Worksheet Grade 6 Science
Ashgrove Water Reclamation: Nitrogen In, Nitrogen Out
A grade 6 worksheet on a fictional reclamation plant, where students find nitrogen removal percent and weigh nitrogen as a river pollutant and a farm resource.
Objectives
- Students will find nitrogen removal as a percent of the nitrogen coming into a plant.
- Students will explain why nitrogen is a useful resource on a farm but a pollutant in a river.
Vocabulary
Key words: nitrogen, nutrient, removal efficiency, reclamation
Teacher overview
Nitrogen is a nutrient. Plants need it to grow, so it is a useful resource on a farm. Yet too much nitrogen in a river feeds heavy algae growth, which harms fish, so the same nitrogen becomes a pollutant. A reclamation plant cleans used water and removes most of its nitrogen before releasing it. This worksheet has students find how much nitrogen the fictional Ashgrove plant removes and think about where the nitrogen could do good instead of harm. A common error is dividing by the nitrogen that is left rather than by the nitrogen that came in; removal is always a share of the incoming amount.
Student Worksheet
The Ashgrove Water Reclamation plant is a fictional plant that cleans used water. It measures nitrogen in milligrams per liter (mg/L). Use these facts for every problem.
- Removal percent = (nitrogen in minus nitrogen out) divided by nitrogen in, times 100.
- Sample 1: the incoming water has 40 mg/L of nitrogen, and the cleaned water has 8 mg/L.
In Sample 1, how many mg/L of nitrogen did the plant remove?
Find the removal percent for Sample 1.
What percent of the incoming nitrogen is still in the cleaned water?
Sample 2 has 50 mg/L of nitrogen coming in and 10 mg/L going out. How many mg/L were removed?
Find the removal percent for Sample 2.
Samples 1 and 2 have different amounts of nitrogen but the same removal percent. Show the two percents and state whether that claim is true.
Write the ratio of nitrogen out to nitrogen in for Sample 1 in simplest form.
Nitrogen makes plants grow. Explain why the cleaned water leaving Ashgrove could still cause an algae bloom in a slow river even at 8 mg/L.
Explain why nitrogen is called a resource on a farm but a pollutant in a river.
Name one way the plant could send its nitrogen where it helps instead of harms, and explain your choice.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: 32 mg/L.
40 mg/L in minus 8 mg/L out = 32 mg/L removed.Answer: 80 percent.
32 mg/L removed divided by 40 mg/L in = 0.8, times 100 = 80 percent.Answer: 20 percent.
8 mg/L left divided by 40 mg/L in = 0.2, times 100 = 20 percent.Answer: 40 mg/L.
50 mg/L in minus 10 mg/L out = 40 mg/L removed.Answer: 80 percent.
40 mg/L removed divided by 50 mg/L in = 0.8, times 100 = 80 percent.Answer: True, both are 80 percent.
Sample 1 removes 80 percent and Sample 2 removes 80 percent, so the removal percent is the same even though the amounts differ.Answer: 1 to 5.
Nitrogen out to nitrogen in is 8 to 40. Both divide by 8 to give 1 to 5.Answer: Even at 8 mg/L, the water still adds nitrogen to the river. In a slow river the nitrogen builds up and feeds algae, so a bloom can still form. Accept answers that connect leftover nitrogen to algae growth.
Answer: On a farm, nitrogen feeds crops, so it is a helpful resource. In a river, extra nitrogen feeds too much algae, which uses up oxygen and harms fish, so it becomes a pollutant. The nitrogen is the same in both places, and where it ends up decides whether it helps or harms.
Answer: One good answer is to use the cleaned, nitrogen-rich water to irrigate farm fields or lawns, where the nitrogen feeds plants instead of feeding river algae. Accept any reuse that puts the nitrogen where plants can take it up.
Differentiation
Support
Give students the removal formula written as a labeled fraction, with Sample 1's numbers filled in, and work problem 2 aloud before they continue. Let them use a calculator and highlight the incoming amount so they always divide by that number.
Extension
Ask students to find the nitrogen-out reading that would give a 90 percent removal from an incoming 40 mg/L, and to show the steps that lead to their answer.
ELL supports
Pre-teach "nitrogen," "nutrient," and "removal" with a picture of a plant growing in one frame and green algae covering a pond in another. Provide the frame "Nitrogen helps plants, but too much in a river causes ___," and allow short-phrase answers for items 8, 9, and 10.