Biology (university) · Part 03
Respiration and photosynthesis
How cells get energy from glucose and how plants capture light energy to build it.
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- Redox reactionA reaction where one substance loses electrons (oxidation) and another gains them (reduction). The two always happen together. Cells use carriers such as NAD+ to move electrons.
- GlycolysisThe first stage of glucose breakdown. It happens in the cytoplasm, needs no oxygen and splits one glucose (6 carbons) into two pyruvate (3 carbons each).
- Citric acid cycleA cycle in the mitochondrial matrix that fully oxidises the carbon from pyruvate to carbon dioxide. It mainly produces electron carriers, NADH and FADH2.
- Electron transport chainA line of proteins in the inner mitochondrial membrane. NADH and FADH2 hand over electrons, which flow down the chain to oxygen. Energy released pumps protons across the membrane.
- ChemiosmosisProtons pumped across a membrane build a gradient, then flow back through ATP synthase, a molecular turbine that makes ATP. The gradient is called the proton-motive force.
- FermentationMaking ATP without oxygen by recycling NADH back to NAD+, so glycolysis can keep going. Humans make lactate. Yeast makes ethanol and carbon dioxide.
- Light reactionsThe first stage of photosynthesis, in the thylakoid membranes of chloroplasts. Light energy splits water, releases oxygen, and makes ATP and NADPH.
- Calvin cycleThe second stage of photosynthesis, in the chloroplast stroma. It uses ATP and NADPH to fix carbon dioxide into sugar. The key enzyme is rubisco.