Chapter Objective 6 The Function of Stems Stems

Chapter Objective • 6. The Function of Stems

Stems • Stem functions include: – 1. Structural support – 2. Food and water transport through a vascular system • Food is transported through tubules called phloem • Water & minerals are transported through tubules called xylem

• The process of moving water from the roots to the leaves is Called transpiration • Water is absorbed through the root tissue, drawn up through the xylem & into the leaves, where it is released through openings on the leaves called stomata

• Water moves upward through the plant by cohesion and adhesion • Cohesion is waters tendency to be attracted to other water molecules due to its polar structure • Adhesion is waters tendency to be attracted to the walls of the xylem due to its polar structure • Together, this is known as the Cohesion-Adhesion Theory

Chapter Objective • 7. The Structure of Leaves

True Leaves • Leaves attach to the stem at areas called nodes • The areas between nodes are called internodes • The little stems that attach leaves to the stem are called petioles

Leaf Structure • Cuticle: waxy covering that protects from water loss • Epidermis: flattened cell layer on the surface of the leaf • Palisade mesophyll: found just under the epidermis & is where most photosynthesis occurs – The cells are packed in tightly to capture the most sunlight

• Spongy mesophyll: less tightly packed irregularly shaped cells that allow for gas (O 2, CO 2) & water exchange • stomata: are usually found only on the underside of the leaf & are surrounded by guard cells • The guard cells open & close the stomata to control water levels in the leaf

The End