Respiration - AQA Past Paper Notes PDF

Unit 5: RESPIRATION (AQA Pages 134-139) The reactions taking place in an organism are collectively known as metabolism. Energy is needed for these reactions to take place. Respiration is an enzyme-controlled process in which high-energy content food (example: glucose) is broken down (catabolism) to...

Unit 5: RESPIRATION (AQA Pages 134-139) The reactions taking place in an organism are collectively known as metabolism. Energy is needed for these reactions to take place. Respiration is an enzyme-controlled process in which high-energy content food (example: glucose) is broken down (catabolism) to release energy. This energy is stored in a molecule in the mitochondria of all cells and is known as ATP (Adenosine Triphosphate). This process occurs in cells. Adenosine Triphosphate Respiration takes place in all living plant and animal cells which contain mitochondria. Mitochondria are in fact called the ‘power houses’ of all cells. The more energy a cell needs, the more mitochondria it has. For example, muscle cells contain many mitochondria, as also the cells covering the villi in the small intestine, which use ATP for active transport of glucose. The cells contain a substance called adenosine di-phosphate (ADP). The energy released during respiration is used to combine another phosphate group to the ADP molecule to form adenosine triphosphate: ADP + phosphate group + energy from cellular respiration → ATP When cells need energy, the reverse reaction takes place such that energy is released from the breakdown of ATP. Not all the energy released during respiration is used to make ATP. Some of it is released as heat; in fact, many animals use this heat to keep warm. adenosine P P P adenosine triphosphate adenosine P P + P + energy adenosine diphosphate Ms Lorraine Vella Bio Year 9 1|Page There are two types of cellular respiration: Aerobic respiration Anaerobic respiration Aerobic respiration Aerobic respiration is the breakdown of food using oxygen. It occurs in the mitochondria of all air-breathing organisms and produces carbon dioxide, water and ATP (Adenosine Tri-Phosphate, an energy-rich chemical). The equation for the reaction is: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38ATP glucose + oxygen → carbon dioxide + water + energy The energy produced during aerobic respiration is used in: ✓ working muscles ✓ transporting chemicals ✓ sending messages along the nerves ✓ growth (building cells) ✓ keeping the body temperature constant Anaerobic respiration Anaerobic respiration is the breakdown of food without using oxygen. Two different processes of anaerobic respiration can occur: 1. Alcoholic fermentation: Certain organisms such as yeast, breakdown sugar to get energy. Carbon dioxide and ethanol (alcohol) are also produced as waste products. The production of alcohol is of economic importance and is known as fermentation. Alcoholic drinks are made by using yeast to ferment sugar in fruit juice. Beer is made by yeast which ferments barley, and cider is made by yeast which ferments apple juice. The equation for the formation of alcohol is: C6H12O6 → 2C2H5OH + 2CO2 + 2ATP glucose → ethanol (alcohol) + carbon dioxide + energy Ms Lorraine Vella Bio Year 9 2|Page  2. Lactic acid fermentation: Sometimes lactic acid is produced instead of alcohol. Sometimes cells need a lot of oxygen very quickly, as when you are in a race. In this case, the cells will continue respiring to produce as much energy as they can to contract the muscles. But eventually, in heavy exercise, a limit is reached, because not enough oxygen reaches the respiring muscle cells. They start to respire anaerobically so that lactic acid (lactate) is produced, without using up oxygen. When you stop running, you will have a lot of lactic acid in your muscles and blood. This acid is poisonous and causes cramps. So, after the race, we keep on panting and breathing faster to take in more oxygen so that the lactic acid is broken down into CO2 and H2O in the liver. The extra oxygen needed by the body during this time is known as the oxygen debt. As a result, athletes start to breathe deeply after a race. The breathing rate will return to normal after all the lactic acid is broken down. The equation for anaerobic respiration during exercise, to produce lactic acid is: C6H12O6 → 2C3H6O3 + 2ATP glucose → lactic acid + energy Exercise and Oxygen debt The following graph shows changes taking place in the body during exercise: Ms Lorraine Vella Bio Year 9 3|Page 1. Blood transports oxygen from the lungs to the body tissue. Before or during mild exercise, the amount of oxygen reaching the body tissue is enough to maintain aerobic respiration. 2. During exercise, the rate of respiration in muscle tissue increases since more energy is needed. The breathing rate and heart rate increases so that more oxygen can be transported to the muscles. However, this amount of oxygen is not enough to maintain aerobic respiration. Now, anaerobic respiration takes place and forms lactic acid in the cells. 3. After exercise, during recovery, the lactic acid (lactate) moves from the muscles to the liver by means of the blood, so that it can be removed. Ms Lorraine Vella Bio Year 9 4|Page Comparison between aerobic and anaerobic respiration Aerobic respiration Anaerobic respiration All air-breathing organisms respire Yeast, tapeworms etc. respire aerobically anaerobically Takes place in the mitochondria Takes place in the cytoplasm A lot of energy is produced A little energy is produced Products of aerobic respiration are Products of anaerobic respiration carbon dioxide and water are: 1. Carbon dioxide and Alcohol (in yeast and plants) or 2. Lactic acid (in animals). No water is ever produced. Oxygen is used Oxygen is not used Energy released by breakdown of Energy released by breakdown of sugar sugar 38ATP is made (2830kJ) 2ATP is made (118kJ) Some energy is lost as heat Some energy is lost as heat Equation: Equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O + C6H12O6 -> 2C2H5OH + 2CO2 + 2ATP 38ATP Glucose + oxygen -> carbon dioxide + water + energy Ms Lorraine Vella Bio Year 9 5|Page Economic use of fermentation Alcoholic fermentation and lactic acid fermentation are used in the production of several food and beverage products like bread, wine and yoghurt. Bread making: Bread is made from dough which contains flour, water, salt, oil and yeast. Wheat flour contains: (a) starch (a source of energy for yeast) (b) amylase (the enzyme which digests starch to maltose) (c) gluten (a protein which gives bread its stretchy texture) 1. The flour is mixed with water. The water activates the enzyme amylase, which breaks down the starch (polysaccharide) into maltose (disaccharide): amylase Starch Maltose 2. The yeast respires anaerobically (ferments) and converts the sugar into alcohol and carbon dioxide. C6H12O6 → 2C2H5OH + 2CO2 + 2ATP glucose → ethanol (alcohol) + carbon dioxide + energy The carbon dioxide is trapped in the dough which causes the dough to rise. The dough is kept at warm temperatures (40ºC) to speed up the process. 3. The dough is then baked in an oven at about 200ºC. At this temperature: The bubbles of carbon dioxide expand. The yeast dies. The alcohol evaporates. Ms Lorraine Vella Bio Year 9 6|Page Wine making: Wine is produced by the alcoholic fermentation of sugars in grape juice by yeast. 1. The grapes are crushed to extract the juice. 2. Sulfur dioxide is added to kill any naturally present microorganisms (yeast and bacteria). 3. The juice is aerated, and the yeast is added to the juice. At this point, the yeast respires aerobically and divides rapidly. 4. Aeration is stopped, and the yeast ferments the sugar in the grape juice to alcohol and carbon dioxide. glucose → ethanol (alcohol) + carbon dioxide + energy 5. The amount of alcohol in the mixture rises and the yeast is killed by it. 6. Low temperatures prolong the fermentation process and produce a higher alcohol content. Yoghurt production: 1. The milk is pasteurized at high temperatures to remove pathogens. 2. A mixture of bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus) is added to milk. 3. The milk is heated to a temperature of 46ºC which allows the bacteria to grow and multiply. The bacteria carry out anaerobic respiration, in which process the lactose in the milk is converted to lactic acid. Lactose Lactic acid 4. The acid causes the milk protein to clump together and form a thick mixture (yoghurt) and gives a sour taste to the yoghurt formed. 5. To yoghurt is cooled to about 5ºC and stored in a fridge. At this temperature, the bacteria stop working. The yoghurt can be mixed with fruit to create different flavours. 6. The yoghurt can be treated to remove any bacteria used in the process. Some yoghurts contain ‘live’ bacterial cultures which help in intestinal digestion. Ms Lorraine Vella Bio Year 9 7|Page