Plant Structure Plant Tissues A tissue is a

Plant Structure

Plant Tissues • A tissue is a group of cells organized to form a functional unit or a structural unit • Plants have 3 tissue systems: • Ground tissue (3 types) • Vascular tissue (xylem and phloem) • Dermal tissue (exterior)

Ground tissue • Parenchyma - found throughout the plant, these tissues perform important functions like photosynthesis • Colenchyma - structural support in herbaceous plants • Sclerenchyma- hard structural support (trees)

Parenchyma • Simple tissue found throughout the plant. Functions include photosynthesis, food storage, secretion

Collenchyma • Provides structural support • Found just under the stem epidermis and along leaf veins • Cells are alive at maturity and function only when they are alive

Sclerenchyma • Hard structural support • may be alive or dead and still function structurally • one type of sclerenchyma is fiber (wood)

Xylem and Phloem • Both add structural support • Xylem - conducts water and minerals, long tapering cells that act as pipes of a sort • Phloem - conducts food

Dermal • Epidermis - outermost layer composed of single layer of ground parenchyma cells • Periderm - many layers thick, found on woody plants, replaces epidermis, parenchyma cells

Growth • Plant growth occurs at specialized areas called meristems (meristematic tissue) • primary growth - increase in length of plant, occurs at apical meristems, • secondary growth - increase in girth, occurs at lateral meristems, vascular cambium (see figure 26 -16, pg 519)

Stems

Leaves

Leaves • Arrangement on stem -pg 509 • • alternate opposite whorled Large surface area to collect light and allow for gas exchange but increases tendency for water loss - cuticle reduces water loss • Hairs on leaves are called trichomes

Leaves • Cuticle is thicker on the top of a leaf than it is on the bottom • Stomata - opening controlled by guard cells. More stomata on bottom of leaves • Mesophyll- photosynthetic tissue of leaf • Xylem and phloem pass through mesophyll (xylem toward the top and phloem toward the bottom)

Mesophyll • Palisade layer - cells stacked more closely together, toward the upper epidermis, primary site of photosynthesis • Spongy layer - cells more loosely organized, toward lower epidermis, some photosynthesis, but primarily engaged in gas diffusion within the leaf

Monocots and Dicots see page 529

Leaf function • Photosynthesis - more later • Transpiration - 99% of water absorbed by plant is lost by transpiration • Guttation- available water is high, transpiration is low • Abscission-allows plant to shed leaves