BiologY Lab report

ARUL VERMAN .R

BIOLOGY LAB REPORT

Aim:

Design an investigation to measure the effect that one of the following factor has, on the rate of respiration in yeast.

Hypothesis

The factor that I have chosen to vary in this experiment is types of carbohydrates used. I think that respiration of the yeast cells greatly depends upon the type of carbohydrate used here is an example supporting my statement: yeast might readily react with Glucose whereas it might not react at all with Lactose. This might be mainly due to the fact that Glucose generally being a simple sugar Is chemically active and is more of an acid, thus makes it easier for yeast cells to break down the molecules producing Ethanol and Carbon dioxide. Whereas Lactose doesn’t react that well because Lactose being a complex sugar and a disaccharide takes up a lot of time for yeast to metabolize…

Apparatus required

1. Yeast – 15ml

2. Test tubes – 2

3. A syringe

4. Sucrose – 12ml

5. Glucose – 12ml

6. Starch – 12ml

7. Lactose – 12ml

8. Maltose – 12ml

9. A beaker

Constants and variables

Constants

Temperature of the reaction: The temperature at which the reaction was carried out was kept constant throughout this investigation. The temperature was kept constant to 40 0 Celsius.

Quantity of the carbohydrate used: The amount of carbohydrate used was kept constant throughout this investigative task. The volume of the carbohydrate was kept constant to 12cm3.

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8. Maltose – 12ml

9. A beaker

Constants and variables

Constants

Temperature of the reaction: The temperature at which the reaction was carried out was kept constant throughout this investigation. The temperature was kept constant to 40 0 Celsius.

Quantity of the carbohydrate used: The amount of carbohydrate used was kept constant throughout this investigative task. The volume of the carbohydrate was kept constant to 12cm3.

Time recorded for each reaction: The time for which each of the reaction between different carbohydrates were recorded was kept constant.. All the reactions were begun to be recorded after 5minutes … and the observation time was 5 minutes... Thus the total time taken for one carbohydrate was 10 min (5minutes of initial time and 5minutes of observation time).

Variables

Independent variable

Type of carbohydrate: The type of carbohydrate used is an Independent variable... since varying this would show a drastic change in everything such as (amount of Co2 produced, )

Dependant variable

Amount of Co2 produced: The amount of carbon dioxide produced is totally dependant on the type of carbohydrate used... Thus a dependant variable .

Procedure

1. Firstly take two test tubes and a interconnecting tube with a cork.

2. Now take 15cm3 of yeast (pre- soaked in water).

3. Take 12ml of different types of carbohydrate.

4. Also take a syringe (for measuring the volume of liquids) and a stop watch.

5. Now take a large sized beaker and a thermometer.

6. After the preparations are ready... Now add 3cm3 of yeast to the test tube 1 and finally add 12ml of a carbohydrate to it .

7. Now pour In a considerable amount of hot water in the large sized beaker and insert a thermometer to keep temperature constant to 400 C

8. Keep the test tube 1 containing the mixture of yeast + carbohydrate immersed in the water bath i.e in the large sized beaker containing hot water.

9. Now pour in water (not hot water) in test tube 2 and keep the interconnecting tube inserted in the water of test tube 2.

10. After that connect the INTERCONNECTING tube and seal it with cork on both test tubes, this is generally done to ensure that the yeast respires anaerobically .

11. Initially wait for about 5minutes and then start counting the no of bubbles that pop out for the next 5minutes ….. Note : ENSURE THAT BOTH TEST TUBES ARE PROPERLY SEALED.

12. To keep temperature constant keep adding hot water when the temperature of the water in water bath comes down.. or if the temperature has raised then add considerable amount of cold water needed to bring down the temperature….

13. Repeat this investigative from steps 6-12 using different types of carbohydrates… and record the no of bubbles popped out in test tube 2.

Observation

NOTE: Quantity of yeast taken was 3cm3 for each carbohydrate and the volume of carbohydrate taken was 12cm3.

The data from the tabulation above clearly proves my statement as in my hypothesis that glucose and sucrose being simple sugars are broken down easily by the yeast cells producing ethanol and carbon dioxide.. The bubbles that were recorded here are the amount of carbon dioxide produced by the anaerobic respiration of the yeast during the reaction … so higher the count of bubbles, more of the carbon dioxide has been produced. The tablature also clearly shows that the yeast cells were not able to metabolize Lactose and Maltose since they were complex sugars, it may also be due to the fact that the enzymes in the yeast were inefficient in transporting lactose or maltose across its cell membrane, or were unable to convert Lactose or Maltose from a disaccharide to a monosaccharide.

Conclusion

From this investigative task I could conclude that types of carbohydrate used greatly affects the fermentation of yeast. This was proved by the readings of reaction between different types of carbohydrates; each reaction was widely different from each other.

Evaluation

Reliability of my method: I think that I have done this experiment in a satisfactory method, meeting all requirements. My results clearly support my hypothesis. However the results of my experiments are not that reliable. As there might have been minor mistakes that I would have done unknowingly or might have occurred due to fault in apparatus. I think that main flaw of my experiment was improper sealing of the test tubes during the reaction since improper sealing could lead to wrong or improper readings.

Questions and Answers

Questions

Why some sugars were not metabolized while other sugars were?

Why do you need to incubate the yeast before starting to monitor the bubbles?

Considering the results of my experiment, do yeast equally utilize all sugars?

Answers

Yeast may not have the proper enzymes to either transport lactose across its cell membrane, or it may not have the enzyme needed to convert it from a disaccharide to a monosaccharide.

The yeast need to be incubated so that the oxygen in the test tube will be completely consumed. If the yeast respire aerobically, no bubbles would occur, because much oxygen is consumed as CO2 is produced. It also takes a few minutes for the yeast to transport the sugar into the cell, to respire at a constant rate, and to reach the proper temperature.

Yeast cannot utilize all of the sugars equally well. While glucose, sucrose, and fructose all can be metabolized by yeast, lactose is not utilized at all.