- Find a problem
- Propose a hypothesis
- Devise an experiment to test the hypothesis
- Collect necessary materials and carry out experiment(s)
- Record observations, analyze results and propose new hypothesis
- Propose additional experiments to test new hypothesis.
- If time, do the next experiment proposed.
- Introduce the topic the week before you plane to begin experiments (30 minutes).
- Require students to research possible topics for their experiments. Homework.
- Assign lab plan to include problem, hypothesis and procedure(s). Homework.
- Review problem, hypothesis and procedures for each lab group (5-10 minutes/group).
- Set up experiment(s), gather materials and make solutions. By arrangement with each group.
- Conduct experiment(s). 1-5 days. Day 1 = 45-50 minute period, succeeding days a part of each period.
The single biggest producer of toxic waste in the USA is the common household, producing more waste than industry, universities, schools, etc. Most of this waste ends up in land fill where it finds its way into our water supplies. Until recently 3/4 of all used motor oil ended up in landfill. Motor oil is toxic from its organic components, but more importantly from the quantities of highly toxic cadmium and vanadium metals that have worn off of engine components. Detergents, bleach, paints, even salad oil can be hazardous if in high enough concentration and in the wrong place. Most of these toxins end up in our streams, ground water, and water supplies and eventually into the oceans. Once in the oceans the toxins work their way up the food chain in ever increasing concentrations until the ultimate consumer eats them (us: what goes around comes around!
It is estimated that a very high percentage of pregnancies in humans end in the first weeks of development before a women even realizes that she is pregnant. In sea urchins, an egg my never become fertilized because of something having gone wrong with the sperm. Environmental factors appear to play a large role. Pollution from a wide variety of sources can interfere with normal sperm function, as can temperature, lighting, oxygen levels, pH, and agitation. The Environmental Protection Agency, in fact, uses sea urchin development as a measure of environmental pollution in a locality.
Important: if you are seriously considering doing experimental work with sea urchin sperm you must use a consistent concentration of sperm in your experiments. To learn how to determine concentration, see the Sperm Dilution lab.
- Sea urchin sperm
- Pollutants: copper sulfate, wood pulp (boil some sawdust in water and save the liquid), insecticides, detergents, bleach, etc.
- pH paper or meter, thermometers, UV light source, etc.
This is highly experimental and can be a lot of fun. It is best if the students design their own experiments within the available materials. Give them a few days to come up with ideas and discuss it among themselves. You could assign groups to different environmental categories such as light, temperature, toxins, etc. to illustrate a variety of influences.
Possible effects to look for:
- Sperm motility (none, erratic, faster?)
- How long are the sperm motile? (remember to compare to a control group.)
- If you have eggs available you can check the sperms ability to fertilize. Score as percentage of eggs with observable membranes compared to a control group. (sperm dilution needed? attachment? fertilization membranes?)
(see Healthy and Toxic animations.)
Careful use of controls is essential. Concentration of the pollutants is important. Best if the concentration can then be related back to something in their own lives.
Example of a possible experiment:
- Start with the concentration of bleach in a wash load and do a serial dilution until no effect is observed. (concentration on bottle diluted into washer load)
- Check with your local water company and ask what the waste water volume produced in your community is for a typical day.
- Relate this to your observed results. How much bleach would be needed to make your communities waste water toxic due to bleach)
- Reports should include drawings, tables or graphs, any math used to determine concentrations and dilutions.
- Most of the experiments can very easily be expanded to an independent research project.
Similar scenarios can be developed for other environmental effects. These might include:
- Temperature - lower and higher than the ideal for each species.
- Salinity - higher and lower than sea water (1/2 to 2x)
- Oils and fuels - salad oil to diesel oils. Is the oil itself toxic or does it need to cover the container to cut off oxygen?
- Detergents - again start with a "typical" use level for a household activity and use serial dilutions to a non-toxic level. (as most of our wastes are diluted when going down the drain)
- Oxygen levels - place a sperm suspension in a tall tube. Using a very narrow glass tube or fine tubing, take samples from various depths and score motility. (This is a hard experiment to perform. What happens to the oxygen levels the moment you remove the sample from the tube?)
- pH - us a pH meter or test paper to vary pH from 4-10. Small amounts of dilute hydrochloric acid and sodium hydroxide can be used to vary the pH. Does the pH of the solution change over time? (It will take only a drop of 1N HCl or NaOH to affect pH.)
- Carbon dioxide - make your artificial sea water with sodium free seltzer water (keep stirring to a minimum as this removes the carbon dioxide from the water). Using varying proportions of the regular sea water and the seltzer sea water. What is the pH of the resulting solutions? How does this relate to the "green house" effect of higher carbon dioxide levels world wide?
- Other pollutants such as copper sulfate (used as a fungicide), wood pulp (boil some sawdust in water and save the liquid) and insecticides. Note: small quantities should be used!
Every report will be different, but almost all will require math skills, especially in regard to dilutions of toxins.
You could easily spend an entire class period "debriefing" from this lab. The closer the experiments are to materials they will encounter themselves the easier it will be for them to see the implications. Almost every town has an industry of some sort. Using the possible pollutants from that industry can really open eyes. (even a tourist town uses gasoline, oil, detergents, etc.).
- There are some inherent problems with scoring for motility as a way of assessing sperm function. Name as many as you can.
- What other ways could you score sperm function? (ability to fertilize an egg, enzyme functions such as protease in the sperm head are some examples)
- What other experiments can you propose to advance your knowledge of your chosen problem?
- Experimental design
- Relevancy to their own lives
- Active participation in carrying out experiments
- Look closely at their choice of 2nd and 3rd experiments. Do they relate to the first, build on results of the first?
- Lab Reports
- Conclusions and Implications