Higher Biology. Unit 2: Metabolism and Survival Topic 2: Respiration. Page 1 of 25

Higher Biology Unit 2: Metabolism and Survival Topic 2: Respiration Page 1 of 25

Sub Topic: Respiration I can state that: All living cells carry out respiration. ATP is the energy currency of the cell and can be regenerated from ADP and inorganic phosphate. ATP has the role of providing the energy requirements for cellular processes. The first stage of respiration is glycolysis. Glycolysis involves the breakdown of glucose to pyruvate in the cytoplasm. During the oxidation of pyruvate the enzyme dehydrogenase promotes the removal of hydrogen and electrons from pyruvate and also the transfer of hydrogen and electrons to its electron acceptor NAD. The process of phosphorylation (the addition of a phosphate group to ADP to form ATP) during glycolysis results in the production of 2 ATP molecules. In the absence of oxygen, pyruvate undergoes fermentation to form lactate (in animals and some bacteria) and ethanol and carbon dioxide (in plants and fungi). The citric acid cycle occurs in the matrix of the mitochondria. During the citric acid cycle acetyl from acetyl co-enzyme A combines with oxaloacetate to produce citrate. Dehydrogenase enzymes catalyse the removal of hydrogen and electrons on 4 occasions from the various respiratory substrates during the cycle: NAD is the hydrogen acceptor on three, FAD once. Hydrogen and electrons are carried by NAD and FAD to the electron transport chain. The electron transport chain is a series of protein carrier molecules. ATP synthase is used to catalyse the production of ATP form ADP and Pi. The electron transport chain occurs on the inner membrane of the mitochondria. The final electron acceptor is oxygen which combines with hydrogen to form water. Most of the ATP generated by cellular respiration occurs as a result of the electron transport chain. The substrates for respiration are the carbohydrates; glucose, starch, glycogen and other sugar molecules. When carbohydrate is not available other substrates such as proteins or fats can be used by the cell. Page 2 of 25

Prior Learning: National 5 Biology: Unit 1: Cell Biology Sub-topic 8: Respiration the chemical energy stored in glucose must be released by all cells through a series of enzyme-controlled reactions called respiration; the energy released from the breakdown of glucose is used to generate ATP from ADP and phosphate; the chemical energy stored in ATP can be released by breaking it down to ADP and phosphate; ATP can be regenerated during respiration; each glucose molecule is broken down via pyruvate to carbon dioxide and water in the presence of oxygen, and yields 38 molecules of ATP; the breakdown of each glucose molecule via the fermentation pathway yields two molecules of ATP; in the absence of oxygen in animal cells, glucose is broken down into lactate via pyruvate; in the absence of oxygen in plant and yeast cells, glucose is broken down into alcohol/ethanol and carbon dioxide via pyruvate; fermentation occurs in the cytoplasm; aerobic respiration starts in the cytoplasm and is completed in the mitochondria Page 3 of 25

The Importance of Adenosine Triphosphate (ATP) Cellular respiration is a series of metabolic pathways which releases the chemical energy from food molecules and makes it available to the cell in the form of ATP. It occurs in all living organisms in each of the three domains of life. The Structure of Adenosine Triphosphate (ATP) The structure of ATP must first be considered to understand how Adenosine Triphosphate (ATP) provides the energy for the chemical reactions in cells. Structure of an ATP and ADP molecules: A molecule of adenosine triphosphate is made up of an adenosine joined to three inorganic phosphates (Pi). ATP is a high energy containing molecule. Energy is released when the high energy bond which holds the third phosphate group to the rest of the molecule is broken down by enzyme action. This results in the formation of Adenosine diphosphate (ADP) which has adenosine and two inorganic phosphate groups with a free inorganic phosphate group as shown below. and ATP is the energy currency in living cells. During cellular respiration energy is released which is used to synthesise ATP from ADP and an inorganic phosphate group. The formation of the ATP is enzyme controlled. The addition of a phosphate group is known as phosphorylation. ATP is made continuously during the process of cellular respiration. Page 4 of 25

ATP and Energy Transfer ATP molecules produced during the catabolic reactions of cellular respiration are used by the cell immediately as a source of energy, to drive anabolic (energy requiring) reactions such as; active transport, muscle contraction and protein synthesis. Energy stored in bond when made ADP + Pi ATP + energy Energy released from bond breaking Because of its energy transfer role, ATP is constantly being synthesised and broken down again. An active cell will synthesise up to 2 million molecules of ATP per second and each molecule of ATP produced will be used up within a second of its formation. Transfer of energy via ATP Complete the diagram below to show the cycle of energy states of ATP and ADP + Pi. Respiration Energy transfer Work done glucose + oxygen muscle contracted Page 5 of 25

Answer the questions below. Why is ATP so important in the cell (include the words anabolic and catabolic reactions in your answer)? Why does the body never have a store of ATP at any given time? Watch your teacher demonstrate the effect of ATP on muscle contraction. Aim: To demonstrate the effect of ATP on muscle tissue. Results Initial length (mm) Final length (mm) Change in Length (mm) Percentage change in length (mm) Muscle 1 in glucose solution Muscle 2 in distilled water Muscle 3 in ATP solution Answer the following questions: Q1. What was the effect of the solution on each muscle strand? Muscle 1 Muscle 2 Muscle 3 Page 6 of 25

Q2. Which liquid provides energy for contraction? Q3. Which two experiments acted as controls and why were they included? Q4. Why was percentage change in length rather that the difference in length used to compare the results? Q5. Why was a 5min interval allowed between measuring the initial and the final measurements? Q6. Write a conclusion for this experiment. Q7. A pupil repeated this experiment, keeping everything the same but using boiled ATP solution instead of fresh ATP solution. Their results were very similar. What does this indicate about the chemical nature of ATP? Page 7 of 25

Metabolic pathways of Cellular Respiration The main respiratory substrates are glucose, starch and glycogen, although other respiratory substrates can be used when required. The overall equation for cellular respiration of glucose is:- glucose + oxygen carbon dioxide + water + ENERGY C6H12O6 + 6O2 6CO2 + 6H2O + 38ATP The process of cellular respiration occurs in all three domains of life. The process consists of many chemical reactions each of which is controlled by a specific enzyme. It involves hydrogen being removed from various respiratory substrates by dehydrogenase enzymes and being used to yield ATP. Cellular respiration experiment Aim: To investigate the activity of dehydrogenase enzyme in yeast. During respiration, glucose is gradually broken down and hydrogen is released at various stages of the respiratory pathway. Each of these stages is controlled by a group of enzymes called dehydrogenase. Yeast cells contain the enzyme dehydrogenase, which removes hydrogen from the small quantities of stored food as the yeast carries out cellular respiration. Resazurin dye is a chemical which reacts with hydrogen and changes colour when hydrogen is added to it: Colour change Stays blue Blue to pink Blue to colourless Result Lacks hydrogen Some hydrogen Much hydrogen Collect: 3 boiling tubes, live yeast suspension, boiled yeast suspension, glucose solution, water and resazurin dye. Page 8 of 25

Method: 1. Place 10ml of live yeast suspension in tubes A and B and 10ml of boiled yeast in tube C. 2. Add 10ml of glucose to both tubes A and C. 3. To tube B add 10ml of water. 4. Now add 1ml of resazurin dye to each tube. 5. Shake vigorously for 20 secs. 6. Then place in a water bath set at 35 O C for 5 mins. Results: Sample A Live yeast suspension + glucose Resazurin Colour change Reason B Live yeast suspension + water C Boiled yeast suspension + glucose Conclusion: Page 9 of 25

Metabolic Pathways of Cellular Respiration Cellular respiration consists of many enzyme controlled steps to ensure that energy is released continuously. Cellular respiration can be spilt into three stages: 1. Glycolysis occurs in the cytoplasm 2. The Citric Acid Cycle occurs in the matrix of the mitchondrion 3. The Electron Transport Chain occurs in the cristae of the mitochondrion Stage 1: Glycolysis Glycolysis occurs in the cytoplasm of the cell and does not require oxygen. It involves a cyclic series of enzyme controlled reactions. Glycolysis means sugar splitting and this describes the splitting of the glucose molecule eventually forming pyruvate. The splitting of one glucose molecule requires 2ATP molecules (the energy investment phase) to start the process. Glucose is broken down to intermediate compounds by the process of phosphorylation (addition of a phosphate donated by ATP ADP + Pi +energy). As the series of reactions proceed 4 ATP molecules are generated (the energy pay off phase). Thus glycolysis gives a net gain of 2 ATP. During glycolysis, dehydrogenase enzymes release the hydrogen and high energy electrons from the respiratory substrate. The coenzyme molecule NAD (nicotinamide adenine dinucleotide) forms NADH to transport these to stage 3 of the process. Glycolysis Occurs in the cytoplasm of the cell The process of glycolysis does not require oxygen. However, NADH only leads to the production of further molecules of ATP at a later stage in the respiratory process if oxygen is present. In the absence of oxygen, fermentation occurs. Page 10 of 25

Structure of the mitochondrion When oxygen is present, aerobic respiration occurs in the cell s mitochondria. These organelles are present in the cytoplasm and have a specialised structure. The mitochondrion is bound by a double unit membrane. The inner membrane has many folds called cristae, which give it a very large surface area. The cristae is the location of the electron transport chain which is the main site of ATP production. The fluid filled central cavity is called the matrix and it is rich with enzymes, which are involved in the citric acid cycle. Name the parts indicated in the diagram of a mitochondrion. A B C D Stage 2: The Citric Acid Cycle The citric acid cycle can only proceed if oxygen is present and it occurs in the central cavity called the matrix of the mitochondrion. This stage involves a series of enzyme controlled cyclic reactions. Pyruvate diffuses into the matrix of the mitochondrion where it is broken down into carbon dioxide and an acetyl group. The acetyl group combines with coenzyme A to form acetyl coenzyme A. It is accompanied by the release of hydrogen and high energy electrons which again bind temporarily to NAD to form NADH. The acetyl coenzyme A releases the acetyl group which combines with a molecule of oxaloacetate to form citrate. Enzymes control a series of reactions which break down citrate to intermediate compounds eventually resulting in the regeneration of oxaloacetate. During these reactions CO2 is released, 2ATP is generated and Page 11 of 25

dehydrogenase enzymes remove hydrogen ions and electrons which are passed to coenzymes NAD and FAD, forming NADH and FADH2 respectively. NAD and FAD transport their hydrogen ions and high energy electrons to the electron transport chain. This is the third and final stage of cellular respiration. To the Electron Transport Chain ADP+Pi ATP Page 12 of 25

Cellular Respiration Diagram Summary To the Electron Transport Chain ADP+Pi ATP Page 13 of 25

Stage 3: The Electron Transport Chain The hydrogen ions and high energy electrons are passed to the electron transport chain on the inner mitochondrial membrane. A great deal of energy is stored in NADH and FADH2 which is then converted to ATP in this final phase of respiration. The electron transport chain consists of 3 protein carrier molecules which act as pumps embedded in the inner membrane of the mitochondrion. Within the electron transport chain the hydrogen ions and electrons separate with the high energy electrons releasing their energy as they flow along the chain of 3 electron acceptors. The energy released is used to pump the hydrogen ions across the inner membrane into the inter membrane space maintaining a higher concentration of hydrogen ions between the inner and outer mitochondrial membranes. This forms a concentration gradient between the two areas. When the electrons come to the end of the chain they combine with the oxygen, the final electron acceptor. At the same time, oxygen combines with a pair of hydrogen ions to form water. As the hydrogen ions return via another protein molecule called ATP synthase they generate ATP. The Synthesis of ATP Page 14 of 25

Hydrogen ions return to the matrix by flowing through a channel in another protein molecule, this time an enzyme called ATP synthase. This movement of hydrogen ions causes part of the enzyme to rotate, driving it to synthesise ATP from ADP and Pi. Most of the energy produced in cellular respiration is produced in this way. The transfer of electrons along the chain of acceptors releases sufficient energy to produce 34 ATP molecules. This is known as oxidative phosphorylation. The complete oxidation of one glucose molecule yields 38 ATP molecules in total; 2 ATP from glycolysis, 2 from Kreb s cycle and a further 34 ATP from the electron transfer chain. Although oxygen only plays its role in this last stage, it is essential for the hydrogen ions to pass along the electron transport chain. Without oxygen being present the oxidation process cannot proceed beyond glycolysis. Answer the Testing Your Knowledge questions from Torrance page 149. Page 15 of 25

Measuring the Rate of Cellular Respiration A respirometer is a device used to measure the rate of cellular respiration. Factors such as oxygen uptake or carbon dioxide production can be used to measure the rate of respiration. As rate involved time, this must be measured during the following experiment. Your teacher will set up the experiment below to measure the rate of respiration in soaked pea seeds. Q1. What is the function of the soda lime? Page 16 of 25

Q2. Describe what happened in experiment A and in the control experiment B. Experiment A Experiment B Q3. What is the function of the syringes? Q4. Explain why the change occurred in experiment A. Q5. Why was it necessary to set up a control experiment? Q6. Calculate the respiration rate in both experiments (i.e. the volume of oxygen used in 1 hour). Experiment A Experiment B.. Collect the Respirometers Question Sheet and answer the questions in your jotter. Page 17 of 25

Other Respiratory Substrates A respiratory substrate is a molecule from which energy can be liberated to produce ATP in living cells. In animal cells for instance: glucose is essential for some cells, e.g. brain cells, red blood cells, and lymphocytes, but some cells, e.g. liver cells also oxidise fats and excess amino acids. Carbohydrates Starch is a complex carbohydrate which is stored in plant cells and glycogen is a complex carbohydrate store in animal cells. These complex molecules are made up of long chains of molecules. They act as respiratory substrate molecules as each can be broken down into as required. Other sugar molecules such as maltose, sucrose and fructose can also be degraded into glucose molecules or intermediates in the glycolytic pathway and therefore used as respiratory substrates. Fats To use fats within cells these are first digested into and. The long carbon chains of these molecules have many atoms, providing a rich source of energy. Glycerol is converted to a glycolytic intermediate. Fatty acids are oxidised in the matrix of the. Enzymes attack the ends of the long fatty acid chain until it has been converted to acetyl coenzyme A. Page 18 of 25

Protein To use proteins within cells they are first digested into individual. Excess cannot be stored in the body. They undergo deamination forming urea and respiratory intermediates as shown in the diagram. These are then converted, through a series of reactions, to substances found in the. Alanine, for example, is converted to, while is converted to acetyl coenzyme A with being converted to an in the citric acid cycle. During starvation, the body proteins can be converted to amino acids which can then be utilised as an alternative respiratory substrate. Answer the testing Your Knowledge questions from Torrance page 155. Page 19 of 25

It is important to remember that carbohydrates are utilised in glycolysis. However, fats and proteins can only be respired aerobically, and do not undergo glycolysis. Both are converted into substances which enter citric acid cycle, and then the electron transport chain. Fermentation This is the process of energy production, in the absence of oxygen, generating only 2 ATP molecules due to the incomplete breakdown of the sugar molecules. As the cells are deprived of oxygen the citric acid cycle and electron transport chain cannot occur. Therefore, only glycolysis can take place and each glucose molecule can only generate 2ATP molecules as it is converted to pyruvate. The respiratory pathway that pyruvate then takes depends on the organism involved. The diagram below outlines the process of fermentation. Under normal circumstances the blood can supply oxygen to mammalian muscle tissue so that it can respire aerobically. However, during vigorous exercise the supply of oxygen to the muscle cells cannot meet the demand. This results in the muscle cells undergoing fermentation. Page 20 of 25

Comparison of aerobic respiration and fermentation. Complete the table below outlining the differences in both processes. Substance Oxygen required? Aerobic respiration Fermentation In yeast In humans Quantity of ATP? Waste products produced? Which type of respiration is most efficient? Give a reason for your answer. Type of respiration: Reason: Page 21 of 25

Summary of Aerobic Respiration and Fermentation Answer the testing Your Knowledge questions from Torrance page 155. Page 22 of 25

Look at the diagram of cellular respiration below and answer the questions below. Q1. Name the compounds labelled A and B in the diagram above. A B Q2. Name the processes labelled 1, 2 and 3 1 2 3 Q3. Name the coenzyme labelled C C Q4. Name the product labelled E. E Q5. Name the final electron acceptor D Page 23 of 25 E

(2.2) Cellular Respiration Complete: Column 1 before your Unit assessment Column 2 before your Prelim Column 3 before your May exam 1 2 3 I can state that: All living cells carry out respiration ATP is the energy currency of the cell and can be regenerated from ADP and inorganic phosphate. ATP has the role of providing the energy requirements for cellular processes. The first stage of respiration is glycolysis. Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm. During the oxidation of pyruvate the enzyme dehydrogenase promotes the removal of hydrogen ions and electrons from pyruvate and also the transfer of hydrogen and electrons to its acceptor NAD. The process of phosphorylation (the addition of a phosphate group to ADP) during glycolysis results in the production of 2 ATP molecules. In the absence of oxygen, pyruvate undergoes fermentation to lactate (in animals) and ethanol and carbon dioxide (in plants in fungi). The citric acid cycle occurs in the matrix of the mitochondria. During the Citric Acid Cycle acetyl co-enzyme A reacts with oxaloacetate to produce citrate. Dehydrogenase enzymes catalyse the removal of hydrogen and electrons on 4 occasions from the various respiratory substrates during the cycle: NAD is the hydrogen acceptor on three, FAD once. Hydrogen ions and electrons are carried by NAD and FAD to the electron transport chain. Page 24 of 25

(2.2) Cellular Respiration (cont.) Complete: Column 1 before your Unit assessment Column 2 before your Prelim Column 3 before your May exam I can state that: 1 2 3 The electron transport chain is a series of protein carrier molecules. ATP synthase is used to catalyse the production of ATP form ADP and Pi. The electron transport chain occurs on the inner membrane of the mitochondria. The final electron acceptor is oxygen which combines with hydrogen ions to form water. Most of the ATP generated by cellular respiration occurs as a result of the electron transport chain. The substrates for respiration are the carbohydrates; glucose, starch, glycogen and other sugar molecules. When carbohydrate is not available other substrates such as proteins or fats can be used by the cell. Page 25 of 25