Science Buddies: "Ask an Expert"

Hi,
My project is seeing if increasing phosphate levels in algae species will promote growth and thus accelerate CO2 fixation. I need to find a quantitative way to measure the algae concentration in 6 containers-chlorophyll and dry weight isn't an option. So is there a way to measure the algae's biomass, but also in a way that I can make sure that all 6 containers of algae will have the same biomass?

If you have access to one, a spectrophotometer would be the easiest way.

Or you could mix them well, and use a hemocytometer slide to count the number of algae cells per volume.

Hello ateronia!

It seems that the most accurate way to measure the concentration of algae is by finding the amount of chlorophyll-a present in your sample. That being said, this is usually very expensive, so here are some methods that you can use at home to measure the amount of algae present in your samples:

Seechi disk: a flat, circular-shaped instrument that is used for testing water quality by measuring the transparency of water. The disk is lowered into the water and the numerical data would be in the form of feet until you can no longer see the disk due to the algae clouding the water. This is not the most accurate method of testing the number of algae in a sample, but is easy to do at home and should provide the data you need for this project to be successful.

Spectrophotometer: Algae absorb light, so by streaming a beam of light through your sample of algae at a certain frequency using this device, you would be able to measure the amount of light that has been blocked which will give you an estimate of the number of algae present in your sample. These devices are available to buy for non-laboratory use.

The best way to ensure that there are very similar quantities of algae in your samples would be making sure that you conduct each trial the exact same way: according to a very specific procedure. That being said, algae is a living organism so growing the exact same number of cells in each sample is extremely difficult. However, if you measure the phosphate additions very carefully, your numbers will be very, very similar.

Best of luck with this project, and if you have any more questions feel free to ask!
-cnoonan180

Hi,
I'm doing a project where I'm attempting to see if the nitrate levels of different algae medium help increase algae growth, its CO2 biofixation rate and lipid production. However - I'm unable to find any methods for extracting lipids that are feasible at home (especially since these COVID times). Any help would be appreciated!

Hello Natalie,

I've merged your recent post into the thread from your previous posts on a similar topic. Keeping posts on a similar topic together helps the experts who were helping you see that you have follow-up questions.

Thanks!
Madeline
Moderator

Hi natalie_21,

This is a very interesting project idea!

I would suggest focusing on how varying nitrate levels increase/decrease the growth of algae and if algae that grow in bodies of water with higher nitrate levels release more oxygen gas (because many, almost all, types of algae photosynthesize meaning they release oxygen). You could perform an experiment like this by growing species of non-harmful algae (some species release toxins harmful to humans and pets- so be careful when working with organisms like algae!) in closed systems, such as jugs or bottles of water that are covered, so none of the product oxygen gas is released into the atmosphere and therefore it can be measured. Oxygen gas sensors are one way you could measure oxygen gas, and I would recommend checking with your school if they have any sensors that you may be able to borrow for this project. You could add different levels of nitrate-containing fertilizers to water containers and have one container be filled with just water for your control, untouched by any extra nutrients or fertilizers (Note that nitrate fertilizers can have a negative effect on the environment, so be careful of how you dispose of your project when finished). You could also use a tool called a Secchi disc to measure how much algae are in your systems. A Secchi disc enables people to measure the transparency of water, so the more algae there is in water, the less transparent water is, and it will be harder to see the disc when it is submerged.

Hope this helps, and reach out with any additional questions!
-cnoonan180

Hello cnoonan180,

I actually plan to do a project similar to that where I'll also use a spectrophotometer to see if increased nitrates promote growth, it's CO2 fixation rate but also absorption. But I'll be using growth media like f/2 medium, and I wanted to know if there's a sensor/probe that can measure the amount of nitrates in each media. I don't think my school has one, and the one I found online is too expensive. Is there any alternative?

Thank you!
- natalie_21