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Respiration In the final topic of our unit about cells, we're going to be learning lots more about a process which is crucial to all cells: respiration. Once again, you'll already know at least something about respiration. This is the process by which we release energy from our food. Learning Outcomes: Identify the source of energy in a cell and the reaction which releases this energy Explain the structure and role of ATP and how it releases energy State the cellular activities that use energy Define aerobic respiration and fermentation and state the locations where they occur Describe the steps involved in aerobic respiration and fermentation in animals and plants Compare aerobic and anaerobic respiration in terms of energy yield and products in both plant and animal cells What is Respiration? Energy is required by all cells in the body for even the simplest of things. We need energy for: Movement For keeping warm Cell division To keep our bodies working as we sleep Aerobic respiration is the enzyme-controlled chemical process where glucose is broken down in the presence of oxygen to release energy (ATP) to allow the body to do work and carbon dioxide and water are released as end products. 1 Learning Activity 1: Measuring the energy content of food. Collect the experiment sheet “Measuring the energy content of food”. Careful – Make sure you follow all instructions on the card. Remember your Bunsen safety! Group work – be a good team player. Help out others in your group if you need to: do not dominate but get involved in the task. Organisation – make sure that everyone in your groups knows what is to be done and that all safety precautions are followed. 1. Write up the experiment: include an aim, a method (including a diagram), your table of results, a graph. 2. For the conclusion, state which type of food contains the most energy per gram. The Release and Use of Energy The energy released from the breakdown of glucose is used to generate molecules of Adenosine triphosphate (ATP) inside cells. ATP is a chemical store of energy: it is generated from molecules of Adenosine diphosphate (ADP) and phosphate (Pi). ATP is formed when the chemical energy released from glucose during respiration is used to join together a single ADP molecule and a single phosphate molecule (Pi). Adenosine Pi + Pi Pi Adenosine diphosphate Adenosine Phosphate Pi Pi Pi Adenosine triphosphate The chemical energy stored in ATP can be released whenever it is required by cells. This is achieved by breaking the last bond in the molecule in order to make ADP and Pi again. 2 Learning Activity 2 1. Draw a simple diagram to show the link between ATP, the energy from respiration and the energy used for cellular activities. 2. Draw a spider diagram in your jotter to show the uses of energy by cells. Aerobic Respiration In order for glucose to be completely broken down during respiration, aerobic conditions must be present. This means that there must be a supply of oxygen present. The basic word equation for aerobic respiration is: Glucose + Oxygen Carbon dioxide + water + energy (38 ATP molecules) This takes place during a number of enzyme-controlled steps. Step 1: Glycolysis This is the process of breaking glucose down into a substance called pyruvate. It takes place in the cytoplasm of a cell. This step does not require aerobic conditions (oxygen). Two ATP molecules are formed as a result. 3 Step 2: Breakdown of Pyruvate The pyruvate is further broken down to produce carbon dioxide and water. This stage does require aerobic conditions (oxygen). It takes place in the mitochondria. During this stage 36 ATP molecules are produced. Pyruvate 36 ADP + 36 Pi 36 ATP Carbon dioxide Water The complete aerobic breakdown of one glucose molecule in the presence of oxygen results in a yield of 38 molecules of ATP. Learning Activity 3 Answer the questions below in full sentences in your jotter: 1. State the number of ATP molecules produced by the first stage of aerobic respiration. 2. State the number of ATP molecules produced by the second stage of aerobic respiration. 3. Name the final products that result from the complete breakdown of glucose. 4. Write down the summary word equation for aerobic respiration. Extension: Create a wall display poster of aerobic respiration. Include diagrams of each stage of the process and make sure you add labels. 4 Measuring the rate of Respiration in plants and animals The rate of respiration can be measured using a respirometer. The diagram shows a simple respirometer used to measure the respiration rate of a woodlouse. Coloured water Woodlouse Sodium hydroxide (to absorb CO2) Gauze The only air available to the woodlouse is inside the tube. Sodium hydroxide is used to absorb carbon dioxide produced by the woodlouse. This way, only the oxygen taken in by the woodlouse is measured. As the organism uses up oxygen inside the tube, the volume of gas decreases. The coloured water moves down the tube to fill the space of the oxygen that has been used up by the woodlouse. The distance that the coloured water moves is used to calculate the rate of respiration. Learning Activity 4 1. Make a copy of the diagram above in your jotter. 2. Answer the following questions in full sentences: a) Write down a suggestion for a suitable control for this experiment. Why do we need a control? b) Why is the respirometer kept at a constant temperature throughout the experiment? c) Explain why the sodium hydroxide must be kept away from the organism? 5 Look at the apparatus below: it was used to measure the rate of respiration in germinating peas: A B Sodium hydroxide cotton wool Water Bath Germinating Peas Glass Beads Coloured water The liquid levels in tube A and B were noted at 10 minute intervals for 1 hour. Time (mins) 0 10 20 30 40 50 60 Tube A (mm3) 0 10 20 30 35 40 40 Tube B (mm3) 0 0 0 0 0 0 0 Learning Activity 5 1. Copy the table of results into your jotter. 2. Plot a line graph of oxygen uptake in mm3 against time on graph paper. 3. Answer these questions in sentences: a) Why is there no change in the volume of coloured liquid in Tube B? b) Calculate the average oxygen uptake per min for Tube A (mm3). c) Give a reason for the oxygen uptake levelling off after 40/50 minutes. 6 Fermentation in Animal Cells In the absence of oxygen, respiration cannot take place as it normally would. Glucose cannot be completely broken down. Instead, the fermentation pathway is followed. Stage 1: Glycolysis This stage happens as normal because it does not require oxygen. Glucose 2 ADP + 2 Pi 2 ATP Pyruvate Stage 2: The incomplete breakdown of pyruvate In the absence of oxygen in animals, pyruvate is broken down into lactic acid. This happens frequently during strenuous exercise. Only 2 molecules of ATP are produced. Pyruvate Lactic Acid Lactic acid builds up inside muscle cells and eventually muscles tire. This is called muscle fatigue. Following a period of recovery, where oxygen becomes available again, the lactic acid can be converted back into pyruvate, and aerobic respiration can resume. 7 Learning Activity 6 Write the answers to the following questions in full sentences: 1. Describe the process of fermentation in animal cells. 2. State the number of ATP molecules produced during fermentation in animal cells. 3. Name the final product that results from fermentation in animal cells. 4. Write down the summary word equation for fermentation in animal cells. Fermentation in Plant and Yeast Cells In plant and yeast cells, in the absence of oxygen a similar situation arises. Glycolysis takes place as before, only this time, pyruvate is broken down into Carbon dioxide and ethanol (alcohol). As carbon dioxide is produced, the reaction cannot be reversed. Pyruvate Carbon dioxide Ethanol Learning Activity 7 Write the answers to the following questions in full sentences: 1. Describe the process of fermentation in plant and yeast cells. 2. State the number of ATP molecules produced during fermentation in plant and yeast cells. 3. Name the final products of fermentation in plant and yeast cells. 4. Write down the word equation for fermentation in plant and yeast cells. Extension: Use the internet and other available classroom resources to find out how fermentation is useful in the production of the following things: 1. Bread 2. Alcohol (beer and wine). Create a poster displaying the information that you have found out. Remember to record all of your sources. 8 Location of aerobic respiration and fermentation The process of aerobic respiration starts in the cytoplasm and is completed in the mitochondrion. The mitochondrion is a sausage-shaped organelle in the cytoplasm of a cell. Cells which require a vast amount of energy have many mitochondria within them. These cells include muscle cells, sperm cells, nerve cells and companion cells, along with many more. The process of fermentation is completed in the cytoplasm. Learning activity 8 1. Copy and complete the following table to compare aerobic respiration and fermentation in plants and animals: Fermentation in Plants Animals and Yeast Aerobic respiration in all cell types Product (s) Number of ATP molecules produced (per molecule of glucose) 2. Choose a cell type that has many mitochondria. Produce an information leaflet on the uses of energy in your chosen cell. You can use AAL to complete this task if no laptops are available. You should include: A drawing of the cell that you have chosen showing many mitochondria present. An explanation of the job of the cell. An explanation of how the cell uses energy. 9