In this lab you will be introduced to the scientific method by investigating the effects of drugs (alcohol and caffeine) on the heartbeat rate in Daphnia magnus. By the end of this lab you will also learn the basic skills needed to use a dissection microscope.


 Biology is more than the description of life forms.  It is a dynamic, and systematic field whose aim is to unravel the mysteries of life and our environment.  Throughout history humans have been intrigued with the world around them.  They have observed natural phenomena and wondered “why?”.  All scientists have certain traits in common, whether it was Aristotle 2,000 years ago or today’s molecular biologists.  Scientists have inquiring minds and great powers of observation, and will use a systematic approach for testing the unknown.

 In this course you will have the opportunity to develop your potential skills as a scientist.  The laboratory exercises are designed to stimulate your thought, heighten your powers of observation and, introduce you to the scientific method.  You may decide to pursue a career in science after this course.

 The scientific method is neither complicated nor unique to science.  It is a powerful tool of logic that can be employed anytime a problem or question about the fundamental nature of something arises.  In fact, we all use elements of the scientific method to solve every day problems and questions.  We accomplish this so quickly and automatically that we are not conscious of the methodology.  In brief, the scientific method consists of observation, prediction, testing and interpretation.  All research begins with a fundamental question.

 In this lab we will ask two questions: How is the heartbeat rate affected by caffeine? How is the heartbeat rate affected by alcohol?


Observation is the most basic element of the scientific method. All biological knowledge is based on situations in which an individual made an observation of a particular event and recorded that observation. Scientists can rely on just their own sense organs, or they can use technological aids that extend their perceptual limits. These aids may be gel electrophoresis to see protein molecules, microscopes to see the very small and spectrophotometers to observe wavelengths of light.

You will base today's experiment on observations of our lifestyles. You have probably observed that when people drink to much coffee they are often hyperactive. They may be jittery, nervous, and may complain of not being able to relax. On the other hand, when people drink alcohol, their speech often slurs, they lose control of muscular coordination, and their reactions may slow down. Too much alcohol may cause them to pass out and loose consciousness.


The next step in the scientific method is to make an "educated guess" or hypotheses, based on your observations and you knowledge of the material. A possible hypothesis as the answer to the above question could be that alcohol causes a decrease in heart rate, whereas caffeine causes an accelerated heart rate.


The next step in the scientific method is to design a controlled experiment. You will use a living water flea Daphnia magna. to test your hypothesis. You must identify an organism by its proper scientific name so that other scientists know what you are talking about. Something is not a "bug" simply because it is small. The advantage of studying Daphnia is that it is nearly transparent. You can observe 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 the circulation system.

For the design of your experiment, you will record the heart beat rate after adding drops of increasing concentrations of caffeine, then drops of increasing concentrations of alcohol. You will also perform a control experiment by determining the heart rate of a Daphnia in water.

In order to observe water fleas, you will need to examine them at a greater magnification than you could observe with the naked eye. To achieve this magnification you will be using a dissecting microscope. You will need to become familiar with the parts of the dissecting microscope.