I'm planning a biology experiment I need to complete. I was planning on measuring the affect of pH on algae growth. I chose chlorella to be the test algae I use (are there any algae that would be easier to test?) and I have no idea how to measure the growth. My school does not have a spectophotometer, just basic biology and chemistry stuff. Also how can I change the pH of the water for my different samples? I'm a beginner and don't really have much experience so any help is appreciated!
2 Answers
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For growth you could measure the mass of algae before and after the experiment. If you have a centrifuge you can pellet the cells or use a filter to remove the culture medium. Alternatively, if you have access to a hemocytometer and a microscope, you could get an accurate cell count that way.
For controlling pH, you'll need a buffer in your culture medium. You should select a buffer with a pKa close to the pH you want to test and then titrate the pH of the medium with a strong acid or base (HCl or NaOH). Make sure to check the pH before and after the experiment to be sure that it didn't change due to growth of the algae.
answered Jul 17, 2017 at 20:39
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$\begingroup$ Maybe also mention cell counting with a haemocytometer- although these are not inexpensive. $\endgroup$ Commented Jul 18, 2017 at 7:38
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$\begingroup$ @AlanBoyd Neither are microscopes... $\endgroup$ Commented Jul 18, 2017 at 17:21
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A slower but easier way than pelleting in a centrifuge is pour off the water and let the algae dry out, then weigh the dried mass.
Get pH paper to check pH of each grow cup full of algae each day.
You can raise pH to around 8 with baking soda (sodium bicarbonate).
You can buy sodium carbonate (washing soda) in a hardware store. It is cheap. That will get your pH to 10+ which is higher than you need.
Make sure to get pure stuff, not with additives like perfume or other surfactants.
You can lower pH down to 2.5 with ascorbic acid or vitamin C. A bottle of 100 is cheap and they crush easily.
Get a bunch of jars or old soda bottles and in each one make a bunch of solution of the pH you want. So you will have a 2.5 stock bottle, a 3 stock bottle, a 4, a 5 on up. Then you can top up your algae grow jars as they dry out. Or better: pour out the old water and pour in new. Don't pour out your algae by accident.
Last: you want this algae to grow like mad when conditions are good. Pure water will be low on nutrients. I recommend a dilute solution of Miracle Grow.
Maybe a teaspoon per liter.
I can envision 8 2liter soda bottles, each filled up and each with a different pH made either with washing soda or vitamin C. Each 2L bottle has 2 tsp of miracle grow in it.
Each algae grow jar is a 12 or 20 ml drinking water bottle. 3 bottles per pH level. Big number on each showing pH. Put them in a row in the sun. Change the water every 2 days. Take a photo every day.
When you are done fish out the seaweed and dry it.
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$\begingroup$ I've never worked with algae, but can you be sure that you aren't pouring out cells with the medium? $\endgroup$ Commented Jul 17, 2017 at 21:59
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$\begingroup$ The algae will probably grow as a sticky mat. A few lost cells will not matter. You can hold it down with a spoon and pour out most of the water then replace. Check this. irnas.eu/bio%20lab%20symbiolab/2016/06/03/… An idea: just use scummy pond water. What grows, grows. You will still be able to determine biomass at the end. But you may find different organism types take over the jar at different pH which is also very cool and shows the flexibility of an ecosystem. $\endgroup$– WillkCommented Jul 18, 2017 at 14:13