Lentil_team, a story of growing lives
During our third week of Biosensors projects, we had to compare the capacity to detect a chemical gradient with both an electronic and a biological sensor.
We chose to work on water gradients and to answer this question:
Are lentils better than an arduino grove moisture sensor when it comes to detecting water?
But first, what is a chemical gradient?
A gradient is the gradual difference in quantity of a substance in an environment.
Imagine pouring yourself a glass of syrup. The syrup is at the bottom and the water on top, and although there is dispersion of syrup in water, you can see that there is still more syrup at the bottom of your glass. This is the gradient.
Imagine pouring yourself a glass of syrup. The syrup is at the bottom and the water on top, and although there is dispersion of syrup in water, you can see that there is still more syrup at the bottom of your glass. This is the gradient.
So we decided to study water gradients in cotton, and the growth of plants.
This touches on water shortages, which promises to be a worldwide issue. We chose lentils because they are part of the organisms that can grow in any type of soil as long as it is well-drained and with little water. Lentils also grow fast, which proved useful for a one-week-long project.
This is equally interesting because working on both living organisms and an electronic components teaches us how to use one to understand, compare, improve or mimic the other.
This transversal approach allowed us to open our minds and learn how to reconsider a problem, looking at it from more diverse perspectives.
This touches on water shortages, which promises to be a worldwide issue. We chose lentils because they are part of the organisms that can grow in any type of soil as long as it is well-drained and with little water. Lentils also grow fast, which proved useful for a one-week-long project.
This is equally interesting because working on both living organisms and an electronic components teaches us how to use one to understand, compare, improve or mimic the other.
This transversal approach allowed us to open our minds and learn how to reconsider a problem, looking at it from more diverse perspectives.
How did we do this comparison between sensors?
1) Lentils (biological sensor)
We put green lentil seeds in petri dishes with cotton. In a first batch, the cotton was dry to see if lentils grew with no water: these were the negative controls.
Fig 1 - Lentil seeds with no water to check if they need water to germinate
In the next batches, the cotton was moisturized with increasing amounts of water (7.5/ 15/ 22.5/ 30 mL of water) equally spread in the petri dishes. We were expecting root growth to be proportional to the water quantity added and initially decided to measure, day by day, the root and stem length.
Fig 2 - Not really growing straight!
We did not realize that roots and stem rarely grow in straight lines… Once we understood that logical biological fact (science is the art of making mistakes), we changed our protocol: instead of measuring the roots length we decided to weigh the plants in order to see if biomass significantly increased from their initial weight as seeds.
Fig 3 - Weighing the plants seems a better idea
2) Arduino Grove moisture sensor (electronic sensor)
For our electronic sensor, we connected the grove moisture sensor to an arduino (a prototyping platform) linked to a computer to access the data generated.
Fig 4 - Arduino grove moisture sensor
The grove moisture sensor is usually used to judge moisture in plants soil which can inform the user about any watering need.
We then dipped our sensor in our plates containing both cotton and the 5 different water quantities tested. We then recorded the obtained data.
What you will obtain if you try to reproduce our experiment?
Fig 5 - Final picture before being weighed
Good news: Our lentils grew!
At 22.5mL and at 30mL, they grew more than at 7.5mL and 15mL of added water.
Bad news: Our biological sensor was neither precise (each experiment was replicated 5 times, and the values between these replicates varied greatly; furthermore the weighing scale wasn’t precise, reducing our values’ precision ) nor accurate (final weight were not good indicators of the actual water quantity).
Regarding our electronic sensor, it was not precise (the values fluctuated) nor accurate (the values were not those expected according to the data sheet).
Better news: The biological sensor was still more accurate than our electronic sensor.
As such, to answer our preliminary question, lentils are a better sensor in detecting water than an arduino Grove moisture system.
So, why did this happen... And then, what can be concluded?:
We observed that the electronic sensor did not work really well. We did research and saw that cotton is a a more insulating material than soil. Therefore, we suppose that the sensor was not calibrated for this resistivity.
Moreover, although the sensor could work with an arduino Leonardo alone, it works better while plugged into a specific shield which is an interface plugged to the arduino that regulates the sensor function. Therefore we supposed that its absence did not help our experiments.
Moreover, although the sensor could work with an arduino Leonardo alone, it works better while plugged into a specific shield which is an interface plugged to the arduino that regulates the sensor function. Therefore we supposed that its absence did not help our experiments.
Fig 6 - What we should have done.
image source here
If we had to do this again, we would use different types of environment instead of just cotton, as well as a calibration function (to take into account resistivity) and use a shield.
Regarding our biological sensor, it DID work but one way to improve our experimental design would be changing the water quantity magnitude: lentils probably do not distinguish our 7,5 mL gap.
Fig 7 - Living happily ever after
To go further:
- What is an Arduino Grove moisture sensor? Click here!
- Want to build a circuit with the Arduino grove moisture sensor? Watch this!
- Want to sprout lentils ? Check this little video! And here are some more info.
- Want to continue making your lentils grow? Check this video here!
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