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Biology IA Setup Advice

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Guest michaelwm


For my Biology IA, I'm going to be investigating the effect of CO2 on mold growth in the life of strawberries. Essentially, I'm going to inoculate a group of strawberry halves with Rhizopus Stolonifer, place them into an incubator, control it's CO2 level, and record the molds growth over a period of days using a time lapse camera. I'm then going to calculate the rate of mold growth on the strawberry using calculus and analyze the results.

The most troubling part of this is the method of controlling the CO2 level within the incubator. Originally, I was simply going to place a solution of yeast, sugar, and water in a corner of the incubator, and increase the yeast / sugar concentration (increasing the CO2 generated). However, this would of led to a loose conclusion, as I could really only relate the mold growth change to a change in yeast / sugar concentration, and not CO2 directly.

So, now, my method was to place a CO2 sensor within the incubator, and have a controllable source of CO2. Essentially, I'd set a setpoint for the CO2, and the source would release CO2 into the incubator until the setpoint was reached, and shut off. If the CO2 level diminished, the source would be reactivated until the setpoint was reaching again. Now comes the issue - what would the CO2 source be?

After some research and visiting nearby hardware stores, purchasing an empty CO2 tank, filling it, purchasing the necessary gauges and solenoid valves, would cost upwards of $300, often more. On the other hand, purchasing a few bottles of pop for a party, drinking and emptying them, filling them with yeast, sugar, and water, attaching them to a couple of check valves and a solenoid valve, would cost less than $20.

Here's my proposed setup:


I've already purchased the CO2 Sensor (using the school's budget), and our school's robotics course teacher is a good friend of mine and I can borrow his arduino's. I've also found an $8 solenoid valve online, and our school has check valves. I've had the time lapse camera for a while, and the CO2 generators are a warehouse store's purchase away. The setup is essentially ready, although I feel like there's an issue somewhere, specifically the CO2 storage.

Now, maybe I just can't think at all at this moment and am going crazy, but wouldn't the CO2, after being created in the generators, head to the storage, and overfill it because of the air already present in there, eventually causing a rupture? Or would this not happen? How can I fix this if it would?

Thank you so much!

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