ATI TEAS · Science
Cellular Respiration and Photosynthesis
How cells capture and release energy — photosynthesis, cellular respiration, and why they are mirror-image processes on the TEAS.
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Living things need a constant supply of usable energy. Two linked processes move that energy through nearly every ecosystem: photosynthesis captures it, and cellular respiration releases it.
Photosynthesis
Photosynthesis takes place in the chloroplasts of plants, algae, and some bacteria. Using light energy, carbon dioxide, and water, it builds glucose and releases oxygen:
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
The light-dependent reactions capture energy from sunlight; the Calvin cycle then uses that energy to assemble glucose.
Cellular respiration
Cellular respiration runs the reaction in reverse, breaking glucose down to release energy the cell can use as ATP:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
It has three stages — glycolysis in the cytoplasm, then the Krebs cycle and the electron transport chain in the mitochondria. Aerobic respiration needs oxygen; without it, cells fall back on less efficient fermentation.
Key takeaways
- Photosynthesis stores energy in glucose; respiration releases it as ATP.
- The two processes are mirror images — the products of one are the reactants of the other.
- Chloroplasts power photosynthesis; mitochondria power respiration.