Edexcel International A Level Biology Respiration PDF

Head to www.savemyexams.com for more awesome resources Edexcel International A Level Your notes Biology Respiration Contents 7.1 Overview of Respiration 7.2 Glycolysis 7.3 Link Reaction & Krebs Cycle 7.4 The Electro...

Head to www.savemyexams.com for more awesome resources Edexcel International A Level Your notes Biology Respiration Contents 7.1 Overview of Respiration 7.2 Glycolysis 7.3 Link Reaction & Krebs Cycle 7.4 The Electron Transport Chain 7.5 Anaerobic Respiration 7.6 Respiratory Quotient 7.7 Core Practical 15: Investigation of Respiration in Yeast 7.8 Core Practical 16: Respirometer to Calculate RQ Page 1 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.1 Overview of Respiration Your notes Overview of Respiration Glucose is the main respiratory substrate used by cells Aerobic respiration is the process of breaking down a respiratory substrate in order to produce ATP using oxygen The equation for aerobic respiration: glucose + oxygen → carbon dioxide + water + energy C6H1206 + 6 O2 → 6 CO2 + 6 H20 + 2870kJ The energy that is released during the process is used to phosphorylate (add a phosphate) ADP to form ATP ATP provides energy for other biological processes in cells The process of aerobic respiration using glucose can be split into four stages which each occurs at a particular location in a eukaryotic cell: Glycolysis takes place in the cell cytoplasm The Link reaction takes place in the matrix of the mitochondria The Krebs cycle takes place in the matrix of the mitochondria Oxidative phosphorylation occurs at the inner membrane of the mitochondria These chemical reactions are controlled by intracellular enzymes that catalyses reactions within the cell Ensuring that the energy trapped within the chemical bonds of the glucose molecule is released gradually and not all at once A sudden release of such a large amount of energy would result in an increase in body temperature to levels that would denature enzymes The enzyme that catalyses these reactions the slowest will determine the overall rate of aerobic respiration Several coenzymes are required during respiration to transfer various molecules involved in the process NAD and FAD are the coenzymes responsible for transferring hydrogen between molecules Depending on whether they give or take hydrogen, they are able to reduce or oxidise a molecule Coenzyme A is responsible for the transfer of acetate (also known as acetic acid) from one molecule to another Although glucose is the main fuel for respiration, organisms can also break down other molecules (such as fatty acids or amino acids) to be respired Four Stages of Respiration Table Page 2 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of mitochondria Mitochondria have two phospholipid membranes The outer membrane is: Smooth Permeable to several small molecules The inner membrane is: Folded (cristae) Less permeable The site of the electron transport chain (used in oxidative phosphorylation) Location of ATP synthase enzymes (used in oxidative phosphorylation) The intermembrane space: Has a low pH due to the high concentration of protons The concentration gradient across the inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis The matrix: Is an aqueous solution within the inner membranes of the mitochondrion Contains ribosomes, enzymes and circular mitochondrial DNA necessary for mitochondria to function Page 3 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The structure of a mitochondrion Exam Tip It’s important to know the exact locations of each stage. It is not enough to say the Krebs cycle takes place in the mitochondria, you need to say it takes place in the matrix of the mitochondria. Page 4 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.2 Glycolysis Your notes Glycolysis Glycolysis is the first stage of respiration It does not require oxygen to take place and is therefore the first step for both aerobic and anaerobic respiration Glucose is only partially oxidised during glycolysis It takes place in the cytoplasm of the cell and involves: Trapping glucose in the cell by phosphorylating the molecule Oxidising triose phosphate (by losing hydrogen) It results in the production of 2 Pyruvate (3C) molecules which moves into the matrix of mitochondria to be used during the link reaction Net gain 2 ATP 2 reduced NAD, which will be used during a later stage called oxidative phosphorylation Under anaerobic conditions, glycolysis produces lactic acid or lactate instead of pyruvate Steps of glycolysis Phosphorylation of glucose (a hexose sugar) Two molecules of ATP are required to provide the two phosphates needed for the phosphorylation of glucose This produces Two molecules of triose phosphate Two molecules of ADP Oxidation of triose phosphate After triose phosphate loses hydrogen, it forms two molecules of pyruvate The hydrogen ions are collected by NAD which reduces the coenzyme This forms two reduced NAD or NADH Even though a total of four ATP molecules were produced during glycolysis, two of them were used to phosphorylate glucose There was therefore a net gain of two ATP molecules Page 5 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The process of glycolysis Exam Tip It may seem strange that ATP is used and also produced during glycolysis. At the start ATP is used to make glucose more reactive (it is usually very stable) and to lower the activation energy of the reaction. Since 2 ATP are used and 4 are produced during the process, there is a net gain of 2 ATP per glucose molecule. Page 6 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.3 Link Reaction & Krebs Cycle Your notes Link Reaction & Krebs Cycle The Link reaction The end product of glycolysis is pyruvate Pyruvate contains a substantial amount of chemical energy that can be further utilised in respiration to produce more ATP The enzymes and coenzymes that are required for the link reaction are found in the mitochondrial matrix When oxygen is available pyruvate will enter the mitochondrial matrix and aerobic respiration will continue Pyruvate moves across the double membrane of the mitochondria via active transport It requires a transport protein and a small amount of ATP Once in the mitochondrial matrix pyruvate takes part in the link reaction Pyruvate enters the mitochondrial matrix from the cytosol (cytoplasm) by active transport The link reaction takes place in the matrix of the mitochondria It is referred to as the link reaction because it links glycolysis to the Krebs cycle The steps are: Pyruvate is oxidised (hydrogen is removed) by enzymes to produce acetate, CH3CO(O) (also known as acetic acid) Pyruvate is also decarboxylated (carbon is removed) in the form of carbon dioxide Reduction of NAD to NADH or reduce NAD by collecting hydrogen from pyruvate Acetate combines with coenzyme A to form acetyl coenzyme A (acetyl CoA) No ATP is produced during the link reaction It produces: Acetyl coA Page 7 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Carbon dioxide (CO2) Reduced NAD (NADH) pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD Your notes The link reaction occurs in the mitochondrial matrix. It dehydrogenates and decarboxylates the three- carbon pyruvate to produce the two-carbon acetyl CoA that can enter the Krebs Cycle Every molecule of glucose produces two pyruvate molecules The link reaction and the Krebs cycle will therefore occur twice for every molecule of glucose Thus, each molecule of glucose will produce: Two molecules of acetyl CoA Two molecules of CO2 Two molecules of reduced NAD The Krebs Cycle The Krebs cycle (sometimes called the citric acid cycle) consists of a series of enzyme-controlled reactions 2 carbon (2C) Acetyl CoA enters the circular pathway from the link reaction in glucose metabolism Acetyl CoA formed from fatty acids (after the breakdown of lipids) and amino acids enters directly into the Krebs Cycle from other metabolic pathways 4 carbon (4C) oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form the 6 carbon (6C) citrate Coenzyme A is released in this reaction to be reused in the next link reaction Citrate is then converted back to oxaloacetate through a series of oxidation-reduction (redox) reactions Page 8 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The Krebs Cycle uses acetyl CoA from the link reaction and the regeneration of oxaloacetate to produce reduced NAD, reduced FAD and ATP Regeneration of oxaloacetate Oxaloacetate is regenerated in the Krebs cycle through a series of redox reactions Decarboxylation of citrate Releasing 2 CO2 as waste gas Oxidation (dehydrogenation) of citrate Releasing H atoms that reduce coenzymes NAD and FAD These will be used during oxidative phosphorylation 3 NAD and 1 FAD → 3NADH + H+ and 1 FADH2 Substrate linked phosphorylation A phosphate is transferred from one of the intermediates to ADP, forming 1 ATP to supply energy Because two acetyl-CoA molecules are produced from each glucose molecule, two cycles are required per glucose molecule Therefore, at the end of two cycles, the products are: Page 9 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Two ATP Six NADH (reduced NAD) Two FADH2 (reduced FAD) Your notes Four CO2 Exam Tip The Krebs cycle is often referred to as cyclical or circular. This is because the acceptor molecule oxaloacetate is regenerated throughout the reaction so that it can start all over again by adding another acetyl CoA. You may be asked to name the important molecules in the Krebs cycle like oxaloacetate and citrate. It is also worth noting how the number of carbon atoms in the substrate molecule changes as the cycle progresses. Page 10 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.4 The Electron Transport Chain Your notes The Electron Transport Chain Oxidative phosphorylation is the last stage of aerobic respiration It takes place at the inner mitochondrial membrane It results in the production of many molecules of ATP and the production of water from oxygen The current model for oxidative phosphorylation is the chemiosmotic theory The model states that energy from electrons is passed through a chain of proteins in the membrane, known as the electron transport chain This energy is used to pump protons (hydrogen ions) against their concentration gradient into the intermembrane space The protons are then allowed to flow by facilitated diffusion through a channel enzyme called ATP synthase into the matrix The energy of the protons flowing down their concentration gradient is harnessed (a bit like water flowing through a hydroelectric damn) resulting in the phosphorylation of ADP into ATP by ATP synthase Outline of oxidative phosphorylation Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) from the Krebs Cycle Hydrogen atoms split into protons (H+ ions) and electrons The high energy electrons enter the electron transport chain and release energy as they move through the electron transport chain The energy released is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space A concentration gradient of protons is established between the intermembrane space and the matrix The protons return to the matrix via facilitated diffusion through the channel enzyme ATP synthase The movement of protons down their concentration gradient provides energy for ATP synthesis Oxygen acts as the 'final electron acceptor' and combines with protons and electrons at the end of the electron transport chain to form water The electron transport chain The electron transport chain is made up of a series of membrane proteins/ electron carriers They are positioned close together which allows the electrons to pass from carrier to carrier The inner membrane of the mitochondria is impermeable to hydrogen ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient Page 11 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Oxidative phosphorylation via the chemiosmotic theory occurs on the inner mitochondrial membrane and requires NADH and FADH2 from the Krebs Cycle. It produces water and many molecules of ATP Oxidative phosphorylation uses energy from reduced NAD and FAD to produce ATP 3 ATP molecules for every reduced NAD molecule 2 ATP molecules for every reduced FAD molecule For every molecule of glucose a total of 38 ATP molecules can be produced during aerobic respiration Number of ATP Molecules Produced During Aerobic Respiration per Glucose Molecule Table Page 12 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Exam Tip Examiners often ask why oxygen is so important for aerobic respiration. Oxygen acts as the final electron acceptor. Without oxygen the electron transport chain cannot continue as the electrons have nowhere to go. Without oxygen accepting the electrons (and hydrogen ions) the reduced coenzymes NADH and FADH2 cannot be oxidised to regenerate NAD and FAD, so they can’t be used in further hydrogen transport. It is important to use the correct terminology when describing hydrogen; ensure you understand when to use "hydrogen" and when to use "hydrogen ions/protons". Page 13 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.5 Anaerobic Respiration Your notes Anaerobic Respiration Sometimes cells experience conditions with little or no oxygen There are several consequences when there is not enough oxygen available for respiration: There is no final acceptor (oxygen) of electrons from the electron transport chain The electron transport chain stops functioning No more ATP is produced via oxidative phosphorylation Reduced NAD and FAD aren’t oxidised by an electron carrier No oxidised NAD and FAD are available for dehydrogenation in the Krebs cycle The Krebs cycle stops The link reaction also stops However, there is still a way for cells to produce some ATP in low oxygen conditions through anaerobic respiration Anaerobic pathways Some cells are able to oxidise the reduced NAD produced during glycolysis so it can be used for further hydrogen transport This means that glycolysis can continue and small amounts of ATP are still produced Different cells use different pathways to achieve this Yeast and microorganisms use ethanol fermentation Other microorganisms and mammalian muscle cells use lactate fermentation Lactate fermentation In this pathway reduced NAD transfers hydrogen to pyruvate to form lactate NAD can now be reused in glycolysis Pyruvate is reduced to lactate by enzyme lactate dehydrogenase Pyruvate is the hydrogen acceptor The final product lactate can be further metabolised A small amount of ATP is produced Page 14 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The pathway of lactate fermentation Processing Lactate Lactate (lactic acid) can build up in the cells after a period of time After lactate is produced two things can happen: It can be oxidised back to pyruvate which is then channelled into the Krebs cycle for ATP production It can be converted into glucose by the liver cells for use during respiration or for storage (in the form of glycogen) The oxidation of lactate back to pyruvate needs extra oxygen This extra oxygen is referred to as an oxygen debt It explains why animals breathe deeper and faster after exercise Ethanol fermentation In this pathway reduced NAD transfers its hydrogens to ethanal to form ethanol In the first step of the pathway pyruvate is decarboxylated to ethanal Producing CO2 Then ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase Ethanal is the hydrogen acceptor Ethanol cannot be further metabolised; it is a waste product Ethanol fermentation occurs in yeast and plant cells Page 15 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The pathway of ethanol fermentation Exam Tip Note that ethanol fermentation is a two-step process (lactate fermentation is a one-step process). Carbon dioxide is also produced alongside the waste ethanol. This waste ethanol is what makes yeast vital in producing alcoholic drinks like beer! Page 16 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.6 Respiratory Quotient Your notes Respiratory Quotient The respiratory quotient (RQ) is the ratio of carbon dioxide molecules produced to oxygen molecules taken in during respiration RQ = CO2 ÷ O2 The formula for the Respiratory Quotient RQ values of different respiratory substrates Carbohydrates, lipids and proteins have different typical RQ values This is because of the number of carbon-hydrogen bonds differs in each type of biological molecule More carbon-hydrogen bonds means that more hydrogen atoms can be used to create a proton gradient More hydrogens means that more ATP molecules can be produced More oxygen is therefore required to breakdown the molecule (in the last step of oxidative phosphorylation to form water) When glucose is aerobically respired equal amounts of carbon dioxide are produced to oxygen taken in, meaning it has an RQ value of 1 During the breakdown of glucose, six molecules of oxygen is used and six molecules of carbon dioxide is produced. This results in an RQ value of 1 (6CO2 ÷ 6O2) RQ Values For Different Respiratory Substrates Table Page 17 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Some questions may ask you to suggest what substrate is being respired during an experiment based on the RQ value – so make yourself familiar with the values in the table Calculating RQ values The respiratory quotient is calculated from respiration equations It involves comparing the ratios of carbon dioxide given out to oxygen taken in The formula for this is: Equation to calculate the RQ value of a respiratory substrate For aerobic respiration the RQ will typically be less than 1 since oxygen is being used to break down the substrate Should the RQ of an organism be greater than 1, it may indicate that anaerobic respiration is occurring, since very little to no oxygen is used If you know the molecular formula of the substrate being aerobically respired then you can create a balanced equation to calculate the RQ value In a balanced equation the number before the chemical formula can be taken as the number of molecules/moles of that compound This is because the same number of molecules of any gas take up the same volume e.g. 12 molecules of carbon dioxide take up the same volume as 12 molecules of oxygen Glucose has a simple 1:1 ratio and RQ value of 1 but other substrates have more complex ratios leading to different RQ values Page 18 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes Linoleic acid (a fatty acid found in nuts) has the molecular formula C18H32O2. Calculate the RQ value of this lipid. Step 1: Write down the respiration equation C18H32O2 + O2 → CO2 + H2O Step 2: Balance the equation C18H32O2 + 25O2 → 18CO2 + 16H2O Step 3: Use the RQ formula RQ = CO2 ÷ O2 RQ = 18 ÷ 25 RQ = 0.72 Worked example During ethanol fermentation in lettuce roots, glucose is partially broken down. This process is represented by the following equation: glucose → ethanol + carbon dioxide Calculate the RQ value. Step 1: Write down the respiration equation C6H12O6 → C2H5OH + CO2 Step 2: Balance the equation C6H12O6 → 2C2H5OH + 2CO2 Step 3: Use the RQ formula RQ = CO2 ÷ O2 RQ = 2 ÷ 0 RQ = ∞ (infinity) Page 19 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes Make sure the respiration equation you are working with is fully balanced before you start doing any calculations to find out the RQ value. Page 20 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.7 Core Practical 15: Investigation of Respiration in Yeast Your notes Investigation of Respiration in Yeast A redox indicator is a substance that changes colour when it is reduced or oxidised DCPIP and methylene blue are redox indicators They are used to investigate the effects of temperature and substrate concentration on the rate of anaerobic respiration in yeast These dyes can be added to a suspension of living yeast cells as they don’t damage cells Yeast can respire both aerobically and anaerobically, in this experiment it is their rate of anaerobic respiration that is being investigated Mechanism Dehydrogenation happens regularly throughout the different stages of aerobic respiration The hydrogens that are removed from substrate molecules are transferred to the final stage of aerobic respiration, oxidative phosphorylation, via the hydrogen carriers NAD and FAD The enzyme dehydrogenase catalyses the production of reduced NAD in glycolysis When DCPIP or methylene blue are present they take up hydrogens from the organic compounds and get reduced instead of NAD Both redox indicators undergo the same colour change when they are reduced Blue → colourless The faster the rate of respiration, the faster the rate of hydrogen release and the faster the dyes get reduced and change colour This means that the rate of colour change can correspond to the rate dehydrogenase would be working at and therefore, the rate of respiration in yeast The rate of respiration is inversely proportional to the time taken Rate of respiration (sec-1) = 1 ÷ time (sec) Apparatus Yeast Glucose solution Test tubes Stopwatch DCPIP Method - Temperature 1. Add a set volume of yeast suspension to test tubes containing a certain concentration of glucose 2. Put the test tube in a temperature-controlled water bath and leave for 5 minutes to ensure the water temperature is correct and not continuing to increase or decrease 3. Add a set volume of DCPIP to the test tube and start the stopwatch immediately Page 21 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4. Stop the stopwatch when the solution becomes colourless or lose all blue colour This is subjective and therefore the same person should be assigned this task for all repeat experiments Your notes 5. Record the time taken for a colour change to occur once the dye is added Repeat across a range of temperatures. For example, 30oC, 35oC, 40oC, 45oC 6. The effect of substrate concentration can be investigated by adding different concentrations of a substrate to the suspension of yeast cells and recording the time taken for a colour change to occur once the dye is added For example, 0.1% glucose, 0.5% glucose, 1.0% glucose Methylene blue or DCPIP is added to a solution of anaerobically respiring yeast cells in a glucose solution. The rate at which the solution turns from blue to colourless gives the rate of dehydrogenase activity Controlling other variables It is important when investigating one variable to ensure that the other variables in the experiment are being controlled Page 22 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Volume of dye added: if there is more dye molecules present then the time taken for the colour change to occur will be longer Volume of yeast suspension: when more yeast cells are present the rate of respiration will be Your notes inflated Type of substrate: yeast cells will respire different substrates at different rates Concentration of substrate: if there is limited substrate in one tube then the respiration of those yeast cells will be limited Temperature: an increase or decrease in temperature can affect the rate of respiration due to energy demands and kinetic energy changes. The temperature of the dye being added also needs to be considered pH: a buffer solution can be used to control the pH level to ensure that no enzymes are denatured Interpretation of results A graph should be plotted of temperature against time As the temperature increases, the rate of respiration also increases so the time taken for the solution to go colourless reduces This means hydrogens are released by the reactions more quickly, hence the DCPIP accepts electrons/hydrogens more quickly until all molecules of DCPIP are reduced. This means that it will take less time to turn from blue to colourless At extreme high temperatures, the enzyme may denature and meaning the colour change may not occur Exam Tip Although the DCPIP and methylene blue undergo a colour change from blue to colourless it is important to remember that the yeast suspension in the test tube may have a slight colour (usually yellow). That means when the dye changes to colourless there may still be an overall yellow colour in the test tube. If this is the case it can be useful to have a control tube containing the same yeast suspension but with no dye added, then you can tell when the dye has completely changed colour. Page 23 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 7.8 Core Practical 16: Respirometer to Calculate RQ Your notes Using a Respirometer to Calculate RQ Respirometers are used to measure and investigate the rate of oxygen consumption during respiration in organisms They can also be used to calculate respiratory quotients The experiments usually involve organisms such as seeds or invertebrates Apparatus Respirometer Glass beads Germinating seeds These will be actively respiring and consuming oxygen Test tubes Soda-lime pellets (or potassium hydroxide) To absorb the carbon dioxide produced Stopwatch Page 24 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A respirometer set up to measure the rate of respiration Method 1. Measure oxygen consumption: set up the respirometer and run the experiment with both tubes for a set amount of time (e.g. 30 minutes) 2. As the seeds consume oxygen, the volume of air in the test tube will decrease (CO2 produced during respiration is absorbed by soda lime or KOH) Page 25 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 3. This reduces the pressure in the capillary tube and manometer fluid will move towards the test tube containing the seeds 4. Measure the distance moved by the liquid in a given time Your notes 5. Use this measurement to calculate the change in gas volume within a given time, x cm3 min-1 6. Reset the apparatus: allow air to re-enter the tubes via the screw cap and reset the manometer fluid using the syringe 7. Run the experiment again: remove the soda-lime from both tubes and use the manometer reading to calculate the change in gas volume in a given time, y cm3 min-1 Equation for calculating change in gas volume The volume of oxygen consumed (cm3 min-1) can be worked out using the diameter of the capillary tube r (cm) and the distance moved by the manometer fluid h (cm) in a minute using the formula: πr 2 h Calculations x tells us the volume of oxygen consumed by respiration within a given time y tells us the volume of oxygen consumed by respiration within a given time minus the volume of carbon dioxide produced within a given time y may be a positive or negative value depending on the direction that the manometer fluid moves (up = positive value, down = negative value) The two measurements x and y can be used to calculate the RQ Equation to calculate RQ values using a respirometer Worked example During a respirometer experiment using blow fly larvae, the volume of oxygen consumed was 2.9 cm3min-1. The soda lime was removed from both test tubes and the experiment was repeated. The change in gas volume was -0.8 cm3min-1. Calculate the RQ value for the blow fly larvae. x = 2.9 cm3min-1 y = -0.8 cm3min-1 Page 26 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Step 1: Write down equation x+y Your notes RQ = x Step 2: Substitute values 2.9 − 0.8 RQ = 2.9 Step 3: Calculate RQ RQ = 0. 72 Interpretation of results Respirometers can be used in experiments to investigate how different factors affect the RQ of organisms over time E.g. temperature – using a series of water baths When an RQ value changes it means the substrate being respired has changed Some cells may also be using a mixture of substrates in respiration e.g. An RQ value of 0.85 suggests both carbohydrates and lipids are being used This is because the RQ of glucose is 1 and the RQ of lipids is 0.7 Under normal cell conditions the order substrates are used in respiration: carbohydrates, lipids then proteins The RQ can also give an indication of under or overfeeding: An RQ value of more than 1 suggests excessive carbohydrate/calorie intake An RQ value of less than 0.7 suggests underfeeding Exam Tip There are several ways you can manage variables and increase the reliability of results in respirometer experiments: Use a controlled water bath to keep the temperature constant Have a control tube with an equal volume of inert material to the volume of the organisms to compensate for changes in atmospheric pressure Repeat the experiment multiple times and use an average Page 27 of 27 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers