How does light intensity influence photosynthesis in Egeria densa

During one week, we, students at the FDV Bachelor program, designed an interdisciplinary scientific project aiming at comparing a biological sensor with an electronic one. We decided to work with Egeria densa, an algae mostly used in aquarium and that releases a lot of oxygen (O2) while doing photosynthesis.

Photosynthesis is a process by which plants form glucose and release O2 using the energy from the sun, water and carbon dioxide (CO2). For more explanations about the photosynthesis process, you can have a look at this video.

In this project, we wanted to see if Egeria densa can be used to measure the intensity of light, regarding how much O2 is released by the algae while doing photosynthesis. We wanted to compare the range, accuracy and precision of the two different sensors. The accuracy of a sensor is how far is the measured value from the true value. The precision is how far are the measured values apart from one another. The range is the limits between which the sensor will be able to measure values.

First, we designed closed wood boxes with holes for the LEDs, in order to have a good control on light intensity exposure. It looked like this :

To do so, we create a protocol in which Egeria densa were put in a syringe with tap water, connected to a clear rubber tube full of ink. When O2 was released by the algae, the ink was moving out of the tube. We also build a device (a box) that blocks noisy emissions of light, and emits a red beam at a certain intensity. Thanks to that, we were able to measure how much O2 was released, and by consequence, to measure the impact of the LED intensity on photosynthesis.

Here are the graphs we obtained :

As we can see on those graphs, there are no obvious trend, even though we can draw some observations.

However, we can see that for the biological sensor, the negative control (0%) and the 25% intensity curves have kind of the same trend, therefore, we can think that the sensor doesn’t sense any changes between 0% and 25%. The same thing between the positive control (100%) and the 75% intensity curves. With those observations, we can say that probably, the range of the biological device is something like 25%-75%, where 75% is the saturation point.

The response time of the biological sensor, we can assume regarding our graphs that it takes approximately an hour for the sensor to have a constant value. This is explained by the fact that the algae has to adapt to the new LED intensity.

As for the response time of the electronic sensor, we measured it at 200ms. Indeed, we took measurements every 100 ms and only the third value was constant. Therefore, we had to wait for 2 values, meaning 100ms x 2 which equal to 200ms, our response time.

To conclude, we cannot really conclude with a statistical approach with the results we got.

Maybe one way to improve our experiment and to have more relevant results would be to use O2 probes, instead of the rubber tube. We could also design another box that is darker, and more easy to adapt and use for the large audience. It could become an interdisciplinary tool to understand that a sensor can be very surprising and innovative.

We also imagine using another organism, such as a bacteria that produces gas, or an enzyme.

For more informations about the ‘Photosynthetic strategies of Egeria densa”, please read this article.

Photosynthesis pictures is from : http://www.factmonster.com/ipka/A0775714.html

Here is our storify : https://t.co/gPgQCCfJzH 

Here is an identity card of our organism : Fiche - Egeria-Densa-Sr.pdf. Accessed January 20, 2017.
http://www.centrederessources-loirenature.com/mediatheque/especes_inva/fiches_FCBN/Fiche%20-%20egeria-densa-sr.pdf 

Thanks for reading ! See you soon !