Cellular Respiration and Energy Acquisition: Study Guide Notes

Cellular Respiration: Obtaining Energy from Food

Key Terms and Definitions

This section defines essential terms related to cellular respiration, metabolism, and energy acquisition in biological systems.

• Slow-twitch muscle fibers: Muscle fibers specialized for endurance and prolonged activity; rely primarily on aerobic respiration.

• Fast-twitch muscle fibers: Muscle fibers adapted for rapid, powerful contractions; rely more on anaerobic respiration.

• Aerobic: Processes that require oxygen.

• Anaerobic: Processes that occur without oxygen.

• Photosynthesis: The process by which autotrophs convert light energy, water, and carbon dioxide into glucose and oxygen.

• Autotroph: Organisms that produce their own food from inorganic substances (e.g., plants, algae).

• Producer: Synonymous with autotroph; forms the base of the food chain.

• Heterotroph: Organisms that obtain energy by consuming other organisms.

• Consumer: Synonymous with heterotroph; relies on producers or other consumers for energy.

• Cellular respiration: The metabolic process by which cells extract energy from glucose and other molecules, producing ATP.

• Redox reaction: Chemical reactions involving the transfer of electrons between substances (reduction and oxidation).

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• NADH: Reduced form of nicotinamide adenine dinucleotide; an electron carrier in cellular respiration.

• FADH2: Reduced form of flavin adenine dinucleotide; another electron carrier.

• Electron transport chain: Series of protein complexes in the mitochondrial membrane that transfer electrons and produce ATP.

• Glycolysis: The first stage of cellular respiration; breaks down glucose into pyruvic acid.

• Citric acid cycle: Also known as the Krebs cycle; completes the breakdown of glucose, producing electron carriers.

• ATP synthase: Enzyme that synthesizes ATP from ADP and inorganic phosphate, powered by a proton gradient.

• Oxidative phosphorylation: Production of ATP using energy derived from the electron transport chain.

• Fermentation: Anaerobic process that allows glycolysis to continue by regenerating NAD+.

• Lactic acid: Product of lactic acid fermentation in animal cells.

• Ethyl alcohol: Product of alcoholic fermentation in yeast and some bacteria.

• Metabolism: All chemical reactions occurring within a living organism.

• Metabolic pathway: A series of chemical reactions that build up or break down molecules in a cell.

• Glucose: A six-carbon sugar; primary fuel for cellular respiration.

• Pyruvic acid: Three-carbon compound produced by glycolysis.

• Acetic acid: Two-carbon compound; intermediate in cellular respiration.

• Coenzyme A: Carrier molecule that transfers acyl groups in metabolism.

• Acetyl Coenzyme A: Compound formed from pyruvate and Coenzyme A; enters the citric acid cycle.

• Diabetes: Disease characterized by impaired regulation of blood glucose.

• Insulin: Hormone that regulates blood glucose levels.

Photosynthesis and Cellular Respiration

Photosynthesis: Reactants, Products, and Purpose

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Reactants: Carbon dioxide (CO2), water (H2O), and light energy

• Products: Glucose (C6H12O6) and oxygen (O2)

• Main purpose: To produce glucose for energy storage and metabolic processes

• Primary product: Glucose

• By-product: Oxygen

Equation:

$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Aerobic Cellular Respiration: Reactants and Products

Aerobic cellular respiration is the process by which cells extract energy from glucose in the presence of oxygen.

• Reactants: Glucose (C6H12O6) and oxygen (O2)

• Products: Carbon dioxide (CO2), water (H2O), and ATP (energy)

Equation:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

Relationship Between Photosynthesis and Cellular Respiration

Photosynthesis and cellular respiration are complementary processes in the global carbon and energy cycles.

• Photosynthesis stores energy in glucose molecules, while cellular respiration releases that energy for cellular work.

• The products of photosynthesis (glucose and oxygen) are the reactants for cellular respiration, and vice versa.

Organisms Performing Photosynthesis and Respiration

• Both photosynthesis and respiration: Plants, algae, and some protists

• Only cellular respiration: Animals, fungi, most bacteria, and non-photosynthetic protists

Breathing and Cellular Respiration

Breathing supplies oxygen to cells and removes carbon dioxide, supporting cellular respiration.

• Oxygen inhaled is used as the final electron acceptor in the electron transport chain.

• Carbon dioxide produced during cellular respiration is exhaled as a waste product.

ATP Yield from Glucose

Each molecule of glucose can produce a significant amount of ATP through aerobic respiration.

• Approximate ATP yield: 30–32 molecules of ATP per glucose molecule

Redox Reactions in Cellular Respiration

Oxidation and Reduction During Cellular Respiration

Cellular respiration involves a series of redox reactions, transferring electrons from glucose to oxygen.

Stage	Oxidized Molecule	Reduced Molecule
Glycolysis	Glucose	NAD+ (to NADH)
Citric Acid Cycle	Acetyl CoA	NAD+, FAD (to NADH, FADH2)
Electron Transport Chain	NADH, FADH2	O2 (to H2O)

Oxygen as an "Electron Grabber"

Oxygen is highly electronegative, making it an effective final electron acceptor in the electron transport chain.

• It "grabs" electrons at the end of the chain, allowing the process to continue and water to form.

"Falling" Electrons and Energy Release

Electrons "fall" from high-energy carriers (NADH, FADH2) to lower energy states as they move through the electron transport chain.

• This "fall" refers to the stepwise transfer of electrons to molecules with increasing electronegativity.

• As electrons move down the chain, energy is released and used to pump protons, creating a gradient for ATP synthesis.

Important event: The released energy is harnessed to produce ATP via oxidative phosphorylation.

Additional info:

• Fermentation allows ATP production in the absence of oxygen by regenerating NAD+, producing lactic acid or ethyl alcohol as by-products.

• Metabolic pathways are regulated by enzymes and can be anabolic (building molecules) or catabolic (breaking down molecules).