Leaves, Roots, Stems - Western Oregon University

Leaves, Roots, Stems Plant organs and their functions Leaves Leaf Parts Two major parts to the leaf: Blade Petiole

Leaf microanatomy Epidermis and cuticle do what? Mesophyl does what? Veins do what? Guard cells in the lower epidermis do

what? Photosythesis The purpose of photosynthesis is to produce organic (carbon-based) molecules (such as sugars). The plants use these molecules for two purposes: As an energy source As building material

Roots Types of root systems Taproot systems: main root, lateral branches. Fibrous root systems: lose the primary root,

replaced by many smaller roots. Root Anatomy Parts of a root: Root cap Root meristem Zone of elongation

Zone of maturation Roots: Epidermis Root epidermis lacks a cuticle, and is porous. Usually has many root hairs. Water enters

through membranes of epidermal cells or through spaces between cells. Roots: Cortex The cortex layer is made up of

parenchyma cells. What is the main function of these cells? Endodermis separates the cortex from the vascular cylinder. Roots: vascular cylinder

Casparian strip around endodermis cells controls water movement. Why? Pericycle: layer of parenchyma cells, inside of endodermis, from which branch

roots can arise. Roots: vascular cylinder Vascular cylinder contains: Phloem: what does phloem do? Xylem: What does xylem do?

Stems Stems: Epidermis In herbaceous plants and young woody plants, the stem is covered with epidermis. Epidermis

secretes cuticle, has stomata, and may be photosynthetic. Stems: Cortex and Pith Cortex layer contains parenchyma cells and vascular

bundles. Pith makes up the center of the stem, and is absent in hollow stems. Stems: vascular tissue Vascular bundles are in the cortex.

Between the xylem and phloem is the vascular cambium, a meristem layer. What is it for? Stems: Secondary growth

Secondary growth is seen in woody plants. This kind of growth produces stronger, thicker stems from the vascular cambium and cork cambium.

Stems: wood and bark What tissue makes up the wood of a tree trunk? (hint: water flows there.) What tissue makes up the green bark? (hint: sap flows there.)

Dead cork cells make up the bark. Stems: Annual Rings Trees in temperate zones grow at different rates in different seasons, causing annual rings to form.

In some parts of the tropics, if seasons vary little, tree rings are indistinct.