measuring algae growth

[scubafreak22]

My friend and i are doing a science project on measuring the rate of growth of alge. we are putting 10 slides in 6 different tanks and hoping that algae will grow on some of them.
After each 24 hour period we take out one slide and put it under a microscope...the only problem is...how do we measure the rate of growth??? someone told us to measure the density...but how do you do that??? PLease HELP!!!

 

[gregzbobo]

Since you have the microscope, you might try counting the cells per square millimeter or something. Will need a little bitty ruler or a graduated slide or something to have a reference. Only a wild guess though.

 

[ophiura]

Yes, I think you can find slides with grids, or a grid that can be used on the ocular of the microscope, so that you can count cells per square mm or something. There are also petri dishes with these grids.
Are you using an algae that will definitely colonize a very smooth surface like glass? Some algae remain suspended, or prefer a rough surface. Depends what kind of algae your going for...just something to think about.
You may want to search online for Carolina biological supply, Ted Pella or some other company specializing in such equipment. I searched Carolina and found "ruled microscope slides."

and integrid petri dishes:

both from: http://www3.carolina.com
You might need to have a teacher order these.
If you are in Miami, it might not be a bad idea to try and contact someone at the famous Rosenstiel School of Marine and Atmospheric Sciences. There are a few people there working on phytoplankton etc that may be able to give advice via email, if not offer more help or supplies. I know of students who have worked in high school, etc, in labs and did excellent projects. They at least might no more about the algae you are working with, and supplies they use.
http://www.rsmas.miami.edu/divs/mbf/

 

[broomer5]

You may want to use several "proofs" that the algae is indeed growing on these slides.
The counting of cells is great if you can get a good view through the scope.
If you have access to a digital camera - A visual progressive "color" change would be good too - providing the back lighting of each sequential " slide shot is held constant - and no monkey business is done on the software or printing to alter the visual changes between slides and photo time intervals.
Scraping and weighing require pretty sophisticated equipment - and are destructive to the test - so that's pretty much out.
Although a final destructive test may be okay at the very end of the project. Weighing the mass - better have access to a lab quality scale - like used in chemistry classrooms.
You can weigh the slide with algae growth on it - then totally clean the slide removing the algae. Then weigh the clean slide.
Do the math = algae mass. Again - this would only be appropriate as the grand finale proof AND providing the amount of slide weight difference can be accurately measured before and after removing the algae growth.
If all "proofs" follow the same trend - then you have even more to back up your theory.
If for some reason all the "proofs" do NOT follow the same trend -then we have a problem.
All proofs MUST be reported though - even if it contradicts what you HOPE will happen. Good science is dictated by reporting all the data - even if some of it blows your original theory.
Bad science - it's easy to do - and is still bad science.

 

[ophiura]

Also keep in mind that taking the slide out and counting and then putting it back can be a problem. If the slide is out too long and the cells dry out, it isn't so good. Perhaps the nice thing about the petri option is that you can use it with a dissecting scope and keep water in it so that things don't dry out and the algae is only minimally disturbed. Regardless, you have to do this pretty fast. And it might be good to have a number of slides in each tank in order to get more data from each.
I agree that having photos of this would be really good. This is one reason that it would be great to hook up with a researcher if possible.