Carbon Cycle Lecture Notes

Objectives

Many students find the carbon cycle challenging, but it's simpler than it seems.

Carbon Cycle Initiation: Begins with carbon dioxide (CO2) in the atmosphere.
Entry into Cycle: Carbon enters the carbon cycle solely through photosynthesis.
- Photosynthesis combines carbon dioxide and water to form glucose.
- Light energy is used; performed by plants.

Photosynthesis:
- Only way for carbon to enter the cycle.
- Plants and algae take in carbon dioxide and convert it into carbohydrates, fats, and proteins.
- Carbon in these compounds forms part of the plant's cells.
Respiration:
- Returns carbon to the atmosphere as carbon dioxide.
- Performed by all living organisms.
- Distinct from breathing; do not confuse the terms.

Carbon Dioxide in Atmosphere:
- Taken up by plants and algae via photosynthesis.
In Plants and Algae:
- Carbon becomes part of plant cells.
- Plants respire, releasing some CO2 back to the atmosphere.
Transfer to Animals:
- Plants are eaten by animals, transferring carbon into animal cells.
- Animals also respire, releasing CO2 back to the atmosphere.
Decomposition:
- Animals produce waste and die; plants also die.
- Dead matter is broken down by decomposers (bacteria and fungi).
- Decomposers respire, returning carbon to the atmosphere as CO2.
- Decomposers release mineral ions to the soil.

Importance:
- Cycle materials through ecosystems.
- Return carbon to the atmosphere.
Limiting Conditions:
- Lack of oxygen can hinder decomposer function.
- In such conditions, carbon can become fossil fuels.

Formation:
- Formed under low-oxygen conditions over millions of years from dead matter.
Effect of Human Activity:
- Burning fossil fuels (coal, oil) significantly increases atmospheric CO2.
- This release of CO2 has accelerated in the past 200 years.

For more questions on the carbon cycle, refer to the revision workbook available online.

Keep these points in mind and review regularly to grasp the carbon cycle thoroughly.