Dear Luke and Wade,

When I get the same question from different kids, I know it’s a good one.

So, I talked about your question with my friend Angeliqua Montoya. She’s a graduate student at Washington State University. She works on a mutualism between pea plants and bacteria.

“I study ecology, which is looking at interactions between different species,” she said. “Mutualisms are interactions where both species benefit.”

Living things interact with each other in lots of ways. When a lion kills a rabbit, that’s an interaction. When a bird builds a nest in a tree, that’s an interaction. When a bee collects pollen from a flower, that’s also an interaction.

Some interactions are good for just one individual and bad for the other. The lion gets a meal. But the rabbit becomes a meal.

Some interactions are good for one individual but neutral for the other. The bird gets a nice place to lay eggs. The tree isn’t helped or harmed.

Some interactions are good for both individuals. The bee collects pollen to feed the colony’s baby bees. As the bee visits flowers, it spreads pollen around. That’s how plants make baby plants. This interaction is a mutualism. It’s good for the bee and the plant.

Sometimes scientists label the type of mutualism. Here are three common ones.

Transportation mutualisms help move stuff around. That’s important for plants because they can’t move on their own. Our bee moving pollen from flower to flower is a transportation mutualism. Another is when a bat eats fruit then flies away and poops out the seeds somewhere else.

Protective mutualisms are about staying safe. Montoya told me some squid let special bacteria live inside their cells. The bacteria make the squid glow. When a hungry predator swims under the squid, they think the squid is the moon—not their dinner.


White roots with reddish orange nodules in the middle
This root has pinkish-orange nodules. Photo: Ninjatacoshell/Wikimedia


Montoya studies a nutrition mutualism. It’s about food. As pea family plants—called legumes—grow, they gather bacteria from the soil. They make lumps called nodules on their roots. The bacteria live inside the nodules. They eat some of the sugar the plants make. In return, the bacteria take in nitrogen from the soil. They change it into a form the plant can use. That helps the plant grow bigger and faster.

“You can go out in the back yard and find a legume like a clover plant,” Montoya said. “If you dig up its roots and wash off the dirt, you’ll see little nodules. They’re filled with bacteria.”

An ancient mutualism is probably why plant and animal cells work the way they do today.

Inside plant and animal cells, there are mitochondria. That’s the part of a cell that turns food energy into energy your body can use. Plant cells also have chloroplasts. That’s the part of a plant cell that changes light energy from the sun into energy for the plant.

More than a billion years ago, there were bacteria that could make usable energy, too. Other one-celled organisms sucked up those bacteria. But they didn’t die. They kept making energy inside their cozy new homes. They evolved to become mitochondria and chloroplasts.

You could say they started something new-tual.


Dr. Universe