effect of temperature on the rate of respiration in yeast

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Effect of temperature on the rate of respiration in yeast


        My aim is to investigate the effect of temperature on the rate of respiration in yeast by using a universal indicator.

Background theory:


Enzymes are organic catalysts that speed up the rate of a chemical reaction without being permanently altered in the process.

Enzyme Characteristics

  • Form reversible complex with substrate.
  • Not consumed in the reaction therefore they are effect in small amounts
  •  - (Induced fit hypothesis) react with only a single substrate.
  • Many need , such as certain vitamins, to be activated.
  • 2000+ enzymes per cell, different cells have different enzymes.
  • Enzymes are produced by genes.
  • Genetic disorders are the result of faulty enzymes.
  • Operate best in optimum conditions of , , etc.
  • Are controlled by feedback mechanisms.

Enzyme mechanism:

Key and theory:

The substrates (reactants) are attracted to the enzyme molecule. They join forming an enzyme-substrate complex. The reaction occurs on an area of the enzyme molecule known as the active site producing new substrates(s) or products. 

Induced fit hypothesis:  

                                     The attraction of the substrate and enzyme form an enzyme-substrate complex. It was originally referred to as the Lock and Key Enzyme Theory. The current theory suggests that the enzyme molecules are in an inactive form. To become active they must undergo a slight change in structure to more specifically accommodate the substrate(s). It is said to be "induced to fit" the substrate. Think of way your hand changes shape slight when you shake a person's hand. (Reference 1 )

Factors affecting rate of reaction:

Effect of temperature on enzyme:

                                                    As the temperature increase in an enzyme catalyzed reaction the rate of reaction also increases. A ten degree Centigrade rise in temperature will increase the activity of most enzymes by 50 to 100%. Variations in reaction temperature as small as 1 or 2 degrees may introduce changes of 10 to 20% in the results.

The rate of reaction increases as the temperature increases. The rate of reaction increases till it reaches it its optimum level; this is when the rate of enzyme activity start to decrease and enzymes started to denatured. (Reference 2)

Collision theory:

                      As the temperature increases particles start to move quickly and collide with each other with greater energy. It also increases the number of particle. It increases the number of high energy collisions which results in a reaction.


      PH doesn’t just changes the change of enzyme but it can also cause denaturation. The concentration of hydrogen ions in a solution is a measure of pH, which determines how acidic or alkaline a solution is. At extreme pH conditions there is low hydrogen ions concentration. As well as that the chemical bonds between the atoms break, causes changes in the shape of the active site, which can also cause denaturation of an enzyme. This can also slow down the rate of reaction. Before that when the pH is increase it also increases the rate of reaction till the pH is reached its optimum level after that the rate of reaction started to decreases the acid or base conditions begin to disrupt some of the hydrogen bonds between loops of the protein chains. If the disruption occurs at or near the active site, the active site becomes distorted and substrate can not fit perfectly. Thus not all enzymes in the solution will be able to catalyze their reaction. With increasing or decreasing pH, more enzymes become denatured, and fewer enzymes are able to form that enzyme-substrate complex. The reaction rate continues to decrease. At some point, all the enzymes are denatured, and the reaction rate falls to zero. (Reference 3)

Enzyme concentration:

                                  Enzyme concentration is directly proportional to the rate of reaction. As the enzyme concentration is increase the rate of reaction will also increase as there are a lot of active site are available for substrate to form enzyme substrate complex. However increasing enzyme concentration beyond some point it would have no effect on rate of reaction as there will be no more active sites available for substrate molecules.

Substrate concentration:

                        The graph shows that when the concentration of enzyme is maintained constant, the reaction rate will increase as the amount of substrate is increased. However, at some point, increasing the amount of substrate does not increase the reaction rate. This is when it reaches V-max. at this point the rate of reaction stays constant. At first there is very little substrate and a lot of enzyme. An increase in the concentration of substrate means that more of the enzyme molecules can be utilized. As more enzymes become involved in reactions, the rate of reaction increases, but when it reaches V-max, all the enzymes are being involved in reactions. When this happens, some of the substrate must "wait" for enzymes to clear their active sites before the enzyme can fit with them (like a "lock and key").  (Reference 4)


                   Coenzymes are small proteins that join to the enzyme molecule to make it active. Like enzymes they are not permanently altered in the reactions. Many of these coenzymes are derived from vitamins and minerals that are essential for life. The absence of these cofactors can lead to vitamin and mineral deficiency diseases. An example of a coenzyme already mentioned in respiration in NAD+, which except a trios phosphate molecule to become reduced NAD+ in glycolysis. (Reference 5)


Competitive inhibitors:

                                       Competitive Inhibition interferes with enzyme activity by binding temporarily to the enzyme's active site. This prevents the enzyme from reacting with its normal substrate. Therefore no product made. Competitive inhibition is reversible and can be overcome by increasing the amount of substrate on which the enzyme works.

Non competitive inhibitors:

                                         Competitive Inhibition interferes with enzyme activity by "binding" permanently to the enzyme therefore it permanently blocks the active site and doesn’t allow any substrate to bind with active site.

Denaturation of enzymes:

                                        When enzymes are placed into a high temperature they start to denature. Denaturation can be defined as the loss of enough structure to render the enzyme inactive. This happens when the temperature reaches its optimum level and the rate reaction to decrease cause of denaturation of enzymes.

                               These denaturing reactions have standard free energies of activation of about 200 - 300 kJ mole-1 (Q10 in the range 6 - 36), which means that, above a critical temperature, there is a rapid rate of loss of activity. The actual loss of activity is the product of this rate and the duration of incubation. It may be due to covalent changes such as the deamination of asparagines residues or non-covalent changes such as the rearrangement of the protein chain. Inactivation by heat denaturation has a profound effect on the enzymes productivity. (Reference 6) 



          Yeasts are unicellular . The precise classification is a field that uses the characteristics of the cell. One of the more well known characteristics is the ability to ferment sugars for the production of ethanol. Yeasts multiply as single cells that divide by budding or direct division and they may grow as simple irregular filaments. These are egged shape that can only be seen by microscope. Yeast cells also digest various sugars like sucrose, fructose and glucose. The yeast's function in baking is to ferment sugars present in the flour or added to the dough. This fermentation gives off carbon dioxide and ethanol. The carbon dioxide is trapped within tiny bubbles and results in the dough expanding, or rising. Sourdough bread is not produced with baker's yeast, rather a combination of wild yeast and acid-generating bacteria. The fermentation of wine is initiated by naturally occurring yeasts present in the vineyards. Many wineries still use nature strains, however many use modern methods of strain maintenance and isolation. The bubbles in sparkling wines are trapped carbon dioxide, the result of yeast fermenting sugars in the grape juice. One yeast cell can ferment approximately its own weight of glucose per hour.

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  (Reference 7)


                   Respiration is the release of energy from glucose or another organic chemical. Respiration most likely takes place under aerobic respiration which means efficient oxygen.

The equation for aerobic respiration:

                     C6H12O6 +  6O2    6CO2  +  6 H2O

But sometime respiration goes under an aerobically which means not enough oxygen is available to respire.

The equation to an aerobic respiration:


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***** A well planned, conducted and written up investigation. A high standard of A level knowledge demonstrated.