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Combined Science: Biology

GCSE · Edexcel · higher

QuestionsFlashcards

Disease
Defence Against Disease
Development of Medicines
- Antibiotics
  4
- Discovery & Development of New Drugs
  6
Non-Communicable Diseases
- Lifestyle & Non-Communicable Disease
  8
- Cardiovascular Disease
  6

The Organism in the Environment
Human Influences on the Environment
- Human Impact on Biodiversity
  6
- Benefits of Maintaining Biodiversity
  6
Cycles within Ecosystems

The Nitrogen Cycle Flashcards

All 7 cards in this deck

What do nitrifying bacteria do in the nitrogen cycle?: They convert ammonia into nitrites and nitrates.
What do denitrifying bacteria do in the nitrogen cycle?: They convert nitrates (or nitrites) back into atmospheric nitrogen gas.
Which organisms break down dead animals and plants into ammonia in the nitrogen cycle?: Decomposers — fungi and decomposing bacteria.
Why do farmers plant leguminous crops such as peas and beans as part of crop rotation?: They have nitrogen-fixing bacteria in root nodules that fix atmospheric nitrogen, increasing nitrate/ammonia levels in the soil.
True or false? Plants absorb nitrogen gas from the air to make proteins.: False. Plants absorb nitrates from the soil through their roots and use them to make amino acids and proteins.
How does spreading manure or compost on a field increase the nitrates in the soil?: Decomposers break down the proteins and wastes in it, returning the nitrogen to the soil, where nitrifying bacteria turn it into nitrates. (Artificial fertilisers add nitrates directly.)
What do nitrogen-fixing bacteria do in the nitrogen cycle?: They convert nitrogen gas from the air into ammonia, which forms ammonium ions that plants can use. Some live free in the soil; others live in the root nodules of legumes.