Cell Biology Sub-Topic (1.6) Respiration On completion of this subtopic I will be able to state that: Glucose is a source of energy in the cell. The chemical energy stored in glucose is released by a series of enzyme-controlled reactions called respiration. Energy released from the breakdown of glucose during respiration is used to synthesise ATP from ADP and Pi. The chemical energy stored in ATP can be released when it is broken down to ADP and Pi. This energy transferred by ATP can be used for cellular activities such as muscle contraction, cell division, protein synthesis and transmission of nerve impulses. Glucose is broken down to two molecules of pyruvate. The breakdown of glucose to pyruvate generates enough energy to yield 2 molecules of ATP. Pyruvate is further broken down to carbon dioxide and water only if oxygen is present. Aerobic respiration (respiration in the presence of oxygen) starts in the cytoplasm and is completed in the mitochondrion. The complete breakdown of glucose in the presence of oxygen yields a large number of ATP per glucose molecule. In the absence of oxygen glucose is broken down by an alternative pathway. This is known as the fermentation pathway. The fermentation pathway (respiration without oxygen) occurs in the cytoplasm. In animals: In the absence of oxygen glucose is broken down to pyruvate. This is further broken down to lactate. In plants and yeast cells: In the absence of oxygen glucose is broken down to pyruvate. This is further broken down to ethanol (alcohol) and carbon dioxide. The breakdown of glucose in the absence of oxygen yields 2 molecules of ATP per glucose molecule. Duncanrig Secondary School 2017 Page 1 of 11
Energy in Food Food contains chemical energy. Energy is measured in joules (J) and (kj) which are measurements of heat energy. The chemical energy in food can be changed into heat energy by burning food in a calorimeter (see diagram). The quantity of heat energy released is estimated by measuring the rise in temperature of the water in the calorimeter and performing a simple calculation. Measuring the energy in foods The experiment below can be carried out in the lab to measure the energy content of foods. In this experiment the heat energy released from the food can be used to heat water. The different temperature rises obtained in different foods allows a comparison of their energy contents to be made. Method 20cm 3 water burning food Results: Food Type thermometer Temperature at Start ( o C) 1. The temperature of the water is measured. 2. A 1g sample of food is weighed out. 3. The sample of food is set on fire and held under the test tube. 4. The food is allowed to burn until it goes out. 5. The temperature of the water is measured again. Temperature at Finish ( o C) Change in Temperature ( o C) Conclusion: State the conclusion that can be drawn from the results. Duncanrig Secondary School 2017 Page 2 of 11
Energy Release When a sugar, such as glucose, is burned in the presence of oxygen, it releases its chemical energy as heat and light energy. thermometer Glucose and oxygen react in cells but the energy is not released rapidly. The energy is released from glucose in a series of enzyme-controlled reactions. This process of energy release is called. During respiration energy is released by cells. The investigation shown in the diagram demonstrates that respiring peas release heat energy. In humans the heat produced by respiring cells keeps the body temperature at O C. Adenosine Triphosphate (ATP) ATP stands for Adenosine triphosphate. It is found in all living cells and is an energy rich molecule containing chemical energy which all cells can use immediately. It is composed of one molecule of adenosine and three molecules of inorganic phosphate (Pi). Duncanrig Secondary School 2017 Page 3 of 11
The effect of ATP on muscle fibre Watch carefully while your teacher demonstrates the experiment below. Results: Complete the table below. Solution Water Initial length (mm) Final length (mm) Decrease (mm) Percentage decrease (%) Glucose ATP Conclusion: State the conclusion that can be drawn from the results. Duncanrig Secondary School 2017 Page 4 of 11
ATP Breakdown and Synthesis Energy stored in an ATP molecule is released when the bond attached to the terminal phosphate is broken down by an enzyme-controlled reaction. This removes the terminal phosphate, leaving ADP (adenosine diphosphate) and a free inorganic phosphate (Pi). The energy released can be used in cellular processes. When energy becomes available, an enzyme reverses the reaction so that ATP is synthesised from ADP (adenosine diphosphate) and inorganic phosphate (Pi). Energy is stored in the ATP molecule formed. The production of ATP is called phosphorylation. The reversible reaction is: Breakdown releasing energy + Build-up requiring energy When an energy-rich substance, such as glucose, is gradually broken down during respiration it releases energy that is used to produce ATP. ATP can rapidly convert to ADP and Pi to provide energy for: 1. 2. 3. 4. ATP is a vital link between energy releasing reactions (respiration) and energy consuming reactions (see the examples above). Duncanrig Secondary School 2017 Page 5 of 11
Complete the diagram below using the following words: protein, amino acids, glucose, water, oxygen, carbon dioxide, ATP, ADP, Pi RESPIRATION energy ENERGY TRANSFER energy SYNTHESIS REACTION Respiration Respiration is the process by which energy is released during the breakdown of glucose. This energy is used to synthesise ATP. Respiration begins in the cytoplasm. Each molecule of glucose is broken down by a series of enzyme controlled reactions to form two molecules of pyruvate. This reaction is called glycolysis. It results in the production of two molecules of ATP per glucose molecule. Location: 2ADP + 2Pi Duncanrig Secondary School 2017 Page 6 of 11
Aerobic Respiration: Respiration in the presence of oxygen When oxygen is present, the breakdown of pyruvate continues through a series of enzyme controlled reactions and is completed in the mitochondrion. Here pyruvate is further broken down to carbon dioxide and water. The carbon dioxide is released as a waste product. Location: + 36ADP + 36Pi The complete breakdown of glucose in the presence of oxygen yields 38 molecules of ATP per molecule of glucose. Respiration in the presence of oxygen can be summarised as follows: glucose + oxygen + 38ADP + 38Pi carbon dioxide + water + 38ATP Duncanrig Secondary School 2017 Page 7 of 11
Respiration in the Absence of Oxygen In the absence of oxygen, glucose is not completely broken down. Instead the breakdown of pyruvate continues in the cytoplasm in an enzyme controlled reaction called fermentation and no further ATP is synthesised. The end products of this reaction depend on the organisms involved. In animals: In animals, the fermentation pathway occurs when no oxygen is available or when the oxygen supply runs out e.g. in humans this occurs during vigorous exercise. The pyruvate is converted into lactate. When pyruvate is converted into lactate this causes muscle fatigue. Location: Complete the box below to show the word equation for the fermentation pathway in animals. glucose + + 2Pi + Duncanrig Secondary School 2017 Page 8 of 11
In plants and yeast cells: In plants and yeast cells, the fermentation pathway occurs when no oxygen is available e.g. when root hair cells become water logged or when yeast cells are deprived of oxygen during wine making. The pyruvate is broken down to ethanol (alcohol) and carbon dioxide. Location: + Complete the box below to show the word equation for the fermentation pathway in plants and yeast cells. glucose + + + + 2ATP The fermentation pathway (respiration without oxygen) yields 2 molecules of ATP per glucose molecule. Duncanrig Secondary School 2017 Page 9 of 11
Comparing respiration with oxygen and respiration without oxygen Complete the summary below: Aerobic Respiration Fermentation pathway Is oxygen needed? Location Number of ATP molecules produced per molecule of glucose Complete or incomplete breakdown of glucose Animals End products Plants Duncanrig Secondary School 2017 Page 10 of 11
Respirometer A respirometer is a piece of apparatus which is used to measure the rate of respiration. Respirometers can be used to study plants and animals to learn more about their respiratory patterns. A respirometer can measure the consumption of oxygen as well as the production of carbon dioxide. This provides information about the respiration rate of the organism being studied. In this experiment, the germinating peas are carrying out respiration, using up oxygen from the air and producing carbon dioxide. Any carbon dioxide produced by the peas is removed by the carbon dioxide absorbing chemical. This causes the volume of air to decrease and so pressure inside the test tube decreases too. To equalise the pressure air is drawn into the test tube from the tube Y. As air is pulled in, the coloured liquid is also drawn up tube Y. The need for a control A control experiment should also be set up because environmental factors such as temperature and air pressure can affect the experiment and cause the liquid to move. Movement in the control (tube X) would need to be taken into account when calculating the respiration rate. In this experiment the control is the replica tube containing the boiled and sterilised peas of equal mass to the germinating peas in the other tube. A syringe can be added to the apparatus and used to push the coloured liquid back along its tube to the original position. The volume of air needed to move the liquid back to its starting position is equal to the volume of oxygen gas used by the germinating peas in that period of time and is equal to the rate of respiration. Duncanrig Secondary School 2017 Page 11 of 11