Chapter 30.2

1. Chapter 30.2 How do Roots Absorb Water and Mineral Ions AP Biology Spring 2011

2. Specialized Absorptive Structures • Root hairs: extensions of the root epidermal cells that constantly form just behind the root top • Greatly increase the absorptive surface

3. Specialized Absorptive Structures • Mycorrhizae: fungi growing around plant roots • Aid in absorbing minerals that are supplied to the plant in exchange for sugars • Symbiotic relationship is beneficial to both

4. Specialized Absorptive Structures • Root nodules of legumes harbor bacteria that convert gaseous nitrogen to ammonia • This is useful in the growth of the plants in the process called nitrogen fixation • This is a form of mutualism

5. How Roots Control Water Uptake • Water and solutes move from the soil across the root epidermis • Seep through and around the root ground tissue until reaching the vascular cylinder

6. Root

7. How Roots Control Water Uptake • A sheetlike layer of cells, the endodermis, surrounds the vascular cylinder, a column of vascular tissue in the center of the root • Waxy secretions from the endodermal cells form the water-repellent Casparian strip forcing water to move into the cells of the endodermis

9. How Roots Control Water Uptake • Membrane transport proteins in the endodermal cells help control the types and amount of absorbed solutes and water that will be distributed throughout the plant

10. How Roots Control Water Uptake • Most flowering plants also have an exodermis • Exodermis: layer of cells just inside the root epidermis • Also has a Casparian strip that functions just like the one next to the root vascular cylinder EX = exodermis EP = epidermis X = xylem Arrows = Casparian strip