Worksheet: The Nitrogen Cycle

In this worksheet, we will practice describing the nitrogen cycle, and explaining the importance of nitrates for plants.

Q1:

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

  • AGaseous nitrogen
  • BNitrous oxide
  • CNitrogen dioxide
  • DNitrites
  • ENitrates

Q2:

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

  • APlants require nitrogen to aid the movement of sucrose through the plant.
  • BPlants require nitrogen to synthesize important nitrogen-containing compounds, like proteins.
  • CPlants require nitrogen to be broken down during cellular respiration to release energy.
  • DPlants require nitrogen as it is a reactant in the process of photosynthesis.

Q3:

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

Root nodules on a pea plant.

The relationship between the bacteria and the pea plant is described as mutualistic; what does this mean?

  • AThe pea plant benefits from the relationship, but the bacteria do not.
  • BThe bacteria benefit from the relationship, but the pea plant does not.
  • CBoth the bacteria and the pea plant benefit from this relationship.
  • DNeither the bacteria nor the pea plant benefits from this relationship.

Q4:

Legumes (e.g., pea plants) are able to increase the level of soil nitrogen where they are planted. Which of the following is a benefit this provides?

  • AAn increase in soil nitrogen means less nitrogen-fixing bacteria will be present in the soil.
  • BThere is more nitrogen available in the soil for other crops that are planted there.
  • CThere is less nitrogen in the soil after they are removed, so there is less to be converted into nitrogen gas.
  • DAn increase in soil nitrogen means this soil can be used as fertilizer elsewhere.

Q5:

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

  • ADecomposers
  • BNitrifying bacteria
  • CDenitrifying bacteria
  • DNitrogen-fixing bacteria

Q6:

Which organisms in the nitrogen cycle convert ammonium ions into nitrites and then into nitrates?

  • ADenitrifying bacteria
  • BDecomposers
  • CNitrogen-fixing bacteria
  • DNitrifying bacteria

Q7:

Which organisms in the nitrogen cycle convert proteins, contained in urea and the bodies of dead organisms, into ammonia?

  • ANitrogen-fixing bacteria
  • BDecomposers
  • CNitrifying bacteria
  • DDenitrifying bacteria

Q8:

Why can plants not absorb nitrogen directly from the atmosphere?

  • AGaseous nitrogen is too unreactive to be absorbed and used by plants.
  • BGaseous nitrogen is too reactive to be taken in directly by plants and must go through the roots.
  • CNitrogen only makes up less than 1% of the gases in the atmosphere, so there is not enough to be absorbed.
  • DNitrogen in the atmosphere evaporates before it can be absorbed.

Q9:

Which organisms involved in the nitrogen cycle convert nitrogen gas into nitrogen compounds in the soil?

  • ANitrifying bacteria
  • BNitrogen-fixing bacteria
  • CDecomposers
  • DDenitrifying bacteria

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