Simulated Gravity : How do electronic and biological sensors perceive it?

 
Simulated Gravity : How do electronic and biological sensors perceive it?

Emelyne Gaudichau, Louise Dagher, François SACQUIN

One variable that has been constant throughout the history of life on Earth, whatever the environment or the climate, is gravity. This has led some organisms to start using this unending force as an evolutionary advantage. That is the case for plants who developed “gravitropism”, the ability to use gravity as a “guide” for their roots to grow deeper in the ground and their stem towards sunlight.

This led us to imagine an experiment to discover the correlation between the gravitational intensity and plant development. Then, if such link could be proven, we could compare the results of our biological “sensor” to data obtained via an electronic sensor. For this task, we chose to use a Movuino : a motion sensing board featuring an accelerometer, a battery and a wifi module. For the plant, we found that lentil seeds were the best and simplest choice to put plants in another gravity.

Through our bibliographical search, we found out that Nasa had already done a lot of research on plant development in zero gravity. However, very little had been done on the other side of the spectrum : hyper-gravity. Our next goal was to find an durable way to apply a simulated gravity to plant seeds for many days without interruption. This would allow us to exercise pressure on a seed during the germination process and compare it.

Picture Description : Germination development of a lentil seed. This shows how germination is moreover a quick process that suits our experiment.

And check out this cool timelapse of lentil seeds germinating in cotton. The fact we only need cotton as support for the seeds helped a lot for this experiment.

Experimental Set-up

To build the centrifuge, we first designed the overall plate using Fusion360 to have 2 concentric rings of 6 and 20 holes. We glued it to a nema 17 stepper motor and hooked up that motor to an arduino and a computer to control its speed. To ensure a certain level of security, we used the webcam of the computer to check on the experiment as often as possible.

Sensor Experiment

Electronic Sensor: We tapped the Movuino on the rings, waited for the centrifuge to reach its intended speed and set it to record 200 acceleration measures over 10 seconds. This was repeated 5 times for each ring and we only analyzed horizontal acceleration.

Biological Sensor: The lentil seeds were pre-germinated for 2 days before the launch of the experiment. We chose the most green seeds and put them in the tubes with cotton and 50 microlitres of water. We had 21 control seeds that stood in the exact same conditions but without rotation. They rotated for 84 hours, stopping every 24 hours for 5 minutes to be watered. After that, they were all weighted and we measured the length of their stem and roots.

The following images show our two types of results: the force applied on the center and on the border of the plate for the electronic sensor and the stage of the lentils for the biological sensor.

The first figure shows that the force applied on the border is higher than the force applied on the center. The values calculated are in Newton (a force unit) and turn around the magnitude 10-5. We can see two different values for the force applied on the border (high force (1) and (2)), we think that the Movuino was not at the same place when we repeated the measures. However, the two values are already higher than the center value (medium force). Moreover, for a normal gravity, the Movuino detects nothing, which means detecting no new force by being fixed.

The second figure shows the size of the root and the stem of the lentils. There are three different stages of the lentils for the three conditions : the lentils on the center of the plate, one the border, and the lentils in normal condition. In our results, we observed to notice an influence of an higher gravity in the development of the stem and not for the roots.

In a nutshell, thanks to our results and literature, we can suggest that hyper-gravity could have an influence on the stem development for plants. Furthermore, by testing the Movuino on this characteristic, we can affirm that it is precise but not accurate based on the theoretical forces calculated. Finally, in a critical view, there are many noises and bias that could have interfered with the experiments, as usual in a scientific project!

But, if this amazing student project made you want to know more, you can consult our Twitter @TerraForceFDV,  our storify and our GitHub!