Lesson plan Grade 11 English Language Arts
Reverse Osmosis at Marisco Bay: An Informative Writing Lesson
A grade 11 ELA lesson where students turn a technical description of reverse osmosis into a clear, well-sequenced exhibit panel for a fictional desal plant.
Objectives
- Students will explain how reverse osmosis separates salt from seawater clearly and accurately for a general museum audience.
- Students will organize a technical explanation so each step builds on the step before it.
- Students will decide which technical details a visitor needs and which to leave out.
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, semipermeable, informative writing
Teacher overview
Informative writing at this grade is often judged by how well a writer orders a complex process so a reader who knows nothing about it can follow along. This lesson gives students a dense technical description of reverse osmosis and asks them to rewrite it as a short exhibit panel for the visitor center of a fictional coastal desalination plant, Marisco Bay. The task tests sequencing and audience judgment rather than research. A common misconception this lesson addresses directly is that a clear explanation is simply a shorter one; students instead learn that clarity comes from ordering the steps so each builds on the one before, keeping the essential science while dropping jargon a visitor does not need.
Procedure
Hook (5 min): Ask students how they would explain to a younger sibling whether you could make fresh water just by boiling seawater and catching the steam. Take two or three answers, then explain that boiling works but costs enormous energy, which is why most large plants use a different method the class will explain today.
Direct instruction (12 min): Distribute the technical description below and read it aloud once.
Technical description (written for this lesson in a deliberately technical register, not a quotation of any source): "Seawater reverse osmosis pressurizes saline feedwater against a semipermeable membrane whose pore structure permits the passage of water molecules while rejecting dissolved salt ions; applied pressure must exceed the osmotic pressure of the feed to drive net permeate flux from the concentrated side to the dilute side, yielding low-salinity product water and a concentrated brine reject stream."
Then explain the same process in plain terms, modeling how to name each step in order: seawater is pushed under high pressure against a membrane; the membrane has openings that let water molecules through but block salt; the pressure has to be strong enough to overcome the salt water's natural pull; what comes out is fresh water on one side and very salty leftover water, called brine, on the other. Note that removing salt this way uses roughly 11 to 15 kilowatt-hours of energy for every 1,000 gallons treated, compared with about 1 to 2 kilowatt-hours for conventional treatment and delivery of fresh water, which is why energy is a major cost of a plant like Carlsbad in California, the largest in the country at about 50 million gallons per day.
Guided practice (13 min): In pairs, students list the process steps in order on the drafting page, then write one sentence per step in plain language for a museum visitor. They underline any word a general reader might not know and write a short substitute beside it.
Independent practice (15 min): Each student writes an exhibit panel of five to seven sentences explaining reverse osmosis for the Marisco Bay visitor center, ending with one sentence on why the process uses so much energy.
Closure / exit ticket (5 min): On an index card, students answer: "Name, in order, the three things that happen to seawater as it becomes drinking water in reverse osmosis." Collect and scan for correct sequencing before dismissal.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Exit ticket answer: In order: seawater is pushed under high pressure against a semipermeable membrane; water molecules pass through the membrane while salt is blocked; the fresh water is collected as product while the leftover salty water leaves as brine. Any answer that keeps this pressure, then separation, then collection order is correct, even if the wording differs.
Differentiation
Support
Provide the process steps already listed in the correct order on the drafting page, so students focus only on rewriting each step in plain language rather than on both ordering and rewriting at once. Allow the panel to be built from four provided sentence frames.
Extension
Ask students to add a second short panel explaining why a plant would choose reverse osmosis over boiling seawater, using only the energy comparison presented in direct instruction rather than outside research, and to name the tradeoff the plant accepts in exchange for a drought-proof supply.
ELL supports
Pre-teach "membrane," "semipermeable," and "pressure" with a simple visual: a labeled diagram of a screen door that lets air through but stops insects. Allow the independent panel to be drafted first as a numbered list of steps, then joined into sentences.