Full version Yeast Respiration

Yeast Respiration

This print version free essay Yeast Respiration.

Category: Science

Autor: reviewessays 27 November 2010

Words: 2285 | Pages: 10

Biology-Respiration-Rate of Yeast Respiration


An investigation to find out how temperature affects the rate of yeast respiration.


Fixed variables:

Through out the investigation I will keep the amount of yeast/glucose solution the same (50 ml). Also the amount of time I will run the experiment for at each reading will remain constant at 1 minute. The one other thing I will keep the same is the concentration of the Glucose as we are not investigating the affect of glucose concentration on the rate of yeast respiration.

Independent variables:

1. temperature

2. concentration of glucose

3. amount of yeast

4. type of yeast

5. oxygen level

Dependent variable:

I will record the level of the water in the burette Everytime I change the temperature of the water one minute after doing so.


As the temperature increases the rate of yeast respiration will increase then it will descend.



Cell reaction. Glucose+oxygen=carbon dioxide+water+energy.


Single celled microbe from the plant kingdom but has no chlorophyll.


Speed at which something happens.


Amount of energy measured in degrees Celsius.

Scientific knowledge:

I made a prediction on the basis on the theory that when the temperature is increased the particles will collide harder and more frequently at certain temperatures most microbes, such as bacteria and yeast, have a temperature range in which they grow best. If it’s either too low or too high then they grow slower and if it’s to low they stop growing at all. Yeast grows best around 30-35 degrees Celsius. At this temperature the particles are colliding harder because its kinetic energy is at its best but if you get much above 40 it won't grow at all and the particles kinetic energy has decreased dramatically. Below 30 its growth slows down dramatically and when you get below about 10 it really doesn't grow much at all. This happens because of the enzymes in the yeast. The enzymes that catalyze the biochemical reactions in the yeast cell function at those temperatures. Enzymes also have an optimal temperature range. When you get below that range there ability to catalyze the reaction slows down. Above that temperature and the enzyme begins to become inactive. Because respiration is a biochemical reaction it needs those enzymes to catalyze the reaction. If those enzymes are inactive, deformed or destroyed respiration will be very slow or if it is exposed to a very high temperature the respiration process won’t go on.


Name of equipment


Unit of Measurement




Measuring cylinder




electric water bath

delivery tube


calculator Hold large amount of water.

To hold the conical flask (which would be attached to the delivery tube) in place.

To measure temperature

To measure liquids

To cool down water

To heat up water

To measure the volume of liquids

To warm up water used for the water bath and keeps it at a constant temperature

Delivers gases from one container to another

A tube fitted with a stopcock, from which accurate volumes may be delivered.

To find the averages of the result.

Degrees Celsius

Millilitres (ml)

Centimetre squared

Millilitres (ml)


Basin measuring cylinder thermometer burette

Calculator ice electric water bath clamp

Kettle delivery tube beaker conical flask


Simulated experiment:

1. First of all log on to a computer which has the programme which simulates the yeast respiration investigation.

2. The icon on the desktop is called science investigations. Click on it twice to open it up. You will see there 3 options; biology, chemistry and physics. Click on biology. You will see a list of investigations to choose from. Click the one titled yeast respiration.

3. On the screen there should be a diagram of the experiment and different boxes in which you can control or change the variables. Also there should be a box which will time the experiment it should start off at 00:00.

4. Set up the experiment by changing the glucose concentration to 25 m, the yeast/glucose solution to 50ml and the temperature to 10 degrees Celsius. Then you are ready to run the experiment.

5. To run the experiment you will see a bar which you can move at the bottom of the window. On the button with an arrow pointing left, hold on to it with the mouse until you see on the timer it has reached I minute.

6. The reading on the burette should be magnified so you can see it easily. Carry on the experiment in exactly the same way but each time change the temperature with an interval of 10 seconds.

Experiment done in the classroom:

1. First set up a clamp. To set up the clamp you need to fix the boss on to a stand. To fix the boss on to the stand you will need to turn a screw which you can see on the boss in a circular motion. Then fix the clamp on to the boss. To do this you will need to insert the rod of the clamp on to the boss where there is another screw. You will see that the rod fits into the boss perfectly. (Make sure the clamp is set up on flat surface. Preferably set the clamp up on a table). Rotate the screw tightly so the clamp is in place. Where there is a kind of mouth on the clamp you will see another screw. Turn it clockwise to open it and anti-clockwise to close it.

2. You will need to get a basin full of water right to the top.

3. In a conical flask get 50 ml of glucose/yeast solution. In a measuring cylinder measure 50 ml of the solution. Make sure you measure it at the meniscus. Then pour it into a conical flask. The solution should be prepared by your teacher and it should have been sitting in an electric water bath.

4. Once you have the solution in the conical flask prepare a water bath in a beaker big enough to hold the conical flask. The water in the beaker should be at the certain temperature you need.

5. If it’s a high temperature use boiled water from a kettle and mix with tap water. If the temperature is below room temperature add ice to tap water to cool it down.

6. To measure the temperatures use a thermometer. Also the water volume should 200 cm cubed.

7. After you have prepared the water bath fix the clamp to the conical flask so it is sitting in the water bath but not touching the bottom of the beaker.

8. Fill a burette with water to the top but make sure the burette is closed so no water leaks out. Have your palm over the top of the burette and then carefully place it into the water filled basin so no water escapes from it.

9. Make sure some one is holding the burette in the water. Then fix a delivery tube tightly to the conical flask and have the other end in the basin but below the water. Get the burette to remain under the water while you place it over the delivery tube.

10. Time the experiment for 1 minute. Record the reading on the burette in a results table. Do the same thing 3 times so you can find an average. Each time you may come up with different results so find out the average by adding each set of results up and dividing by three. You may end up with a decimal number which is recurring so just round it off to the nearest number for example:


Test 1 Test 2 Test 3 average

7.4 6.5 6.4 6.8


19 ч 3=6.333

Round it off and end up with 6.8.

You will use the average number for when you draw a graph

Obtaining evidence:


C Volume of carbon dioxide in 1 min (cm )

1st 2nd 3rd Average volume of gas

(cm ) Rate

1/average volume of gas (cm )

1 0

2 10

3 20

4 30

5 40

6 50

7 60

8 70


My prediction was that as temperature increases the rate of yeast respiration will go up and come down again. After doing the experiment I have concluded that my prediction was correct. You can see from my graph that my prediction was right as the curve on the graph goes up and then goes down again.

At point a on the graph the temperature is at 10 degrees Celsius. From the low volume of gas you can see that here the particles aren’t colliding much because the temperature is too low for them to produce a lot of kinetic energy. When temperature is higher particles collide harder and faster and when particles do this it means reactions will occur faster but because the temperature is low the reaction will occur very slowly. The force at which the yeast cell and the glucose molecules must be very low because the volume of carbon dioxide was very low. The enzymes catalyzed the respiration reaction very slowly because at low temperatures it doesn’t function properly.

Diagram of an enzyme

Diagram of yeast cell

Diagram of a glucose molecule

At point b the temperature is 30 degrees Celsius. Here the collision rate is much higher because you can see on the graph that the curve is starting to rise from point b very quickly. This is because the temperature has been increased to the yeasts optimal temperature so that means reactions will occur faster. The volume of carbon dioxide is six times than what it was at point a so that means the yeast cells and the glucose molecules also have a much higher collision rate. Also the enzymes are working at there optimal temperature also. The temperature affected the yeast cells for good as it is allowing it to function properly

Point C is the highest peak of the curve on the graph. It is at 40 degrees Celsius. The collision rate of the glucose molecules and the yeast cells is at its highest. This is the maximum temperature at which it will function correctly. Also because the force at which the glucose molecules and yeast cells are colliding is at its highest the respiration rate will also be at its highest and from the graph you can see that it is.

Point D is where the curve on the graph has decreased dramatically. The number of times the molecules and cells collide is now lower and the force at which they collide has decreased also. This was because the water was too hot (50 degrees Celsius) and when the water is too hot the enzyme deforms and changes shape. The high temperature means that the respiration process will be very slow. Eventually the yeast will not be able to do its job properly as the cells would have deformed so much that it can’t respire probably.

Point E is at 70 degrees Celsius but at it the volume of carbon dioxide is the same as at point A. the force and collision rate is all the same. This is because the temperature had gotten too hot so the enzymes in the yeast. All the yeast cells have been destroyed due to exposure to very high temperatures.

My results were quit reliable except for on result at 20 degrees Celsius was below the line of best fit. It means that the glucose is breaking down slower than it should. I think this is because at 20 degrees, reactions would be slow because the temperature is too low for the molecules and cells to collide very fast, frequently and hard.

As the temperature was increased the rate of respiration went higher and then came back down to the point at which it started.

In my investigation the yeast cell works fastest at 30 degrees Celsius to 40 degrees Celsius.


My results are very reliable al there is not much difference between the actual results and the average results.

On my graph I have plotted 8 points. Of these 8 points only one point is off the line of best fit. My results are fairly reliable because there is only 1 coordinate off the line of fit.

In this investigation I could not control the fact that the water bath would gradually decrease in temperature. To avoid this from happening I could have used an electric water bath which would have kept the water at a constant temperature.

Another way of measuring the reaction is that I could have had the same solution that is in the conical flask (glucose and yeast) and the conical flask in a water bath on top of scales. The scales would measure the weight of reaction. How I would intend to do this is:

1. Fill a conical flask with 50ml of yeast and glucose solution.

2. Place it in a 200 centimetre cubed water bath at a temperature between 0-70 Celsius changing it with intervals of 10 Everytime.

3. Put the beaker of water bath on top of scales and take a reading every 5 minutes.

What I predict will happen is that the reaction will weigh high at first then low and stay constant, I think this will happen because at first the water bath will be too cold for a lot of reaction to happen so the mass of the reaction will stay as heavy as it was originally. Then when it is at its ideal temperature the enzymes will start using up a lot of the glucose and lighten the solution. When it gets too hot the weight will remain constant as no reaction is taking place.