IB MYP Integrated Science- Biology - Carbon cycle-Study Notes - New Syllabus

Carbon Cycle

🌱 Introduction

The carbon cycle is the natural movement of carbon between the atmosphere, living organisms, oceans, and the Earth.
It helps maintain the balance of CO₂, controls climate, and supports life processes like photosynthesis and respiration.

Carbon exists as:

• CO₂: Carbon dioxide in the atmosphere.
• Glucose: Carbohydrates in plants and animals.
• Fossil fuels: Coal, oil, and natural gas.
• Carbonates: Found in rocks and shells.
• Biomass: Organic carbon in living tissues.

🌤️ Main Processes of the Carbon Cycle

1) Photosynthesis

Plants, algae, and some bacteria take in CO₂ from the air and convert it into glucose, storing carbon in their tissues.
Equation: $$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

This is the entry point of carbon into the food chain.

2) Respiration

All living organisms (plants, animals, microbes) break down glucose for energy and release CO₂ back to the atmosphere.
This process balances photosynthesis.

3) Feeding & Assimilation

Carbon moves through the food web: Herbivores → Carnivores → Top Predators. It is stored as organic molecules in body tissues.
This forms the trophic carbon flow.

4) Decomposition

Decomposers (bacteria and fungi) break down dead plants and animals, releasing CO₂ (aerobic) or CH₄ (anaerobic).
This prevents carbon accumulation in dead matter.

5) Fossil Fuel Formation

If dead organisms are not decomposed completely, pressure and heat over millions of years turn them into coal, oil, and natural gas.
This is long-term carbon storage.

6) Combustion

Burning fossil fuels, wood, or biomass releases stored CO₂ back into the atmosphere.
This is a major contributor to global warming.

7) Ocean Uptake & Release

Oceans act as carbon sinks: CO₂ dissolves in water, is used by phytoplankton, and forms carbonates ($CaCO_3$) for shells.
Oceans store significantly more carbon than the atmosphere.

8) Rock Weathering & Volcanic Activity

Weathering of rocks releases carbonates, while volcanic eruptions release CO₂.
These are very slow, long-term processes.

🔁 Summary Table – Carbon Movement

📦 Quick Recap
• Carbon Cycle = continuous movement of carbon between atmosphere, organisms, oceans, and Earth.
• Plants absorb CO₂; animals feed; respiration and decomposition return CO₂.
• Fossil fuels and oceans act as major storage areas.
• Trick (PCR-DOC-FV): Photosynthesis, Combustion, Respiration, Decomposition, Ocean processes, Carbonate rocks, Fossil fuel formation, Volcanic activity.