Plant Metabolism and Photosynthesis
Plants convert sunlight and carbon dioxide into the organic molecules that feed nearly all life, then process those molecules through respiration and elaborate them into a vast array of specialized compounds.
Definition
Plant metabolism is the set of biochemical reactions sustaining plant life, centered on photosynthesis — the light-driven fixation of carbon dioxide into organic matter — together with respiration and specialized (secondary) metabolism.
Scope
This area covers the energy and carbon metabolism of plants: photosynthetic light reactions and carbon fixation, cellular respiration and energy metabolism, and the biosynthesis of the secondary metabolites that mediate plant defense, signaling, and color.
Sub-topics
Core questions
- How do plants capture light energy and use it to fix carbon dioxide into sugars?
- How is the energy stored in sugars released through respiration?
- How and why do plants produce the immense diversity of secondary metabolites?
Key theories
- Two-stage photosynthesis
- Photosynthesis proceeds in light reactions that convert light energy into ATP and NADPH, and carbon reactions (the Calvin–Benson cycle) that use this chemical energy to fix carbon dioxide into carbohydrate.
- Chemiosmotic energy coupling
- Both photosynthesis and respiration couple electron transport to the pumping of protons across a membrane, and the resulting gradient drives ATP synthesis.
Clinical relevance
Photosynthesis is the ultimate source of food and oxygen and a central lever on the global carbon cycle; understanding plant metabolism informs efforts to raise crop yields, engineer stress tolerance, and produce pharmaceuticals and other compounds from plant secondary metabolism.
History
The path of carbon in photosynthesis was traced by Calvin and Benson with radioactive tracers in the mid-twentieth century, while Mitchell's chemiosmotic theory unified the energy-transducing membranes of chloroplasts and mitochondria.
Key figures
- Melvin Calvin
- Andrew Benson
- Rudolph Marcus
- Peter Mitchell
Related topics
Seminal works
- buchanan2015
- taiz2015
Frequently asked questions
- What are the two stages of photosynthesis?
- The light reactions in the thylakoid membranes capture light to make ATP and NADPH and release oxygen, and the carbon reactions of the Calvin–Benson cycle use that ATP and NADPH to fix carbon dioxide into sugar.
- Why do plants make secondary metabolites?
- Secondary metabolites are not required for basic growth but serve ecological roles — defending against herbivores and pathogens, attracting pollinators, and protecting against ultraviolet light and other stresses.