Biology Project

Effect of Effect of Different pH Different pH on Anaerobicon Anaerobic Respiration of YeastRespiration of Yeast

s

Aim

To investigate the effect of different pH on anaerobic respiration of yeast.

Yeast is a type of enzyme. Enzyme, which is made up of protein, will denature in extreme pH and work best in its optimum pH, therefore, it should only work in a certain range of pH. Since enzyme will loss its biological function once denatured, changes in the rate of the anaerobic respiration is a very sensitive measure of denaturation.

IPR N

CI

PL

E

When yeast carries out anaerobic respiration, it will give out both ethanol and carbon dioxide as bi-products. By putting yeast in solutions of differentpH value and study the amount of gas (carbon dioxide) produced, which implies its rate of anaerobic respiration, we should be able to tell the range of pH it works best in.

IPR N

CI

PL

E

To measure the amount of carbon dioxide produced ， we can measure the pressure of the gas in a fixed volume of space ， since amount of gas producedis directly proportional to the pressure it exerted on the container.

IPR N

CI

PL

E

Beaker(250cm3) × 3Beaker(500cm3) × 3Buffer solution of pH 4, 7 and 10 × 3cm3 eachComputer × 1Data logger × 1Electron balance × 1Glucose solution × 450cm3

IceMeasuring cylinder × 3OilHigh Pressure Sensor × 3Thermometer × 3Yeast × 1g

Material

Procedure:

Procedure:

1. Computer was set up with data logger and sensors connected, and the software Science Workshop was chosen.

2. 100g of glucose solution was weighted using the electronic balance. Water was added to it to makeup a solution of 500cm3.

3. Icy water was poured into the 3 500cm3 beakers

to make 3 water baths in order to keep thetemperature of the solutions constant.

4. 150cm3 of glucose solution was poured into 3 250cm3 beakers and 3cm3 of buffer solution of different pH value was added to each of thebeakers separately.

Procedure:

Procedure:

5. The 3 beakers of solution was then boiled. After it was boiled, a layer of oil was added to it and it was then put into the water baths.Thermometers are put into the beakers ofsolution to monitor the temperature.

6. 0.3g of yeast was weighted and grinded into small particles. It was then poured into the syringe. The plunger was slowly pushed until no room was left.

7. After the temperatures of the 3 solutions became 15oC, the syringe of yeast wasinserted into it to suck 15cm3 of solution up.

Procedure:

Procedure:

8. The syringes were connected to the high pressuresensors.

9. Recording was started. Pressure in the three syringes were adjusted by pulling out or pushingin the plunger until they are of 100kPa.

10. Recording was stopped. Previous records were deleted.

11. Recording was started again for 600s to plot agraph of pressure against time.

This is the set up...

R

E

S

U

L

T

Pressure of gas produced in solution of pH4 ， pH7 ， pH10 against time

R

E

S

U

L

T

Yeast works best between neutral to slightly alkaline medium.

From the graphs obtained, we can see that the enzymes in yeast will denature in acidic medium and work best in neutral and alkaline medium.

When the pH of a solution containing protein is changed, the protonation state of the amino and carboxylate groups changes, and ionic bonds in the proteins will be disrupted. This will need to changes in the shape of the protein molecule that cause it to loss its biological function. The protein is then said to be denatured.

DiscussionDiscussion

Since yeast is made up of protein, if the protein denature, the yeast can no longer respire. The pressure of gas produced in fixed volume of space during anaerobic respiration reveals the ability of anaerobic respiration of yeast, which in turns reveals the ability of protein to resist denaturation. From the graphs obtained, we see that the proteins which made up yeast is capable to work in both neutral and alkaline medium.

DiscussionDiscussion

Small amount of oxygen present in the syringe

E r r o r s

Increase the volume of the mixture to reduce the percentage error.

Difference in starting pressure affects the experimental result.

Increase or decrease the volume of the syringe so as to split the different.

E r r o r s

Yeast is not totally dissolved

Grind the yeast before mixing it with thesolution to increase its surface area which enhance better dissolution.

Slight difference in starting temperature

Put all the solutions in one water bath instead of three.

Yeast works best between neutral to slightly alkaline condition.

ConclusionConclusion

Sandy Au Yeung (1)Stephanie Cheung (6)Winnie Ip (13)Bernice Law (14)Amy Wu (28)

6AS

Member List

The End