Nutrient Cycle Flashcards
What is the role of decomposers in the nutrient cycle?
Decomposers break down organic matter, releasing nutrients like nitrogen and phosphorus back into the soil.
Name two types of nitrogen-fixing bacteria.
Rhizobium (in root nodules) and Azotobacter (free-living in soil).
What is nitrification?
The process where ammonia is oxidized to nitrites (NO2-) by Nitrosomonas and then to nitrates (NO3-) by Nitrobacter.
How do plants absorb nitrogen?
In the form of nitrates (NO3-) or ammonium ions (NH4+).
State the process by which nitrogen gas is converted into ammonia.
Nitrogen fixation.
Explain how plowing fields can affect the nitrogen cycle.
Plowing aerates the soil, increasing oxygen levels and promoting nitrification by nitrifying bacteria.
Why do farmers add fertilizers to soil?
To replace nutrients like nitrogen and phosphorus removed by crop harvesting, ensuring continued plant growth.
A field is waterlogged. Explain how this affects nitrogen availability.
Waterlogging creates anaerobic conditions, promoting denitrification, which reduces nitrate availability.
Describe how crop rotation helps maintain soil fertility.
Including leguminous plants in rotation fixes atmospheric nitrogen, replenishing soil nitrate levels.
How do mycorrhizae benefit plants?
Mycorrhizae are fungi that form symbiotic relationships with roots, increasing surface area for nutrient and water absorption.
A graph shows nitrogen content in soil over a growing season. Explain why it decreases.
Nitrogen is absorbed by plants for growth and lost through leaching and denitrification.
A farmer notices increased crop yield after adding phosphate fertilizer. Explain why.
Phosphates are essential for DNA, RNA, ATP, and phospholipids, supporting growth and energy transfer.
Explain the role of ammonification in the nitrogen cycle.
Ammonification is the conversion of organic nitrogen in dead organisms into ammonium ions (NH4+) by decomposers.
Describe the stages of the nitrogen cycle.
- Nitrogen fixation: Nitrogen gas is converted into ammonia by bacteria or lightning. 2. Ammonification: Organic nitrogen is decomposed into ammonium ions. 3. Nitrification: Ammonium is oxidized to nitrites and then nitrates. 4. Assimilation: Plants absorb nitrates. 5. Denitrification: Nitrates are reduced to nitrogen gas under anaerobic conditions.
Outline the phosphorus cycle.
Phosphate ions are released from weathered rocks. Absorbed by plants and passed through the food chain. Decomposers return phosphates to soil or water. Some are deposited in sediment and form new rocks over time.
Explain how human activities disrupt the nitrogen cycle.
Fertilizers add excess nitrates, leading to leaching and eutrophication. Burning fossil fuels releases nitrogen oxides, contributing to acid rain.
Compare and contrast nitrogen and phosphorus cycles.
Both involve uptake by plants and recycling through decomposers. The nitrogen cycle includes atmospheric components (e.g., fixation), while the phosphorus cycle is sediment-based.
How does eutrophication occur?
Excess nutrients (nitrates and phosphates) from fertilizers run off into water bodies, causing algal blooms. Decomposition of algae depletes oxygen, leading to fish deaths.
Suggest a method to prevent eutrophication from agricultural runoff.
Use buffer strips of vegetation to absorb nutrients before they enter water bodies.
Why is crop harvesting a disruption to the nutrient cycle?
Harvesting removes biomass that would otherwise decompose and recycle nutrients back into the soil.
Explain how legumes improve soil fertility.
Legumes form root nodules with Rhizobium, fixing atmospheric nitrogen into a form usable by plants.
Explain the role of saprobionts in the carbon and nitrogen cycles.
Saprobionts decompose organic matter, releasing carbon dioxide (via respiration) and ammonium ions (via ammonification).
How does deforestation affect nutrient cycles?
It reduces biomass decomposition, decreasing nutrient recycling, and increases runoff, causing leaching.
Suggest how global warming could impact the nutrient cycle.
Warmer temperatures may speed up decomposition and nitrogen fixation but increase denitrification due to more anaerobic conditions in waterlogged soils.
Describe how the use of artificial fertilizers impacts ecosystems.
Artificial fertilizers add excess nutrients, disrupting natural cycles, leading to leaching, eutrophication, and loss of biodiversity.
