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?
- 22 mg per kg
- 8 mg per kg
- 34 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.
- 4 mg per kg per week
- 1 mg per kg per week
- 2 mg per kg per week
- 8 mg per kg per week
Luz reads the graph. Which statement explains why the two lines moved apart?
Use the picture in question 1.
- Nitrogen taken up by grass was used up, and beans gained by chance
- Bean leaves took N₂ gas from the air, but grass leaves could not
- Decomposers destroyed nitrogen in the grass plot, but not in the bean plot
- Rhizobium in the bean roots added fixed nitrogen, while grass took nitrate up
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 falls, because nothing in the nodules fixes N₂
- It stays the same, because soil nitrogen does not run out
- It rises, because the bacteria were taking nitrogen from the beans
- It stays the same, because bean leaves take N₂ from the air
In a model soil sample, denitrifying bacteria become more active. Luz predicts what changes in the soil.
- More N₂ becomes usable nitrogen, so soil nitrate rises
- 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
A pile of leaf remains and wastes lies in a model plot, and decomposers start work. Noah predicts what rises in the soil first.
- Ammonium, made by ammonification
- Nothing, since decomposers destroy the nitrogen in remains
- N₂ gas, released by the decomposers
- Nitrate, made straight from the remains
Read this first
Use this
Flow diagram (model, not to scale), soil and air. Boxes: N₂ gas in air; living things (organic nitrogen); wastes and remains; ammonium. Arrows: from N₂ gas in air to living things (organic nitrogen): process nitrogen fixation, by Rhizobium bacteria in legume root nodules. from living things (organic nitrogen) to wastes and remains: process wastes and remains pass to the soil. from wastes and remains to ammonium: process ammonification, by decomposer bacteria and fungi. Notebook, 3 lines. Line 1: Rhizobium bacteria in the pea root nodules fix N₂. Line 2: The pea plant also takes in N₂ gas through its leaves. Line 3: Remains of the pea plant are changed into ammonium by decomposers.
Pia reads a notebook entry about a pea plot. Which line has a flaw?
- Line 1: Rhizobium harm the pea, so they should not fix N₂
- Line 2: plants cannot use N₂ from the air until it is fixed
- Line 3: decomposers destroy the nitrogen, so no ammonium forms
- No line has a flaw, since nitrogen a plant takes in is used up
Use this
Flow diagram (model, not to scale), soil and air. Boxes: nitrate; N₂ gas in air. Arrows: from nitrate to N₂ gas in air: process denitrification, by denitrifying bacteria such as Pseudomonas and Clostridium. Notebook, 3 lines.
Ren reads a notebook entry about denitrification. Which line has a flaw?
- Line 2: the nitrogen is used up, so nothing returns to the air
- Line 1: nitrifying bacteria, not denitrifying ones, change nitrate to N₂
- No line has a flaw, since denitrification and fixation are one step
- Line 3: plants cannot use N₂, and fixation makes usable forms
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
- Agree: decomposers destroy nitrogen in remains, so less returns each year
- Disagree: nitrogen in wastes and remains returns to the soil as ammonium
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 9.
- 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
- Disagree: plants need no bacteria, since leaves take N₂ from the air
