ATP is generated by chemiosmosis, where a proton gradient across the inner mitochondrial membrane drives ATP synthesis via ATP synthase.

Oxygen accepts electrons at the end of the ETC and combines with protons to form water.

Sunlight provides the energy to excite electrons in chlorophyll, driving the light-dependent reactions of photosynthesis.

Electrons are passed from cytochrome a to cytochrome a3 in the ETC, leading to oxygen reduction.

Plastocyanin (Pc) is a copper-containing protein that transfers electrons in the photosynthetic ETC in plants.

NADPH, produced in the light-dependent reactions, donates electrons to reduce carbon dioxide into glucose during the Calvin cycle.

The proton gradient across the inner mitochondrial membrane drives ATP synthesis via ATP synthase during oxidative phosphorylation.

The electron transport chain drives oxidative phosphorylation, producing the most ATP (up to 34 per glucose) in mitochondria.

Cristae of the inner mitochondrial membrane house enzymes for oxidative phosphorylation, increasing surface area.

Each NADH contributes to approximately 2.5 ATPs via the ETC, rounded to 2 in modern bioenergetics for simplicity.

Glycolysis occurs in the cytoplasm and can proceed anaerobically, producing ATP without oxygen.

The Calvin cycle fixes carbon dioxide into glucose, an energy-rich compound, in photosynthetic organisms.

Acetyl CoA combines with oxaloacetate to form citrate, initiating a new round of the Krebs cycle.

Hexokinase catalyzes the first step of glycolysis by phosphorylating glucose to glucose-6-phosphate.

Glucose undergoes glycolysis to form pyruvate, which is then converted to acetyl CoA to enter the Krebs cycle.

Hexokinase phosphorylates glucose in both glycolysis and the pentose phosphate pathway, initiating sugar metabolism.

Succinate is oxidized to fumarate in the Krebs cycle, reducing FAD to FADH2.

Reduction involves gaining electrons, protons (often as hydrogen), and stored chemical energy.

ATP synthase is embedded in the inner mitochondrial membrane, where it uses the proton gradient to synthesize ATP.

Oxaloacetate is regenerated at the end of the Krebs cycle to combine with acetyl CoA for the next cycle.