Science Buddies: "Ask an Expert"

My science project is seeing whether geotropism has an affect on plants placed on a constantly rotating turntable and the effects on them. Two of the effects could be that if the centrifugal force causes the plants to lean from a vertical axis because of the additional horizontal force being exerted on them or if a centripetal force causes the plants to lean from a vertical axis inwards. This could also apply to the roots, causing them to grow inwards or outwards because of the same or similar forces. At the end of my experement, the plants on the turntable (super sugar snap peas) altogether grew away from the center of the turn table. The plants that I had that were not on the turntable grew at a greater amount away from their vertical axis though, and they also grew taller.

My questions now are:
1. Why did the plants that were not growing on the turntable grow more away from their vertical axis?
2. Why did they also grow taller?

My interview is due by Tuesday, and is now URGENT, so I would greatly appreciate the help!
-Charlie

Hi Charlie,

I'm sorry no one has responded to your post yet. I seem to have missed your post when I went through the forum on Saturday!

You have an extremely interesting project, and great follow-up questions. While this is not my area of expertise, I will offer some speculation as to the answers to your questions.

First, though, I wanted to note that your control group would be the plants that were not growing on the turntable, as plants do not usually grow on a turntable. Your group of plants on the turntable would be your experimental group. That means you should consider the growth of the plants not on the turntable as normal, and compare the growth of the turntable plants to those.

charlies wrote:1. Why did the plants that were not growing on the turntable grow more away from their vertical axis?

A better way to ask this (based on your new understanding of control vs. experimental) is, "Why did the plants growing on the turntable grow less away from their vertical axis?" By this, do you mean that the experimental plants actually grew straighter than the control plants? If so, that is quite interesting! Could it be that your control plants were growing toward a light source that was not placed directly above them? In addition to geotropism, plants also have phototropism, and often grow towards a light. If so, the control plants may have leaned toward a light source, while the turntable plants would not have the chance to respond to the direction of the light because it would be constantly changing for them.

charlies wrote:2. Why did they also grow taller?

Again, let's instead ask why the turntable (experimental) plants did not grow as tall as the control plants. I would guess that this is probably related to the centrifugal forces in some way. You noticed that they all grew away from the center of the turntable. Perhaps the centrifugal forces the plants were overcoming also impeded their vertical growth.

I hope this helps. Best of luck with your project, and please post back if you have further questions.

Heather