Cellular Respiration Process Quiz (C3)

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.