C1.2 Cell Respiration (IB SL + HL) - Learning Outcomes
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What is ATP and why is it a cellular energy currency?
A: ATP = adenosine triphosphate (adenine + ribose + 3 phosphate groups). High-energy phosphate bonds release energy during ATP hydrolysis → powers cellular processes. Keywords: ATP, hydrolysis, ADP + Pi, energy currency.
Link ATP structure to its function.
3 phosphates → high chemical potential energy; hydrolysis drives endergonic reactions; small, soluble, rapidly recycled. Keywords: high-energy phosphate, endergonic, reversible, phosphorylation.
What life processes require ATP? (IB-required examples)
Active transport (Na⁺/K⁺ pump), muscle contraction, DNA replication, cell division, protein synthesis, and vesicle transport (exocytosis). Keywords: active transport, biosynthesis, mitosis, motor proteins.
Describe ATP ↔ ADP energy transfers.
ATP hydrolysis → releases energy; ADP phosphorylation (using energy from respiration) → stores energy. Keywords: hydrolysis, phosphorylation, ATP/ADP cycle.
Distinguish gas exchange from cell respiration.
Gas exchange: Diffusion of O₂ in / CO₂ out of an organism. Cell respiration: Chemical reactions in cells releasing energy (ATP) from organic molecules. Keywords: diffusion, mitochondria, metabolic pathway.
Reactants and products of aerobic respiration.
Glucose + O₂ → CO₂ + H₂O + ATP. Keywords: oxidation, final electron acceptor, ATP yield.
Compare anaerobic and aerobic respiration using word equations.
Aerobic: glucose + oxygen → carbon dioxide + water + ATP Anaerobic (humans): glucose → lactate + small amount of ATP Anaerobic (yeast): glucose → ethanol + CO₂ + small amount of ATP Keywords: lactate, ethanol, CO₂ release.
Advantages of anaerobic respiration.
Rapid ATP production when O₂ is low; allows intense exercise in muscle cells. Real-world: Humans during sprinting; yeast in bread and alcohol production. Keywords: NAD⁺ regeneration, limited ATP.
Variables affecting rate of respiration.
Temperature, substrate concentration, organism type, oxygen availability. Keywords: controlled variables, rate calculation.
How to calculate respiration rate from raw/secondary data.
Measure CO₂ production or O₂ consumption per unit time; use slope of graph (Δy/Δt). Keywords: rate, respirometer, CO₂/O₂ change.
Explain the role of NAD in cell respiration.
NAD is an electron (H) carrier. It is reduced to NADH + H⁺ in glycolysis, link, and Krebs; it delivers high-energy electrons to the ETC for ATP production. Keywords: reduction, NADH, electron carrier, oxidation–reduction.
Key steps of glycolysis (IB-required simplified pathway)
Phosphorylation of glucose (uses 2 ATP). Lysis → splits into two triose phosphates. Oxidation → NADH produced. ATP produced by substrate-level phosphorylation. Net: 2 ATP + 2 NADH + 2 pyruvate. Keywords: phosphorylation, lysis, oxidation, substrate-level ATP.
How pyruvate → lactate in anaerobic respiration (humans).
Pyruvate is reduced by NADH → lactate; NAD⁺ is regenerated so glycolysis continues. Keywords: lactate dehydrogenase, NAD⁺ regeneration.
Why NAD regeneration is essential in anaerobic respiration.
Without NAD⁺, glycolysis stops, stopping ATP production; regeneration keeps minimal ATP production going. Keywords: NAD⁺, glycolysis continuation.
Elaborate on pyruvate oxidation (link reaction).
In matrix: Pyruvate decarboxylated → CO₂ Oxidized → NADH Combines with CoA → acetyl-CoA Keywords: decarboxylation, oxidation, acetyl-CoA.
Key events of the Krebs cycle (HL required level).
Acetyl-CoA + oxaloacetate → citrate Decarboxylation → 2 CO₂ Oxidation → 3 NADH + 1 FADH₂ Substrate-level phosphorylation → 1 ATP Per glucose: double these values. Keywords: NADH, FADH₂, CO₂, substrate-level ATP.
How does the ETC create a proton gradient?
Complexes I, III, and IV pump H⁺ into the intermembrane space, creating proton motive force. Keywords: proton pump, electrochemical gradient.
Explain how energy is transferred in the ETC.
NADH/FADH₂ donate electrons; electrons pass through Complex I–IV, losing energy; energy used to pump H⁺ into intermembrane space. Keywords: redox reactions, electron flow, complexes.
Describe chemiosmosis and ATP synthesis.
H⁺ flows down gradient through ATP synthase; energy drives ADP + Pi → ATP. Keywords: ATP synthase, proton flow, oxidative phosphorylation.
Why does respiration need oxygen?
O₂ accepts electrons + protons → H₂O; keeps ETC functioning; without O₂, electron carriers stay reduced and ATP production stops. Keywords: terminal electron acceptor, water formation.
Compare lipids and carbohydrates as respiratory substrates.
Lipids: higher energy density; β-oxidation → lots of acetyl-CoA; more NADH/FADH₂ → more ATP. Carbohydrates: quicker to metabolize; used first. Keywords: β-oxidation, energy yield, rapid mobilization.