Biology: The Production of CO2 by Yeast

In this experiment, we investigated whether or not different wavelengths of light affected the rate of anaerobic respiration. It is a well-known fact that different wavelengths of light affect the rate of photosynthesis as lights aerobically respire, which then led us to the above question. As seen in the results obtained, whilst exposing the yeast and sugar solution to different wavelengths of light, there was no change in the amount of carbon dioxide produced. When the yeast and sugar solution was exposed to normal light and ultraviolet light, 15 cm³ of carbon dioxide was evolved. Hence, it can be concluded that different wavelengths of light have no effect on anaerobic respiration.

As stated earlier, we investigated the effect of different wavelengths of light on anaerobic respiration, and in effect we were also investigating the effect of heat energy on anaerobic respiration. Throughout the trials, we noted the temperature change to see if a change in temperature had any bearing on the results. When the yeast and sugar solution was exposed to visible light and ultraviolet, a similar change in temperature was noted which gave rise to similar results. However, when the yeast and sugar solution was exposed to infra-red light, there was a significant increase in the environment temperature (after 10 minutes, the temperature had reached in excess of 100 degrees Celsius). After this trial, the yeast and sugar solution had become a thicky paste, which then led us to believe that the enzymes had become denatured, which would explain why no carbon dioxide was produced. Enzymes are biological catalysts which are temperature, pH and substrate sensitive which can be seen in the diagram below:

Upon further investigation, we discovered that yeast’s optimum temperature was 25 degrees Celsius and because we were conducting the experiment in a room whose temperature was set at 22 degrees Celsius, the rate of the reaction would be less than the optimum rate of reaction. However, it could also be inferred from this that infrared energy would result in the greatest production of carbon dioxide as the yeast’s environmental temperature would be closer to that of its optimum. However, as stated earlier, over the duration of the trial (10 minutes) temperatures reached 100 degrees which was significantly higher than yeast’s optimum temperature which led to the denaturation of yeast and because of the permanent change in its structure, the yeast was unable to react witht eh sugar solution and so no carbon dioxide was produced.
 

Chemistry: Light Energy and the Rate of Reaction

As we found out during our undertaking of this practical from a passing teacher the reaction between yeast and sugar does not derive any of its energy from light at all as we first thought but the energy required to break and reform the bonds is sourced from the reactants alone. This would means that the light and different wavelengths of light that were impact on the conical flask with the reaction taking place should have had no effect on the reaction rate. As seen in the results the reaction rate varied from 4.5 cm per 10 minutes of reaction to 21 cm per 10 minutes of reaction.

The large difference in the rate of the reaction is most likely due to the heat generated from the globes that were being used. The IR had the highest rate of reaction due to the intense amounts of heat that were very direct onto the conical flask. The heat was so intense that the yeast denatured and the reaction ceased once that temperature was reached. This means that the actual rate of reaction for the fermentation of glucose is the control, which is 4.5 cm of CO₂ per 10 minutes of reaction.

The sugar was used to reaction glucose with the yeast making it ferment.

This reaction is

C₆H₁₂O₆ --------------> 2CO₂ + 2C₂H₅OH

This reaction has an enthalpy change of -13.5 KJ mol^-1 as worked out by using the average bond enthalpies and the equation below.

ΔH = Bonds Broken – Bonds Formed

This is a relatively small enthalpy change indicating that very little energy was released during this reaction. This means that nearly the entire rise in the temperature during the reaction was because of the lamps heat incident on the conical flask. 

Control

1. Rate of reaction

= 13.5-9 cm

=4.5 cm per 10 minutes

2. Rate = Scratched

3. Rate= 4.5 cm per 10 minutes

4. Rate = 9 cm per 10 minutes (outlier)

Average = 4.5 cm per 10 minutes

UV Light

1.Rate = 8.7 cm per 10 minutes

2. Rate= 1 cm per 10 minutes (outlier) water leaked into tube

3. Rate = 12 cm per 10 minutes

Average= 10.4 cm per 10 minutes

IR Light

1.Rate= 21 cm per 10 minutes

Orange Light

1. Rate =10.5 cm per 10 minutes

Green Light

1. Rate = 18 cm per 10 minutes

Blue Light

1. Rate = 19.5 cm per 10 minutes

Red Light

1. Rate = 19 cm per 10 minutes

Purple Light

1. Rate = 18 cm per 10 minutes

Physics: Differing Wavelengths of Light and Energy

The practical aspect of the physics behind our practical became somewhat irrelevant upon our discovery of the negligible effect of photosynthesis on the rate of fermentation of yeast. Despite this, the theoretical aspect of the physics behind the practical still stands itself in good stead.

The theory behind the experiment was the effect of differing wavelengths producing different energies. The formula E = hf, where h = Planck's Constant (6.6 x 10^-32 Js) proves that there is a relationship between the varying frequencies of light and the Energy produced. This relationship can be expanded to the formula v = fλ, whereby given the constant velocity of the speed of light (3x10^8 ms^-1), it can be seen of the inverse proportionality of frequency and wavelength. The effect this has on the experiment is the inverse proportionality of wavelength to energy. As the wavelength of the light increases, the energy decreases and whilst in practice this has no effect on the rate of reaction, the theory behind the action, despite not being observable is still theoretically sound.

The wavelength was measured by way of a wavelength spectroscope that allowed us to approximate to an appropriate amount, the wavelength of light passing through in m of each piece of cellophane.