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?
- 10 mg per kg
- 34 mg per kg
- 8 mg per kg
- 22 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
- 8 mg per kg per week
- 2 mg per kg per week
Luz reads the graph. Which statement explains why the two lines moved apart?
Use the picture in question 1.
- Bean leaves took N₂ gas from the air, but grass leaves could not
- 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
- 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 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.
- More nitrate becomes N₂ gas, so soil nitrate falls
- More ammonium becomes nitrite, so soil nitrite falls
- More N₂ becomes usable nitrogen, so soil nitrate rises
- Nitrate stays equal, since decomposers destroy the extra nitrogen
A pile of leaf remains and wastes lies in a model plot, and decomposers start work. Noah predicts what rises in the soil first.
- N₂ gas, released by the decomposers
- Nothing, since decomposers destroy the nitrogen in remains
- Ammonium, made by ammonification
- Nitrate, made straight from the remains
Read this first
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
- No line has a flaw, since denitrification and fixation are one step
- Line 1: nitrifying bacteria, not denitrifying ones, change nitrate to N₂
- Line 3: plants cannot use N₂, and fixation makes usable forms
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?
- No line has a flaw, since the bean plot gained the full 23
- Line 2: decomposers destroyed the nitrate the grass lost
- Line 3: the bean plot gained 23 − 15 = 8 mg per kg
- Line 1: grass makes nitrate from the N₂ in the air
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
Esme's friend says fixation and denitrification are the same process, since both change N₂. Which reply is best?
Use the picture in question 9.
- Disagree: fixation returns N₂ to the air, and denitrification makes it usable
- Disagree: fixation makes ammonium from remains, and denitrification makes nitrate
- Disagree: fixation makes N₂ usable; denitrification turns nitrate into N₂
- Agree: both processes turn N₂ into forms plants can use