A-Level Biology: Respiration
Respiration is the other half of A-level bioenergetics, and its four-stage architecture — glycolysis, link reaction, Krebs cycle, oxidative phosphorylation — is examined stage by stage, coenzyme by coenzyme. This quiz tracks the whole pathway at specification depth.
Glycolysis opens the set with its two-phase logic: the energy-investment phosphorylation of glucose — tested on why ATP is spent before any is made — and the net yield question (four made, two spent, net two) that anchors the arithmetic. The link reaction and Krebs cycle follow, with a dedicated question on exactly which coenzymes the cycle reduces (NAD and FAD, with coenzyme A tested as the carrier that is not reduced — a distinction verified during this set's quality pass).
Oxidative phosphorylation gets the structural and chemiosmotic treatment: cristae as surface area for the electron transport chain, the proton gradient's role in driving ATP synthase, and oxygen tested by its precise job — final electron acceptor, combining with protons to form water — with the follow-on question of what happens when it is absent.
The anaerobic questions cover both fates of pyruvate: lactate in animals — with NAD regeneration as the actual point of the detour — and ethanol with carbon dioxide in yeast. Alternative substrates close the set: lipids entering via beta-oxidation to acetyl-CoA, and deaminated amino acids entering at pyruvate, acetyl-CoA or Krebs intermediates.
Every explanation names the enzyme, location and carrier precisely — the level of specificity that distinguishes top-band biochemistry answers.
- Trace glycolysis through investment and payoff phases with correct ATP arithmetic
- Identify what the link reaction and Krebs cycle produce, and which coenzymes are reduced
- Explain chemiosmosis and oxygen's role as final electron acceptor
- Contrast lactate and ethanol pathways and their NAD-regeneration purpose
- Show how lipids and amino acids enter the respiratory pathway
Topic scope follows the energy transfers content of the DfE A level biology subject content as delivered in current exam-board specifications: glycolysis, the link reaction, the Krebs cycle, oxidative phosphorylation and anaerobic pathways.
Sample question
During the energy investment phase of glycolysis, what is the specific role of ATP in the phosphorylation of glucose?
- It provides the energy to reduce NAD to NADH
- It provides a phosphate group to destabilize the glucose molecule
- It acts as a coenzyme to facilitate the action of phosphofructokinase
- It is used to directly convert pyruvate into acetyl-CoA
See the answer
It provides a phosphate group to destabilize the glucose molecule
In glycolysis, two ATP molecules are used to phosphorylate glucose, which increases its energy level and makes it more reactive (destabilized) for subsequent splitting into triose phosphate.