IGCSE Nitrogen Cycle & Eutrophication

Which of the following is true about nitrogen?

• It is the most common gas in air

• It is unreactive as a gas

• It is needed to make all proteins

• It is taken up as a gas through the roots of plants

What is true of nitrogen fixation?

• It converts nitrogen gas to nitrates

• It is carried out by bacteria but can also happen by lightning

• It converts ammonia to nitrates

• It converts nitrogen gas to ammonia

Which is true of nitrification?

• It converts ammonia to nitrates

• It converts nitrates to nitrogen gas

• It is carried out by bacteria

• It requires nitrogen gas

Which is true of denitrification?

• It converts ammonia to nitrates

• It can occur due to lightning

• It converts nitrates to nitrogen gas

• It benefits the plant

How can nitrogen become part of animal proteins?

• Animals inhale nitrogen gas

• Animals feed on plants

• Animals eat carbohydrates

• Animals inhale nitrous oxide gas

In the nitrogen cycle, in what form do decomposers release nitrogen from dead plants and animals?

• nitrogen gas

• ammonia

• nitrate ions

• nitrous oxide gas

Which of the following stages in the nitrogen cycle require bacteria?

• nitrogen fixation

• nitrification

• decomposition

• denitrification

What can be a source of nitrates for eutrophication in rivers?

• fertilisers

• plastic bottles

• paper

• sewage

What is the very next thing that happens after fertilisers enter a river in eutrophication?

• Fish die due to a lack of oxygen

• Plants below the surface die due to a lack of sunlight

• The number of aerobic bacteria increases

• Fast growth of plants

What is the very next thing that happens after fast growth of plants in eutrophication?

• Fish die due to a lack of oxygen

• Plants below the surface die due to a lack of sunlight

• The number of aerobic bacteria increases

• Plants on the surface die due to too much sunlight