Biology Unit 4 Edexcel

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Biology – Topic 5 – On the wild side. Photosynthesis Photosynthesis is the process where energy from light is used to break apart strong bonds in H20 molecules – hydrogen is combined with CO2 to form glucose, and O2 is released into the atmosphere. Photosynthesis occurs in a series of reactions, but the overall reaction is: 6CO2 + 6H20 + Energy → C6H12O6 + 6O2 The energy is stored in the glucose until the plants release it by respiration. Plant and animal cells release energy from glucose, this is called respiration. There are two types of respiration: Aerobic (using oxygen) and Anaerobic (no oxygen). Aerobic respiration produces carbon dioxide and water and releases energy. The equation is: C6H12O6 + 6O2 → 6CO2 + 6H20 + Energy ATP A cell cannot get its energy directly from glucose, so during respiration the energy released from the breakdown of glucose is used to make ATP (adenosine triphosphate). ATP is made from the nucleotide base adenine, combined with a ribose sugar and three phosphate groups. It carries energy around the cell to where it’s needed. ATP is synthesised from ADP and inorganic phosphate (Pi) using energy from an energy-releasing reaction e.g the breakdown of glucose in respiration. The energy is stored as chemical energy in the phosphate bond, the enzyme ATP synthase catalyses this reaction. ATP diffuses to the part of the cell that needs energy. Here it’s broken down back into ADP and inorganic phosphate (Pi). Chemical energy is released from the phosphate bond and used by the cell, ATPase catalyses this reaction. The ADP and inorganic phosphate are recycled and the process starts again. Key words Phosphorylation – adding phosphate to a molecule e.g ADP is phosphorylated to ATP Photophosphorylation – adding a phosphate molecule using light Photolysis – the splitting of a molecule using light energy Hydrolysis – the splitting of

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