Do It
Activity #1
Protocol
The protocol for this activity is outlined clearly in the student hand out. Click on the link below to view or download the handout :
Helpful Hints
Encourage students to make careful observations of the worms and to do careful, detailed drawings of what they see. Remind them to make detailed notes regarding locomotion patterns and other observable behaviors, such as nose-wrinkling,backing up, defecation cycles - worms defecate every 45 seconds!, reaction to light tapping on lid of petri dish,etc. Encourage students to estimate the percentage of worms in each developmental stage and to note if there are more eggs present in certain areas of the plate than in others.
Caution: students must sterilize the pick each time they use it to pick a worm. The pick is sterilized by holding it in the flame of the lamp or burner until the wire glows red. The pick should cool for a second or two - students may touch it to the plate near the edge to cool it quickly. It is a good idea to demonstrate sterilizing the pick at the beginning of the lab if you did not do so the day before.
Caution: students should avoid "digging" into the agar. This will make trenches that the worms will burrow into and observing their behavior will become very difficult. The best technique for picking is to touch the pick to the surface of the plate to make it "goopy", then touch the goopy part of the wire to a worm. The worm should stick to the pick. Quickly remove the plate, substituting the clean, seeded plate. Touch the pick to the surface of the new plate, avoiding digging into the agar. The worm will crawl off the pick and onto the new plate.
If you have any concerns regarding your students' safety when using alcohol lamps or bunsen burners, an alternative to supplying a device for every two groups is to set up a "Picking Station" as described in View It! You will supervise and rotate groups through this station. You should be able to supervise four groups of students using four microscopes and two flame sources. Students waiting to pick can proceed with observations, notes, and drawings.
Note: This option will require extra microscopes.
Clean-Up and Disposal
Newly picked worm plates should be stored at room temperature. The original plates (the ones students picked from) should be disposed of in the following manner:
Using a transfer pipette (non sterile is fine), drop enough chlorine bleach on the plate to cover the surface. Allow it to sit for 10 minutes, place the cover on the plate, and place in a biohazard bag. Tightly close the bag when all plates have been bleached and dispose of bag, following your district guidelines for biohazard disposal.
Activity #2
Protocol
The protocol for this activity is outlined clearly in the student hand out. Click on the link below to view or download the handout :
Helpful Hints
It is a good idea to demonstrate the spreading and the "washing" (washing materials) procedures before having students do them. Students often have difficulty evenly distributing worms over two plates. Caution them to be careful not to "squirt" all the worms onto the first plate!
Remind students to label all plates before using them and to place covers on plates while alcohol is "drying" in order to avoid evaporation.
Safety Concerns
As ethanol is highly flammable, students must be cautioned to keep ethanol-containing tubes away from flame sources. As is Activity #1, if you feel uneasy about students sharing flame sources, you can set up an Ethanol Plate Station which you will supervise. Students simply bring their labeled clean plates to the station, pipette the ethanol concentrations onto them, sterilize the spreader and spread at the station. Again, you should be able to supervise 2 to 4 groups of students at a time. Groups who are waiting can begin the S-basal washing process.
Caution: stress to the students that the spreaders are glass and will be extremely sharp if broken. You should have a covered box , clearly marked "SHARPS" with slit in the top for disposal of any damaged spreaders.
Clean-Up and Disposal
Used pipettes should be placed in a biohazard bag and disposed of according to district policy. Spreaders should be heat sterilized and stored in a safe place. Worm plates should be treated with bleach as outlined above and disposed of according to district policy.