Overview
In this introductory physiology lab, students determine the contraction rate of the dorsal blood vessel of the blackworm Lumbriculus. Students then design and conduct an experiment to determine the effect of temperature change or chemical exposure on the contraction rate.
Needed Materials*
- Lumbriculus culture (141720 for 30 students)
- dropping pipets (158981)
- Bibulous Paper (634050)
- or paper towel
- stopwatches (preferred),
- watches with second hands, or phones with stopwatch application
- microscope slides
- coverslips
- springwater
- stereomicroscopes (or compound microscopes with 40x viewing option)
*Need for other materials will depend on student’s experimental plans.
Safety
Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules. Cultures remaining after the completion of the activities may be added to a classroom aquarium. Alternatively, dispose of them by flushing down a sink with tap water. The chlorine and chloramine in most tap water will kill blackworms. If your tap water is not chlorinated, pipet 1 mL of household bleach (sodium hypochlorite solution) or isopropanol (rubbing alcohol) into the culture and wait 15 minutes before flushing down the sink.
Procedures
Students work in pairs to count blood vessel pulsations.
Hold your Lumbriculus culture for at least a day without feeding before doing the activity. This gives time for food to clear from the intestine. (If you are culturing Lumbriculus, remove them from culture and place them in a bowl with springwater until their intestines clear.) Otherwise, intestinal contents and their movements may obscure blood vessel pulsations. Peristalsis is easily distinguished from blood vessel pulsations, however, because the blood vessel pulses from posterior to anterior, while intestinal contractions travel in the opposite direction. To help students recognize blood vessel pulsation, have them watch the video at the following link. http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/INT-ANIMA-dbv-vel.htm
For best microscope viewing, light must pass through the worm’s body before entering the eye. This requires that your stereomicroscopes have bottom (in-base) illumination. If they do not, then use a standard microscope with a scanning lens (i.e., view at 40x). LED or fluorescent microscope lights work best for this activity. Halogen bulbs heat the slide and increase the pulse rate, requiring that data be collected quickly before the heat builds up.
Set up workstations with the following materials:
Lumbriculus culture
dropping pipets
beaker or cup of springwater
Follow the introductory activity with a brainstorm on factors that might influence contraction rate. Among the factors that students might test are the effects of temperature and chemicals. For temperature, test between 5°C and 35°C. Would cutting the worms into three sections alter the results? If you test this, cut the worms on the day before testing. Lumbriculus readily regenerates, so no damage will be done. In fact, fragmentation is a normal method of reproduction for Lumbriculus.
Some substances, such as nicotine, stimulate contraction rate, while others, such as alcohol, depress the rate. Some substances may be banned from your classroom, so check your local regulations before approving a given substance. Use the following general guidelines for test solutions. Remember, though, that these are commercial products and that the actual values may not match what is given here.
- 8 oz (240 mL) of brewed regular coffee contains 100 to 200 mg caffeine.
- 8 oz (240 mL) of brewed decaffeinated coffee contains 2 to 12 mg caffeine.
- One regular cigarette contains 1 to 2 mg nicotine (extract in 70 mL springwater at 60°C with stirring for 15 minutes and filter through cheesecloth).
- One light cigarette contains 0.5 to 1 mg nicotine.
- Vodka (40% ethanol). Mix 31 mL in 469 mL springwater for a 2.5% solution.
- Tablets (e.g., caffeine, diet, decongestant). Crush two tablets and dissolve in 400 mL springwater. Use heat and stirring if necessary. (The tablets may contain some fillers that will not dissolve.)
The above solutions may be used full strength and diluted 1:10 and 1:100 with springwater to test the effect of varying the concentration. For uniformity of results, keep worms in the test solution for the same amount of time. We recommend exposure for 15 minutes before transfer to a slide for counting. (Students may run time trials to determine the optimal exposure time.) After testing, return the worm to pure springwater for recovery.
Optional:
Have students compare their results to studies of how the test substances affect human heart rate. Advanced students may research and report on the mode of action of the substances.
Students who check for temperature’s influence can calculate the temperature coefficient (Q10) for contraction rate. This is the factor by which a reaction or process increases as temperature increases. Reactions that are not influenced by temperature have a Q10 of 1. Temperature-dependent reactions have a Q10 greater than 1.
where
t1 = lower temperature
t2 = higher temperature
k1 = rate at temperature t1
k2 = rate at temperature t2
Here is an example based on the heart rate of Daphnia magna.
t1 = 10°C
t2 = 20°C
k1 = 195 contractions/minute
k2 = 385 contractions/minute
Another interesting math activity is to estimate the volume of blood flow per hour.
c = velocity of blood per second as measured by the time in seconds required for a contraction to travel a measured distance in millimeters.
D = measured diameter of dorsal blood vessel in millimeters.
r = ½D
V = volume of blood or volume of a cylinder (in this case, cross-sectional area of the dorsal blood vessel times c).
If c = 0.2 mm/sec, and D = 0.2 mm, then cross-sectional area of dorsal blood vessel is (using A = πr 2 ) 3.14(0.1 mm)2 = 0.03 mm2 .
V = A x c (0.03 mm2 )(0.2 mm/sec) = 0.006 mm3 /sec
Convert to volume of blood per hour (60 sec/min x 60 min/hour)
0.006 mm3 /sec x 3600 sec/hour = 21.6 mm3 /hour
Convert to milliliters of blood per hour
1000 mm3 = 1 mL 21.6 mm3 /1000 mm3 = 0.02 mL/hour
Contraction Rate of Dorsal Blood Vessel
| Body Section | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 | Trial 6 | Total | Average | Contractions/minute (Average x 2) |
|---|---|---|---|---|---|---|---|---|---|
| Posterior | 5 | 4 | 5 | 3 | 4 | 4 | 27 | 5 | 10 |
| Middle | 3 | 5 | 3 | 3 | 3 | 4 | 21 | 4 | 8 |
| Anterior | 3 | 2 | 3 | 3 | 2 | 4 | 2 | 3 | 6 |
Is the contraction rate the same for all three regions? Explain
No. Generally the contraction rate is greatest at the posterior. The contractions begin here and travel toward the anterior. Some of the contractions do not propagate all the way, so the rate falls toward the anterior. Note: Although this is the normal pattern, it is not inviolate.
