Research Challenge #1:
What are the best conditions for lettuce germination and growth?
When you carry out a Reference Toxicity Test, the goal is to determine how lettuce seed germination and growth will be affected by whatever chemical compound is being studied. The reference test involves measuring the response of lettuce seeds to exposure to solutions with a wide range of concentrations. In the case of sodium chloride, concentrations ranging from 0.025M to 2M NaCl commonly are used. But in order to make the comparison valid, you also want to know how well the seeds will grow when not exposed to any salt. Therefore, the reference test includes seeds grown in distilled water rather than in a NaCl solution. This provides the control to your experiment, and it is the baseline against which the experimental treatment can be compared.

When a scientist designs an experiment, how does he or she decide what would make a good control? In this case, it seems rather simple -- it makes sense to expose the seeds to exactly the same conditions as in the treatments, leaving out only the NaCl (or whatever chemical is being tested). This makes sense, but what if the seeds in some of the treatments grow even better than in the control? Does this mean you've done something wrong? No! It is quite possible that the conditions we have specified actually are not the best possible conditions for lettuce seed germination and growth. Perhaps in low enough concentration, dissolved salts enhance rather than inhibit lettuce seed development.

There are many experiments you could do to better define the optimal conditions for lettuce seed bioassays. For example, consider what experiments you might carry out to answer questions such as these:

• What is the optimal pH for lettuce seed germination or radicle growth?
• What is the best amount of solution to use in each petri dish? (It varies in the scientific literature, with some investigators using less than 1 ml/dish and others using 5 or 10 ml/dish.)
• Can you design a minimal salts solution that promotes better germination and growth rates than you get with deionized or distilled water?
• What temperature is optimal?

These are important questions, and the answers to them are not available in the published scientific literature. The results of your experiments will add to what currently is known about the optimal conditions for lettuce seed germination and growth.

Some Ideas for Research Challenge #1

Research Challenge #2
Research Challenge #3