The Nitrogen Cycle

AQA A-level BiologyNutrient CyclesLesson 3 of 13

Nitrogen is needed to make amino acids (and so proteins) and nucleotides (DNA, RNA and ATP). The air is about 78% nitrogen gas (N₂), but plants and animals cannot use it directly. Plants absorb nitrogen from the soil, mainly as nitrate ions (NO₃⁻), by active transport. Animals obtain nitrogen by eating plants or other animals.

Four processes, all carried out by bacteria, move nitrogen around the cycle:

More in Nutrient Cycles

• Nutrient Cycles
• Role of Saprobionts
• Nitrogen Fixation
• Ammonification
• Nitrification
• Denitrification
• The Phosphorus Cycle
• Mycorrhizae

All 13 lessons in Nutrient Cycles · All AQA A-level Biology topics