Nutrient cycles Flashcards – Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028)

How do plants incorporate atmospheric carbon into organic substances?

They take in carbon dioxide during photosynthesis and incorporate its carbon into organic substances.

How is carbon transferred between organisms through feeding?

Carbon passes from one organism to another when one feeds on the other.

Which organisms release carbon dioxide through respiration?

Plants, animals and decomposers.

How does decomposition transfer carbon to decomposers?

Decomposers break down dead organisms and waste, taking in their carbon.

How can carbon in buried remains become part of fossil fuels?

Some buried remains may eventually form fossil fuels.

How does combustion of fossil fuels return carbon to the atmosphere?

It releases stored carbon as carbon dioxide.

Between which three parts of the environment does nitrogen move in the nitrogen cycle?

The atmosphere, soil and living organisms, in different chemical forms.

What do nitrogen-fixing bacteria convert atmospheric nitrogen into?

Ammonium compounds.

How does lightning bring atmospheric nitrogen into the soil?

It causes atmospheric nitrogen to form compounds that enter the soil as nitrates.

What is the sequence of conversions carried out by nitrifying bacteria?

Ammonium ions → nitrite ions → nitrate ions.

How do plants use the nitrogen they absorb from soil?

They absorb nitrate ions and use the nitrogen to make amino acids and proteins.

How do animals obtain and use nitrogen from dietary proteins?

Feeding transfers proteins to animals. Digestion breaks them into amino acids, which animals can use to make their own proteins.

How do decomposer microorganisms return nitrogen from dead organisms and waste to the soil?

They break down proteins, releasing ammonium ions into the soil.

What happens during deamination of excess amino acids in animals?

The nitrogen-containing part is removed, producing nitrogen-containing waste that can return to the environment.

What do denitrifying bacteria do in the nitrogen cycle?

They convert soil nitrate ions into nitrogen gas, returning nitrogen to the atmosphere.