Nutrient Cycle Notes

Nutrient Cycle

Nutrient cycling ensures that nutrients are reused rather than lost to the environment.

Objective

• Define carbon, water, oxygen, and nitrogen cycles.
• Explain the process of cycling.
• Describe the importance of these nutrients in nature.
• Explain decomposition in nature.
• Identify types of decomposers (micro and macro decomposers).
• Outline the roles of decomposers.

Nutrient Cycling in Nature

• Nutrient cycles ensure nutrients are reused.
• Examples:
  • Hydrological cycle (water cycle)
  • Carbon cycle
  • Oxygen cycle
  • Nitrogen cycle

The Water Cycle (Hydrological Cycle)

• Continuous movement of water from Earth to the atmosphere and back.
• Processes:
  • Evaporation: Liquid to water vapor (gas).
  • Condensation: Water vapor (gas) to liquid.
  • Precipitation: Atmospheric water vapor falling to Earth (rain, freezing rain, snow, sleet, hail).
  • Transpiration: Evaporation of water from plants (leaves, stems, flowers, roots).

The Carbon Cycle

• Biogeochemical cycle of carbon exchange among biosphere, pedosphere, geosphere, hydrosphere, and atmosphere.
• Processes releasing $CO_2$ into the environment:
  • Respiration of living organisms.
  • Combustion of fossil fuels (industry and vehicle emissions).
  • Decay of dead organisms (plants and animals).
• Processes removing $CO_2$ from the environment:
  • Photosynthesis of plants (using sunlight and chlorophyll to make glucose and oxygen).
  • Storage of carbon compounds in animals.
  • Storage of carbon compounds in fossil fuels.

The Oxygen Cycle

• Movement of oxygen through the atmosphere, biosphere, and lithosphere.
• Oxygen constitutes 21% of atmospheric gases.
• Processes removing oxygen from the atmosphere: respiration, decay, and combustion.
• Process releasing oxygen into the atmosphere: photosynthesis.
• Uses of Oxygen:
  • Rusting
  • Decomposition
  • Inhalation
  • Expiration
  • Combustion
  • Breathing

The Nitrogen Cycle

• Nitrogen makes up about 78% of the atmosphere ($N_2$).
• Step 1: Nitrogen Fixation
  • Gaseous nitrogen ($N<em>2$) converted to ammonia ($NH</em>3$).
  • Nitrogen fixation: Addition of hydrogen to nitrogen ($N<em>2 + H = NH</em>3$).
  • Biological fixation: Nitrogen-fixing bacteria (Rhizobium, blue-green algae, Azotobacter, Bacillus).
  • Non-biological fixation: Lightning, volcanic eruptions, industrial fertilizers.
• Step 2: Nitrification
  • Ammonia ($NH<em>3$) converted to nitrite ($NO</em>2^-$) by nitrifying bacteria (Nitrosomonas).
  • Nitrite ($NO<em>2^-$) converted to nitrate ($NO</em>3^-$) by bacteria (Nitrobacter).
• Step 3: Assimilation
  • Plants take up nitrates ($NO_3^-$) from the soil.
• Step 4: Ammonification
  • Organic nitrogen (amino acids, DNA) in dead plants and animals converted to ammonia ($NH_3$) by ammonifying bacteria (fungi).
• Step 5: Denitrification
  • Remaining soil nitrate ($NO<em>3^-$) converted back to nitrogen ($N</em>2$).
  • Removes fixed nitrogen (nitrate) from the ecosystem and returns it to the atmosphere.

Decomposition in Nature

• Process by which organisms (bacteria and saprophytes) break down dead organic materials of plant or animal origin.
• Types of Decomposers:
  • Micro decomposers: Microscopic organisms (certain bacteria and fungi).
  • Macro decomposers: Bigger organisms (earthworms, termites, snails, mushrooms).

Process of Decomposition

• Decomposers secrete enzymes onto their food source (decaying organisms).
• Enzymes break down complex organic compounds (carbohydrates) into simple soluble inorganic compounds.
• Decomposers absorb a small amount of nutrients and energy; the rest is released into the soil, air, and water.
• When decomposers die, other decomposers feed on them, and the released nutrients are used by plants.
• Products released during decomposition: carbon dioxide, hydrogen sulfide, ammonia, water vapor, heat energy, nitrates, sulfates, phosphate ions.

Role of Decomposers

1. Enrich the soil with nutrients required for plant growth.
2. Contribute to environmental pollution.
3. Useful in making cheese and yogurt.
4. Enable the recycling of nutrients, allowing the ecosystem to function.
5. Prevent unsightly accumulation of remains and wastes on the Earth's surface.