, while the whale is neither helped nor harmed in any meaningful way.
In parasitism, one species (the parasite) benefits while the other (the host) is harmed, though usually not killed outright, since a parasite that quickly kills its host loses its own home and food source. A tick feeding on a deer's blood is a parasite; the deer loses a small amount of blood and can be exposed to disease, while the tick gains a meal. Classifying a relationship means asking one clear question for each partner: does it benefit, stay unaffected, or get harmed?
Mastery looks like: They can classify a new relationship example as mutualism, commensalism, or parasitism and justify the classification using both partners' outcomes.
Common stumbles: Assuming any close relationship between species must be harmful; confusing commensalism (one unaffected) with mutualism (both benefit).