Science Buddies: "Ask an Expert"

Thank you so much!

The phytoplankton at first increased slightly in number and then gradually decreased. After the second addition of iron, decreases occured. I'm guessing the greater amount of iron stressed the phytoplankton or poisoned them.
So, what would that say about the phosphate growth? Was it autolysis?

Also, I decided to test pH, phosphates, and dissolved oxygen because of availability. Unfortunately, I do not think this would be a valid answer when presenting my project to a panel of judges at the science fair. Is it valid? or is there a better explanation?

Hi Oriculum,

If your control (no iron) sample showed a similar pattern of cell death, then the results was not due to iron, but to some other nutrient deficiency/toxicity you didn't test for. It would be perfectly reasonable to explain to a judge what happened, and what you would have to do to measure the cause of the cell death (e.g. silica, nitrogen, exact number of phytoplankton cells, etc). You could explain what you would do the next time to prove your hypothesis (perhaps start with fresh ocean water samples, use larger volume containers). You did as much as possible with your available resources, and you have a controlled experiment, so your project is completely acceptable. The judges will be interested in knowing if you understand the science behind your experiment and in the details of your experimental design.

I just had a thought. You ordered phytoplankton for your experiment. Did you order salt water or fresh water phytoplankton? If you used fresh water phytoplankton, then the cells died of osmotic shock in the ocean water.

Donna Hardy