Research Challenge #1:
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
- What is the optimal pH for lettuce seed germination or radicle
- 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
- 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