Overview
This lecture explains the carbon cycle, focusing on how carbon dioxide is used by plants in photosynthesis and released by living things through respiration.
The Carbon Cycle and Carbon Dioxide
- Carbon dioxide (CO₂) makes up about 0.4% of today’s air; it was only 0.28% before fossil fuel use.
- Plants absorb COâ‚‚ from the air for growth, using sunlight, water, and minerals.
- Carbon captured by plants is eventually returned to the air as COâ‚‚ through respiration in plants and animals.
Photosynthesis
- Photosynthesis is the process where plants use sunlight to convert COâ‚‚ and water into oxygen (Oâ‚‚) and carbohydrates (CHâ‚‚O).
- Chloroplasts in plant leaves perform photosynthesis, using the pigment chlorophyll, whose active site contains magnesium.
- Chlorophyll absorbs blue and red sunlight, reflecting green light, which gives plants their color.
- Photosynthesis requires enzymes (catalysts) and takes place in several complex stages.
- Blue-green algae (cyanobacteria) were among the first organisms to perform photosynthesis.
Respiration
- Respiration is the process of releasing energy by combining Oâ‚‚ with carbohydrates, producing COâ‚‚ and water.
- This process happens in mitochondria within cells and requires enzymes.
- In animals and humans, blood carries Oâ‚‚ and food to cells and removes COâ‚‚ to the lungs.
- Plants also respire, mainly noticeable at night or in roots/seeds that lack sunlight.
Energy Flow: Combustion vs. Respiration
- Respiration in cells and combustion both release energy by combining Oâ‚‚ with fuel (food or combustible materials).
- Respiration occurs at normal temperatures with enzymes, while combustion needs high temperatures and no catalyst.
Key Terms & Definitions
- Photosynthesis — process by which plants use sunlight to convert CO₂ and water into carbohydrates and O₂.
- Respiration — process where living organisms release energy by combining carbohydrates with O₂, producing CO₂ and water.
- Chlorophyll — green pigment in chloroplasts that absorbs sunlight for photosynthesis.
- Enzyme — protein that speeds up (catalyzes) chemical reactions in living things.
- Mitochondria — cell structures where respiration occurs.
- Cyanobacteria (blue-green algae) — early bacteria capable of photosynthesis.
Action Items / Next Steps
- Review diagrams of photosynthesis and respiration.
- Think about how roots and seeds obtain energy without sunlight.
- Prepare for questions on the differences between respiration and combustion.