Chapter 23: Roots, Stems, and Leaves

The three principle organs of seed plants

Roots • absorb water and dissolved nutrients• anchor plants in the ground• hold plants upright through wind and rain

Stems• support the plant• transports nutrients to the rest of the plant• compete for sunlight by holding leaves higher

Leaves• are the principle organ for photosynthesis• have broad, flat surfaces, inc S.A. for sunlight• pores conserve water and allow gas exchange

Meristem TissueStem

RootThe only plant tissue that produces new

cells by mitosis

Apical meristem is found at the tips of stems and roots.

Tissue Systems

Plants consist of 3 tissue systems:• Dermal tissue – outermost layer; forms the “skin” of the plant• Vascular tissue – transports water & nutrients; “bloodstream”• Ground tissue – tissue between the dermal and ground tissues

Dermal tissue – generally consists of a single layer of epidermal cells.

The outer layer is often covered with a thick, waxy layer called the cuticle, which protects against water loss and injury.

Vascular tissue – contains several different cell types; transporting water and nutrients around the plant.

Ground tissue – cells that lie between the dermal and vascular tissues.

RootsRoots absorb water and dissolved nutrients from the soil. Plants have a one-way system to generate enough pressure to move water out of the soil and into the body of the plant.

The water has no where else to go, but UP!

Fibrous roots Tap roots

Root hairs increase surface area!

StemsStems have 3 important functions:• Produce leaves, branches and flowers• hold leaves up in the sunlight• transport substances between roots and leaves

Leaves are attached to a stem at structures called nodes.

Some stems can alsocarry out photosynthesis

Formation of Wood

The most important “stem” is the stem of the tree.Wood is actually layers of xylem!

Read p. 592

Leaves

Maple tree leaves

Black Walnut tree leaves

Transpiration – The loss of water from a plant through its leaves