The nitrogen cycle

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Use the table

   Card (model data). Garden plots at the end of one season.

   plot	crop	nitrate at start (mg per kg)	nitrate at end (mg per kg)
   1	peas	10	16
   2	grass	10	7
   3	beans	12	19
   4	grass	12	9

2. 1.

   Zee compares two plots on the card. At the end, how much more nitrate does Plot 1 have than Plot 2?

   • 6 mg per kg
   • 3 mg per kg
   • 23 mg per kg
   • 9 mg per kg
3. 2.

   Bo reads the card. Which statement does the card support?

   • Nitrate rose in the legume plots and fell in the grass plots
   • The crop made no difference to the change in nitrate
   • Nitrate rose most in Plot 4, which grew grass
   • Nitrate fell in the legume plots and rose in the grass plots
4. 3.

   Esme reads the card of ways N₂ gets fixed. Which fixer is not a living thing?

   • Rhizobium, since it needs a plant root to live in
   • Azotobacter, since it lives apart from any plant
   • Lightning
   • Cyanobacteria, since they live in the water
5. 4.

   Jun finds fixed nitrogen in a sunlit pond. Which fixer on the card could be at work there?

   • Rhizobium bacteria in legume root nodules
   • Denitrifying bacteria turning nitrate into N₂
   • No fixer, since bacteria in pond water harm plants rather than help
   • Cyanobacteria
6. 5.

   Kira compares two fixers on the card. How does lightning fixation differ from fixation by Rhizobium?

   • Lightning splits N₂ in the air; Rhizobium fix it inside root nodules
   • Lightning is a living thing, but Rhizobium is not a living thing
   • Plants take N₂ straight from lightning, but cannot take it from Rhizobium
   • Rhizobium bacteria harm the plant, but lightning gives it nitrogen
7. 6.

   Ari follows one nitrogen atom. Remains of a pea plant reach the soil. What belongs in the blank box?

   • Nothing, since decomposers destroy the nitrogen
   • N₂ gas
   • Ammonium
   • Nitrate
8. 7.

   Luz follows nitrogen that grass roots took up as nitrate. Which route in the diagram returns it to the soil?

   • No route, since nitrogen that plants take up is used up
   • Fixation, which reverses the uptake by roots
   • Denitrification, which makes ammonium from nitrate
   • Wastes and remains, then ammonification
9. 8.

   Farmers add ammonium nitrate fertilizer to soil. Milo asks which forms of nitrogen plant roots can take up from it.

   • Nitrate and ammonium
   • Nitrite, which fixation makes from N₂ gas
   • N₂ gas, which fills the air spaces in the soil
   • Wastes and remains, before decomposers change them

10. Use the table

    Card (model data). Soil nitrate in one plot over one week.

    item	mg per kg
    nitrate at the start of the week	20
    added by nitrification	9
    removed by plant uptake	6
    removed by denitrification	2

11. 9.

    Noah reads a budget card for one plot. How much nitrate is in the soil at the end of the week?

    • 25 mg per kg
    • 37 mg per kg
    • 21 mg per kg
    • 23 mg per kg
12. 10.

    Pia reads a card for Plot 2. Grass roots took up nitrate, and the nitrate in the soil fell. What can happen to that nitrogen later?

    • It is used up, so it cannot return to the soil
    • It is destroyed by decomposers in the soil
    • It joins wastes and remains, then returns to the soil as ammonium
    • It moves into root nodules, where Rhizobium fix it