Algae Science Project

[connie08]

Hello,

My science project this year is about the investigation of temperature and pH on coccolithophorid algae. I want to find the best combination of temperature and pH to maximize the growth of this algae because it absorbs a lot of CO2. The range of temperature that I want to test is 13°C-17°C and the range of pH is from 6-10. I'm not exactly sure on what my control should be. I was thinking about using my prediction of the best combination as the control, which would be a temperature of 15°C and pH of 8. Is that okay?

Could you help me with changing the pH levels without killing the algae as well? As for the temperature, I was thinking about putting the algae under a heat lamp but I'm not sure if that would work. Also, how could I keep the pH and temperature the same throughout the whole experiment? I was going to let the algae grow for two weeks but as the algae grows, it will change the pH level.

Sorry if this is a lot of questions but I need a lot of help. Thank you!

[deleted-71417]

Hi,

Your control sounds fine to me, as long as the conditions are reproducible.

As to how to control pH< one way would be to add a drop or two of ph indicator solution to your algae growth medium, then titrate the sample to the same color each day, using acid or base as required.. Alternatively you could try to add a buffer solution to your samples. You might look into phosphate buffers.

Carefully adjusting a heat lamp should give acceptable temperature control.

[deleted-71536]

Hi Connie,

Barrett has given you some good advice. I wanted to address your question about how to change the pH without killing the algae. You have chosen a very large pH range - keep in mind that each pH unit represents a ten-fold difference in hydrogen ion concentration! If you find that certain pH levels kill your algae, that is an interesting result. It tells you that those pH levels are not tolerated by the organism, and that is still interesting.

As Barrett suggested, I think that adding a buffer to your solution may help control your pH levels as the algae grows. You might also consider talking to someone at an aquarium shop. They usually have solutions for controlling the pH of aquaria.

I hope that helps!

Heather

[connie08]

Thank you guys!

Sorry, but I have a few more questions. How do I lower the temperature of water to 10 degress Celsius while my algae is growing?
And I only have a little for than a month to do my experiment, so which would be better: if I had the algae grow for 3 days so that I could do more trials or if I let if grow for a week but I'd have fewer trials?

[carolinethorn]

Hi Connie,

In general, the more repetitions you have the easier it is to tell if there is any difference between conditions, however if the time is too short for any of them to grow then you won't see a difference with the different variables. Maybe in your background research there is some data about how fast the algae grows under standard conditions?

Also since you don't have much time left maybe you should stick to varying one condition only - just changing the pH rather than temperature as well. For reducing the temperature and keeping it at a consistent 10C you would likely need to use special water baths that refrigerate and have a thermostat for keeping at a low temperature.

If you have enough growing containers you can grow all your sets of algae at once. Say, if you had 9 containers you could do 3 each for 3 different pH conditions. You should have plenty of time then to let them grow for a week, analyse the data and be done within the month.

Best of luck,
Caroline

[connie08]

Thanks! I'll probably just test one variable then.

Also, I'm recording how much CO2 is absorbed so would I keep the algae in water bottles that are capped? That way I could measure everyday the changes in CO2. But would the algae die since they don't get more oxygen? I would keep the bottle uncapped but then I wouldn't be able to measure the CO2.

[deleted-71536]

Hi Connie,

You are right - the algae do need oxygen, so closing the bottles for an extended period of time could cause problems for your algae. Also, measuring CO2 is rather complicated (even if you do have a closed container!) and typically requires specialized equipment.

One thing to keep in mind is that CO2 makes water acidic. So measuring the pH changes of your water every day can be used as a proxy (kind of a substitute) for measuring CO2 changes.

It works like this. When CO2 comes together with water, it makes carbonic acid, which dissociates into hydrogen ions and bicarbonate ion:

CO2 + H2O <--> H2CO3 <--> H+ + HCO3-

Because H+ ions lower the pH, higher CO2 levels actually lower the pH of water. So, by measuring pH changes caused by the algae, you can get an idea of how much CO2 the algae may be producing.

I hope that helps!

Heather

[connie08]

Thanks that helps! But for my experiment, I'm testing to see which pH my algae grows best in. I will be testing three different pH levels (6, 8, 10) and I was planning on keeping the pH level constant while my algae grew. If I I have to let my pH levels change to measure CO2, then how do I know what level my algae grows best in?

[MelissaB]

Connie,

In that case, I think you should just leave the bottles uncapped and not measure CO2 levels. Perhaps instead if you're measuring how much algae grew, you can find a relationship in some other study or paper that suggest how much CO2 each alga (or a certain amount of algae) can fix per day. Then you wouldn't need to measure CO2 levels and can keep the water oxygenated.

[connie08]

Could I instead keep it capped and trap the CO2 with KOH (potassium hydroxide) as KHCO3 (potassium bicarbonate, a solid). And then use a wet cotton ball or paper tissue with KOH, weigh it, then stopper up the test tube with it. When its done, take it out and weigh it again and use the difference in weight as the weight of the CO2 consumed by my algae?

Or would that kill the algae because it won't be aerated??