The first step in aerobic respiration occurs in the cytoplasm of the cell and involves breaking down glucose. Each glucose molecule is made up of six carbon atoms plus hydrogen and oxygen. When the glucose molecule splits, two pyruvic acid molecules form, each of which contains three carbon atoms. These reactions result in the formation of two molecules of ATP. Some hydrogen is also released in the process.
In the second step, pyruvic acid passes from the cytoplasm into tiny cellular structures called mitochondria, where the remaining reactions occur. Within the mitochondria each pyruvic acid molecule combines with a molecule of coenzyme A to form one molecule of acetyl coenzyme A, which has two carbon atoms, and one molecule of carbon dioxide, which has one carbon atom. Hydrogen is also a by-product of this reaction.
In the third step, acetyl coenzyme A molecules combine with four-carbon molecules to form citric acid, a six-carbon molecule. The citric acid then undergoes a series of energy-liberating reactions, known as the citric acid, or Krebs, cycle. In the course of the citric acid cycle, the citric acid is progressively broken down into five-carbon and then four-carbon compounds. The final four-carbon compound produced in the cycle combines with a new molecule of acetyl coenzyme A to form citric acid, and the cycle continues. During this Krebs cycle large amounts of energy are released and two molecules of ATP are formed. Hydrogen is liberated, and carbon dioxide is formed from the carbon atoms lost from the six-carbon compound.
In the final stage of aerobic respiration, the hydrogen released during the first three stages passes along a chain of enzymes and ultimately combines with oxygen to form water. The energy released from these reactions results in the formation of 34 molecules of ATP. This brings to 38 the total number of ATP molecules resulting from the oxidation of each molecule of glucose. "Respiration," Microsoft® Encarta® 98 Encyclopedia. © 1993-1997 Microsoft Corporation. All rights reserved.
That segment of text tells us more about the scientific facts towards this experiment. To understand the experiment clearly I feel that it is necessary to explain the enzyme theory. Enzymes are large proteins that speed up chemical reactions. They bring together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate. This description of the enzyme is known as the lock and key method. To illustrate this theory on below is a diagram showing an enzyme structure and Function.
Before I explain my method etc. I have taken various safety measures. As I will be heating the equipment I will not exceed 45’c. To heat up the apparatus I will use controlled heated beakers. I will use boiling water to keep the same temperature according to the individual experiment. The water bath method would also have the same results.
I think that the rate of respiration will increase as the conical flask gets hotter. My reason for this is that anything that gets hot expands due to the molecules moving around. The molecules start to move around slowly but as the heat level rises the molecules race around quickly. When these molecules race around it is known as the collision theory. As the heat energy increases the molecules have more kinetic energy. The particles can only react if they collide into each other. So the molecules are more likely to react when they are going faster. To show the effect that heat has on respiration on page 6 is a graph (Fig.1) taken from the ‘ “A” Level Biology by Jones and Jones’:
Looking at the graph it shows how the rate of reaction rapidly rises. As you can see the optimum temperature is 42’c. Once it has hit the optimum temperature you can see that the rate of reaction falls. This is due to denaturation, as the temperature reaches 42’c the enzyme becomes inactive as the temperature is to high.
During the experiment I will observe each experiment to see whether there is a difference in the volume of each measuring cylinder. I will setup the experiment five times. To see whether heat has an effect on the rate of respiration I will measure the volume of the measuring cylinder before the experiment is started and then from then on every 10 minutes. My reason for using more water than sugar and yeast is because if there were a low amount of water the mixture would be very sticky and thick similar to glue.
Equipment
? Conical flask – 250ml
? Bung
? Measuring Syringe * 5
? Water – 150ml
? Yeast – 3g
? Sugar – 3g
? Rubber tubing
? Thermometer
? Bubble wrap (insulation)
? Kettle
? Timer
Diagram
Method
1) First of all setup the experiment as shown above using the same apparatus explained 5 times.
2) Once each of the 5 experiments are setup add boiling water to each beaker according to the temperature using the thermometer. Place each separate experiment at 30’c, 35’c, 37’5, 40’c, and 45’ c. To cool the temperature down so that you can reach the required temperature just add cold tap water.
3) Once all 5 of the experiments have been setup properly, then take a reading of the volume from each measuring syringe every 10 minutes using the timer. Take the measurement to the nearest cm3
4) Keep the experiments going for 50 minutes. Therefore you should have five results for every experiment.
Prediction
My prediction for this experiment is that the volume of the measuring syringe will increase according to the temperature. As the temperature gets hotter the volume in the measuring cylinder will increase. But as the temperature reaches 40’c to 45’c we will see that the volume in the cylinder has started to fall as it is starting to denature. After looking at all the experiments data collection you will see a gradual incline in the volume of the measuring cylinder.
