Photosynthesis, Cellular Respiration, and the Carbon Cycle

Module 3 (9/15–9/21) · Photosynthesis and Cellular Respiration; Carbon Cycle and Global Climate Change · Blueprint Pillar 3 · PGCC Outcome 2 · Download .docx

Objectives

Write and interpret the equations for photosynthesis and cellular respiration.
Trace carbon through the four main reservoirs of the carbon cycle.
Distinguish carbon sinks from carbon sources.
Explain the greenhouse effect and positive feedback loops in climate.

Key terms

Photosynthesis: Process by which plants and algae convert CO₂, water, and sunlight into glucose and oxygen.
Cellular respiration: Process by which organisms break down glucose with oxygen to release ATP energy, producing CO₂ and water.
Carbon reservoir: Any system that stores carbon: atmosphere, biosphere, hydrosphere, lithosphere.
Carbon sink: Reservoir that absorbs more carbon than it releases (forests, oceans).
Carbon source: System that releases more carbon than it absorbs (fossil fuel combustion, deforestation).
Greenhouse gas: Gas that traps outgoing infrared radiation in the atmosphere: CO₂, CH₄, N₂O, H₂O vapor.
Greenhouse effect: Natural warming of Earth caused by atmospheric gases trapping heat from the sun.
Enhanced greenhouse effect: Human-driven intensification of the greenhouse effect through fossil fuel combustion and land use change.
Positive feedback loop: A cycle where an initial change produces effects that amplify the original change.
IPCC: Intergovernmental Panel on Climate Change — international body that synthesizes peer-reviewed climate science for policymakers.
Permafrost: Permanently frozen soil in polar and alpine regions; thaws as temperatures rise, releasing stored CH₄.
Parts per million (ppm): Unit measuring trace gas concentration; atmospheric CO₂ is now above 420 ppm.

The concept

Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Plants, algae, and cyanobacteria use sunlight to convert carbon dioxide and water into glucose and oxygen. Cellular respiration reverses this: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Nearly all organisms, including plants at night, break down glucose to release energy and produce carbon dioxide.

The carbon cycle moves carbon through four main reservoirs: atmosphere (CO₂, CH₄), biosphere (living organisms), hydrosphere (dissolved CO₂ in oceans), and lithosphere (fossil fuels, limestone). Carbon sinks absorb more than they release; carbon sources release more than they absorb. Human burning of fossil fuels and deforestation have shifted the balance toward sources.

The greenhouse effect is natural and essential: CO₂, CH₄, N₂O, and water vapor trap outgoing heat and keep Earth habitable. The enhanced greenhouse effect is the human-driven amplification of this process. Positive feedback loops — such as Arctic ice melting to expose dark ocean — accelerate warming. Atmospheric CO₂ is now above 420 ppm, the highest in at least 800,000 years.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. Which product is released by photosynthesis that is consumed by cellular respiration?

2. A carbon sink differs from a carbon source in that a carbon sink:

3. The natural greenhouse effect is best described as:

4. Permafrost thaw is an example of a positive feedback loop because:

5. Atmospheric CO₂ concentration is now above 420 ppm. What is the significance of this level?

Canvas is the official record. This companion enhances the PGCC curriculum; it does not replace it. Last name and class year only. Students with a 504 plan or IEP: your accommodations apply.

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