Respiration (A-Level) — A-Level Biology Revision

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What is Respiration (A-Level)?

Respiration is the process that releases energy from glucose in cells, making it available for all life processes. A-Level Biology focuses on aerobic respiration, which involves four main stages: glycolysis in the cytoplasm, the link reaction and the Krebs cycle in the mitochondrial matrix, and oxidative phosphorylation on the inner mitochondrial membrane. This process yields a large amount of ATP, the universal energy currency of cells.

Board notes: All A-Level Biology boards (AQA, Edexcel, OCR) cover the four stages of aerobic respiration in detail. The specific number of ATP molecules produced at each stage and the names of the intermediate compounds in the Krebs cycle may have minor variations in emphasis between boards.

Worked example

Common mistakes

• 1Confusing respiration with breathing. Breathing (or gas exchange) is the physical process of taking in oxygen and releasing carbon dioxide, while respiration is the chemical process that releases energy from food inside cells.
• 2Not knowing the specific locations of each stage. Glycolysis occurs in the cytoplasm, the link reaction and Krebs cycle are in the mitochondrial matrix, and oxidative phosphorylation takes place on the inner mitochondrial membrane (cristae).
• 3Forgetting the roles of NAD and FAD. These are coenzymes that act as hydrogen carriers. They are reduced during glycolysis, the link reaction, and the Krebs cycle, and then carry the hydrogen atoms to the electron transport chain for oxidative phosphorylation.

Respiration (A-Level) exam questions

Exam-style questions for Respiration (A-Level) with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the difference between aerobic and anaerobic respiration?

  Aerobic respiration requires oxygen and produces a large amount of ATP. Anaerobic respiration does not require oxygen and produces a much smaller amount of ATP, along with lactate (in animals) or ethanol and carbon dioxide (in plants and yeast).

• What is oxidative phosphorylation?

  Oxidative phosphorylation is the final stage of aerobic respiration, where the energy carried by electrons from reduced NAD and FAD is used to generate a large amount of ATP. It involves the electron transport chain and chemiosmosis.