Cellular Respiration (Answer)

Cellular Respiration-An Overview What are the phases of cellular respiration? Why? All cells need energy all the time, and their primary source of energy is ATP. The methods cells use to make ATP vary depending on the availability of oxygen and their biological make-up. In many cases the cells are in an oxygen-rich environment. For example, as you sit and read this sentence, you are breathing in oxygen, which is then carried throughout your body by red blood cells. But, some cells grow in envi-ronments without oxygen (yeast in wine-making or the bacteria that cause botulism in canned food), and occasionally animal cells must function without sufficient oxygen (as in running sprints). In this activity you will begin to look at the aerobic and anaerobic processes that are used by all organisms to produce ATP. Model 1 - Cellular Respiration Cell Membrane Cytoplasm Glucose 2. Pyruvate Glycolysis 2. ATP Link 2 CO 2 Acetyl CoA 4 CO 2 ATP 2. NADH 2 NADH 6 NADH 2 FADH CHO 60, 600, 6H₂O+ Energy 1. According to Model 1, what are the reactants of cellular respiration? Glucose and oxygen. 2. According to Model 1, what are the products of cellular respiration? Carbon dioxide, water, and ATP (or energy). 3. Cellular respiration occurs in four phases: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation. 4. Which phase of cellular respiration occurs in the cytoplasm of the cell? Glycolysis. b. Which phases of cellular respiration occur in the mitochondria? The link reaction, the Krebs cycle, and oxidative phosphorylation. 4. Which of the four phases of cellular respiration require oxygen? Oxidative phosphorylation. d. Which of the four phases of cellular respiration produce carbon dioxide? The link reaction and the Krebs cycle. e. Which of the four phases of cellular respiration produce water? Oxidative phosphorylation. 4. The goal of cellular respiration is to provide the cell with energy in the form of ATP. 4. Which of the four phases of cellular respiration result in the production of ATP? Glycolysis, the Krebs cycle, and oxidative phosphorylation. b. How many ATPs (total) are produced for every glucose molecule that undergoes cellular respiration? Each glucose molecule results in 38 ATPs being produced. c. What reactants of ATP must be available in the cell in order to produce ATP? In order to make ATP, the cell must have ADP and P available. d. Brainstorm several cellular processes for which energy or ATP is necessary. Answers will vary, but may include movement and muscle contraction, biochemical reactions, and growth and metabolism. Read This! Glucose, or any carbon-based molecule, can be burned in oxygen (oxidized) to produce carbon dioxide and water. Combustion reactions release large amounts of energy. However, the energy release is uncontrolled. An organism would not be able to handle all that energy at once to do the work of the cell. Cellular respiration is essentially the same reaction as combustion, but the oxidation of glucose occurs in several controlled steps. The same amount of energy is ultimately released, but it is gradually released in small, controlled amounts. High potential energy molecules of ATP are produced while the carbon atoms are used to form various other molecules of lower potential energy. Each of these steps is catalyzed by an enzyme specific to that step. Model 1 illustrates the ideal circumstances for cellular respiration. In some situations, however, one glucose molecule may not result in 38 ATP molecules being produced. 5. Consider Model 1. Besides ATP, what other molecules appear to be high potential energy molecules (free energy carriers) during cellular respiration? NADH and FADH Model 2 - Electron Acceptor Molecules 2e+ 2e+ 2e NAD+ FAD H+ 2H+ 20, + 2H+ NADH FADH, H₂O 6. Nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD) are coenzymes used in cellular respiration to transport high potential energy electrons to the electron transport chain (a step in oxidative phosphorylation) in the mitochondria. Ar the conclusion of cellular respiration, oxygen is the final electron acceptor. The reactions in Model 2 show these electron acceptors in the process of picking up an electron. 4. How many electrons are in a hydrogen ion (H+)? Zero. b. Is a hydrogen ion with its positive charge likely to be attracted to NAD+, FAD or O, without an input of free energy? Explain your reasoning. No, a positive hydrogen ion would only be attracted to a negatively charged particle. c. Consider the charges in the first reaction in Model 2. Can two positive particles combine to form a neutral particle? Explain your reasoning. No, if two positive particles combine, the resulting particle would have a +2 charge. 7. The reactions in Model 2 are missing very important particles-electrons. 4. What is the charge on an electron? Electrons have a negative charge. b. For each reaction in Model 2, predict the number of electrons that must be involved in the reaction to make the charges in the reaction balance. Two electrons are required to balance the +2 charge on the reactants side of the equation. c. Add electrons to each reaction in Model 2 on either the reactant or product side of the equation to complete the reactions. See Model 2. Read This! Oxidation is a loss of electrons. Reduction is a gain of electrons. The two processes must go hand-in-hand. In other words, electrons cannot be added to something from thin air, they must have been taken off of something first. 8. Are the reactions in Model 2 oxidation or reduction reactions? Electrons are being gained, so the reactions are reduction. 9. Which form of nicotinamide adenine dinucleotide is the "reduced" form, NAD+ or NADH? Explain your reasoning. NADH is the reduced form as it has the electrons that were gained in the process of reduction.