Bobby and the O2 factory
Hello dear visitor! Do you like aquariums? Yes? Well, then, let me introduce you
Bobby. Bobby is a fish who wants to move out from the river and go living in this great
apartment he found on ​
rentaplace.sea​
. His new aquarium is well enlightened 8 hours a
day. Because it was empty, he bought some ​
Egeria densa ​
(an algae) to furnish his
apartment. But he has a problem : he doesn’t know how to heat his flat to get enough
oxygen to live. Well don’t worry Bobby, we will help you!
We are three students, and we have one week, some ​
Egeria densa ​
seedlings, light and
pH sensors, thermometers, a lab and a plant incubator to give Bobby an answer.
Before we start, it might be important for you to know that plants are doing respiration
all the time like any living being, but photosynthesis only occurs when there is light. In
Bobby's aquarium, this is 8 hours a day.
On Figure 1, you can look at the exchanges made during photosynthesis. As you can
see, the plant produces O​
2 during this process. To go back to Bobby : the more oxygen it
releases in the aquarium the better it is for him.
Our question is “At which temperature is ​
Egeria densa ​
has the higher photosynthesis
rate ?”. To answer this question, we will try to quantify the photosynthesis rate at
several different temperatures.
When the temperature increases during a reaction, it usually makes the reaction go
faster. That is because the reactant and their components are agitated by temperature
and bump more into each other. However in our case we can't increase temperature
too much for fear of burning plants or even poor Bobby.
We chose four conditions to test : 15°C, 25°C, 35°C and one at room temperature (if
Bobby can’t afford heating!). Among these four, two are controls which are made to
ensure that the response we get is due to the changed parameter. That is why we chose
one to leave at room temperature, and another one at 35°C (which should increase a lot
the photosynthesis rate).
But then, how can we quantify something like photosynthesis? The answer is simple:
by measuring the 0​
2​
production.
To be able to do it, we designed the following protocol : in a big beaker we immersed
smaller tubes full of water with the plant in it. And we put it under a strong light. The
plants then did photosynthesis and released 0​
2​
. Thanks to the pressure it creates, a
volume of water (equal to the 0​
2 produced volume) is ejected by a straw attached at the
bottom of the tube (see Figure 2).
After almost an hour and a half (80 minutes), we measured O​
2 volume in our tubes. To
do so, we measured the volume of the air bubble that appeared.
We had three tubes for each temperature, and we made a mean of photosynthesis rate
for each condition (see Figure 3).
You have to keep in mind that we were not able to check if the air was pure O​
2 so we
can't be sure it was indeed O​
2​
. However it seems to be the most probable, because even
though plants also release CO​
2​
when it breathes the quantity can be neglected when
compared to O​
2.
As you can see the more you increase the temperature, the higher the photosynthesis
rate is. However, it seems that a threshold is reached and temperature doesn’t
influence photosynthesis rate anymore.
So Bobby, in conclusion what we can tell you is to heat your aquarium around 25°C. Of
course you could heat it higher, but you have to be reasonable, think of the climate
change and be more environmentally friendly!
Bobby is now happy to live in his great new aquarium with plenty of oxygen!
Unfortunately, not every Bobby has the same chance. And nowadays, climate change
has a great influence on photosynthesis. When the temperature is too high,
conformation of some enzyme in plants might change. It is called denaturation and it
prevents the plants to do photosynthesis and might even cause death. So be careful,
think of your environment!
If you want to go further:
→ A first approach on photosynthesis for basics
http://www.larecherche.fr/savoirs/pas-si-simple/photosynthese-01-01-2003-81087
→ Two articles to go further on the photosynthesis subject :
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3659369/
http://www.sciencedirect.com/science/article/pii/0304377087900842
→ For people who don’t know what photosynthesis watch this really cool video :
https://www.youtube.com/watch?v=sQK3Yr4Sc_k
Links to team members’ CRI website page:
Valentine ​
http://students.cri-paris.org/profile/Valentine-Le_Gall/
Hélène ​
http://students.cri-paris.org/profile/Helene-Dumont/
Julie ​
http://students.cri-paris.org/profile/Julie-Le_Naour/