State where each of the four stages in aerobic respiration occurs in eukaryotic cells: glycolysis in the cytoplasm, link reaction in the mitochondrial matrix, Krebs cycle in the mitochondrial matrix, oxidative phosphorylation on the inner membrane of

Published by Patrick Mutisya · 14 days ago

Cambridge A-Level Biology 9700 – Respiration

Respiration

Learning Objective

State where each of the four stages in aerobic respiration occurs in eukaryotic cells:

  • Glycolysis – cytoplasm

  • Link reaction – mitochondrial matrix

  • Krebs cycle – mitochondrial matrix

  • Oxidative phosphorylation – inner membrane of mitochondria

Overview of the Four Stages

Aerobic respiration can be divided into four distinct stages. Each stage takes place in a specific cellular compartment, allowing the coordinated flow of electrons and the production of ATP.

StageLocation in the CellMain Products
GlycolysisCytoplasm (cytosol)2 ATP, 2 NADH, 2 pyruvate
Link Reaction (Pyruvate Oxidation)Mitochondrial matrix2 CO₂, 2 NADH, 2 acetyl‑CoA
Krebs Cycle (Citric Acid Cycle)Mitochondrial matrix2 ATP (or GTP), 6 NADH, 2 FADH₂, 4 CO₂
Oxidative PhosphorylationInner mitochondrial membrane (cristae)≈30 ATP, H₂O

Key Points for Each Stage

1. Glycolysis

Occurs in the cytoplasm where glucose (a six‑carbon sugar) is split into two molecules of pyruvate. Energy is invested and then released, giving a net gain of 2 ATP and 2 NADH.

2. Link Reaction

Each pyruvate enters the mitochondrion and is decarboxylated in the matrix, forming acetyl‑CoA. This step also produces one NADH per pyruvate.

3. Krebs Cycle

Acetyl‑CoA combines with oxaloacetate to form citrate, which then undergoes a series of reactions that release CO₂ and generate NADH, FADH₂ and a small amount of ATP (or GTP). All reactions take place in the matrix.

4. Oxidative Phosphorylation

The NADH and FADH₂ produced in the earlier stages donate electrons to the electron transport chain (ETC) embedded in the inner mitochondrial membrane. The flow of electrons drives proton pumping, creating a proton gradient that powers ATP synthase to produce the bulk of cellular ATP.

The overall equation for aerobic respiration can be written as:

\$\text{C}6\text{H}{12}\text{O}6 + 6\text{O}2 \rightarrow 6\text{CO}2 + 6\text{H}2\text{O} + \approx 38\text{ATP}\$

Suggested diagram: A schematic of a eukaryotic cell showing the cytoplasm, mitochondrion, matrix, and inner membrane with arrows indicating the location of each respiration stage.