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Name: Renee
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How much oxygen does green-blue algae produce, and how big are they?

Blue-green algae (cyanobacteria) are generally under one micron (1e-6 meter) in diameter, mostly in the 0.5-1.0 range.

How much oxygen they make depends on how many there are already and how fast they're growing. Let's say you start out with about 1 mg in 1 liter of water, and they're doubling once per day (that is, 24 hours later you now have 2 mg in 1 liter). Although cells aren't entirely carbohydrate, it's a good enough first approximation for photosynthesis:

6 CO2 + 6 H20 > C6H1206 + 6 O2

1e-3g / 180g per mole glucose = .0056e-3 moles glucose

Since they make 6 moles O2 for every mole of glucose, they make 6 x .0056e-3 = .03e-3 moles O2, and since O2 is 32g per mole, that's 1.07e-3g O2, or a little more than 1 mg O2 per day, for 1 mg of new cells per day (dried weight).

Donald Yee Ph.D.

Dear Renee,

They're microscopic (cyanophyta or cyanobacteria).

Anthony R. Brach, Ph.D.

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