Premodule: Scientific method and plant growth
Teacher suggestion for premodule
This is a classic plant growth experiment that has made its way into many biology texts and lab manuals in one form or another. This one differs in that it works with a seed that the students are not familiar with and has some unfamiliar growing conditions (cold shock, top soil placement). It also differs in that it has the students conduct “real science” based on previous work done by other scientists. The lab lends itself as a good starter lab for experimental design, data collection and error analysis. I have often used it as the first lab for a biology class but it could be done anytime during the year. It could also be timed so that the plants will be ready for use in the future modules (4– 6 weeks ahead). In that case, makes sure to get the kids growing the wild-type plants and grow the AKT-1 mutants on your own.
- 1 period (45– 60 minutes) for setup
- 5– 10 minutes at the start of subsequent classes for data collection and recording
- The lab lasts as long as you want it to (from 3 weeks to 2 months)
What you need to set up per 24 students
- 20– 40 seeds per group wild-type Arabidopsis (strain CS60000 or other wild type, there are many, ask at www.arabidopsis.org when ordering)
- Pots to grow seeds in (number depends on type of pot used)
- I have seen the plants grown in anything from plastic caps from 2-liter soda bottles to full-size pots
- I have had luck using 2” square plastic pots placed in a plastic tray that supplies them water from below
- Students may want to test this as a variable!
- Soil for growth of seeds
- Any potting soil should work for this but this is another variable that students might want to test
- Students may want to try alternative methods, i.e. agar or hydroponic growth methods
- Arabidopsis growth instructions (see index for sections of the manual providingthis information)
- Graduated cylinders, scales, beakers for measuring soil
- Variables for students to test
- Different-sized containers
- Soil types (sand, potting soil, etc.)
- Grow lights
- Colored cellophane
- A sunny place to grow plants (a windowsill should work)
What the students need
- Notebook to keep data in
Lab set up
It’s easiest to set up stations of materials around the room for this lab, i.e. one with seeds, one with pots, one with measuring glassware, etc. You can give out the seeds in prepackaged 1.5ml tubes if you prefer. The students will be on their own in groups to design and setup their experiment but I always have them run their plan by me first to make sure they really have a plan. This also gives me a chance to make sure that they have thought of: measuring their materials (soil, water, etc.), control group and control variables, method of data collection, etc.
Have the students read the Greenthumb Memo and the “Growing Arabidopsis thaliana in a Lab Environment” research paper for homework. This reading will offer a basis for the students to design their experiment the next day.
Prelab 10 minutes
This lab is a good introduction to characteristics of a well-designed experiment versus a poorly designed one. The prelab also gives the teacher a chance to “suggest” ideas for experiments. For example, if you have different-sized containers that you would like to have the students use, suggest it at the start of the lab as an “option” and some group will take the bait. A good way to suggest the students to work is to compare the two protocols, identify which of the two worked better according to the study, find the differences between them and choose one to act as your independent variable. So in essence, the students start with the TAIR protocol and change one factor to see how much of an effect it has on the germination and growth of the seeds.
Lab 40– 50 minutes
During the actual lab, students should break into groups and decide on the factor that they would like to test. They should have one student write up the plan for their experiment and have the teacher approve it. Once the students have their experiments designed they should be able to spread out the work and complete the lab fairly soon after. For the most part, the groups will be on their own for the lab designing and setting up their experiment. Your job is mostly to guide them in their planning, make sure that their plan is good, and answer questions they have.
Each group will need a few minutes at the start or end of subsequent classes to gather data on their plants as they germinate and grow. What data they collect is something that needs to be looked at as a class. During a future class, before the data collection has started, a discussion of good data specific to this experiment might be helpful.
The postlab for this experiment consists of a class discussion of the data collected, and how the well the student lab designs worked (or didn’t in some cases). It is most appropriate to have the post lab after all of the data is collected and the students are either writing their final reports or have already written them. The teacher can moderate a discussion of what worked well for students and what did not work well.
The final lab report is the major homework aspect of this activity. A fairly simple- to-use lab report format and explanation for students was designed for this module (see index). It is based on the lab report format used in the Connecticut Academic Performance Test (CAPT; Connecticut Academic Performance Test - Second Generation, Science Handbook, 2001) with some modifications. It is also possible to have the students use their results to produce a poster or oral presentation rather than a lab report. This is a chance to show students another side of science.