A recipe for self-sufficiency
Plants use photosynthesis to harness energy from the sun
‘Big Picture: Plants’ (2016)
Plants make their own food – glucose – through photosynthesis, using water, light energy from the sun, and carbon dioxide from the air. That glucose is used to build cellulose, starch, fats and oils – and to power the complementary process of respiration.
At the cellular level, photosynthesis begins in clusters of molecules called photosystems in the inner membranes of chloroplasts (see ‘The secrets of plant cell structure’). Sunlight kickstarts the light-dependent reactions of the process, by transferring energy to chlorophyll pigments in reaction centres, setting up a chain of further reactions. The second part of the process, the light-independent reactions produces chemical energy in the form of glucose. This is the key feature of photosynthesis: the ability to convert light energy into chemical energy. Plants are capable of making millions of molecules of this sugar every single second.
The light energy that plants harness accounts for almost all of the energy entering Earth’s ecosystems, the exception being ecosystems based on chemosynthetic bacteria like those around deep-sea vents. Plants’ carbon-fixing capabilities also make them the starting-point for the carbon cycle, while the ability of bean-family plants like peas and clover to absorb nitrogen from the air spaces in soil gives them a vital role in the nitrogen cycle.
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