SBI4U: Cellular Respiration (Fermentation) Lab

Cellular Respiration

SBI4u

April 2014

TUN TUN OO

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Cellular respiration

Purpose

To determine the ability of yeast to produce gaseous end products. Using different carbohydrates during alcoholic fermentation within specific time and temperature.

Hypothesis

The ability of yeast to break carbohydrate is faster for smaller carbohydrate molecules.

Principles

Cellular respiration is the process by which the chemical energy of "food" molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is most commonly used as an example to examine the reactions and pathways involved.

There are two types of cellular respiration, aerobic cellular respiration and anaerobic cellular respiration. Aerobic respiration takes place in the presence of oxygen and involves glycolysis, the Krebs Cycle and the electron transport chain. Its end products are 38ATP, H₂O and CO₂. It is very efficient at extracting the energy out of the glucose molecule.

Anaerobic respiration (also known as Fermentation) takes place without presence of oxygen and it only involves glycolysis. After Glycolysis it produces 2ATP and left with two pyruvate molecules. In skeletal muscles, pyruvate is converted to lactic acid and expelled from the cell. In yeasts, the waste product is usually ethanol. Since the only energy yield comes from glycolysis, anaerobic respiration is quite inefficient and there is still a lot of energy remaining in the discarded waste.

In aerobic respiration:

C₆H₁₂O₆ (aq) + 6O₂ (g) → 6H₂O (l) + 6CO₂ (g) + energy (36-38 ATP + Heat)

In anaerobic respiration (alcoholic fermentation):

C₆H₁₂O₆ (aq) → 2C₂H₅OH (aq) + 2CO₂ (g) + energy (2 ATP + Heat)

Carbohydrates

Carbohydrate can be simplified into monosaccharide of one glucose molecule and disaccharide of two glucose molecules.

Glucose and fructose are monosaccharide of having the same molecular formula but different in structure known as isomers. Monosaccharides are small in size and are soluble in water which allows them easy to pass through the cell membrane into the cell. Energy is released when the molecules are metabolised (C₆H₁₂O₆ + 6O₂  →  6CO₂ + 6H₂O). This is part of the process of respiration. Monosaccharides are used very quickly by cells. However, a cell may not need all the energy immediately and it may need to store it.

Maltose and Lactose are disaccharide, made up of joining two monosaccharides by glycosidic linkage into one molecule. Two glucose molecules are joined to form maltose while galactose and glucose are joined to form lactose. Disaccharides are soluble in water, but they are too big to pass through the cell membrane by diffusion. They are broken down in the small intestine during digestion to give the smaller monosaccharides that pass into the blood and through cell membranes into cells.

 Yeast

Yeast is a microscopic fungus consisting of single oval cells that reproduce by budding, and are capable of converting sugar into alcohol and carbon dioxide by the process of alcoholic fermentation or anaerobic respiration.

In this experiment yeast is used to breakdown two monosaccharides and two disaccharides.

Variables

Attempts: 2 times

Measurement of Dependent Variables

Volume of CO₂, V=πd³/3 + πd²h/4

Where V = volume, d=diameter of tube, h=height of gas inside a tube

Materials

• Electronic Scale
• 4 different carbohydrates
• Glucose (2g)
• Fructose (2g)
• Maltose (2g)
• Lactose (2g)
• Thermometer
• 4 small test tubes
• Test tube rack
• 4 graduated cylinders
• Pipettes
• Water (2 ml for each test)
• Yeast solution (4 ml for each test)         
• Dropper
• Tape
• Metric Ruler

Procedure

• Measure 2 grams of glucose, fructose, maltose, and lactose.
• Label each test tube with tape for identification.
• Each test tube is filled with 4ml of yeast solution using a pipette.
• Transfer the carbohydrates into the test tube with the yeast solution.
• Add 2 ml of water.
• Each test tube is pushed all the way into a larger test tube from down to up position using a finger then inverted both the test tubes so that the opening of the larger test tube is at up position.
• Position the test tubs back on the test tube rack.
• Mark the volume on each test tube.
• The height of gas produced in each test tube is observed for 40 minutes.
• Collect all data including the difference in volume and the amount of CO₂ produced.

 

 Observations

·         Glucose developed the most gas at the fastest rate followed by fructose

·         Maltose and lactose developed the most gas at the slowest rate

·         All of the carbohydrates developed some bubbles in the test tube as well as CO2.

·         At 40 minutes, glucose has already reached the equilibrium while fructose has not reached it fully

·         Maltose and lactose developed very slowly compared to glucose and fructose

·         Within 40 minutes maltose and lactose has still not reached half of the test tube

·         After the equilibrium is reached gas is still evolving for glucose and fructose. Due to equilibrium stage of water levels inside and outside of the test tubes, the amount of gas developed can no longer be identified due to the gas leaking from the test tubes.

 Sources of errors

1. The duration of 40 minutes fermentation process for each carbohydrate may not be exactly same and may differ in few. The maximum time difference between the first and last carbohydrate might be less than 2 minutes to begin the fermentation.
2. The temperature of the beginning and the end of the experiment may be different.
3. In the first attempt 1gm of carbohydrate was used without water and this resulted almost no reaction in the experiment. This shows reasonable yeast amount is required to see faster fermentation process.

Data

Diameter of test tube, d = 1.1 cm

Volume of CO₂, V=πd³/3 + πd²h/4

The above observation shows that the fermentation process in Glucose and fructose which are small in molecular size are fast compared to maltose and lactose which are large molecules.

Analysis

The single-celled fungi Yeast which look like egg-shaped digest sugars to obtain energy for growth. Yeast uses fermentation process to breakdown carbohydrates or sugars and produces carbon dioxide gas and ethyl alcohol as byproducts.

Fermentation is commonly used in brewing beer, leaving bread production of yogurt, cheese, other dairy products and beverages.

The advantages of anaerobic respiration or fermentation is it can operate without oxygen and produces energy to recharge a few ATPs (2 or 4) but the disadvantages are it also yields carbon dioxide and alcohol which are unwanted products for living cells. But the gas evolving from fermentation is important to leaven bread and the alcohol produced from fermentation is also essential to produce alcoholic related food and beverage products.

On the other hand, the aerobic respiration only works with sufficient oxygen, but it makes a vastly superior amount of energy: enough to recharge 36 ATPs and it is very important process of respiration in Homo sapiens. It doesn't have the bad of byproducts as anaerobic respiration or fermentation does.

In the experiment the fermentation process of yeast to different carbohydrates it is observed that the small molecules like glucose and fructose are easily processed compared the larger molecules like maltose and lactose.

Conclusion

The experiment proved that gas was evolved in all the test tubes and it was observed that the gas evolved was displacing the solution from the test tubes which confirms the successful fermentation process of yeast to each carbohydrate.

The experiment also proved that the amount of gas evolved for each carbohydrate was different. The experiment showed that the smaller carbohydrate molecules were processed much faster compared to the larger molecular structure of carbohydrates which took longer time to produce the same amount of gas.

This experiment proved that the ability of yeast to break carbohydrate is faster for smaller carbohydrate molecules than larger carbohydrate molecules by the process of fermentation or anaerobic respiration.