Energy transfers: photosynthesis and respiration: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Biology Topic 5, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
In the thylakoid membranes: light excites chlorophyll electrons, water is photolysed, and ATP and reduced NADP are produced.
Photolysis
Light-driven splitting of water into protons, electrons and oxygen. It replaces the electrons lost from chlorophyll.
Chemiosmosis
Protons pumped across a membrane flow back through ATP synthase, and that flow drives ATP production.
Calvin cycle
In the stroma: carbon dioxide joins ribulose bisphosphate to make glycerate 3-phosphate, which is reduced to triose phosphate using ATP and reduced NADP.
Rubisco
The enzyme fixing carbon dioxide onto ribulose bisphosphate. It works slowly, which makes it a major limit on photosynthetic rate.
Limiting factor
The factor in shortest supply that caps the rate of a process. In photosynthesis, typically light intensity, carbon dioxide or temperature.
Glycolysis
Splits glucose into two pyruvate molecules in the cytoplasm, giving a net gain of two ATP and two reduced NAD. It needs no oxygen.
Link reaction
Pyruvate is decarboxylated and oxidised to acetate, joins coenzyme A, and produces reduced NAD and carbon dioxide.
Krebs cycle
Acetyl coenzyme A joins a four-carbon molecule; a series of decarboxylations and oxidations regenerates it, yielding reduced coenzymes, ATP and carbon dioxide.
Oxidative phosphorylation
Electrons from reduced coenzymes pass down the electron transport chain, pumping protons for chemiosmosis. Most ATP is made here.
Role of oxygen in respiration
Acts as the final electron acceptor, combining with electrons and protons to form water. Without it the chain backs up and stops.
Anaerobic respiration
Regenerates NAD without oxygen — lactate in animals, ethanol and carbon dioxide in yeast — so glycolysis alone can continue.
Respiratory substrate
A molecule that can be respired. Lipids release the most energy per gram because they are the most reduced.
Gross vs net primary production
Gross is the total chemical energy plants fix; net is what remains after respiratory losses and is what passes to consumers.
Energy transfer efficiency
Only around 10 per cent of energy passes between trophic levels, lost as heat, in respiration and in indigestible material.
Saprobiont
An organism feeding on dead material by extracellular digestion, releasing nitrogen and phosphorus back into the ecosystem.