The carbon cycle is one of the most important biogeochemical cycles on Earth. It describes how carbon atoms move between the atmosphere, biosphere, hydrosphere, and geosphere, ensuring that this essential element is recycled through all living and non-living systems. In IB Biology, understanding the carbon cycle connects ecology, climate science, and human impact — key areas for both Paper 2 and Paper 3 success.
Quick Start Checklist for IB Biology Students
- Define the carbon cycle and identify its major processes
- Learn how photosynthesis, respiration, and decomposition move carbon
- Understand carbon sinks and sources
- Analyze how human activities alter the carbon balance
- Review diagrams and IB-style data questions with RevisionDojo’s IB Biology tools
What Is Carbon and Why Does It Matter?
Carbon is the backbone of all organic molecules — including carbohydrates, lipids, proteins, and nucleic acids. Because all living organisms depend on these molecules, the continuous movement of carbon through ecosystems is vital for life.
Main Processes in the Carbon Cycle
- Photosynthesis:
Plants, algae, and cyanobacteria absorb carbon dioxide (CO₂) from the atmosphere or water and convert it into glucose using sunlight. This process captures carbon into the biosphere. - Respiration:
All living organisms release CO₂ back into the atmosphere through cellular respiration when they break down glucose for energy. - Decomposition:
When organisms die, decomposers such as bacteria and fungi break down organic matter, returning carbon to the soil, water, and air. - Combustion:
The burning of fossil fuels or biomass releases stored carbon into the atmosphere as CO₂, contributing to climate change. - Ocean Uptake and Release:
Oceans act as massive carbon sinks, absorbing CO₂ from the atmosphere. Some carbon dissolves, while some is used by marine organisms to form shells and skeletons. - Fossilization and Sedimentation:
Over millions of years, dead organisms can become fossil fuels or limestone, storing carbon deep within the Earth — a process that temporarily removes it from circulation.
The Carbon Cycle and Climate Change
The natural carbon cycle keeps atmospheric CO₂ levels relatively balanced. However, human activities — especially burning fossil fuels and deforestation — have disrupted this equilibrium. Increased CO₂ traps more heat in the atmosphere, intensifying the greenhouse effect and accelerating global warming.
In IB Biology, students must understand how the carbon cycle links biological processes with environmental impact. This includes evaluating carbon fluxes, climate feedbacks, and sustainable solutions such as reforestation and carbon sequestration.
The IB Biology Connection
The carbon cycle is covered in Topic 4: Ecology, where students analyze how carbon moves through living and non-living systems. IB exams may include data on atmospheric CO₂ trends, ocean acidification, or carbon flux measurements.
RevisionDojo’s IB Biology course provides clear diagrams, practice questions, and revision notes that make these complex interactions easier to visualize and explain in essays or data-based questions.
FAQs
What is the carbon cycle in simple terms?
It’s the process by which carbon moves between the atmosphere, living organisms, oceans, and the Earth, keeping life and climate in balance.
Why is the carbon cycle important to life?
It recycles carbon atoms needed to build essential biological molecules and maintains the planet’s energy balance.
How do humans affect the carbon cycle?
Through fossil fuel combustion, deforestation, and industrial processes, humans increase atmospheric CO₂, contributing to climate change and ocean acidification.
