Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of xylem and phloem.
• Explain how roots absorb water.
• Explain the process of transpiration.
• Describe the cohesion-tension theory of water transport.
• Explain translocation of sugars in the phloem.

Lesson summary

The efficient transport of water and nutrients is crucial for plant survival and growth. In South Africa, understanding these transport systems is particularly important because our diverse climate, ranging from arid deserts to subtropical regions, presents unique challenges for plant life. From the baobab tree storing water in its trunk to the drought-resistant fynbos species, plants have evolved remarkable adaptations for water and nutrient transport. This week, we'll delve into the intricate mechanisms that allow plants to thrive in varying environmental conditions.

Lesson notes

2.1 Xylem and Phloem: The Plant's Vascular System Just like animals have blood vessels, plants have vascular tissues called xylem and phloem, which are responsible for transporting substances throughout the plant.

Xylem: The primary function of xylem is to transport water and dissolved mineral salts from the roots to the rest of the plant. Xylem is composed of dead cells, primarily tracheids and vessel elements, which are elongated and have thick, lignified cell walls. This lignin provides support and prevents the xylem vessels from collapsing under the negative pressure created by transpiration. The cells are arranged end-to-end to form continuous tubes. Tracheids have pits (small openings) that allow water to move laterally between adjacent cells. Vessel elements have perforations (larger openings) at their ends, providing a less resistant pathway for water flow compared to tracheids. Think of xylem as the plumbing system of the plant.