Cellular Respiration

What Cellular Respiration covers

Cellular Respiration is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper. It covers glycolysis and the link reaction, the Krebs cycle, oxidative phosphorylation and anaerobic respiration, respiratory substrates and respiratory quotients and measuring the rate of respiration.

The 5 subtopics

Each one has its own page.

• Glycolysis and the link reactionRecall questions on enzyme-controlled metabolic pathways, the phosphorylation, lysis and oxidation stages of glycolysis, dehydrogenases and NAD, substrate-level phosphorylation, the net yield of glycolysis, and the link reaction in the mitochondrial matrix and the role of coenzyme A.Open →
• The Krebs cycleRecall questions on where the Krebs cycle happens, forming citrate from acetyl coenzyme A and oxaloacetate, decarboxylation and dehydrogenation, the carbon dioxide, reduced NAD, reduced FAD and ATP produced per turn and per glucose, its purposes, and why it stops without oxygen.Open →
• Oxidative phosphorylation and anaerobic respirationRecall questions on the electron transport chain and cristae, the proton gradient and chemiosmosis, ATP synthase, oxygen as final electron acceptor, ATP yields and cyanide, lactate production in muscle, ethanol production in yeast, and the low ATP yield and fatigue of anaerobic respiration.Open →
• Respiratory substrates and respiratory quotientsRecall questions on respiratory substrates, calculating and interpreting respiratory quotients for carbohydrate, lipid and protein, quotients above 1.0 and in fermenting yeast, the energy released per gram by lipid and carbohydrate, and how amino acids enter respiration.Open →
• Measuring the rate of respirationRecall questions on using a respirometer with soda lime and a control tube, calculating oxygen consumption and respiratory quotients from manometer readings, following yeast respiration with methylene blue, investigating temperature and sugar type, creating anaerobic conditions, and sources of error.Open →

What you need to know

Answer each one before you reveal it.

Take Cellular Respiration further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Substrate-level phosphorylation vs Oxidative phosphorylation

  Substrate-level phosphorylation: ATP formed directly from an intermediate of glycolysis or the Krebs cycle, with no electron carriers and no proton gradient involved. Oxidative phosphorylation: ATP formed by ATP synthase as protons flow back across the inner mitochondrial membrane down the gradient set up by the electron carriers.

• Link reaction vs Krebs cycle

  Link reaction: the single conversion of pyruvate to acetyl coenzyme A in the mitochondrial matrix, releasing carbon dioxide and reducing NAD. Krebs cycle: the closed sequence of steps in which acetyl coenzyme A joins a four-carbon acid and is fully oxidised, regenerating the acceptor each turn.

• Electron transport chain vs Chemiosmosis

  Electron transport chain: a series of carriers in the inner mitochondrial membrane that release energy in steps and use it to pump protons out of the matrix. Chemiosmosis: the flow of protons back into the matrix through ATP synthase, which is what actually drives the synthesis of ATP.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is meant by an enzyme-controlled metabolic pathway?

   Model answer

   It is a sequence of reactions in which each step is catalysed by its own specific enzyme, and the product of one reaction becomes the substrate of the next.

2. 2

   Give two advantages of releasing the energy in glucose through a long metabolic pathway rather than in a single step.

   Model answer

   Energy is released in small amounts that can be captured as ATP rather than lost as heat, and the rate of the whole pathway can be controlled by regulating individual enzymes.

3. 3

   Where in the cell does glycolysis take place?

   Model answer

   In the cytoplasm, where its enzymes are dissolved in the cytosol.

4. 4

   Describe the phosphorylation stage of glycolysis.

   Model answer

   Glucose is phosphorylated using a phosphate group from ATP, and the product is phosphorylated again using a second ATP, giving a hexose bisphosphate.

5. 5

   Explain why two molecules of ATP are used at the start of glycolysis.

   Model answer

   Adding the phosphate groups destabilises the sugar and lowers the activation energy for splitting it, and the charged phosphate also prevents the sugar leaving the cell.

6. 6

   What happens to hexose bisphosphate in the lysis stage of glycolysis?

   Model answer

   It is split into two molecules of triose phosphate, each with three carbon atoms.

What is inside Levo

Six ways to work the same material.

Cellular Respiration revision questions

What does Cellular Respiration cover in OCR A-Level Biology B?

5 subtopics: glycolysis and the link reaction, the krebs cycle, oxidative phosphorylation and anaerobic respiration, respiratory substrates and respiratory quotients and measuring the rate of respiration. Each one has its own page with questions and model answers.

How is Cellular Respiration organised?

By the OCR H422 specification, subtopic by subtopic, so it matches the order you are taught it in.