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Lesson plan Grade 8 English Language Arts

How Sable Fork Turns Salty Groundwater Into Tap Water

A 50-minute grade 8 lesson where students read about reverse osmosis at a fictional plant and write an explanatory paragraph of the process in order.

Objectives

  1. Students will explain the reverse osmosis process in the correct order using sequence transitions.
  2. Students will use the terms membrane, pressure, and concentrate accurately in an explanatory paragraph.

Vocabulary

Reverse osmosis
Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.

Also: membrane, pressure, concentrate, brackish

Teacher overview

Explaining a process clearly is a skill students can practice on almost any topic, and a water treatment plant gives them a real one with a definite order. This lesson uses a fictional plant that removes salt from brackish groundwater by reverse osmosis. Students read a short account of how the process works, then write an explanatory paragraph that puts the steps in order with precise vocabulary. The lesson keeps the science light so the focus stays on organizing and wording an explanation.

Procedure

Hook (5 min): Show a glass of clear water and a glass of salt water that look identical, and keep both for display only, with no tasting. Ask students how a town might turn the salty one into safe drinking water. Collect a few ideas on the board.

Direct instruction (12 min): Explain the process. Sable Fork is a fictional inland town whose groundwater is brackish, meaning slightly salty. Its plant uses reverse osmosis. First, a strong pump raises the salty water to high pressure. Next, that pressure forces the water against a semipermeable membrane, a thin sheet with holes so small that water molecules slip through while salt is held back. Then the clean water collects on the far side and moves on toward homes. Finally, the salty water left behind, called the concentrate, is carried away for disposal. Because it needs strong pumps, reverse osmosis uses more energy than ordinary treatment of fresh water. Removing salt from seawater this way takes roughly 11 to 15 kWh for each 1,000 gallons, compared with about 1 to 2 kWh for ordinary treatment, and less-salty brackish water takes less.

Model (8 min): On the board, turn the process into one explanatory paragraph. Think aloud as you choose sequence transitions (first, next, then, finally) and precise nouns (membrane, pressure, concentrate). Point out that an explanation names each step and connects them in order, rather than listing facts at random.

Guided practice (12 min): In pairs, students complete Part A of the handout, defining the key terms and ordering the four steps. Circulate to confirm they can state what the membrane does before they try to write about it.

Independent practice (8 min): Each student writes the explanatory paragraph in Part B, using the three required terms and at least two sequence transitions.

Closure and formative check (5 min): Ask students to hold up their step order from item 4. Confirm the correct sequence as a class, and use any disagreement to reteach the order before collecting the paragraphs.

How Sable Fork Turns Salty Groundwater Into Tap Water — Grade 8 English Language Arts
Name: ____________________________ Date: ______________

Student Handout

The town of Sable Fork removes salt from its brackish groundwater by reverse osmosis. Use the lesson to answer each item.

Part A.

  1. In your own words, what does a semipermeable membrane do?
  2. What provides the push that forces water through the membrane?
  3. After the clean water passes through, what is left behind, and what is that leftover stream called?
  4. Number these four events 1 to 4 in the order they happen: (a) the salty water is pumped to high pressure; (b) clean water collects on the far side; (c) water is forced through the membrane while salt is held back; (d) the leftover concentrate is carried away.

Part B.

  1. Write an informative paragraph of four to six sentences that explains how reverse osmosis makes salty water drinkable. Use the words membrane, pressure, and concentrate, and use at least two sequence transitions such as first, next, then, or finally.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: A semipermeable membrane lets water molecules pass through its tiny holes while holding back the salt, so the water that gets through is cleaner than the water going in.
  2. Answer: A strong pump provides the push by raising the salty water to high pressure, which forces it against the membrane.
  3. Answer: The salt that could not pass through is left behind in a saltier stream of water called the concentrate.
  4. Answer: The order is a, c, b, d (a = 1, c = 2, b = 3, d = 4). The water is pumped to pressure, forced through the membrane while salt is held back, collected clean on the far side, and the concentrate is carried away.
  5. Answer: Answers will vary. A proficient paragraph explains the steps in order, uses membrane, pressure, and concentrate correctly, and includes at least two sequence transitions.

Differentiation

Support

Give students the four step cards from item 4 as physical strips to arrange on their desk before they number them, and provide a partly completed paragraph with the transitions already in place for them to finish.

Extension

Ask students to add one or two sentences explaining why the plant must dispose of the concentrate carefully, and why reverse osmosis costs more to run than ordinary treatment, using the energy comparison from the lesson.

ELL supports

Pre-teach "membrane," "pressure," "concentrate," and "brackish" with a simple cross-section showing water squeezing through a barrier while salt stays behind. Provide a word bank of sequence transitions and allow students to draw and label the steps before writing the paragraph.