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Biological Molecules    Cell Structure    Cell Transport    Immunology    Exchange    Mass Transport    DNA, Genes & Protein Synthesis    Genetic Diversity    Biodiversity    Photosynthesis    Respiration    Energy & Ecosystems    Stimuli and Response    Nervous Coordination & Muscles    Homeostasis    Inheritance    Populations & Evolution    Ecosystems    Gene Expression    Recombinant DNA Technology   


Respiration is the process of releasing ATP from glucose. There are 4 major stages within aerobic respiration in which we will go into detail with the following notes. They are Glycolysis, Link Reaction, Kreb's Cycle and Oxidative Phosphorylation.

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Glycolysis is the first step of respiration and occurs in the cytoplasm.

Glucose is being phosphorylated to produce glucose-phosphate. Then glucose phosphate is being split into 2 x Triose-Phosphates (TP). Each phosphate then loses a hydrogen to produce 2 x NADH. 2 x ATP is also produced. TP is then oxidised to produce pyruvate which enters the Link Reaction.

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2️⃣Link Reaction

Link Reaction is the second step of respiration and occurs in the mitochondria matrix.

Link Reaction is where pyruvate is is turned into acetate by losing a carbon by releasing carbon dioxide as a waste product. A hydrogen is also lost to form NADH. Acetate is then combined with coenzyme A to form acetyl Coenzyme A which enters the Krebs Cycle.

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3️⃣Krebs Cycle

Krebs Cycle is the third step of respiration and occurs in the mitochondria matrix.

Within the Krebs Cycle, acetyl CoA enters the cycle and combines with OAA to form citrate and releases CoA to return to the Link Reaction. A series of redox reactions releases reduced coenzymes NADH and FADH2 and subtrate-level phosphorylation also occurs to produce ATP.

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4️⃣Oxidative Phosphorylation

Oxidative Phosphorylation is the final and fourth step of respiration and occurs in the mitochondria matrix.

Within the oxidative phosphorylation, NADH and FADH released from glycolysis, Link Reaction and most from the Krebs Cycle release electrons to the first electron carrier. Electrons then pass down the electron transport chain via a series of redox reactions. These energy are used to pump protons from the matrix into the inner-membrane space. Protons then diffuse back to the matrix down a concentration gradient via ATP synthase. This movement generates ATP from ADP and Pi. Oxygen is the terminal electron acceptor of electrons to form water.

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Anaerobic Respiration

Anaerobic respiration occurs without oxygen and only yields 2 ATP per glucose. This is because only glycolysis occurs. In animals, lactate is produced using NADH, this regenerates NAD for further glycolysis. In plants, ethanol and carbon dioxide is produced.

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