| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: relate the structure of xylem vessel elements, phloem sieve tube elements and companion cells to their functions |
Learning Objective/s:
- Describe the key structural features of xylem vessel elements, phloem sieve tube elements, and companion cells.
- Explain how these structures enable efficient transport of water, minerals, and photosynthates.
- Apply the pressure‑flow model to predict the direction of phloem transport under different source‑sink conditions.
- Compare the functional differences between xylem and phloem transport tissues.
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Materials Needed:
- Projector or interactive whiteboard
- PowerPoint slides with diagrams of xylem and phloem cells
- Handouts of the structure‑function summary table
- Microscopy images or virtual slide of plant vascular tissue
- Worksheet with pressure‑flow calculations
- Markers and chart paper for group diagramming
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Introduction:
Begin with a quick image of a towering tree and ask students how water and sugars travel from roots to leaves and back. Recall previous learning about transpiration pull and source‑sink concepts. Today we will investigate how the microscopic architecture of xylem vessels, phloem sieve tubes, and companion cells underpins these transport processes, and we will use a checklist to assess our understanding.
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Lesson Structure:
- Do‑now (5’) – Students label a blank diagram of a vascular bundle (review of xylem vs phloem).
- Mini‑lecture (10’) – Present key structural features of xylem vessel elements with slide annotations.
- Interactive model (10’) – Demonstrate water flow through a straw model representing lignified vessels; discuss low‑resistance conduit.
- Guided inquiry (12’) – In pairs, examine microscope images of phloem; identify sieve plates, reduced cytoplasm, and companion cells; fill in worksheet.
- Think‑pair‑share (8’) – Explain how companion cells supply energy for phloem loading; teacher clarifies misconceptions.
- Pressure‑flow simulation (10’) – Use an online animation to trace sucrose loading, osmotic water entry, pressure gradient formation, and bulk flow; students predict effect of altering tube radius.
- Quick check (5’) – Exit ticket: one sentence describing why xylem vessels are dead at maturity and how that benefits water transport.
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Conclusion:
Summarise how the specialised structures of each transport cell type create efficient pathways for water and nutrients. Students complete an exit ticket linking a structural feature to its function, reinforcing the pressure‑flow concept. For homework, assign a short problem set calculating flow rate using the Hagen‑Poiseuille equation for a sieve tube.
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