Here are some answers:
1. If you use 1/8 tsp in 9/8 tsp of water, this is a 1:10 dilution, so you are using 10% of the concentration from the label.
2. If you use 1 tsp in 1/4 cup of solution, this is a 1:17 dilution. (1 tsp plus 16 tsp)
3. If you do a 1:10 dilution and a 1:17 dilution in series on the same sample, the final dilution is 1:170.
Thanks for the pH information; so we can discard the pH theory. What is the pH of the solutions? Is it optimum for yeast growth?
I think you have a good idea. Yeast can grow aerobically or anaerobically. If they grow aerobically, then 6 carbon dioxide molecules are produced for one molecule of glucose but the cells obtain significantly more energy per glucose ; if they grow in low oxygen conditions, then 2 molecules of carbon dioxide will be released for every glucose molecule, but the yeast have to use more glucose to obtain the same amount of energy . So if the control cells are initially growing with aerobic metabolism, and the cells with the antifungals are growing anaerobically, there could be a difference if he CO2 produced.
There is a Science Buddies project on this topic:http://www.sciencebuddies.org/science-f ... #procedure
The experiments to confirm this hypothesis are beyond the scope of your science project, but certainly a possible topic of future investigation. And, you can definitely include this is your discussion.
The next step would be to investigate all of the components of the antifungals to determine if any of the molecules will inhibit aerobic metabolism. Do you know what the molecular basis of action of all of the antifungals are?
I will post again if I think of anything else.