A-Level Biology AQA 7402

Respiration produces ATP.

Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process.

Glycolysis involves the following stages:

• phosphorylation of glucose to glucose phosphate, using ATP
• production of triose phosphate
• oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.

If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis.

If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport.

Aerobic respiration in such detail as to show that:

• pyruvate is oxidised to acetate, producing reduced NAD in the process
• acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A
• acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-carbon molecule that enters the Krebs cycle
• in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost
• synthesis of ATP by oxidative phosphorylation is associated with the transfer of electrons down the electron transfer chain and passage of protons across inner mitochondrial membranes and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory)
• other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle.

Required practical 9

Investigation into the effect of a named variable on the rate of respiration of cultures of single-celled organisms.