Energy for biological processes - ATP, photosynthesis and respiration

All organisms need energy. Life depends on the transfer of energy. ATP is an important source of energy for biological processes. Energy is transferred from molecules such as glucose, to an intermediate energy source, ATP.

ATP is a reservoir of potential chemical energy and acts as a common intermediate in metabolism, linking energy requiring and energy yielding reactions. A level biologists need to know the structure of ATP, its uses and its role in biological processes.

In photosynthesis energy is transferred to ATP in the light-dependent stage and the ATP is utilised during synthesis in the light-independent stage. Students should know in detail the chemical process of photosynthesis. This topic often proves very challenging for students and they can easily become confused, making simple mistakes such as pigments absorb light rather than absord light energy.

In cellular respiration, glycolysis takes place in the cytoplasm and the remaining steps in the mitochondria. ATP synthesis is associated with the electron transfer chain in the membranes of mitochondria. Students need to be able to explain the process of glycolysis, with the resulting production of ATP and reduced NAD. They then need to be able to describe and explain the remaining steps, in terms of the link reaction, Krebs cycle and electron transport chain.

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