Experiments start with a question. As a team, you will need to identify at least 3 questions that you could potentially answer with an experiment. You'll then develop those experiments, and ultimately conduct them.
Use the information and conditions established in your pilot experiment to determine appropriate “standard” conditions for your main experiments and to address your overall causal question.
I can procure a fairly wide range of different supplies for your main experiments. The cost of these materials comes from our course budget – please do not pay out of pocket for supplies. You must get a supply list to me as soon as possible, including the total amounts needed, to ensure that I can get your materials to you with enough time to complete your experiments. Here are a couple of ideas for types of supplies to consider, but do not let these ideas limit your imagination.
● Lettuce (Lactuca sativa) seeds, Salad Bowl variety (obtained from Burpee)
● Filter paper discs, small Petri dishes, and Parafilm to seal the edges
● Aluminum foil
● Aliquots of Gibberellic acid (a.k.a. the plant hormone gibberellin) at a wide range of possible concentrations
● Aliquots of Abscisic acid (a.k.a. the plant hormone ABA), both at a wide range of possible concentrations
● Utility lamps with, full-spectrum, red, and far-red lightbulbs. Use these to construct a light chamber with a cardboard box: cut a hole in the top of the box and then carefully duct tape around the edges of the lamp to ensure that room light does not leak into your light chamber.
Some questions you might consider:
How long do plants need to be exposed to light for germination to be triggered? Open different foil packets for different lengths of time (e.g., 30, 60, 120, 300, and 600 seconds) and compare percent germination. Be sure to use multiple (e.g., at least five) dishes for each treatment so that you can calculate means and standard deviations, and be sure to think about appropriate positive and negative control treatments.
Is it the full light spectrum that’s needed, or only specific wavelengths? You may want to use outcomes from #1 above to decide the most appropriate exposure time to use. In particular, we have utility lamps plus specialized lightbulbs that produce only red or far-red light wavelengths.
How do plant hormones factor in? Hormones facilitate communication and coordination between cells and can be involved in either producing a “go ahead” or “slow down/stop” signal.
How long does the developmental cue for light last? Some seeds can stay in the dormant stage for days—they can be fully imbibed with water, but still not be able to germinate unless provided with light. How long does that capability last? What is the timescale for far-red light exposure for triggering dormancy?
Transfer seeds to foil within 5 min of placing them on the wet filter paper.
Do NOT open the foil once the seeds are inside UNTIL YOU ARE READY TO MEASURE GERMINATION. The only exception is if you are purposely exposing the seeds to light. (For follow-up experiments each treatment should have its own foil packet). It may be that only very short (seconds to minutes, not hours!) exposures to light will induce germination / dormancy.
If you plan to induce germination with brief exposures to light, be sure the plants have been on the wet filter paper for at least an hour prior to light exposure.
For experiments where seeds are exposed to red or far-red wavelengths, the room lights should be off until the seeds have been positioned inside of your light chamber. If you have access to one, a green safe-light may be used for room illumination.
Always think about appropriate negative and positive controls in your experimental design. For example, you will always need to verify that the seeds you are working with are actually viable and capable of germinating. So if the seeds do not germinate in the dark, you will need to subsequently expose those seeds to light for 24 hours and check them again for successful germination.
You may discover that it is simpler to have each individual specialize on one main experiment, rather than having every team member participate equally in every main experiment. That said, other logistical approaches are certainly possible. This is something that your team will want to consider in planning the main experiments.
Regardless, the team will need to think carefully about how many times each experiment will need to be replicated to have adequate sample sizes. You'll also need to communicate effectively about how the experiment was carried out, how data were collected, and what the quantitative measurements represent.