Describe the electron transport chain with a neat diagram.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. The electron transport chain (respiratory chain) is a series of carriers in the inner mitochondrial membrane. It passes electrons from NADH and FADH2 to oxygen, forming water and releasing energy.
2 · Draw the chain. [Diagram: inner membrane with Complexes I–IV, CoQ and cytochrome c; NADH entering at I, FADH2 at II; ½O2 → H2O at IV; H+ arrows into the intermembrane space]
3 · Explain biological oxidation. Oxidation is loss of electrons or hydrogen. Dehydrogenases transfer hydrogen from food to NAD+ or FAD, forming NADH and FADH2.
4 · Describe each complex.
Complex I: NADH → FMN → Fe-S → CoQ.
Complex II: succinate → FAD → Fe-S → CoQ.
Complex III: CoQ → cyt b → cyt c1 → cyt c.
Complex IV: cyt c → cyt a → a3 (Cu) → O2 → H2O.
5 · Mobile carriers and proton pumping. CoQ and cytochrome c shuttle electrons between complexes. Complexes I, III and IV pump protons out, building the gradient used to make ATP.
6 · Significance. Main source of ATP in aerobic cells and the place where most inhaled oxygen is used. Cyanide blocks it, which is why cyanide is so deadly.
7 · Nutrition link. NAD+ from niacin, FMN and FAD from riboflavin, iron in cytochromes, copper in Complex IV.
8 · Close in one line. The ETC turns hydrogen removed from food into water and a proton gradient that powers ATP synthesis.
Scoring tip: Write the carrier order as one clean arrow line before explaining. The diagram and that sequence carry most of the marks.
Write-up practice
The check looks for key words only. It does not grade your answer and never writes it for you.