The nitrogen cycle

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   Ari reads a flow diagram of a pea field. The process on the arrow from N₂ gas in air to living things is blank. Which process is it?

   • Ammonification, which makes ammonium from remains
   • Denitrification, which sends nitrate back to the air
   • Nitrogen fixation
   • Nitrification, which makes nitrate from ammonium
2. 2.

   Bo reads a flow diagram. The process on the arrow from nitrate to N₂ gas in air is blank. Which process is it?

   • Denitrification
   • Nitrogen fixation, which makes N₂ usable for plants
   • Uptake by roots, which removes nitrate for good
   • Nitrification, which makes nitrate from nitrite
3. 3.

   Esme reads a flow diagram of a forest floor. The process on the arrow from wastes and remains to ammonium is blank. Which process is it?

   • Ammonification
   • Nitrification, which makes nitrite from ammonium
   • Denitrification, which sends nitrate back to the air
   • Destruction, which removes the nitrogen in the remains
4. 4.

   Jun learns the term nitrogen fixation. Which sentence gives its meaning?

   • N₂ gas is changed into a form living things can use
   • Plants use up the nitrogen in the soil so the soil runs out
   • Plants take in N₂ gas through their leaves and use it as it is
   • Bacteria change nitrate back into N₂ gas, which returns to the air
5. 5.

   Luz learns the term root nodule. Which sentence gives its meaning?

   • A small opening on a leaf where a plant takes in N₂ gas
   • A small part of a legume root where Rhizobium bacteria live
   • A small seed case that holds the nitrogen a bean plant needs
   • A small pocket in the soil where decomposers store nitrogen
6. 6.

   Ammonium; nitrate; N₂ gas; nitrite. Ammonification has just made the ammonium from wastes and remains. Milo lists forms of nitrogen in the order bacteria change them. Which order is right?

   • Ammonium, nitrite, nitrate, N₂ gas
   • Nitrate, nitrite, ammonium, N₂ gas
   • N₂ gas, ammonium, nitrite, nitrate
   • Ammonium, nitrate, nitrite, N₂ gas
7. 7.

   Noah follows one nitrogen atom from the air, into a pea plant, through the soil and back to the air. Which order of processes is right?

   • Fixation, ammonification, nitrification, denitrification
   • Denitrification, fixation, ammonification, nitrification
   • Fixation, nitrification, ammonification, denitrification
   • Ammonification, fixation, denitrification, nitrification
8. 8.

   Pia learns that gardeners grow peas to add nitrogen to the soil. Why do peas help?

   • Their roots make nitrogen from sunlight and water
   • Their leaves take N₂ gas from the air and store it in the soil
   • Bacteria around their roots are harmful, so peas make nitrogen alone
   • Rhizobium bacteria in their root nodules fix N₂ gas
9. 9.

   Ren looks at the roots of a bean plant. Which living things in the root nodules fix N₂?

   • Rhizobium bacteria
   • Decomposer fungi that make ammonium
   • Cyanobacteria from sunlit water
   • Pockets of N₂ gas the leaves took in
10. 10.

    Tala learns that Rhizobium bacteria live with a pea plant. Where in the plant do they fix N₂?

    • In the seeds, where the plant stores its nitrogen
    • In nodules on the roots
    • On the leaves, where air enters the plant
    • Nowhere, since peas fix N₂ without any bacteria