2.4  Respiration and energy generation

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During respiration, the product pair from photosynthesis (O2 and reduced carbon) are reunited to yield energy. Cellular metabolites are oxidised as electrons are transferred through a series of electron carriers to O2. Water and CO2 are formed and energy is captured as ATP and other forms suitable for metabolic work. Sucrose and starch are prime sources of respiratory substrates in plants, although other carbohydrates such as fructans and sugar alcohols are also utilised. In comparison to sucrose and starch, the contribution of proteins and lipids as sources of respiratory substrates in most plant tissues is minor; exceptions to this generalisation are the storage tissues of seeds such as castor bean and soybean, in which amino acids and lipids may provide respiratory substrates.