I think we can all agree that plants are some pretty basic forms of life right? I mean all they do is drink water, bathe in sun, and grow.* That’s where YOU’RE WRONG! It seems easy enough to grow, but how do they know which direction to grow? They don’t have brains like us, so they can’t even tell which direction they’re facing. Instead plants have some pretty smart mechanisms that allow them to sense where the light is and which way is down.

When you plant a seed in the ground, you can plant it pretty much any direction you want, yet the roots always grow down into the ground, and the leaves always sprout above. But how do the little guys always figure out which way they should shoot out their roots and leaves? The answer is they sense gravity! (and light but that’s not as exciting to me) When I first heard this, I thought maybe the plants are able to sense the gravitational field somehow, but honestly it’s way more simple and smart than that.

Imagine you zoom into the tip of a single root, which is composed of many root cells. Zoom in even further, and you’ll see some tiny spheres that look like rocks. These are called statoliths, which are tiny densely packed sacs in the root cells. Basically to form these tiny rocks, the root cells pack a whole bunch of starch into the sacs which makes them heavy like little marbles in a jar. If you flip the jar over, the heavy marbles will fall due to gravity, which is exactly what the statoliths do inside the root cells! Once the statoliths fall and press up against the side of a cell, it mechanically activates channels in the cell that redirects a special chemical called auxin. Auxin is the chemical that is responsible for controlling where the roots grow. When auxin is rerouted by the statoliths pressing on one side of the root cell, auxin is rerouted to that direction, causing the roots to grow in the direction the statoliths fell!

So to recap: Imagine holding a balloon with marbles inside . When you flip the balloon, the marbles will fall in the direction of gravity. The balloon is the root cell and the marbles are the statoliths. Once the marbles fall, it will alter the shape of the balloon, which the plant can sense. This change in shape causes the plant to send an alarm to send auxin in this direction. Once the auxin is rerouted in this direction, roots start growing.

Things like this amaze me about biology. It is such a simple mechanism, like a rube goldberg machine, but it is so effective. Plants are simple and goal oriented. Plants have such simple and efficient but complex means of reaching their one goal: to grow.

*side note: did you know that plants are always growing given the right living conditions? To me that’s like a human that never stops getting taller! Honestly I don’t think many other things on earth never stop growing. Plants are truly alien.