Overview
This lecture covers the recycling of elements on Earth, focusing on the roles of bacteria in the nitrogen cycle and how nitrogen is made available to living organisms.
Recycling of Elements on Earth
- Elements are continuously recycled between the living (biotic) and nonliving (abiotic) parts of the environment.
- Organisms like bacteria break down complex organic molecules, returning elements to air, water, soil, and rocks.
- Elements move from nonliving reservoirs (air, water, soil) into living organisms and back again.
Importance and Forms of Nitrogen
- Nitrogen is essential for making DNA, proteins, amino acids, and vitamins.
- 78% of Earth's atmosphere is nitrogen gas (Nā), but most organisms can't use it directly.
- Nitrogen must be converted into a usable form called nitrates for plants to absorb.
The Nitrogen Cycle
- Nitrogen gas (Nā) is converted to nitrates by nitrogen-fixing bacteria or by lightning (nitrogen fixation).
- Nitrogen-fixing bacteria live in soil or in root nodules of legumes (special plants).
- Plants absorb nitrates to make proteins and other compounds; animals obtain nitrogen by eating plants.
- When plants and animals die or excrete waste, decomposer bacteria convert nitrogen compounds into ammonia in the soil.
- Nitrifying bacteria then convert ammonia first to nitrites and then to nitrates, which plants can use.
- Denitrifying bacteria convert excess nitrates in the soil back to nitrogen gas, returning it to the atmosphere.
Types of Bacteria in the Nitrogen Cycle
- Nitrogen-fixing bacteria: Convert nitrogen gas to nitrates.
- Decomposer bacteria: Break down dead material to release ammonia.
- Nitrifying bacteria: Convert ammonia to nitrites and then nitrates.
- Denitrifying bacteria: Convert nitrates back to nitrogen gas.
Key Terms & Definitions
- Nitrogen fixation ā Conversion of nitrogen gas into usable nitrates by bacteria or lightning.
- Nitrates ā Usable form of nitrogen for plants.
- Ammonia ā Nitrogen compound produced by decomposers from dead organic matter.
- Nitrifying bacteria ā Bacteria that convert ammonia into nitrites and then nitrates.
- Denitrification ā Conversion of nitrates back to nitrogen gas by bacteria.
Action Items / Next Steps
- Learn and memorize the four types of bacteria and their roles in the nitrogen cycle.
- Review the nitrogen cycle diagram and be able to explain each step.