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.

   Tala reads the card. By how much did the nitrate in Plot 1 change from the start to the end?

   • It fell by 6 mg per kg
   • It rose by 16 mg per kg
   • It rose by 26 mg per kg
   • It rose by 6 mg per kg
3. 2.

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

   • 3 mg per kg
   • 23 mg per kg
   • 6 mg per kg
   • 9 mg per kg
4. 3.

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

   • Nitrate rose in the legume plots and fell in the grass plots
   • Nitrate rose most in Plot 4, which grew grass
   • Nitrate fell in the legume plots and rose in the grass plots
   • The crop made no difference to the change in nitrate
5. 4.

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

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

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

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

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

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

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

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

   Esme follows an ammonium ion in the soil. What does it become next, and which bacteria change it?

   • Nitrate, by nitrifying bacteria such as Nitrosomonas
   • Nitrite, by denitrifying bacteria such as Pseudomonas
   • Nitrite, by nitrifying bacteria such as Nitrosomonas
   • N₂ gas, by denitrifying bacteria such as Pseudomonas

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
    • 23 mg per kg
    • 37 mg per kg
    • 21 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