Cycles of Matter in Ecosystems

Carbon Cycle

• Carbon is a key element for all living things.
• Carbon continually cycles through:
  • Atmosphere.
  • Land.
  • Water.
  • Living organisms.
• Plants use carbon dioxide ($CO_2$) from the air to make food via photosynthesis.
• Consumers obtain carbon by eating plants or other animals.
• Decomposers break down dead organisms, returning carbon to the soil.
• Burning fossil fuels and clear-cutting forests release $CO_2$ into the atmosphere.

Nitrogen Cycle

• Nitrogen is a key component of DNA and proteins.
• Most organisms cannot directly use free nitrogen gas.
• Nitrogen fixation: bacteria convert nitrogen gas into usable forms.
• Plants absorb nitrogen compounds from the soil via their roots.
• Animals obtain nitrogen by consuming plants or other animals.
• Decomposers return nitrogen to the soil and air.
• Fertilizers and nitrogen-fixing crops (e.g., peas, clovers, beans) can replenish soil nitrogen.

Water Cycle

• Water is essential for all life.
• Water is recycled through the water cycle: movement of water through living and nonliving parts of the environment.
• Key processes:
  • Evaporation: liquid water becomes water vapor.
  • Transpiration: water evaporates from plant leaves.
  • Condensation: water vapor cools and forms liquid droplets in clouds.
  • Precipitation: water falls back to Earth as rain, snow, sleet, or hail.
  • Runoff: precipitation that flows over the land surface.
  • Groundwater: precipitation that seeps into the soil.