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UNIVERSITI TEKNOLOGI MARA

INTERNATIONAL EDUCATION COLLEGE

(INTEC)

DEMONSTRATING OXYGEN UPTAKE

Name : Abdul Afiq bin Abdul Hamid

ID : 2010615814

Group : 11M11

Lecturer’s Name : ASSOC. Prof. Madya Dr. Nor’aini binti Mohd. Fadzillah

ABSTRACT

Every living organism respires throughout their whole life in order to stay alive. The aim of this experiment is to demonstrate the uptake of oxygen in respiration. In this experiment, yeast is used to represent the organisms and the amount of oxygen uptake for five minutes is measured. A replicate of the experiment is also done by changing the amount of yeast tested and any difference of the oxygen uptake is recorded. From the results obtained, an increase of the amount of yeast seems to increase the amount of oxygen uptake thus the rate of respiration is higher.

INTRODUCTION

Yeast

Yeast are unicellular fungi. Yeast are characterized by a wide dispersion of natural habitats. Common on plant leaves and flowers, soil and salt water. Yeast are also found on the skin surfaces and in the intestinal tracts of warm-blooded animals, where they may live symbiotically or as parasites.  Yeast multiply as single cells that divide by budding (eg Saccharomyces) or direct division (fission, eg. Schizosaccharomyces), or they may grow as simple irregular filaments (mycelium). In sexual reproduction most yeast form asci, which contain up to eight haploid ascospores. These ascospores may fuse with adjoining nuclei and multiply through vegetative division or, as with certain yeast, fuse with other ascospores.1 Yeast species either require oxygen for aerobic cellular respiration (obligate aerobes), or are anaerobic, but also have aerobic methods of energy production (facultative anaerobes). Yeasts grow best in a neutral or slightly acidic pH environment.2

The useful physiological properties of yeast have led to their use in the field of biotechnology.  Fermentation of sugars by yeast is the oldest and largest application of this technology. Many types of yeasts are used for making many foods: baker's yeast in bread production; brewer's yeast in beer fermentation; yeast in wine fermentation and for xylitol production. Below is an equation showing yeast fermentation.3

C6H12O6 → 2(CH3CH2OH) + 2(CO2) + Energy

1 http://www.yeastgenome.org/VL-what_are_yeast.shtml2 http://en.wikipedia.org/wiki/Yeast3 http://en.wikipedia.org/wiki/Yeast

Respirometer

A respirometer is a device used to measure the rate of respiration of a living organism by measuring its rate of exchange of oxygen and/or carbon dioxide. A simple whole animal respirometer designed to measure oxygen uptake consists of a sealed container with the living specimen together with a substance to absorb the carbon dioxide given off during respiration, such as soda lime pellets or cotton wads soaked with potassium hydroxide. The oxygen uptake is detected by displacement of manometric fluid in a thin glass U-tube connected to the container. When the organism takes in oxygen it gives off an equal volume of carbon dioxide. As this is absorbed by the soda lime, air is sucked in from the U-tube to keep the pressure

constant, displacing the liquid. 4

4 http://en.wikipedia.org/wiki/Respirometer

Figure 1: Baker’s yeast, Saccharomyces cerevisiae

Source: http://www.azurebio.com/img/yeast1.jpg

Figure 2: A simple Respirometer

Source: http://t3.gstatic.com/images?q=tbn:ANd9GcS0lOMw0fA4DvbNVbn9CX3quTGL_PQC_PuGdlsVMcjChxOkvdTmAg

HYPOTHESIS

The amount of oxygen uptake is higher with more organisms.

NULL HYPOTHESIS

The amount of oxygen uptake is the same despite of the increase in the number of organisms.

VARIABLES

Manipulated : Number of filter paper covered with yeast

Responding : The distanced of coloured liquid travelled in U-tube

Fixed : Temperature of surrounding, volume of potassium hydroxide

MATERIALS

Potassium hydroxide, filter paper covered with yeast, coloured liquid

APPARATUS

U-tube, boiling tube, stopwatch, micropipette, syringe, three-way tap, gauze basket, measuring cylinder

PROCEDURE

1. The apparatus was set up as shown below without the filter paper rolled and also the seeds are replaced with a filter paper containing yeast. The coloured liquid was placed in the U-tube by using the micropipette.

2. The stopwatch was started and any movement of the coloured liquid are recorded in a five minutes interval.

3. The experiment was repeated by replacing the current yeast with two filter paper containing yeast.

RESULTS

Time (min) Tube Distance moved by the

marker fluid (cm)Yeast Control

0 6.30 5.60

1 6.50 5.40 0.20

2 6.50 5.40 0.00

3 6.60 5.30 0.10

4 6.70 5.20 0.10

5 6.75 5.15 0.05

Total 0.45

Table 1: The amount of oxygen uptake by yeast in 1 filter paper for 5 minutes

Time (min) Tube Distance moved by the

marker fluid (cm)Yeast Control

0 7.90 5.60

1 8.30 5.20 0.40

2 8.35 5.15 0.05

3 8.40 5.10 0.05

4 8.50 5.00 0.10

5 8.55 4.95 0.05

Total 0.65

Table 2: The amount of oxygen uptake by yeast in 2 filter papers for 5 minutes

DISCUSSION

When carrying out this experiment, certain factors need to be taken note to enable the

experiment can be done without any problems. First of all, the usage of potassium hydroxide is

to absorb carbon dioxide in the boiling tube. Since respiration uses oxygen and produce carbon

dioxide, potassium hydroxide reacts with the carbon dioxide thus allowing measurement the

oxygen uptake to be done without measuring the carbon dioxide as well. The reaction shows

how carbon dioxide reacts with potassium hydroxide which produce potassium hydrogen

carbonate, KOH + CO2 → KHCO3. Besides that, the usage of coloured liquid in the U-tube allow

easier reading of the scale since the U-tube is very small and the readings could be deceiving.

In this experiment, the aim is to demonstrate the respiration in living organisms and from

the results obtained in this experiment, it is clear that living organisms do carry out respiration in

order to stay alive. It can be seen in both table (table 1 and 2), the coloured liquid seems to

move at a certain distance. These shows that there are some reduction in the volume of the

boiling tubes containing yeast, thus allowing the coloured liquid in the U-tube to move towards it.

As a result, it can be concluded that the yeast used up the oxygen in the boiling tube for

respiration leading to a lower volume.

Besides than demonstrating respiration in this experiment, another aim of the

experiment which is to determine either different number of organisms have different total

uptake of oxygen or not is also demonstrated. In table 1, it can be seen that with only one filter

paper, the distance moved by the coloured liquid in the U-tube is only 0.45 cm. In contrast, in

table 2 which contained two filter papers covered with yeast, the colour liquid moved by 0.65 cm

during the five minutes. This means that more oxygen is taken up in the boiling tube with two

filter papers than with one filter paper. Consequently, the movement of coloured liquid is further

in the boiling tube with two filter papers. Therefore, the numbers of organisms do affect the total

oxygen uptake. More organisms are present causing more oxygen being used up for

respiration.

As for ethical issue, the usage of yeast does not rise any ethical issue since yeast are

used widely in many things besides in experiment such as in bakery. Therefore, this experiment

is quite ethical and also humane.

SAFETY MEASURES

There are a few safety measures that must be taken when carrying out this experiment.

Firstly, as usual, all the laboratory safety measure must be followed. This is to ensure that

experiment can be conducted without problems. Lab coats must be worn at all times in the

laboratory as a standard protocol when conducting the experiment. Besides that, in this

experiment potassium hydroxide is used to absorb the carbon dioxide. Potassium hydroxide is

a corrosive substance therefore can be quiet dangerous. If any potassium hydroxide is split on

our hand, quickly wash it with water to dilute it. Eye goggles should also be worn to prevent any

splash of the potassium hydroxide from entering the eyes.

LIMITATION AND SOURCE OF ERRORS

There are some errors that might contribute to inaccuracy of the results of the

experiment. One of it is the setting up of apparatus. The apparatus set up may be not well

done and may causes air to leak out from the boiling tube. This may cause the reading to move

only a little or not at all. Besides that, unequal pressure on both boiling tube when connecting

the tubes to the U-tube may also cause the reading to be imbalanced at the start of the

experiment. Parallax error might also in this experiment, since the reading of the scale on the

U-tube is very small, some reading may be taken wrongly if the eye is not perpendicular at the

right level.

As for the limitations in this experiment, the amount of oxygen in the boiling tubes may

be limited once it is sealed and closed using the three-way tap, this may causes the yeast to

carry out anaerobic respiration if the oxygen content is depleted. These anaerobe yeast does

not need oxygen to respire but will produce carbon dioxide and ethanol instead. The production

of carbon dioxide is not a problem because it will react with potassium hydroxide but ethanol

may causes an inaccuracy in the results. The production of ethanol may cause the volume of

the boiling tube to increase thus moving the coloured liquid in an opposite way.

SUGGESTION FOR IMPROVEMENT

Some improvements can be done in this experiment to allow it to give more accurate

results. First of all, the set up of the apparatus must be completely tight to prevent any air from

leaking out of the tube or entering the tube. As to prevent the imbalance pressure, make sure

that both three-way tap on each tubes are not close when setting up the experiment. Having

someone with a good eye sight or use a magnifying glass to read the scale of the U-tube is also

a good alternative to avoid any parallax error. Besides that, since in this experiment

temperature of surrounding is set to constant, immersing the boiling tubes in a water bath could

be done to avoid any unnecessary error.

At the same time, limitations could also be reduced in this experiment during the set up

of the experiment. Making sure that the three-way tap is not close at all before starting the

experiment is a good way to avoid the oxygen content from being used before the experiment is

even started. Only close the three-way tap when the experiment start could minimise the

probability of oxygen being depleted during the five minutes. This in turn would also prevent the

yeast from carrying out fermentation and therefore avoiding the production of ethanol.

FURTHER WORK

A further work that can be done using the same set of apparatus is by demonstrating

respiration in different temperature. Besides that, the experiment could also be done to study

the uptake of oxygen at different temperature. This experiment can be done by immersing the

boiling tubes in water baths of different temperature allows the temperature to be manipulated.

Figure 4: A Respirometer immersed in a water bath

Source: http://www.practicalbiology.org/data/images/originals/measuring-rate-of-metabolism-respirometer-in-use-500-346.jpg

CONCLUSION

From the results obtained in this experiment, it can be seen that the increase in the number of yeast increases the amount of oxygen uptake. Therefore, the amount of oxygen uptake is higher with more organisms. Hypothesis is accepted.

REFRENCE

1. Edexcel A2 Biology Student’s Book, Ann Fullick – Pearson Education

2. http://www.practicalbiology.org/areas/advanced/energy/gas-balance-in-respiration-and-

photosynthesis/measuring-the-rate-of-metabolism,117,EXP.html

3. http://en.wikipedia.org/wiki/Potassium_hydroxide

4. http://en.wikipedia.org/wiki/Yeast

5. http://www.yeastgenome.org/VL-what_are_yeast.shtml

6. http://en.wikipedia.org/wiki/Respirometer