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How temperature affects the rate at which bread dough rises and find out the optimum temperature for yeast to work?

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Irfan Enayet Year 11 GCSE BIOLOGY COURSEWORK FERMENTATION AND YEAST 1) Introduction: To begin, I will first describe the factors that can affect the rate at which the bread dough rises. * Amount of sugar: when we add more sugar, the reaction speeds up, as there are more sugar particles in the given space. This causes more collisions to take place therefore the reaction goes faster and the bread dough rises quickly. * Amount of Yeast: increasing the amount of yeast provides more enzymes for the reaction in other words the active sites are filled up quickly; consequently the reaction is faster. * Amount of flour: excess flour would slow down the reaction, it means if the quantity of flour is bigger than yeast then the reaction goes slow! This is because the action of the enzyme in yeast is weakened; the reaction slows down. * Temperature: this variable has to be handled very carefully. If too high, the enzyme in yeast is denatured; when too low the reaction is slow so in order to make it a fair test the temperature should: - Make the particles travel faster resulting to more collisions - If the movement exceeds activation energy (energy required for movement of particles) then reaction speeds up * Ph Level: the Ph level of yeast should be kept at an optimum to give a successful reaction. To see the effect of temperature on the reaction! An increase in temperature increases the rate as the particles are given more energy to collide! But a certain amount of activation energy must be reached to let the particles collide between them and this is known as the collision theory. The temperature also increases the potential for the enzyme in yeast that too speeds up the reaction. The kinetic theory also explains that temperature increases the rate of a reaction as it makes the particles move faster after reaching a necessary amount of activation energy. ...read more.


Very high temperature above optimum may denature the enzymes because it makes the particles vibrate too fast and bursts the enzyme made of protein molecules. Temperature makes particles move faster NB: Diagram from 'GCSE SCIENCE " Oxford Press PLANNING: For my experiment, I will first used a fixed amount of yeast and keep on changing the temperature; one to see how it affects the reaction; second to find out the optimum temperature for zymase. Once I will find the optimum temperature I will keep it constant and then change the amount of yeast each time to prove how this factor affects the rate at which bread dough rises. How have I planned the experiment? * Varying temperature and finding the optimum - I will begin using 3 grams of sugar, 10 grams of flour and 10 cm of yeast. I will start with tap water (about room temperature: 20'C) then continue heating the water up to 80'C each time varying it by 10'C. Once I will find the optimum then I will change the amount of yeast by 3cm each time beginning with 10cm keeping all other variables constant and optimum temperature. - For more accuracy, I will repeat the experiment three times and use average results. How will I measure the yeast? I will take a measuring cylinder then fill the desired amount of yeast in it and measure it in centimeters. The water temperature will change by heating it up which will play the role of changing temperature. Precautions. While letting the bread dough to rise I will make sure the mixture does not touch the walls or side of the container otherwise the bread would not be allowed to rise properly, pressure would increase and so volume would decrease resulting in an error in the results. PREDICTIONS: * As the temperature increases up to the optimum the reaction speeds up accordingly as particles move faster resulting more collisions (Kinetic theory) ...read more.


The amount of yeast gives more enzymes to the reaction so more molecules of substrates fit the active site thus more products are formed at a faster rate. The optimum temperature is the ideal concentration for the enzyme because enzymes work the best at body temperatures. At very high temperature the enzyme is denatured it means it bursts so loses its active site. All of my predictions were true. I predicted that as temperature increased the dough would rise quickly (Collision and Kinetic Theory). As the amount of yeast increases more enzymes are present for the reaction then the reaction speeds up as more active sites are filled forming more products. All the results show that as soon the yeast is added to the mixture it soon starts to respire and makes the dough rose quickly but high temperatures immediately denature the enzyme and stop fermentation. This was a fair test as all the amounts were varied proportionally and all the safety measures and precautions were properly taken. The results were sensible and were following a proper reasonable pattern. 6) Evaluation How could the experiment be improved? * Due to a lack of time I could not measure the volume of the mixture for forty minutes otherwise this would have given me a wide range of observations and results and I could have seen what happens as the temperature of the water cools down after those twenty minutes I did the experiment. * I can use different variable (ex: sugar, flour) to obtain better evidences and also to see how these factors affect the rate of the dough rise. * I could have measured the Ph to draw more conclusions about Ph levels of enzymes to support the experiment. Test my prediction as I think Enzymes work the best at Ph 6. * I can use more oxygen to produce more pressure that increases the number of collisions during the reaction. My results effectively didn't contain so many mistakes and went fairly well. It easily allowed me to draw conclusions and properly analyze my results reasonably. ...read more.

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