Carbon and nitrogen cycles

What is the carbon cycle?

The recycling of carbon between the atmosphere, plants, animals, and decomposers.

What processes remove CO₂ from the atmosphere?

Photosynthesis (plants and algae).

What processes return CO₂ to the atmosphere?

Respiration (plants, animals, microbes), combustion of fossil fuels, decomposition of dead organisms.

How does deforestation affect the carbon cycle?

Reduces photosynthesis → more CO₂ in the atmosphere → contributes to global warming.

What is the role of decomposers in the carbon cycle?

Break down dead material → release CO₂ during respiration.

Why is nitrogen important?

Needed to make amino acids, proteins, and DNA.

Can plants use nitrogen directly from the air?

No, nitrogen gas (N₂) is inert. It must be converted to nitrates or ammonium compounds.

What is nitrogen fixation?

Conversion of nitrogen gas (N₂) into ammonia (NH₃) or nitrates (NO₃⁻) that plants can use.

How does nitrogen fixation occur?

• Lightning → converts N₂ to nitrates in soil.

• Nitrogen-fixing bacteria (in root nodules of legumes).

What is nitrification?

Conversion of ammonium (NH₄⁺) → nitrites (NO₂⁻) → nitrates (NO₃⁻) by nitrifying bacteria in soil.

What is nitrogen assimilation?

Plants absorb nitrates from soil → used to make amino acids and proteins.

How do animals get nitrogen?

By eating plants or other animals → use amino acids to make proteins.

What is ammonification?

Decomposition of dead organisms and animal waste → forms ammonium compounds in the soil.

What is denitrification?

Conversion of nitrates back into nitrogen gas (N₂) by denitrifying bacteria, reducing soil fertility.

How do fertilisers affect the nitrogen cycle?

Add extra nitrates → increases crop yield but can cause eutrophication in water bodies.

How does burning fossil fuels affect the carbon cycle?

Releases stored carbon → increases atmospheric CO₂ → contributes to global warming.

How does deforestation affect both cycles?

Less photosynthesis → more CO₂ in atmosphere, fewer nitrogen-fixing plants → reduced soil fertility.