Material Cycles — Carbon & Nitrogen

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FreeScienceLessons · AQA BiologyThe Carbon Cycle

Key facts

Carbon cycle — key processes

Photosynthesis — removes CO₂ from air; plants fix carbon into glucose
Respiration (all organisms) — releases CO₂ back to atmosphere
Feeding — carbon passes from plants to animals through food chains
Decomposition — decomposers (bacteria, fungi) break down dead organic matter, releasing CO₂ through respiration
Combustion — burning fossil fuels/wood releases stored carbon as CO₂

Nitrogen cycle — key processes

Nitrogen fixation — nitrogen-fixing bacteria in soil/root nodules convert N₂ → ammonia/nitrates
Decomposition — decomposers break down proteins and urea → ammonia
Nitrification — nitrifying bacteria convert ammonia → nitrates
Denitrification — denitrifying bacteria convert nitrates → N₂ (returns to atmosphere)
Plants absorb nitrates through roots for making amino acids and proteins

Exam questions — 3 questions · 10 marks total

1 markDecomposersAQA 8461 style

What is the role of decomposers in the carbon cycle?

A They convert carbon dioxide into glucose

B They break down dead organic matter, releasing carbon dioxide through respiration

C They absorb carbon from the soil into their cells

D They produce oxygen from carbon dioxide

6 marksDescribe the carbon cycleAQA Jun 2023 P2 Q4 — real 6-mark question

Describe how carbon is cycled between living organisms and the atmosphere. (6 marks)

Hint: Trace carbon through the whole cycle: CO₂ → photosynthesis → plant glucose → eaten by animals → respiration → CO₂. Include decomposers and combustion for Level 3.

+60 XP

3 marksNitrogen cycleAQA 8461 style

Describe the role of bacteria in the nitrogen cycle. Name at least two different types of bacteria and explain what each does. (3 marks)

Hint: Name the type of bacteria, then say exactly what they convert and what they produce.

+30 XP

Material Cycles — Carbon & Nitrogen

Carbon cycle — key processes

Nitrogen cycle — key processes

Module complete! 🎉