Module 3: Photosynthesis, Cellular Respiration, and the Carbon Cycle

1. Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Plants, algae, and cyanobacteria use sunlight to convert CO₂ and water into glucose and oxygen.
2. Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP energy. Nearly all organisms (including plants at night) break down glucose to release energy, producing CO₂.
3. 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).
4. Carbon sinks absorb more carbon than they release (forests, oceans). Carbon sources release more than they absorb (burning fossil fuels, deforestation). Human activity has shifted the balance toward sources.
5. The greenhouse effect is natural: CO₂, CH₄, N₂O, and water vapor in the atmosphere trap outgoing heat radiation, keeping Earth habitable. The enhanced greenhouse effect is human-driven amplification of this process.
6. Positive feedback loops amplify warming: melting Arctic ice exposes darker ocean (less reflection), which absorbs more heat, which melts more ice. Permafrost thaw releases stored CH₄, which traps more heat.
7. The Intergovernmental Panel on Climate Change (IPCC) synthesizes global climate science. Its reports are consensus documents reviewed by thousands of scientists.
8. Atmospheric CO₂ is now above 420 ppm — the highest in at least 800,000 years, based on ice core data. Pre-industrial level was ~280 ppm.

Discussion post

1. Open with one specific piece of evidence for climate change that surprised you — something you did not know before this module.
2. Explain the connection between that evidence and the carbon cycle using the vocabulary from the module (reservoir, source, sink, feedback).
3. Connect to Course Outcome 5: name one consumer or voter choice you could make that would reduce carbon sources or protect carbon sinks.
4. Reply to two classmates: do you agree with their proposed action? What barrier might prevent most people from taking it?

Netiquette from the syllabus: address ideas, not people. Complete sentences, correct spelling. Personal matters go to email, never the board.

Ask at home: If we stopped burning all fossil fuels tomorrow, how long do you think it would take for the climate to stabilize — and why?

En español: Si dejáramos de quemar todos los combustibles fósiles mañana, ¿cuánto tiempo crees que tardaría el clima en estabilizarse — y por qué?