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💡 The backbone of life
Every protein, fat and strand of DNA is built on carbon. It shuttles between air, living things, rocks and oceans — sometimes in days, sometimes over millions of years.
What is the carbon cycle?
- In the fast cycle (days to years), plants convert atmospheric CO₂ into glucose by photosynthesis ; respiration and decomposition return CO₂ to the air.
- In the slow cycle (millions of years), dead organisms become fossil fuels; burning them releases CO₂ quickly. Oceans absorb CO₂ to form carbonates, and phytoplankton and shells store carbon.
- Human activity (burning fuels, deforestation) has raised atmospheric CO₂ by about 35% since 1960 (about 315 to 420 ppm, Fig. 13.14), intensifying the greenhouse effect.
NCERT Question 9 — Explain with suitable diagram the
Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using CO₂ from the atmosphere.
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NCERT Question 10 — Why is an excess of
Why is an excess of CO₂ in the atmosphere considered undesirable even though it is required by plants?
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🧵 Threads of Curiosity
Carbon makes up about 49% of the dry weight of living organisms. Of the total global carbon, about 71% is found in the oceans, and this oceanic reservoir regulates atmospheric carbon dioxide. Remarkably, the atmosphere holds only a very small fraction — about 1% — of the total global carbon.
⏸▶ Pause and Ponder
4. When global temperature rises, the CO₂ dissolved in the ocean is disturbed — warmer water holds less CO₂ and turns more acidic, threatening plankton, corals and the marine life that depends on them.
