Jessica’s little brother William walked into the kitchen one day to find Jessica making herself a sandwich. William asked, “Can I have one?” So, Jessica made her brother a sandwich as well. The two of them sat down at the kitchen table and started talking to each other while they ate their lunch.

Can you make me a sandwich too?

William thanked his sister for the sandwich and she replied with, “You’re welcome. That is an example of a commensalism relationship. I made you a sandwich which doesn’t affect me, but it benefits you!” This made William start to wonder if there were other kinds of relationships, so he asked his sister.

That is commensalism!

Are there other relationships?

Jessica told him that there were three different kinds of symbiotic relationships that organisms can take part in. She said, “A symbiotic relationship is when two organisms, usually of different species, interact with one another to produce different outcomes. So, even though we are both humans, it is the same idea! You received a sandwich that I made. It does not hurt or help me to make you lunch so that would be like a commensalism relationship.”

Symbiosis! Commensalism!

William was starting to catch on. “Oh! So are there other kinds of relationships?” Jessica responded with, “There are two other kinds. A parasitic relationship and a mutualistic relationship. In a parasitic relationship, one organism gets harmed, but the other organism benefits off of them. In a mutualistic relationship, both organisms benefit. Can you think of a mutualistic relationship?”

There are two other kinds of symbiosis! Parasitism and mutualism.

William said that he wasn’t quite sure he could come up with the different relationships on his own so he asked Jessica to come up with some first. “Well,” she said, “an example of a mutualistic relationship is like when a bee pollinates flowers. The bee gets to collect the pollen from each flower in order to make food, but when the bee flies from flower to flower, it also pollinates other plants! This benefits both the bee and the plants.”

Next was the parasitic relationship. Jessica asked William if he was sure he didn’t want to try to come up with one. He said that he didn’t think he knew quite enough yet to come up with a good one. “Well, do you remember seeing things on TV about how people can get sick from things like ticks or worms getting inside them?” Jessica asked. William nodded his head yes so Jessica continued. “If you can remember that, then you already know what a parasitic relationship is! It is parasitic because the tick benefits but the human is harmed by the tick.”