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Questions and Answers
What is produced during anaerobic respiration when oxygen is not available?
What is the main metabolic pathway for organisms to produce ATP in the absence of oxygen?
What happens to pyruvate when oxygen is available?
Which of the following is a by-product of ethanol fermentation?
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What molecule does Acetyl CoA bond with to enter the Krebs Cycle?
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What happens to lactate after oxygen becomes available again?
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In which conditions is lactate fermentation primarily utilized by muscles?
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What is the primary purpose of the Krebs Cycle?
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Which of the following molecules is produced as a by-product of the Krebs Cycle?
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Where does the majority of ATP production occur in cellular respiration?
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What is the role of oxygen in the Electron Transport Chain?
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Where does the Krebs Cycle take place within the cell?
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Which of the following processes is responsible for generating ATP in the Electron Transport Chain?
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What will happen to aerobic cellular respiration if oxygen is not present?
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Which molecule is generated as a by-product during the Electron Transport Chain?
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What is the primary purpose of cellular respiration?
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Where does cellular respiration occur within the cell?
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Which of the following products is produced during aerobic respiration?
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What is the main difference between aerobic and anaerobic respiration?
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What is the energy yield of aerobic respiration?
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What role does ATP play in cellular metabolism?
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What is a consequence of anaerobic respiration in animals?
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Which statement is true about fermentation?
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What is the primary purpose of glycolysis in cellular respiration?
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Which stage of aerobic respiration occurs outside the mitochondria?
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What is produced during glycolysis besides ATP?
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How many net ATP molecules are produced from glycolysis?
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What type of reaction is glycolysis classified as?
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What is the main reason cellular respiration is necessary for cells?
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Which of the following molecules is a direct product of glycolysis?
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What role does NAD+ play during glycolysis?
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Study Notes
Cellular Respiration
- Cellular respiration is the process by which plants and animals break down glucose (C6H12O6) to release energy.
- The chemical equation for cellular respiration is: C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l) + energy.
- Cellular respiration occurs in the mitochondria, a cellular organelle.
- Cellular respiration releases the energy stored in glucose molecules.
- Glucose is oxidized to CO2, releasing energy and producing water.
- Photosynthesis and cellular respiration are complementary processes.
- Photosynthesis needs light energy and water, while cellular respiration produces water.
- Photosynthesis produces glucose, while cellular respiration needs glucose.
- Photosynthesis occurs in the chloroplast, while cellular respiration occurs in the mitochondria.
Releasing Stored Energy
- Cellular respiration synthesizes ATP (adenosine triphosphate) from glucose, a form of energy usable by cells.
- Cellular respiration can occur with or without oxygen.
- Aerobic respiration occurs in organisms that live in oxygen-rich environments (oxic environments), such as fungi, bacteria, and plants.
- Anaerobic respiration occurs in organisms that live in oxygen-poor environments (anoxic environments), such as deep ocean producers and nitrogen-fixing bacteria.
- Fermentation is a modified form of anaerobic respiration, carried out by organisms like yeast and bacteria that cause milk to sour.
Aerobic vs Anaerobic Respiration
- Aerobic respiration requires oxygen while anaerobic respiration does not.
- Aerobic respiration yields high energy (36 ATP) whereas anaerobic respiration yields low energy (2 ATP).
- Aerobic respiration produces CO2 and H2O as products.
- Anaerobic respiration produces lactic acid in animals and ethanol and CO2 in yeast.
- Aerobic respiration takes place in both the cytoplasm and mitochondria.
- Anaerobic respiration takes place only in the cytoplasm.
- Aerobic respiration includes Glycolysis, the Krebs cycle, and the Electron Transport System.
- Anaerobic respiration includes Glycolysis and Fermentation.
Glucose
- All cells use energy from ATP molecules to meet their energy needs.
- ATP has a relatively low amount of energy per molecule.
- Carbohydrates are the most usable source of energy for cells.
- Molecules with a higher energy content are useful for:
- Long-term storage of chemical energy
- Bulk transportation of chemical energy
- Glucose (our blood sugar) has a high energy content and is small, highly soluble, and ideal for transportation within cells.
Aerobic Cellular Respiration
- Aerobic cellular respiration is an oxidation reaction where electrons are transferred from high-energy molecules like glucose and oxygen.
- It produces most of the energy in plants, animals, and most eukaryotic cells.
- The process starts with glycolysis, an anaerobic reaction in the cytoplasm.
Glycolysis
- Glycolysis is the first step of both aerobic and anaerobic cellular respiration.
- Its main purpose is to split glucose into two molecules of pyruvate through a series of reactions.
- Glycolysis does not require oxygen and takes place in the cytoplasm.
- It produces 4 ATP while consuming 2 ATP, resulting in a net production of 2 ATP.
- It produces 2 reduced NADH molecules.
Fate of Pyruvate
- Pyruvate can proceed through two possible pathways:
- If oxygen is available, pyruvate is transported from the cytoplasm into the mitochondria for aerobic cellular respiration.
- If oxygen is not available, pyruvate will proceed through fermentation for anaerobic cellular respiration.
Prep
- Before entering the Krebs cycle, pyruvate must lose one carbon atom in the form of CO2.
- The remaining two carbon atoms bind to Coenzyme A (CoA) to become Acetyl Coenzyme A (acetyl CoA).
- This reaction reduces another NAD+ molecule to NADH.
- Acetyl CoA enters the mitochondria to initiate the Krebs cycle.
Krebs Cycle
- The Krebs cycle, discovered by Sir Hans Adolf Krebs, produces more high-energy compounds (NADH and FADH2) for use in the Electron Transport Chain (ETC).
- It occurs in the mitochondrial matrix.
- Once acetyl CoA enters the mitochondria, it undergoes a series of reactions to generate:
- 3 molecules of NADH from NAD+
- 1 molecule of ATP from ADP
- 1 molecule of FADH2 from FAD
- These products are multiplied by two for an entire glucose molecule.
- CO2 is also released as a by-product.
Electron Transport Chain
- The majority of ATP is produced by the Electron Transport Chain (ETC), which takes place across the inner membrane of the mitochondria.
- ETC involves the passing of high-energy electrons (NADH and FADH2) from carrier to carrier.
- As electrons are passed down the chain, energy is released, which is used to pump hydrogen ions (H+) across the membrane from the matrix to the intermembrane space.
- This creates a concentration gradient, forcing H+ ions through ATP synthase, a membrane-embedded protein, generating ATP via the reduction of ADP.
- Oxygen is the final electron acceptor in the chain, accepting both electrons and H+ ions, resulting in the production of water as a byproduct.
Summary of Aerobic Cellular Respiration
- Aerobic cellular respiration involves three stages:
- Glycolysis
- Prep and the Krebs cycle
- Electron Transport Chain
- Pyruvate oxidation occurs in the mitochondria, producing 2 NADH and 2 CO2.
- The Krebs cycle occurs in the mitochondrial matrix.
- The ETC in the inner mitochondrial membrane transports electrons, producing an electrochemical gradient.
- Chemiosmosis: Protons (H+) move through ATP complexes embedded in the membrane, releasing free energy and causing ATP synthesis.
- Oxygen is the final electron acceptor in the ETC.
- Without oxygen, aerobic cellular respiration cannot take place.
Anaerobic Respiration
- When oxygen is unavailable (anoxic conditions), a different chemical acts as the final electron acceptor.
- Anaerobic respiration is less efficient than aerobic respiration and produces less ATP.
- Organisms living in such environments use inorganic chemicals like sulfate, nitrate, and CO2 as acceptors.
Fermentation
- Fermentation is a metabolic pathway producing ATP when organisms lack oxygen.
- It only produces ATP during glycolysis, making it less efficient than aerobic respiration.
- Many single-celled organisms carry out fermentation.
- There are two main types of fermentation:
- Lactate fermentation
- Ethanol fermentation
Lactate Fermentation
- Cells temporarily without oxygen carry out lactate fermentation.
- This occurs when energy demands exceed oxygen supply, creating an oxygen deficit.
- Cells convert pyruvate molecules from glycolysis to lactate/lactic acid molecules, using NADH as an energy source.
- Lactate is then started.
- When oxygen content increases, lactate is converted back to pyruvate, which continues in the Krebs cycle for the aerobic pathway.
- This is the fermentation our muscles use when they have limited access to oxygen; the buildup of lactic acid causes muscle cramps.
Ethanol Fermentation
- Some organisms function both aerobically and anaerobically.
- In anaerobic conditions, they carry out ethanol fermentation.
- It involves two steps:
- After glycolysis produces pyruvate, pyruvate is converted into a 2-carbon compound with the release of CO2.
- The 2-carbon molecule is then reduced by NADH to form ethanol.
- The byproduct of this fermentation is alcohol, a process utilized for manufacturing products like wine and beer.
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Description
Test your knowledge on the process of cellular respiration, including its stages, chemical equations, and its relationship with photosynthesis. This quiz will cover key concepts such as ATP synthesis and the role of mitochondria in energy production. Dive into the fascinating world of how organisms convert glucose to energy!
