Carbon Cycle

Lecture Content Introduction Carbon is a fundamental element of life, forming the backbone of organic molecules such as carbohydrates, proteins, and nucleic acids. The carbon cycle describes how carbon moves between living organisms and the environment, ensuring continuity of life.

Definition The carbon cycle is the biogeochemical cycle that describes the movement of carbon among the atmosphere, hydrosphere, lithosphere, and biosphere.

Major Reservoirs of Carbon

• Atmosphere: Carbon dioxide (CO₂).

• Biosphere: Plants, animals, microbes.

• Hydrosphere: Oceans (dissolved CO₂, carbonate, bicarbonate).

• Lithosphere: Fossil fuels, sedimentary rocks (limestone).

Steps in the Carbon Cycle

1. Photosynthesis

   • Plants absorb CO₂ and convert it into glucose.

   • Example:

2. Respiration

   • Animals and plants release CO₂ back into the atmosphere.

3. Decomposition

   • Microbes break down dead organisms, releasing carbon.

4. Combustion

   • Burning of fossil fuels releases stored carbon as CO₂.

5. Sedimentation

   • Carbon stored in rocks and shells (calcium carbonate).

6. Ocean Exchange

   • Oceans absorb and release CO₂, regulating atmospheric levels.

Ecological Importance

• Provides carbon for organic molecules essential to life.

• Regulates Earth’s climate by controlling CO₂ levels.

• Supports photosynthesis and energy flow in ecosystems.

• Human activities (deforestation, burning fossil fuels) disrupt the cycle, causing global warming.

Quick Revision Table

Summary / Key Takeaways

• Carbon cycle = movement of carbon through atmosphere, biosphere, hydrosphere, lithosphere.

• Driven by photosynthesis, respiration, decomposition, combustion, sedimentation, and ocean exchange.

• Essential for life, climate regulation, and ecosystem stability.

• Human activities disrupt the cycle, leading to climate change.