bio lab rep daphnia.docx

7/27/2019 Bio Lab Rep Daphnia.docx

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THE EFFECT OF CAFFEIN ON HEART RATE

OBJECTIVE

To investigate the effect of caffeine on the heart rate of Daphnia sp. (water fleas) To highlight experimental and investigative skills

INTRODUCTION

PROBLEM STATEMENT

What is the effect of concentration of caffeine on the heart rate of water fleas (Daphnia sp.)?

HYPOTHESIS

There is a relationship between the concentrations of caffeine on the heart rate of water fleas

(Daphnia sp.). In this experiment, the greater the concentration of caffeine, the higher the

heart rate of water fleas (Daphnia sp.).

VARIABLE

Independent variable : The concentration of caffeine solution

Dependent variable : The heart rate of Daphnia sp.

Constant variable : Temperature and pH of the environment of Daphnia sp., time to

record the heartbeat of Daphnia sp., the type of Daphnia sp. used

APPARATUS

Pippeters, cavity slides, scientific calculator, spatula, weighing dish, electronic mass balance,

250 ml beakers, 100 ml measuring cylinders, glass rod, stopwatch and light microscope.

MATERIALS

A culture of Daphnia sp., filter paper or tissue paper, distilled water or pond water, caffeine

powder (coffee powder)

PROCEDURE


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1. 5 beakers containing 100 ml distilled water is prepared by measuring 100 ml distilledwater using a 100 ml measuring cylinder and placing it in a 250 ml beaker.

2. Using an electronic balance, caffeine powder of mass 0.1g, 0.2g, 0.3g, 0.4g and 0.5gis measured. Firstly, an empty weighing dish is placed on the electronic balance and

the mass of the weighing dish is noted. Then, with the weighing dish still on the

electronic balance, the measured mass is set to 0g. After that, by using a spatula, a

small amount of caffeine powder is placed inside the weighing dish and the desired

mass of caffeine powder is obtained.

3. To prepare 0.1% caffeine solution, 0.1g of caffeine powder is dissolved in 100mldistilled water. A glass rod is used to ensure that all the caffeine powder has

dissolved. This step is repeated by dissolving caffeine powder of mass 0.2g, 0.3g,

0.4g and 0.5g into 100ml distilled water respectively to obtain caffeine solutions of

0.2%, 0.3%, 0.4% and 0.5%.

4. A light microscope is set up. A low power objective lens of 40 magnification isused.

5. One single Daphnia sp. is selected from the Daphnia sp. culture. By using a pippeter,the selected Daphnia sp. is carefully sucked out of the culture and then transferred to a

cavity slide along with an appropriate amount of pond water.

6. By using a filter paper, the excess water on the cavity slide is absorbed so that theDaphnia sp. lays on its side and has limited movement so that it can be easily viewed

under the microscope. However a small amout amount if water is left so that the

Daphnia sp. can survive.

7. The cavity slide is then place on the microscope stage and held in position using stageclips.

8. The microscope is adjusted by first adjusting the coarse focusing knob and the finefocusing knob until a fine image of the Daphnia sp. is observed. The position of the

cavity slide is adjusted until the heart of the Daphnia sp. can be seen clearly.

9. .One student from the group is assigned to observe the Daphnia sp. using amicroscope and count the number of heart beat or leg beat made by the Daphnia sp.

within 15 seconds. A scientific calculator is programmed so that every successive

tapping of the = button records one heart beat or beating of legs. Another student is

assigned to record the time by using a stopwatch. This step is repeated again to obtain

a second reading. The average of value of the readings is worked out.


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10.The Daphnia sp. is then returned to a beaker containing the same pond as the Daphniasp. culture.

11.Then another Daphnia sp. from the Daphnia sp. culture is obtained using the samemethods in step 5 and 6.

12.A few drops of caffeine solution of concentration 0.1% is added to the Daphnia sp..The Daphnia sp. is left in the caffeine solution for 1 minute. After that, its heartbeat is

counted by the same student and same methods as in step 9.

13.Steps 10 to 12 are repeated by using caffeine solutions 0.2%, 0.3%, 0.4% and 0.5%respectively.

12.Each average value of heart beat of Daphnia sp. is multiplied by four to obtain thevalue of heart beat of Daphnia sp. in unit of beats per minute.

13.The results of the experiment are tabulated in Table 1.14.A bar graph showing the comparisons of the heartbeat of Daphnia sp. with treatments

(addition of caffeine solution) and without treatments is plotted

15.A line graph of the heartbeat ofDaphnia sp. per minute against the concentration ofcaffeine solution is drawn

RESULT

Concentration of

caffeine solution (%)

The heart rate of Daphnia sp. (beats per minute)

Reading 1 Reading 2 Average

0.0 (control) 328 336 332

0.1 376 384 380

0.2 392 400 396

0.3 396 412 404

0.4 376 384 380

0.5 372 368 370


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0

50

100

150

200

250

300

350

400

450

0 0.1 0.2 0.3 0.4 0.5

Heart rate of

Daphnia sp. (beats

per minute)

Concentration of caffeine solution (%)

Bar Graph of Heart Rate of Daphnia sp. (beats

per minute) against The Concentration of

Caffeine Solution (%)


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0

50

100

150

200

250

300

350

400

450

0 0.1 0.2 0.3 0.4 0.5 0.6

Heart Rate Of

Daphnia sp. (beats

per minute)

Concentration of Caffeine solution (%)

Graph of heart rate of Daphnia sp. (beats per

minute) against the concentration of caffeine

solution (%)


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DISCUSSION

0

10

20

30

40

50

60

70

80

0 0.1 0.2 0.3 0.4 0.5 0.6

Increment of Heart

Rate of Daphnia

Concentration Of Caffeine Solution (%)

Increment of Heart Rate of Daphnia against the

Concentration Of Caffeine Solution (%)


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The aim of this experiment is to investigate the effects of concentration of caffeine on

the heart rate of living organisms. In this case, to investigate the effect of concentration of

caffeine on the heart rate of Daphnia sp. or more commonly known as water fleas. The

hypothesis is that the greater the concentration of caffeine solution the higher the heart rate of

Daphnia sp.. While conducting this experiment, we can also equip ourselves with laboratory

skills and investigative skills.

The independent variable of this experiment is the concentration of caffeine solution.

This variable is controlled by measuring different amounts of caffeine powder (coffee

powder) that is 0.1g, 0.2g, 0.3g, 0.4g and 0.5g using an electronic balance and dissolving the

caffeine powder in exactly 100ml of distilled water. By using this method, we obtain caffeine

solutions of different known concentrations that is 0.1%, 0.2%, 0.3%, 0.4% and 0.5%.

Distilled water is used instead of tap water because distilled water is pure and does not

contain any other organisms that may disturb our view of the Daphnia sp.. The concentration

of caffeine solution is set from 0.1% to 0.5% only because in this concentration the Daphnia

sp. can still stay alive and carry out its metabolic functions as usual thus making the

experiment possible. If caffeine solution of concentration higher than 1.0% is used, the

Daphnia sp. will automatically die when exposed to this solution, making it impossible to

carry out the experiment.

The dependent variable in this experiment is the heart rate of Daphnia sp.. The

technique used to measure this is by observing the heart beats of the Daphnia sp. which can

be seen clearly when viewed under a microscope. The heart rate of Daphnia sp. when in its

natural habitat that is in the pond water without any treatments is set as a control so that

comparisons between the heart rate in different caffeine concentration can be made. The heart

beats of the Daphnia sp. can sometimes be hard to observe. Another method that can be used

to count the heart beat is by observing the leg beat of Daphnia sp. which is proportional to its

heart beat. To make observations and counting of the heart beat easier, a scientific calculator

is used. Another method involves tapping a pencil on a piece of paper and counting the dots

made afterwards. The best way to count the heartbeat is actually by capturing a video of the

Daphnia sp. in the 15 seconds time frame and replays it in slow motion to count the heart

beats. However because of limited resources, the calculator method is chosen.

The constant variables in this experiment include temperature and pH of the

environment of Daphnia sp., time to record the heartbeat of Daphnia sp. and the type of


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Daphnia sp. used. The temperature and pH of the environment of Daphnia sp. is controlled by

carrying out the experiment in an air conditioned laboratory where the temperature is set to

25oplacing the Daphnia sp. in a culture containing pond water from its natural habitat. Other

than that, distilled water is used to make the caffeine solutions to ensure a stable pH where

the Daphnia sp. can survive in. the time to record the heart beats of the Daphnia sp. is set to

15 seconds by using a stopwatch. The counted heart beats in 15 seconds is then multiplied by

4 to obtain the number of heart beats per minute. The same type of Daphnia sp. from the

same species and breed is used for every repetitions of the experiment.

FURTHER STUDIES

SAFETY PRECAUTION

Throughout the experiment, some safety precautions are exercised to ensure the accuracy and

reliability of the results.

1. Lab coats and closed toe shoes must be worn at all times inside the laboratory whencarrying out the experiment to protect ourselves from any injuries caused by broken

apparatus.

2. Eye protections must be worn to protect ourselves from any toxic chemicals or anymicroorganisms that is found inside the pond water of the Daphnia sp. culture.

3. The experiment must be done in an air conditioned room which temperature is set tobelow 30oC. This is because Daphnia sp. are cold climate creatures and may die from

high temperatures.

4. When carrying out the experiment, students must treat the Daphnia sp. very carefullyas the number of Daphnia sp. available in the laboratory is very limited. Therefore

students need to be extra careful when handling the Daphnia sp. to avoid them from

dying.

5. When observing the Daphnia sp. under microscope, ensure that the light used is not sobright. This is to prevent the Daphnia sp. from dying from overheating due to the

exposure to bright light.


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6. When placing the Daphnia sp. on the cavity slide, make sure that there is only a smallamount of water on it. This is to prevent the Daphnia sp. from moving around on the

cavity slide which makes it hard to observe under the microscope.

7. In contrast, ensure that there is enough water on the cavity slide to ensure that theDaphnia sp. can survive. Too little water causes the Daphnia sp. to suffocate and die.

8. Filter paper should be used in this experiment instead of muslin cloth as suggested bythe manual. This is because the muslin cloth is too absorbent and may remove the

Daphnia sp. from the glass side. In addition, muslin cloth has fibres that may stain the

cavity slide and make observations of Daphnia sp. harder.

9. The experiment for each concentration must be repeated at least twice to obtain theaverage count of heart beat. This is to increase the validity and reliability of the

experiments

10.A new Daphnia sp. should be used for every different concentration of caffeinesolution. This is to avoid the Daphnia sp. from developing tolerance towards caffeine

which cab affect the results greatly.

LIMITATIONS

There is unavoidable existence of limitations that could affect the outcomes of the

experiments. They are

1. When the Daphnia sp. is placed on the microscope stage and exposed to themicroscope light, it can cause the Daphnia sp. to be overheated. This can increase the

heart rate of Daphnia sp. which affects the validity of the results. This can also cause

the Daphnia sp. to die from overheating.

2. The heartbeat of Daphnia sp. when immersed in caffeine solution of 0.3% to 0.5% isvery fast. Missing a few heartbeats when counting is inevitable. Therefore the results

obtained may or may not be accurate to the actual number of heartbeats of the

Daphnia sp..

3. The use of scientific calculators may also affect the number of heartbeats counted.Because the tapping of the calculator is very fast because of the fast Daphnia sp.

heartbeat, the number of tapping and the number that is shown on the calculator

screen may not be the same thus affects the results of the experiment.


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4. The same Daphnia sp. is used by two or more groups therefore it may be injured orhurt while being transferred from one container to the other. Therefore the heartbeat

rate may change and affects the results.

5. Long exposure of the Daphnia sp. to caffeine solution causes the Daphnia sp. todevelop tolerance against the caffeine solution where the heart rate does not increase

even when the concentration of caffeine solution is increased. Therefore the results is

not accurate or obey the theory/hypothesis anymore.

6. Since the Daphnia sp. is not observed under its natural habitat, its stress level mayincrease which causes a fluctuation in its heart rate. Therefore the counting of the

heartbeat must be done as soon as the Daphnia sp. is ready to be observed.

CONCLUSION

REFERENCE

1. Edexcel AS Biology, Students book, Pearson company, 20082. Edexcel Biology for AS, CJ Clegg, Hodder Education, 20083. Text PREU Biology Volume 1, Lee Ching, PEARSON Longman, 20084. International Edition Biology Seventh Edition, Campbell, Reece, Pearson Benjamin

Cummings, 2005

5. Advanced Biology Principles & Applications Study Guide, CJ Clegg with DGMackean, PH Openshaw and RC Reynolds, John Murray (Publishers) Ltd, 1996

6. Carpenter, SR, & Kitchell, JF (1993) The Trophic Cascade In Lakes. CambridgeUniversity Press, London, England.

7. Davidson College Department of Biology (1999)http://www.bio.davidson.edu/index.html.

8. Rith, J (1988) Plant succession on abandoned railways in rural New York State.Proceedings of the 73rd Annual Meeting of the Ecological Society of America, Davis,

CA.

9. www.sciencebuddies.org/mentoring/project_ideas/Pharm_p009.shtml10.http://en.wikipedia.org/wiki/Daphnia sp.11.http://en.wikipedia.org/wiki/Caffeine12.http://www.caudata.org/Daphnia sp./


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