Effects of alcohol on heart rate of daphnia magna

The design of experiments to test hypotheses requires considerable thought. The variables must be identified, appropriate measures developed, and influences outside of the experimental variables must be controlled. The independent variable is that which will be varied during the experiment; it is the cause. The dependent variable is the effect; it should change as a result of varying the independent variable. Controlled variables are also identified and are kept constant throughout the experiment. Their influence on the dependent variable is not known, but it is postulated that if kept constant they cannot cause changes in the dependent variable and confuse the interpretation of the experiment. For example, suppose you were growing plants with the intention of studying how the amount of water affects their growth. In that case, the independent variable would be the amount of water provided (the variable that you are purposely changing). The dependent variable could be the length of the stem (that is, what changes as the amount of water is purposely changed), and controlled variables would include the amount and quality of light provided, temperature, minerals provided and so on.

Going back to the initial experiment about the role of potassium in pepper plants, you could conduct your experiment based on a technique discovered in the literature search. You could grow your pepper plants hydroponically (in water with plant nutrients and no soil). In your experiment, you would have two groups of plants, each group consisting of six pepper plants of the same variety and all are the same age, size, and general state of health. In addition, both groups of plants would be grown under exactly the same environmental conditions of heat, light, container size, etc. It is important that all of the conditions (except the one being investigated, potassium) be exactly the same for both groups. The only difference between the two groups is that one will be grown with complete nutrients, the other with all nutrients except potassium.

When your experiment is run, the plants should be allowed to grow for a few weeks, after which time the plants would be compared. In this design, the plants growing in the complete nutrient solution serve as the control group, which is the group forming the basis for judging any differences that may appear in the experimental group, the group grown without potassium. A control is essential in any experiment because it reveals any differences in the experimental situation.

6. Form a conclusion based on the results.

The validity of the hypothesis may or may not be determined. Either the results of the experiment support the hypothesis or the results show that the hypothesis needs modification. If you found the control plants to be lush and green with a height increase of three inches since the experiment began, and the experimental plants to have no increase in height, to have weak stems, and to have yellowish leaves with brown spots, you would have supported your hypothesis.

The experiment does not PROVE your hypothesis to be correct beyond all shadow of doubt. What the experiment does show is that under the conditions of the experiment, potassium appears necessary, and the hypothesis is supported.

The scientific method is neither complicated nor intimidating – nor is it unique to science. It is a powerful tool of logic that can be employed any time a problem or question about the fundamental nature of something. In fact, we all use elements of the scientific method to solve little problems every day, but we do it so quickly and automatically that we are not conscious of the methodology. In brief, the scientific method consists of observing, predicting, testing, and interpreting.

You will base today’s experiment on observations of twentieth-century American lifestyles. You have probably observed that when people drink too much coffee, they are often hyperactive. They may be jittery, nervous, and complain about being unable to relax. On the other hand, often when people consume alcoholic beverages, their speech can become slurred, they may lose control of their muscular coordination, and their reactions may slow down. You will be looking at the effect of alcohol and caffeine on Daphnia magna , a small water crustacean. You will evaluate the effects of these drugs by measuring the heart rate of Daphnia when exposed to various concentrations of alcohol and caffeine.

NOTE: All organisms are classified by Latin names that specifically identify them. You must always identify an organism by its proper scientific name so that other scientists know what you are talking about. You must also remember to ALWAYS italicize or underline the Latin names (genus and species) of organisms EVERY TIME YOU USE THEM!

The advantage of studying Daphnia is that they are almost transparent. You can see the heart beating, the squeezing action of the intestine, muscular movements, and occasionally, babies in the brood pouch. Also, because Daphnia is a small, aquatic organism, it makes an excellent subject for studying the effects of drugs on circulation.