Rate of respiration in Yeast.

Aim: I am going to investigate the rate of respiration of yeast cells in the presence of two different sugar solutions: glucose, sucrose. I will examine the two solutions seeing which one makes the yeast respire faster. I will be able to tell which sugar solution is faster at making the yeast respire by counting the number of bubbles passed through 20cm of water after the yeast and glucose solutions have been mixed.

Prediction: I predict that the glucose solution will provide the yeast with a better medium by which it will produce a faster rate of respiration. This is because glucose is the simplest type of carbohydrate (monosaccharide). However sucrose is a complex sugar it contains large molecules making it a disaccharide.

Due to the large molecules being saturated and the small molecules being unsaturated this will allow the glucose to mix easily with the yeast therefore making it respire more frequently. The sucrose sugar however having larger molecules will find it harder to mix in with the yeast; this will make the rate of respiration in the sucrose much slower as it is not as efficient as the glucose.

Yeast requires enzymes to digest the food on which the yeast is living. The enzymes digest the food the yeast is living on (normally sugars such as Glucose and Sucrose) breaking down the large molecules into smaller ones. It takes longer to break down the large molecules rather than the smaller molecules. This means that the yeast does not need to do any work when provided with small molecule foods such as glucose. The small molecule foods allow the yeast to respire easily.

By already having a small molecule sugar in this experiment it makes sense that the small molecule food will use less energy from the yeast therefore allowing it to respire more efficiently. Whereas the large molecule food (Sucrose) will take longer to break down because of its large molecules, this will waste the energy of the yeast as it has to break down the large molecules into smaller molecules before it can use them.

This means that the sucrose is not as efficient as the glucose at providing the yeast with a better medium by which it will produce a faster rate of respiration.

Theory: Yeast is a single celled fungus. It feeds saprophytically (secreting enzymes from cells) the enzymes digest the food on which the yeast is living. The enzymes digest the food the yeast is living on (normally sugars such as Glucose and Sucrose) breaking down the large molecules into smaller ones. It takes longer to break down the large molecules making them less efficient than the smaller molecules. This means that the yeast does not need to do any work when provided with small molecule foods such as glucose. The small molecule foods allow the yeast to respire easily.

The glucose should allow the yeast to respire more because it is already a small molecule sugar whereas the sucrose is a large molecule sugar this will mean that the yeast can use the glucose straight away without breaking it down, whereas with the sucrose it has to break it down into a simple sugar before it can use it this will take time and it means that the glucose is more efficient at making the yeast respire.

As yeast secretes enzymes from the cells to break down the food (sugars) it would need an ideal temperature ...

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As yeast secretes enzymes from the cells to break down the food (sugars) it would need an ideal temperature of approximately 40-50 degrees Celsius in order to make the enzymes work effectively and so they can break down the sugars in as fast a time as possible.

Safety: Keep equipment away from edge of bench, wear goggles (optional).

Apparatus: 6 test tubes, 4 syringes, 2 beakers, delivery tube, thermometer, yeast, sucrose, glucose and test tube rack.

Fair test: To ensure that I carried out a fair test I would use the same amounts of yeast, glucose and sucrose, as using different amounts could manipulate my results e.g. making respiration in the yeast at a much slower rate etc. I will repeat the test five times so that I can get accurate fair results. I will also change the test tubes as previous remains of the yeast and sugars could still be in there and this could manipulate my results. I will try to keep the temperature of the water in the large beaker at 45 degrees Celsius as enzymes work best at this temperature. By changing the temperature the enzymes might not work as efficiently. I will count the number of bubbles given off by counting them as they appear in a test tube of water for 2 minutes. I will empty the test tube and replace it with clean water after doing the test with each sugar, so that it doesn’t manipulate my results.

I will try to enforce these factors in order to keep the test fair.

Plan: I intend to count the number of bubbles that appear in a test tube of water when I mix yeast with glucose or sucrose. The number of bubbles that appear will tell me the rate of respiration in the yeast. I will repeat each test five times in order to gain accurate results. I will set up my equipment. First I will add 3cm of yeast into the test tube and then I will add 6cm of glucose or sucrose to it. I will let it warm in the 45 degree warm water which will be inside a beaker. After letting it heat for 1 minute I will take I out and place a delivery tube on to the top of the solution of yeast and sugar. In another test tube I will place 15 cm of water. Into this test tube I will place the other end of the delivery tube. I will start the stopwatch and begin counting the number of bubbles that come through into the water. If no bubbles appear then I will gently shake the test tube full of yeast and sugar this may allow any blockages in the delivery tube to clear and we will be able to see if any bubbles form in the water.

After two minutes are over I will record the number of bubbles that appeared and record on a sheet of paper. I will dispose of the contents of the test tubes and replace them with new ones.

I will repeat the test for both the glucose and sucrose five times in the same manner.

Method: After collecting all of my equipment and setting it up. I measured out 3cm of yeast and placed it inside a test tube. To this I added 5cm of glucose solution. I allowed it to heat inside a beaker full of warm water which was at 45 degrees Celsius. After leaving the test tube in there for 1 minute I collected another test tube and inside it I placed 15cm of water. I attached a delivery tube on to the two test tubes. The rubber bung was placed inside the yeast and glucose test tube. I began my stop watch for two minutes and counted the number of bubbles that appeared inside the test tube that was filled with water. By counting the number of bubbles inside the test tube full of water it gave me an indication of the rate of respiration in the yeast.

After two minutes were up I stopped counting the bubbles and recorded the number that appeared on a piece of paper. I emptied the contents of the two test tubes and replaced them with new contents. I repeated the test for the glucose four more times.

After repeating the test for four times I changed the type of sugar that I was using. I now did the experiment again but with the sugar sucrose. I did the test in exactly the same way and repeated it five times. I used the same amount so f each substance and timed them for the same amount of time.

I recorded my results, and calculated an average time for both the sugars glucose and sucrose. I packed away all of my equipment that I had used and deposited any remaining substances that I had left behind.

Diagram:

Results:

Average number of bubbles formed for glucose- 54 bubbles formed

Average number of bubbles formed for sucrose- 43 bubbles formed

Reliability of results: I think that my results are quite reliable as I conducted a fair test repeating it five times for each sugar. I did not receive any anomalous results as I repeated the test a number of times, if a mistake was made then it would be noticeable amongst the results. Therefore I am confident that the experiment I conducted was a fair and accurate one.

Graphs:

Analysis of graph: The graphs show that the glucose had the greater number of bubbles formed. The averages for the two sugars also show that the glucose has a greater number of bubbles of formed. The line graph has a similar pattern for both the sugars on the first trial it goes up significantly and up to the fourth it dips down and on the fifth rises back up again.

Conclusion: From my experiment I can conclude that that the glucose sugar made the yeast respire at a much faster rate. The experiment turned out just how I predicted it. The reason for this was because of the glucose being a simple sugar this meant that the yeast did not need to break it down into anything smaller and it could use it straight away. Whereas the sucrose was a complex sugar and required the east to break it down into a simple sugar using enzymes. The enzymes required time to break the sucrose down into a simple sugar which meant that on the rate of respiration it was much slower than the glucose because it needed to be broken down into a simpler form first.

This meant that the sucrose was not as efficient as the glucose at making the yeast respire. It took time for the enzymes to secrete on to the cells to break the sucrose down this took up time and meant that the sucrose was not as fast as the glucose at making the yeast respire.

The bubbles formed in the water were Carbon dioxide. The equation for the glucose experiment was- Glucose---- alcohol + carbon dioxide + energy. The carbon dioxide was being released and was visible in the water. For the sucrose experiment the same equation is used.

Both the graphs back my ideas as they show that the glucose wads the more efficient at making the yeast respire. This is shown in a linear form on graph one and it is shown as an average in graph two.

Evaluation: I think that the experiment that I conducted was accurate and reliable the reason for this is that I conducted a fair and safe test and timed carefully with precision in order to gain good reliable results that were not biased in any way. I received no anomalous results.

We should have had another sugar to use as we could have compared it to the glucose and sucrose and this would have provided us with better results. I think that there was enough evidence to draw a conclusion however if we had used another type of sugar it would have made the evidence much more precise and clearer. I don’t think that my method could have been improved in any way unless another sugar was utilized.

There were some things that were difficult to keep constant in the experiment and this is where my results may have wavered slightly. It was difficult to keep the temperature of the warm water constant as it dipped at times which could have had an effect on how efficient the enzymes were. The delivery tubes were becoming blocked sometimes and by shaking the test tube it cleared them. However as we shook the test tube a large number of bubbles were formed which may not have formed if we didn’t shake the test tube. Also we might have been shaking the test tubes at different speed which may have caused a greater number of bubbles to be released.

Overall I felt that the experiment was accurate and reliable and there was not much that could have been changed on it.

By Omar Jamshad 10S