(A Level) Energy and respiration

Learning objectives

Outline what organisms use energy for (movement, active transport, and building large molecules in protein synthesis and DNA replication), explain the features that make ATP the universal energy currency, and state that ATP is made by substrate-linked phosphorylation and by chemiosmosis in mitochondria and chloroplasts.

Explain why lipids release more energy per gram than carbohydrates or proteins, calculate respiratory quotients from respiration equations (RQ = CO₂ given out ÷ O₂ taken in), and describe how simple respirometers (with and without a CO₂ absorber) measure the RQ of small invertebrates such as blowfly larvae or of germinating seeds, and how temperature affects respiration rate.

Describe glycolysis in the cytoplasm (phosphorylation of glucose, splitting of fructose 1,6-bisphosphate into two triose phosphates, oxidation to pyruvate with a net gain of ATP and reduced NAD) and the link reaction in the mitochondrial matrix, including the role of coenzyme A.

Outline the Krebs cycle, in which oxaloacetate accepts an acetyl group to form citrate, and explain how decarboxylation and dehydrogenation reduce NAD and FAD, which then carry hydrogen to the inner mitochondrial membrane.

Explain oxidative phosphorylation (electron transport, proton pumping into the intermembrane space, chemiosmosis through ATP synthase, oxygen as the final electron acceptor), and relate the structure of mitochondria in diagrams and electron micrographs to their function.

Compare lactate fermentation in mammals and ethanol fermentation in yeast and explain their much lower ATP yield, explain how rice tolerates flooded roots (aerenchyma, ethanol fermentation, rapid stem growth), and describe how the redox indicators DCPIP and methylene blue measure the rate of respiration of yeast.