Lesson Overview 23.2 Roots

THINK ABOUT IT Can you guess how large a typical plant’s root system is?   A study of a single rye plant showed that the length of all the branches in its root system was an astonishing 663 kilometers (412 miles). The surface area of these roots was more than 600 square meters—130 times greater than the combined areas of its stems and leaves!

Root Structure and Growth When a seed sprouts, roots develop first to draw water and nutrients from the soil Rapid cell growth pushes the tips of the growing roots into the soil The new roots provide raw materials for the developing stems and leaves before the stems and leaves even emerge from the soil

1) Taproot systems are found mainly in dicots 2 Main Types of Root Systems 1) Taproot systems are found mainly in dicots primary root grows long and thick & gives rise to smaller branch roots oak and hickory tree taproots grow so long that they can reach water several meters below the surface Dandelions also have a taproot system

2) Fibrous root systems are found mainly in monocots 2 Main Types of Root Systems 2) Fibrous root systems are found mainly in monocots system begins with one primary root soon replaced by many equally sized branch roots that grow separately from the base of the stem The extensive fibrous root systems produced by many plants help prevent topsoil from being washed away by heavy rain Grasses have a fibrous root system

Which is fibrous? Which is taproot?

Specialized Tissues: 1) Dermal Tissue: Epidermis functions = protection and absorption surface covered with thin cellular projections called root hairs penetrate the spaces between soil increase surface area for absorption of water and minerals

cortex = stores the products of photosynthesis (like starch) 2) Ground Tissue cortex = stores the products of photosynthesis (like starch) Located inside the epidermis Water and minerals move through the cortex from the epidermis toward the center of the root

endodermis = encloses the vascular cylinder Ground Tissue endodermis = encloses the vascular cylinder essential for movement of water and minerals into the center of the root

3) Vascular Tissue vascular cylinder = xylem and phloem together at the center of the root (yellow ring below)

grow in length = apical meristems produce new cells near root tips root cap = protects the meristem as root tip forces its way through the soil secretes a slippery substance that helps root move through the soil  Cells at the tip of root cap are constantly scraped away and new root cap cells are continually added by the meristem

Uptake of Plant Nutrients To grow, flower, and produce seeds, plants require a variety of inorganic nutrients nutrients needed in largest amounts = nitrogen, phosphorus, potassium, magnesium, & calcium

Uptake of Plant Nutrients The functions of these essential nutrients within a plant are described below.

Uptake of Plant Nutrients Small amounts of trace elements are also important = sulfur, iron, zinc, molybdenum, boron, copper, manganese, and chlorine  As important as they are, excessive amounts of any of these nutrients in soil can also be poisonous to plants