Lesson Plan

• Describe the roles of source, sink, sieve‑tube elements, and companion cells in phloem transport.
• Explain the Münch pressure‑flow hypothesis and how osmotic loading creates a hydrostatic pressure gradient.
• Apply the flow equation to predict how changes in tube radius, viscosity, or concentration affect mass flow.
• Analyse common misconceptions about phloem transport and correct them.

• Projector and PowerPoint slides
• Printed diagram of a plant showing source, phloem sieve tubes, and sink
• Worksheet with flow‑rate calculations
• Colored sucrose solution model (to illustrate loading/unloading)
• Interactive phloem‑flow simulation (e.g., Phloem Flow app)
• Whiteboard and markers

Begin with a striking image of a fruit‑bearing plant and ask students how sugars travel from leaves to the fruit. Review prior knowledge of xylem transport and highlight that phloem moves nutrients in the opposite direction. State that by the end of the lesson they will be able to explain the pressure‑driven mass‑flow mechanism and solve a simple flow problem.

1. Do‑now (5') – Quick quiz on differences between xylem and phloem functions; students submit answers on sticky notes.
2. Mini‑lecture (10') – Present key concepts (source, sink, sieve‑tube, companion cell) and the Münch pressure‑flow hypothesis using slides.
3. Guided analysis (12') – Examine the step‑by‑step table; students label a printed diagram with loading, bulk flow, and unloading stages.
4. Calculation activity (10') – Using Q = (πr⁴/8ηL)ΔP, groups solve a worksheet problem predicting flow changes when tube radius varies.
5. Concept check (5') – Think‑pair‑share to address the two common misconceptions about phloem activity.
6. Summary & exit ticket (3') – Each student writes one sentence summarising mass flow and answers a prompt on what creates the pressure gradient.

Recap the sequence from sucrose loading at the source to unloading at the sink and how the resulting pressure difference drives bulk flow. Collect exit tickets to gauge understanding and assign a short homework: research a real‑world example (e.g., transport to developing seeds) and write a paragraph linking it to the pressure‑flow model.