CHAPTER 8 Cellular Respiration
Starting Points (Page 34) 1. (a) Organisms use the oxygen they absorb in cellular respiration to accept two electrons from the electron transport chain to produce water. (b) The carbon in carbon dioxide is from the carbon atoms found in the glucose molecule (C6H12O6). (c) Carbon dioxide is excreted by the body because it is fully oxidized and cannot provide any further energy. Carbon dioxide reacts with water to form carbonic acid. The buildup of carbonic acid may lower pH to toxic levels, which will denature proteins. 2. (a) Bakers add yeast to flour to produce carbon dioxide gas, which causes the baked product to rise. (b) The gas produced in fermentation is carbon dioxide. (c) The bubbling will stop when the glucose is used up. A high concentration of ethanol (a product of alcoholic fermentation) kills the remaining yeast cells. (d) Wine is produced. (e) The name of this process is alcoholic fermentation 3. (a) The reasons your muscles feel stiff after a long, hard run is because of the accumulation of lactic acid in the cells of your muscle tissues. (b) Panting at the end of a run increases your oxygen uptake and this helps your body to convert the lactic acid back into pyruvate.
Exploration: Clothespins and Muscle Fatigue (Page 35) (a)
(b) The strength of your squeezes should decrease with each successive trial. (c) Your hand and fingers will ache after the experiment. (d) Factors that may cause you to become less fatigued would be the size of the contracting muscles, adaptation to this type of activity, and the use of those muscles recently. (e) Your dominant hand should be able to contract more often than your nondominant hand. This reduction of fatigue is due to adaptation and increased strength of the muscles in your dominant hand. (f) After 10 minutes’ rest, you can repeat the same experiment with the same results because your body has removed metabolic wastes and replenished lost nutrients.
8.1 USABLE FORMS OF ENERGY
Section 8.1 Questions (Page 41) 1. from lowest to highest energy: iv) glycogen, ii) maltose, i) glucose, iii) ATP, v) ADP. 2. In some reactions the formation of new products requires more energy than the breaking of the original bonds releases. This would result in the reaction needing energy to occur. In other reactions, the energy released during the breaking of reactant bonds is greater than the energy needed to form the bonds of the products. 3. Glucose has a high energy content, is relatively small, and is highly soluble. 4. Two processes that require the use of ATP are the movement of material up the concentration gradient (low to high concentration) and the movement of specific molecules through proteins in the cell membrane. Both of these processes require ATP in order to change the nature of the cell membrane or activate the membrane proteins. 5. Both animals use the waste energy (heat) to keep their bodies warm . Both organisms are warm blooded.
8.2 GLYCOLYSIS
Section 8.2 Questions (Page 44) 1. Cellular respiration is required to convert stored food energy into the usable form of ATP. 2. Glycolysis, Pyruvate Oxidation, Kreb’s Cycle, and Oxidative Phosphorylation. 3. C6H12O6+ Æ 2 C3H6O3 (glucose) (pyruvate) 4. (a) Glycolysis refers to the breaking of the glucose molecule into two pyruvate molecules. (b) 2 pyruvate, 2 NADH, 2 ADP, 4 ATP 5. NADH and the 2 pyruvate molecules
8.3 AEROBIC RESPIRATION
Investigation 8.1: Measuring Oxygen Consumption in Germinating Seeds (Pages 45, 65-66)
Purpose To examine how oxygen consumption by dry and germinating pea seeds differs.
Problem How does the rate of oxygen consumption by germinating and non-germinating pea seed vary?
Hypothesis Since they are growing, germinating peas will have a higher need for energy and therefore a higher rate of cellular respiration than will non-germinating peas.
Prediction (a) Students should predict that the germinating pea seed would consume more oxygen than the non-germinating pea seeds.
Design The rate of production of CO2 gas will be measured in order to compare the respiration rate of germinating and non- germinating pea seeds. The seeds will be placed in a gas-tight sealed test-tube, along with potassium hydroxide. The potassium hydroxide will react any CO2 gas and form potassium carbonate (a solid) and liquid water. As a result, production of CO2 gas will cause a proportional decrease in the volume of gas in the sealed chamber. This will be detected by the movement of liquid in glass tubing. The manipulated variable the status of the pea seeds (germinating or non- germinating) and the responding variable is the rate of production of CO2. Controlled variables include the size of the test- tube and glass tube, the number of pea seeds, the number of KOH pellets, the time, and the temperature.
Materials pea seeds (dry and pre-soaked) water paper towels nonabsorbent cotton laboratory scoop or forceps potassium hydroxide pellets (KOH) petroleum jelly liquid food colouring tape safety goggles laboratory apron 2 straight glass tubes 2 bent glass tubes 2 two-hole test-tube stoppers 2 large test tubes 2 millimetre rulers 2 pinch clamps 2 pieces of rubber tubing 2 test-tube clamps 2 retort stands medicine dropper
Procedure 1. 30 dry pea seeds were placed in a large test tube and a layer of cotton was placed on top of the seeds. Using forceps or a scoop, approximately 30 KOH pellets were placed on top of the cotton. 2. A respirometer was assembled as shown in Figure 1. A millimetre ruler was attached to the end of the bent glass tubing, using tape. All stopper openings were sealed with petroleum jelly. 3. Steps 1 and 2 were repeated with 30 pre-soaked, germinating pea seeds. 4. Both respirometers were allowed to stand undisturbed for 5 min. 5. With the medicine dropper, a few drops of food colouring was added to the ends of the bent glass tubing. 6. A pinch clamp was added to the rubber tubing on each respirometer and closed. The time at which the pinch clamps were closed and the position of the food colouring were noted. 7. The movement of the food colouring in each respirometer was recorded every minute for 15 min.
Evidence Students should include a table with the initial time at which the pinch clamp was closed, and then data at equal time-points (usually 1 min intervals) and the corresponding measurement of the food dye in the class tubing (distance from the open end of the tube). Data for both the germinating and non-germinating seeds may be included on one table or on two separate tables. (b) The food colouring will move toward the test tube. (c) The ruler is used to measure, indirectly, the rate of carbon dioxide production in terms of distance (mm). (d) The cotton is used to protect the seeds from the caustic KOH pellets.
Analysis (g) The respirometer works by showing the consumption of air (oxygen) by monitoring the movement of food colouring. Respiration uses oxygen and produces carbon dioxide and water, the oxygen and carbon dioxide are gaseous. The carbon dioxide is removed by KOH so that it cannot influence the oxygen volumes in the apparatus. As oxygen gas is used, a partial vacuum is created in the test tube. External air pressure pushes the coloured water toward the test tube. By timing the movement of the coloured water, a relative rate of oxygen consumption can be established. (h) The openings are sealed to allow for only the oxygen inside the respirometer to be used to show the movement of food colouring and thus the use of oxygen. (i) Cellular respiration (j) The graph will vary with the data. It should be an upward diagonal straight line.
(k) Sample calculation: Germinating Seeds Oxygen Consumption = total distance traveled / total time = 10 mm/10 min = 1 mL Nongerminating (Dry) Seeds Oxygen Consumption = total distance traveled / total time = 4 mm/10 min = 0.4 mL (l) The rate of oxygen consumption was much higher in the germinating pea seeds.
Evaluation (m) The prediction is seen to be accurate. The rate of oxygen consumption in the germinating seed is 2.5 times that of the nongerminating seed. (n)The germinating seed will consume more oxygen than the nongerminating seed. This occurs because germinating seeds are growing and use more energy to do this. The energy comes from cellular respiration and oxygen is a reactant in the process. (o) If KOH had not been added, the level of air in the respirometer would have remained the same. As oxygen was used, carbon dioxide would have been produced and the food colouring would not have moved. (p) Photosynthesis. The peas are not photosynthesizing. Only leaves and to a certain degree stems are involved in photosynthesis. (q) The seeds themselves contain starch and other sugars that can be converted into glucose needed for cellular respiration.
Synthesis (r) If seeds are too wet, there may not be enough oxygen to perform cellular respiration. In wet soil, there may not be enough dissolved oxygen and this will prevent cellular respiration from occurring and therefore the energy needed to grow will not be available. In addition, if seeds are too wet they may rot. (s) Begin by setting up a number of designs similar to that used in this experiment. Separate the seeds into a number of categories. Assign a minimum temperature to each group. Use a difference of 10 °C to separate the different groups. Keep each packet of seeds at the given temperature for 30 min. Record the oxygen consumed by each group.
Section 8.3 Questions (Page 53) 1. Adenosine diphosphate (ADP) has two inorganic phosphate groups attached to an adenosine molecule, whereas adenosine triphosphate (ATP) has three inorganic phosphate groups attached to an adenosine molecule. The ATP molecule has 31 kJ/mol more potential energy than ADP due to the third phosphate bond. 2. Heart muscle cells have the most mitochondria, as they require the most energy to contract (approximately 70 times per minute). Nerve cells have the second most mitochondria, as they need to maintain the membrane potential necessary to conduct a nerve impulse. Skin cells are next, as their functions require little energy, followed by fat cells, which provide insulate and nutrient storage for the body and therefore contain few mitochondia.. 3 (a) Glycolysis occurs in the cytoplasm of eukaryotic organisms. (b) The two products of glycolysis that enter the mitochondria are pyruvate and NADH. 4. Mitochondrial membranes perform several vital roles in energy metabolism. The outer membrane of the mitrochondria acts as a cell membrane and houses transport proteins that allow substances in and out of the mitochondria. For instance, the outer membrane houses transport proteins, which move the two pyruvate molecules formed during glycolysis from the cytoplasm into the mitrochondria, where they undergo pyruvate oxidation before entering the Krebs cycle. The inner membrane of mitrochondria serves several functions. It divides the mitochondrion into two compartments: the matrix and the intermembrane space. Both of these areas play important roles in energy metabolism. For instance, the matrix is where most of the Krebs cycle reactions take place and the intermembrane space is where protons are pumped as they are produced by the electron transport chain. These protons are used to create the electrochemical gradient that stores free energy, which is necessary to create ATP. The inner membrane of a mitochondria also houses the numerous proteins and cofactors required ultimately to generate ATP. NADH hydrogenase, cytochrome b-c1 complex, cytochrome oxidase complex, and ATP synthase are all found in the inner mitochondrial membrane. 5. The function of NAD+ and FAD in cellular respiration is to act as coenzymes that harvest energy from the reactions of glycolysis, pyruvate oxidation, and the Krebs cycle and carry it to power ATP synthesis by oxidative phosphorylation. NAD+ removes two hydrogen atoms from a part of the original glucose molecule. Two electrons and one proton attach to NAD+, reducing it to NADH (NAD+ is the oxidized form of NADH). This reduction occurs during glycolysis, pyruvate oxidation, and the Krebs cycle. FAD functions in a similar manner to NAD+. FAD is reduced by two hydrogen atoms from the original glucose molecule to FADH2. This is done during the Krebs cycle. These reductions are energy harvesting and will transfer their free energy to ATP molecules. Reduced NAD+ and FAD move free energy from one place to another and from one molecule to another. 6. The final products of cellular respiration are 6 CO2, 6 H2O, and 36 ATP. 7. Glycolysis is not considered a highly effective energy-harnessing mechanism, because it only transfers about 2.1% of the free energy available in one mol of glucose into ATP. Most of the energy is still trapped in two pyruvate molecules and two NADH molecules. Aerobic respiration further processes the pyruvate and NADH during pyruvate oxidation, the Krebs cycle, chemiosmosis, and electron transport. During pyruvate oxidation, the pyruvate and NADH are transformed into two molecules each of acetyl-CoA, hydrogen, carbon dioxide, and NADH. Acetyl-CoA enters the Krebs cycle and increases ATP production. By the end of the Krebs cycle, the entire original glucose molecule is consumed. It has been transformed into six CO2 molecules, which are released as waste, and energy, which is stored as four ATP molecules and 12 reduced coenzymes (NADH and FADH2). Most of the free energy stored in NADH and FADH2 will be transformed to ATP in the final stage of aerobic respiration, chemiosmosis, and electron transport. By the end of aerobic respiration, all the energy available in glucose has been harnessed. 8. After glycolysis, pyruvate oxidation, and the Krebs cycle, the rest of the energy not captured in the form of ATP is stored as FADH2 and NADH. 9 (a) The hydrogens (b) The electron transport chain creates a proton gradient by pumping electrons from the matrix to the inner membrane. The membrane becomes impermeable to protons due to their high concentration and forces the protons to move through proton channels to form ATP. (c) The potential energy stored in this gradient causes the protons to move through special protein channels and the energy released is used to form ATP. (d) This process is termed chemiosmosis or oxidative phosphorylation. (e) Chemiosmosis was discovered by Peter Mitchell in 1961. 10. (a) An electron carrier is a molecule that can accept and donate electrons from and to various enzymes. An terminal electron acceptor is the final substance that receives electrons in an oxidation-reduction reaction. (b) The final electron acceptor in aerobic respiration is oxygen. 11. The equation does not show the formation of energy. It also does not include the fact that water is required on the reactant side of the equation. 12. CO2 cannot serve as a source of free energy because the carbon atoms are fully oxidized; there are no H atoms bonded to any of the C valence electron positions. Thus, its chemical potential energy is 0 kJ/mole. The bond in ATP is easy to break and releases abundant energy.
Mini Investigation : Facultative Microbes (Page 56) (a) Initial conditions were aerobic. (b) Yeast is an anaerobic organism. (c) Carbon dioxide is produced and oxygen is consumed. the balloon would swell as carbon dioxide is produced. (d) Carbon dioxide is produced and would cause the balloon to swell. (e) In aerobic respiration, there will be more CO2 produced than in anaerobic fermentation. However, oxygen will be consumed in the process of aerobic respiration while it is not in aerobic respiration. the size of the balloon will get larger when anaerobic respiration is occurring. (f) The smell of yeast is greater as is the smell of ethanol. (g) Aerobic conditions could be maintained by not mixing the solution, providing a larger container with more air, or by leaving the flask open.
Explore an Issue: Aerobic versus Anaerobic Waste Treatment (Page 58) 1. Oxygen can be provided through aeration of the soil or water, or simply mixing the water to allow air to be dissolved. 2. Sewage processing uses mostly aerobic bacteria. This requires oxygen levels to remain high during the processing of organic waste. If the oxygen level drops too low, aerobic respiration will stop and the conversion of these wastes will slow. 3. Anaerobic processing is cheaper as there is no need to incorporate oxygen into the system. It is, however, a slower process. Ethanol production occurs during the anaerobic process and holds great value as an energy source. 4. The main source of ethanol is biomass and other wastes. Ethanol added to gasoline increases the fuel efficiency, decreases pollutants such as carbon dioxide, and decreases the reliance on non renewable resources such as oil for the production of gasoline.
Lab Exercise 8.A: Estimating VO2 max (Page 61)
Evidence Results for a typical female student
Analysis Sample Calculation VO2 max = 132.8530 – 0.1696(51) – 0.3877(14) + 6.3150(0) – 3.2649(19) – 0.1565(110) VO2 max = 132.8530 – 8.6496 – 5.4278 + 0 – 62.0331 – 17.215 VO2 max = 39.528 mL/kg/min
Evaluation (b) Students should compare their calculated value to the values found in Tables 2 and 3 on page 60 of the Student Book.
In this example, based on the VO2 max charts, 39.528 mL/kg/min is in the excellent range, meaning that the student possesses excellent cardiorespiratory (aerobic) fitness. (c) VO2 max can be influenced by a number of other factors including health, smoking, and other physiological factors. Some of the sources of error may include maintaining the same maximum pace throughout the experiment. If this is not maintained, the max level may not be reached. This could be changed by having the experiment performed on a treadmill where the subject would have to keep up to the pace set by the machine. (d) Males have a greater VO2 max due to a number of factors including muscle mass composition and proportion. This would require a greater amount of ATP and therefore a higher VO2 max requirement.
Mini Investigation: Metabolic Poisons (Page 63) (a) Cyanide and hydrogen sulfide prevent oxygen from bonding. This stops the process of cellular respiration after glycolysis is completed. (b) They interfere with oxygen. (c) Hydrogen sulfide acts as a vasodilator and is used by the brain in forming short term memory. Cyanide is used in the production of plastics and other chemicals and in mining. (d) Hydrogen sulfide can be produced naturally. It is found in the mouth (causing bad breath) and by some cells in the body. It is also formed during volcanic eruptions. Certain bacteria and fungi produce cyanide as do some plants and fruits (almonds contain cyanide) (e) Hydrogen sulfide is produced during industrial processes such as food processing, sewage treatment, paper mills, tanneries, and petroleum refineries. Cyanide in the environment is produced as a byproduct of ore refining and industrial processing. (f) Human health is affected based on the amount of either chemical someone comes into contact with. Hydrogen sulfide can be lethal in a single breath because it halts the process of cellular respiration. The inhalation or ingestion of cyanide has a similar effect. (g) The levels of these compounds are difficult to reduce once they are in the environment. Governments have imposed bans on their use in certain countries, and fines are given to companies who fail to comply. Sulfur reducing bacteria have shown to be effective in cleaning up areas contaminated with hydrogen sulfide.
Section 8.4 Questions (Page 64) 1. Two differences in aerobic respiration and fermentation are: • aerobic respiration yields 36 ATP molecules per glucose molecule whereas fermentation yields 2 ATP molecules per glucose molecule • aerobic respiration produces water and carbon dioxide whereas fermentation produces ethanol or lactic acid. 2. Anaerobic respiration can occur with or without oxygen. This is beneficial to organisms in low oxygen environment such as in the soil, aquatic systems, and the human digestive system. 3. The student will feel soreness in her chest and legs due to the build up of lactic acid in her muscle tissues. This build-up of lactic acid occurs because she has a low VO2 max as a result of the longer low-level running that she usually does. 4. A non-alcoholic fermentation product is carbon dioxide. 5. The final products of alcohol fermentation are ATP, carbon dioxide, and ethanol. The final products of lactic acid fermentation are ATP and lactate. 6. (a) Two molecules of ethanol are produced for every molecule of glucose in alcoholic fermentation. (b) Two molecules of carbon dioxide are produced during alcoholic fermentation, while lactic acid fermentation produces no carbon dioxide. (c) Fermentation is an anaerobic process and does not require oxygen. 7. Alcohol fermentation is carried out by yeast and by plant roots when they are submerged. 8. Fermentation is used to produce alcoholic beverages, bread, and certain types of cheese. 9. Both types of respiration can be used in waste treatment. Aerobic respiration is quick but expensive. Anaerobic respiration takes longer, but is inexpensive and is capable of removing toxic properties from the waste that aerobic respiration can not. 10. The presence of lactic acid in the muscle tissues leads to stiffness, soreness, and fatigue. 11. Maximum oxygen consumption, VO2 max, is a measure of a body’s capacity to generate the energy required for physical activity. It is the maximum volume of oxygen that the cells of the body can remove from the bloodstream in one minute per kilogram of body mass while the body experiences maximal exertion. 12. VO2 max generally decreases with age. Since VO2 max is expressed in terms of body weight (mass), an increase in weight can result in a decrease in VO2 max. 13. VO2 max values are not perfectly correlated with overall athletic performance because of differences in mental attitude, running efficiency, and the amount of lactate produced during exercise. 14. (a) The lactate threshold is 3.0 mmol/L. (b) This value refers to a threshold. Below this level, an individual can sustain exercise for long periods; above the threshold, an individual cannot sustain exercise for long periods. Once the body passes the lactate threshold, the concentration of lactate in the blood increases sharply, causing pain, muscle stiffness, and fatigue. 15. (a) Student answers may vary depending on their research. Some possible advantages and disadvantages of gasohol include the following: Advantages of Gasohol • It burns more slowly, coolly, and completely than gasoline, thereby reducing emissions of some pollutants. • It aids the agricultural economy. Gasohol is made of gasoline and ethanol. The ethanol is produced from corn, so the demand for corn would be high, aiding the agricultural economy. • It would replace gasoline imports from other countries. • Alcohol mixes easily with water and prevents ice formation in cold weather. Alcohol has a higher octane rating than gasoline, resulting in better engine performance. Disadvantages of Gasohol • Gasohol is very expensive and energy intensive to produce. • It can damage rubber seals and diaphragms and can damage some paint finishes. • Gasohol vaporizes more easily than gasoline and can aggravate ozone pollution during warm weather. • It has a lower energy content than gasoline. • It is hard to use during cold weather – it needs chemical additives to run a car in winter. • Ethanol has relatively low volatility. In hot weather, the fuel vaporizes easily resulting in fuel boiling in the distribution lines. This can make the engine run rough or even prevent it form running altogether. (b) Currently, only one major fuel company in Canada supplies fuel containing alcohol. Competition between conventional fuels such as gasoline and diesel and alternatives like alcohol will ultimately determine the role of alcohol as a transportation fuel in Canada. One of the most important factors regarding the use of alcohol as a fuel in Canada will be our ability to produce it at a cost that makes it economically attractive in comparison with the common fuels. 16. Alcoholic fermentation was most likely discovered when a plant product was inadvertently left to rot in an environment free of oxygen. The resultant liquid mixture was consumed and the effect discovered. 17. (a) The lactate threshold is the point where lactate begins to accumulate in the bloodstream. While running at a comfortable pace, the lactate generated is easily removed and doesn’t build up in the muscles. As the pace increases, eventually a point is reached where the anaerobic production of lactate is greater than its removal, resulting in a build- up of lactate in muscle – the lactate threshold is reached. Lactate build-up causes muscle fatigue and pain. Long- distance athletes learn to identify signs of lactate build-up and train to run at a pace that keeps their blood lactate levels just below the threshold to avoid the negative effects of lactate build-up. (b) Blood doping is the intravenous infusion of blood (red blood cells) to increase a person’s blood oxygen-carrying capacity, increasing ATP production and decreasing lactic acid build-up. This is done to increase athletic performance; however, a large infusion of red blood cells could increase blood viscosity. This may result in a decrease in cardiac output, blood flow velocity, and reduced peripheral oxygen content – all of which would reduce aerobic capacity and a decrease in performance. Other potential dangers include blood clotting, heart failure, bacterial infections, and embolisms. Diseases such as hepatitis and AIDS may be contracted from the infusion process. 18. Before the introduction of the horse in North America, Aboriginal people hunted by chasing after buffalo and other animals. This would have increased their VO2 max and their lactic acid threshold. This would have likely matched them with some of today’s top distance runners.
Make a Summary (Page 67) 1. Student answers will vary. Ensure that all processes of cellular respiration are completely covered and that the yields of each process are correct. The overall look of the poster could look similar to Figure 2 on page 46 of the Student Book. 2. Students’ responses to the Starting Point questions should show greater understanding of the concepts than at the start of the chapter, and they should be able to describe any misconceptions that they have since revised.
CHAPTER 8 REVIEW (Pages 68-69)
Part 1 1. C 2. B 3. B 4. C 5. B
Part 2 6. (a) The net gain in ATP after one molecule of glucose undergoes cellular respiration is 36 ATP. (b) The net gain in ATP after one molecule of glucose undergoes alcoholic fermentation is 2 ATP. 7. i. Glycolysis occurs in the cytoplasm ii. Pyruvate oxidation occurs in the mitochondrial matrix. iii. Krebs Cycle occurs in the mitochondrial matrix. iv. The electron transport chain and chemiosmosis occur in the inner membrane of the mitochondria. 8. Yeast cells produce ATP from glucose by alcoholic fermentation. NADH passes its hydrogen atoms to acetylaldehyde, which is formed when a carbon dioxide molecule is removed from pyruvate using pyruvate decarboxylase. This produces ATP, ethanol, and carbon dioxide. 9. Lactic acid is more likely to accumulate. 10. Walking breaks would allow lactic acid to be transported to the liver where it is converted into pyruvate and continue through the process of aerobic respiration. 11. It is essential that muscle cells continue to convert pyruvate to lactate or else the muscle cells would cease to contract and the cells would die. 12. Test tube A contains aerobic yeast. You can identify it because it has a faster growth rate as a result of higher ATP production. 13. Seal the test tubes and observe the effect of decreased oxygen on yeast growth. 14.
15. The runner’s resting VO2 max is 15 mL/kg/min. 16. The runner’s oxygen consumption is 1125 mL/min (15 mL/kg/min x 75 kg) at rest and 6750 mL/min (90 mL/kg/min x 75 kg) during his highest VO2 max. 17. During the first 60 minutes, the runner’s body is acclimating to the exercise. From 60 minutes to 150 minutes, his body is unable to keep up a high VO2 max and plateaus at 65 mL/kg/min. After 150 minutes until the end of the race, his body slowly lowers its VO2 max. 18. The oxygen consumption after the race will still be high due to oxygen debt. The excess oxygen requirement will be made by the liver to convert the lactate into pyruvate using oxygen. This will only occur after the muscles requirements for oxygen are met.
Unit 20 C Performance Task: Student Aquarist (Pages 70-71) Please note that what follows is an example of a performance task. Student results will vary depending on the condition on which the student focuses.
Purpose To determine how temperature, light conditions, pH, dissolved ammonia, dissolved oxygen, and dissolved carbon dioxide affect the metabolic health of plants, fish, and snails in a freshwater ecosystem
Problem How do temperature, light conditions, pH, dissolved ammonia, dissolved oxygen, and dissolved carbon dioxide affect the metabolic health of plants, fish, and snails in a freshwater ecosystem? (Students will focus on just one). Hypotheses/Predictions (a)
Experimental Design (b) If plants lose their green colour and start to turn brown, perform the following experiment: Increase light intensity by exposing the aquarium to a brighter light source for a specified time, without increasing the temperature of the water. To accomplish this, a “white light” spotlight can be used, with a heat shield between the light bulb and the aquarium. An effective shield is a large beaker or small aquarium of water placed between the light source and the aquarium. An electric timer can be used to control the duration of light exposure. To experimentally control the duration of exposure, the aquarium should be exposed to the brighter light for the same period that it was previously exposed to the dimmer light. All other variables should be unchanged. The manipulated variation is light intensity, and the responding variable is the colour of the plants.
Materials 10 L aquarium tank or fish bowl tap water thermometer wide-range pH paper and colour chart or pH test kit aquarium gravel water quality test kits for O2(aq), CO2(aq), and NH3(aq) water plants (Elodea or Anacharis) 1 or 2 guppies 1 small- to medium-sized snail aquarium heater (if required) fish food (if required) other materials as required
Procedure Student procedures will vary.
Evidence (c) The data will vary depending on aquarium conditions.
Analysis (d) • Most natural water is slightly acidic. Therefore, most aquatic plants and animals can tolerate pH values between 5.8 and 7.5. • Plants and animals require approximately 5 mg/L to 7 mg/L of dissolved oxygen to remain healthy. • Plants require approximately 10 mg/L to 30 mg/L of dissolved CO2 to remain healthy and grow. Low CO2 concentrations will negatively affect plants by impeding photosynthesis. High CO2 concentrations will negatively affect the health of fish and other animals in the aquarium. • Ammonia, a toxic nitrogenous waste, is normally converted to poisonous nitrite, the harmless nitrate by bacteria in the aquarium. The bacteria use oxygen in carrying out this process. If oxygen concentrations are low, or if there are too many animals producing nitrogenous wastes (or too few bacteria growing in the aquarium), then ammonia and nitrite will accumulate, causing animals, and possibly plants, to die.
Evaluation (e) Answers will vary. (f) Answers will vary. Synthesis (g) Aquariums are artificial ecosystems. The glass walls keep biotic and abiotic components relatively concentrated. Artificial filtration systems are needed to make up for the lack of sufficient natural systems. Aquarium filters remove suspended matter like loose pieces of plant material and decaying matter from the water. Bacterial colonies in the filter convert waste products, such as ammonia, and organic matter into substances that do not harm the animals or plants. (h) Ammonia is produced in protein catabolism in animals and is excreted as waste. Bacteria convert ammonia into harmless nitrite. (i) Oxygen is produced by plants through photosynthesis and dissolves into the water from the air. Carbon dioxide is produced by animals and plants as a waste product of cellular respiration. The CO2 /O2 equilibrium is maintained by having aquarium water exposed to air and by having a suitable animal to plant ratio in the aquarium. (j) No. An aquarium with plants in it needs an external source of light energy to power photosynthesis and thus provide food for animals and plants. It also needs an external source of heat to maintain temperature conditions that support the reactions of life.
Unit 20 C REVIEW (Pages 72-73)
Part 1 1. C 2. D 3. B 4. B 5. C 6. C 7. C 8. D Part 2 9. During the light reactions of photosynthesis, light energy is absorbed by photosynthetic pigments and then transferred to the electron carrier, NADPH, and ATP is synthesized because of the build-up of a proton gradient, driven by the splitting of water molecules. 10. The equations of photosynthesis and aerobic respiration are the reverse of each other. The difference is the energy involved. Solar energy is the type used in photosynthesis. ATP is the energy produced in cellular respiration. 11. In brown fat, because the inner membrane is permeable to hydrogen, more ATP can be produced. Protons can pass through special membrane proteins responsible for the formation of ATP when the potential energy is released. 12. Since more ATP is produced, a higher metabolic rate will be achieved resulting in more energy being released in the form of heat. 13. The deaths might have occurred either because these people used up their energy reserves and overheated or from dehydration due to increased metabolic activity. 14. (a) When there is not enough oxygen in a muscle cell to support the electron transport chain, lactic acid is produced in the muscle cells. This causes fatigue and muscle cramping. (b) Deep breathing repays the oxygen debt created due to a lack of oxygen in the tissue. This allows time for the liver to convert lactic acid into pyruvate that can re-enter the Krebs cycle. 15. (a) Only 5% of the energy that hits a leaf is available for photosynthesis because 60% is lost in the atmosphere, 19% is used to drive metabolism, 8% is reflected or transmitted, and 8% is radiated as heat. (b) A biological engineer would try to design a plant to reduce reflection, transmission, and radiation, all of which reduce the energy available to plants. The more energy that plants could capture, the greater the rate of photosynthetic activity. 16. Photosynthesis produces oxygen gas. 17. Cellular respiration consumes oxygen gas. 18. Glucose would be accumulating in the ecosystem, and carbon dioxide gas would be decreasing in the atmosphere. 19. The total biomass would increase over time. 20. No, this could no continue indefinitely because there is limited space for this matter to be stored. Also, there are limited resources available. 21. Forest fire, disease, drought, changes in abiotic conditions. 22. Deforestation and burning fossil fuels adds carbon dioxide to the atmosphere and is thought to be involved in climate change. By understanding the effect plants have on maintaining a balance in the level of carbon dioxide in our atmosphere, scientists will be able to develop strategies to attempt to combat climate change.