LAB 03 Scientific Method PDF

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PRELAB SCIENTIFIC METHOD

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1. The scientific method is A) a method designed to test and prove hypotheses B) an organized inquiry process that uses experimentation to find an answer C) the way scientists present their information in scientific journals D) a series of described steps needed to find absolute answers

variable, is the variable A) that is manipulated by the scientist B) that does not change during the experiment C) that is plotted on the y axis D) that describes the result of the experiment 8. In a controlled experiment, subjects or samples being studied are separated into the experimental group and A) the statistics group B) the control group C) the dependent group D) the Independent group

2. What living organism are we studying in the lab ? A) Lactobacillus, the bacteria found in yogurt B) an anole lizard C) an aquatic crustacean D) yeast, a unicellular fungus 3. What is the scientific name of the organism we are studying? A) Daphnia B) Daphnia Magna C) Daphnia magna D) Daphnia Magna

9. Which of these should be controlled variables throughout the Daphnia experiment? A) the temperature of the liquid where the Daphnia is B) the amount of light that the Daphnia receives from the microscope C) the amount of liquid present in the depression slide D) the gender, age and size of the organism

4. What instrument will be used in the lab to observe this organism?

10. If the Daphnia's heart beats 43 times in 15 seconds, the Daphnia's heart rate equals BPM.

5. What is being investigated in this lab experiment with respect to Daphnia? (Select all that apply) A) The effect of light on the twitching of its eyes. B) The effect of alcohol, caffeine and an experimental beverage on its heart rate. C) The effect of body size on its metabolic rate. D) The effect of heat on its heart rate.

11. Why are we measuring the heart rate three times for each concentration tested? A) because the third trial always gives the correct answer ("the third is the charm") B) because the scientific method states that experiments must be repeated three times C) because that allows us to determine an average that is closer to the true value D)because 2 is too few and 4 is too many 

6. Select all the attributes of a scientific hypothesis: (Select all that apply) A) makes a prediction B) is falsifiable C) is based on previous knowledge D) is the same as a theory

12. Where is the heart in the Daphnia? A B C D

7. In a scientific experiment, the independent

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Laboratory 3 The Scientific Method Objectives     

Understand the steps involved in the scientific method Define and identify: independent, dependent and control variables Calculate the heartbeat of Daphnia under various experimental conditions Analyze the data obtained Make conclusions regarding the various variables tested and Daphnia’s heart rate

Background Information All fields of science have one unifying principle that is a common tie among these diverse scientific disciplines. That unifying theme is the scientific method. The scientific method is simply an organized, methodical, and structured way of observing and/or investigating a situation in an effort to find information about what is being observed. There are six steps to the scientific method. 1. Identification of the situation to be investigated. This is vital because no progress can be made towards understanding the situation unless one knows exactly what is being investigated. Let’s consider an example. Suppose that you notice (observe) a list of essential nutrients on the label of a box of plant fertilizer. You wonder how plant growth might be affected if plants are deprived of just one of those essential nutrients. You decide to investigate the effect of the lack of potassium on pepper plants. 2. Obtain information about the situation being investigated. One of the biggest advantages in problem solving is knowing the background information about what is being investigated. This is why researchers do searches of the scientific literature when writing a paper or conducting research. Accordingly, you would go to the library and read as much as you can about plant nutrition and how potassium affects plant growth. 3. Formulation of a hypothesis. A hypothesis is a possible explanation of the problem or situation based only on what it is known about it so far. The hypothesis must be testable: an experiment must be designed to test its validity. Another important characteristic of a hypothesis is that it must be falsifiable. This means that the hypothesis must make predictions that could be proven false by experimental results. Your first hypothesis might be, “Plants grown in a medium lacking potassium will show some specific signs of malnutrition.

4. Predict the results. Assuming your hypothesis is correct, you ought to be able to predict the outcome of a situation where your hypothesis was actually applied to the problem. You might now try to imagine how a pepper plant would look when grown in a potassium-free medium. Perhaps there would be obvious changes in the leaves and/or the stem height. 5. Design and conduct an experiment to test the hypothesis. An experiment is an investigation conducted under very specific conditions in which all variables are controlled except the one being studied. A variable is an event or condition subject to change. In the potassium study, the lack of potassium is the variable being investigated. If, at the end of the experiment, the hypothesis should be found to be wrong, then it can be modified, further tested or completely discarded. The scientific method commonly results in a long series of repeated testing and hypothesis modification. A hypothesis can never be proven right unequivocally. With more and more experimental evidence to support it, a hypothesis gradually evolves into becoming more and more valid for the situation or problem. The evolution of a hypothesis is based on conducting experiments, making observations, gathering data, etc., all of which are done to investigate the validity and to challenge the hypothesis under consideration. 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. Even if you performed all of your experiments carefully, you cannot be certain that the effect you see is due to the drugs. Perhaps the change in heart beat rate that you may observe between the alcohol and caffeine is caused by the heat of the microscope light, or perhaps it is affected by the removal or addition of solutions. Without a control experiment, your data are meaningless. You will begin the experiment by performing the control procedures and getting a base heart rate for Daphnia before it is exposed to the drug solutions.

Activity 3-1: Control Procedure The control procedure must be performed exactly as the experimental procedure. The only difference is that the variable is omitted. In this case that means that alcohol and caffeine are not added. 1. Capture a living Daphnia and place it in a small drop of water on a depression slide. In order to easily observe and study the Daphnia you will need to obtain 3 threads and arrange the threads on the slide around the Daphnia in order to restrict it to a small area (Figure 3-1).

Daphnia

Fig. 3-1 Set up your depression slide with threads as indicated in the figure. The black dot represents the Daphnia. This arrangement will confine the Daphnia to a small space and make it easier for you to identify the heart.

2. Observe the Daphnia under the LOWEST POWER OBJECTIVE on a compound microscope. 3. Using Fig. 3-2 as a reference, locate the following structures: The most obvious structure is the eye. The brain is a light-colored organ lying above the eye. The pairs of antennae protrude from the head. These are used for locomotion and to sense the environment.  Inside the exoskeleton are five pairs of legs. Comb-like gills are attached to some of the legs. When the legs kick forward, they bring a stream of water across the gills and wash bits of food up to the mouth, which lies just beneath the beak.  From the mouth, the esophagus runs up into the head and then down into the body, where it widens into the stomach, which connects to the intestine.  The heart lies in the upper part of the Daphnia (above the digestive tract), it is a clear structure and will be contracting rapidly. Before you continue with the lab you will need to take some time observing the Daphnia and make sure you can find the heart.  In females, a large brood chamber is located behind the heart. Usually it will contain eggs, but occasionally it may be filled with baby Daphnia. The brood pouch will probably not be present in most Daphnia. 4. Working in pairs, one person should keep track of the time while the other person is counting the number of heartbeats in 15 seconds. The heart rate in a healthy Daphnia will be very rapid (3-5 beats per second).  

5. You will take 3 readings of normal Daphnia heart rate. After each 15 seconds of observation you must absorb the water from the slide using a KimWipe. To do this, gently place the KimWipe at one edge of the water and all of the water will be absorbed.

Antennae heart intestine ovary eye egg

anus Drawing by Carlos Pacheco-Perez, 2004

Figure 3-2. Use this image as a reference for locating the indicated structures and organs in Daphnia.

6. As soon as the water is gone, use a the plastic transfer pipet on your tray to add another drop of distilled water to the Daphnia and count the heart rate for the next 15 second observation period. It is important to not let the Daphnia dry out. However, you must absorb the distilled water between each 15-second reading as this will be the same procedure that you will follow when you are testing the various alcohol and caffeine solutions. In order to maintain good scientific practices, you must follow the exact same procedure for the control that you do for the experiment. 7. When you are finished taking the control measurements, leave the Daphnia in a drop of water. 8. Record your data in Table 3-1 as the control values and calculate the number of beats per minute. One way to do this is to use ratios. For example, if you count 10 beats in 15 seconds, the calculations are as follows: X beats = 10 beats 60 seconds 15 seconds;

X = 600 15 or 40 beats/minute

Another (simpler way) is to count beats for 15 seconds and multiply that by 4. Calculate the average Daphnia heart rate per minute. Record in Table 3-1.

Applying the Scientific Method Note: Make sure that you have read the introduction to the lab before attempting to answer these questions. You will now begin testing the reaction of Daphnia to different concentrations of caffeine and alcohol solutions. All tests will be done by each pair of students in the lab. Before you begin the experiment, answer the following questions (A-E) which ask you to apply the scientific method to this experiment. If you need more space for your answers, you can use a separate sheet of paper to continue your answers to these questions: A. Identify the situation that you are investigating.

B. Where can you obtain information about the situation that you are investigating? What kind of information would you look for?

C. Which variable do you think is the independent variable (the one that is varied to invoke a response)? Which variable do you think is the dependent variable (the one that is the effect)? Which variables will be controlled and how will they be controlled?

D. What do you think will happen in this experiment? Predict what results are possible; what you think may realistically happen in this experiment.

Activity 3-2: Measuring the heart rate of Daphnia under two different conditions 1. Use a KimWipe to absorb the water in the depression slide. Place one drop of 1% alcohol on the Daphnia. Wait 1 minute and then count the heartbeats for 15 seconds. Record the data in Table 3-1. 2. After counting the heartbeats for 15 sec, absorb the 1% alcohol solution using a KimWipe as you did earlier. Immediately add 3-5 drops of distilled water to the Daphnia and monitor its heart rate. It is very important that you give the Daphnia time to recover and allow its heart rate to return to normal between each different solution. Turn off the microscope and wait 3-5 minutes. Why is this important step?

3. When the heart rate reaches the average rate observed in the control experiment, you are ready to proceed with the experiment. Absorb the distilled water with a KimWipe and add a drop of 3% alcohol. Wait 1 minute and count the heartbeats for 15 seconds. Record your results in Table 3-1. 4. Quickly absorb the 3% alcohol solution with a KimWipe and add 3-5 drops of distilled water and repeat step 2. When the heart rate returns to normal, continue this process using the 5% alcohol solution. Record your data from these tests in Table 3-1. 5. At the end of the alcohol series of tests, substitute 1% and 2% caffeine solutions for the alcohol concentration solutions and repeat the tests. Make sure to remove the caffeine solutions, add water to the Daphnia, and let the heart rate stabilize between the caffeine solutions. Record your results in Table 3-1. 6. When you are finished with the caffeine series, let your Daphnia recover in water.

Table 3-1. Results from the alcohol and caffeine test series.

Experiment Control

Alcohol 1%

Alcohol 3%

Alcohol 5%

Caffeine 1%

Caffeine 2%

Beats/15 sec.

BPM (beats per min.)

Activity 3-3 Experimental Solution There are many popular bottled beverages on the market these days that are advertised to help improve your daily life in a variety of ways. Some drinks are advertised as being able to improve your immune system; some are supposed to help you think, while others are supposed to boost your energy levels. Do you believe the claims made by these products? Today in lab you will be testing different concentrations of a popular beverage (see your instructor for the exact drink) to see what effect this beverage has on Daphnia. Use the solutions on your tray labeled “Experimental Beverage” and test the Daphnia according to the steps above. Record your results in Table 3-2.

Table 3-2. Results from the test series using the “Experimental Beverage”. Experimental Beverage Concentration

Beats/15 sec.

Beats/minute

2% Red Bull

10% Red Bull

Once you have finished testing the different solutions, analyze your data. Are the effects of the Experimental Beverage on Daphnia more similar to the effects of alcohol or caffeine? What do you think your results today indicate about the effects this beverage might have on you if you were to consume it? Collecting Data During these biology labs, you will occasionally have an experime...