Nitrogen in the Earth's Atmosphere

In what form do plants absorb the majority of nitrogen from the soil?

• Gaseous Nitrogen

• Nitrous Oxide

• Nitrogen Dioxide

• Nitrites

• Nitrates

Which of the following best explains why plants need to absorb nitrogen from the soil?

• Plants require nitrogen to aid the movement of sucrose through the plant.

• Plants require nitrogen to synthesize important nitrogen-containing compounds, like proteins.

• Plants require nitrogen to be broken down during cellular respiration to release energy.

• Plants require nitrogen as it is a reactant in the process of photosynthesis.

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Why is the nitrogen cycle important for living things?

• It helps them use water.

• It releases carbon dioxide.

• It helps build proteins (in cells and DNA).

• It cools the body.

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What percentage of Earth’s atmosphere is nitrogen gas (“free” nitrogen)?

Can most organisms use “free” nitrogen gas in the atmosphere?

• Yes

• No

Which of the following performs most nitrogen fixation?

• Plants

• Bacteria

• Animals

• Soil

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What do decomposers (decomposition) do in the nitrogen cycle?

• change nitrogen to gas

• put nitrogen into soil

• put nitrogen into the air

• get rid of bacteria

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Bacteria break down organic matter and return carbon dioxide to the environment. This is an example of

• denitrification

• decomposition

• nitrogen fixation

• symbiosis

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The picture shows root nodules on a pea plant. Those root nodules are colonized by nitrogen-fixing bacteria.

• The pea plant benefits from the relationship, but the bacteria do not.

• The bacteria benefit from the relationship, but the pea plant does not.

• Both the bacteria and the pea plant benefit from this relationship.

• Neither the bacteria nor the pea plant benefits from this relationship.

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Which organisms convert nitrates in the soil back into atmospheric nitrogen?

• Decomposers

• Nitrifying bacteria

• Denitrifying bacteria

• Nitrogen-fixing bacteria

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