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This lesson brings together the concepts of photosynthesis and respiration into a unified understanding of energy transfer in living systems. It covers the role of ATP, the coupling of metabolic reactions, and the integration of anabolic and catabolic pathways as required by the Edexcel A-Level Biology (9BI0) specification.
Adenosine triphosphate (ATP) is the immediate energy source for virtually all cellular processes. It is often described as the "energy currency" of the cell.
ATP consists of:
When the terminal phosphate bond is broken by the enzyme ATPase (or ATP hydrolase), energy is released:
ATP + H₂O → ADP + Pᵢ + energy (~30.5 kJ mol⁻¹)
This is an exergonic (energy-releasing) reaction.
ATP is synthesised from ADP and inorganic phosphate (Pᵢ) in a condensation reaction:
ADP + Pᵢ + energy → ATP + H₂O
This is an endergonic (energy-requiring) reaction.
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