Roots & Stems Plant anatomy

Plant anatomy Roots absorb water and dissolved nutrients. Copyright Pearson Prentice Hall Plant anatomy Roots absorb water and dissolved nutrients. anchor plants in the ground. protect the plant from harmful soil bacteria and fungi.

Root Structure and Growth The root’s surface is covered with cellular projections called root hairs. Root hairs provide a large surface area through which water can enter the plant. Root hairs A root consists of a central vascular cylinder surrounded by ground tissue and the epidermis. Root hairs along the surface of the root aid in water absorption.

Root Structure and Growth Roots grow in length as their apical meristem produces new cells near the root tip. These new cells are covered by the root cap that protects the root as it forces its way through the soil. Only the cells in the root tip divide. In the area just behind the root tip, the newly divided cells increase in length, pushing the root tip farther into the soil. The root cap, located just ahead of the root tip, protects the dividing cells as they are pushed forward. Apical meristem Root cap

Types of Roots The two main types of roots are: Copyright Pearson Prentice Hall Types of Roots The two main types of roots are: Taproots - primary root that grows long and thick Ex: carrot Fibrous roots - branch to such an extent that no single root grows larger than the rest. Ex: grasses

Plant anatomy Stems produce leaves, branches and flowers hold leaves up to the sunlight transport substances between roots and leaves

Primary Growth of Stems Copyright Pearson Prentice Hall Primary Growth of Stems Stem growth All seed plants undergo primary growth, which is an increase in length. For the entire life of the plant, new cells are produced at the tips of roots and shoots. Primary growth Apical meristem Primary growth All seed plants undergo primary growth, which is an increase in length. Every year, apical meristems, shown in red, divide to produce new growth. The primary growth for one season consists of a stem and several leaves. Leaf scar Year 3 Year 2 Year 1

Secondary Growth of Stems Copyright Pearson Prentice Hall Secondary Growth of Stems Secondary Growth of Stems The method of growth in which stems increase in width is called secondary growth. In conifers and dicots, secondary growth takes place in the vascular cambium and cork cambium.

Secondary Growth of Stems Copyright Pearson Prentice Hall Secondary Growth of Stems Bark Secondary Growth of Stems The method of growth in which stems increase in width is called secondary growth. In conifers and dicots, secondary growth takes place in the vascular cambium and cork cambium. Produces wood Wood  In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.