The nitrogen cycle
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Ari reads a graph of two plots. By how many mg per kg do the two lines differ at week 6?
- 8 mg per kg
- 34 mg per kg
- 22 mg per kg
- 10 mg per kg
Zee reads the graph. What was the bean plot's average gain per week from week 0 to week 8?
Use the picture in question 1.
- 2 mg per kg per week
- 1 mg per kg per week
- 8 mg per kg per week
- 4 mg per kg per week
Luz reads the graph. Which statement explains why the two lines moved apart?
Use the picture in question 1.
- Rhizobium in the bean roots added fixed nitrogen, while grass took nitrate up
- Nitrogen taken up by grass was used up, and beans gained by chance
- Decomposers destroyed nitrogen in the grass plot, but not in the bean plot
- Bean leaves took N₂ gas from the air, but grass leaves could not
In a model bean plot, Rhizobium bacteria are missing from the root nodules. Bo predicts what happens to the nitrogen the beans can use.
- It rises, because the bacteria were taking nitrogen from the beans
- It stays the same, because bean leaves take N₂ from the air
- It falls, because nothing in the nodules fixes N₂
- It stays the same, because soil nitrogen does not run out
In a model soil sample, denitrifying bacteria become more active. Luz predicts what changes in the soil.
- Nitrate stays equal, since decomposers destroy the extra nitrogen
- More ammonium becomes nitrite, so soil nitrite falls
- More nitrate becomes N₂ gas, so soil nitrate falls
- More N₂ becomes usable nitrogen, so soil nitrate rises
A pile of leaf remains and wastes lies in a model plot, and decomposers start work. Noah predicts what rises in the soil first.
- Nothing, since decomposers destroy the nitrogen in remains
- N₂ gas, released by the decomposers
- Nitrate, made straight from the remains
- Ammonium, made by ammonification
Read this first
Use the table
Card (model data). Soil nitrate at the start and at week 8.
plot crop start (mg per kg) week 8 (mg per kg) 1 grass 15 11 2 beans 15 23 3 peas 12 18 Notebook, 3 lines. Line 1: Grass roots took up nitrate, so the grass plot fell from 15 to 11 mg per kg. Line 2: So the grass plot lost nitrate. Line 3: The bean plot went from 15 to 23, so it gained 23 mg per kg.
Tala reads a notebook entry about two plots. Which line has a flaw?
- Line 2: decomposers destroyed the nitrate the grass lost
- Line 1: grass makes nitrate from the N₂ in the air
- No line has a flaw, since the bean plot gained the full 23
- Line 3: the bean plot gained 23 − 15 = 8 mg per kg
Ari's friend says plants use up the nitrogen in soil, so soil always runs short. Which reply is best?
- Disagree: plants take N₂ from the air, so soil nitrogen does not matter
- Agree: the nitrogen a plant takes up leaves the cycle for good
- Disagree: nitrogen in wastes and remains returns to the soil as ammonium
- Agree: decomposers destroy nitrogen in remains, so less returns each year
Kira's friend says bacteria in soil only harm plants, so soil would be better without them. Which reply is best?
Use the picture in question 8.
- Disagree: plants need no bacteria, since leaves take N₂ from the air
- Disagree: soil bacteria turn nitrate into N₂ gas, which plants use
- Agree: bacteria compete with roots for the nitrogen in the soil
- Disagree: soil bacteria fix N₂ and make nitrate that roots take up
Esme's friend says fixation and denitrification are the same process, since both change N₂. Which reply is best?
Use the picture in question 8.
- Disagree: fixation makes ammonium from remains, and denitrification makes nitrate
- Disagree: fixation returns N₂ to the air, and denitrification makes it usable
- Agree: both processes turn N₂ into forms plants can use
- Disagree: fixation makes N₂ usable; denitrification turns nitrate into N₂