Plant Tissues AP Biology

Typical Plant Structure Shoots: above ground structures Roots: below ground Structures consist of three major tissue systems: ground tissue, vascular tissue, and dermal tissue

Simple vs Complex Tissues Simple tissues consist of only one cell type Complex tissues consist of more than one cell type

Simple tissues Parenchyma Collenchyma Sclerenchyma parenchyma

Simple Tissues Parenchyma: most of the soft, moist, primary growth; pliable, thin, flexible walls, and many sided. The least specialized Generally has a large vacuole for storage, secretion

Simple Tissues Collenchyma: thicker walls, but not evenly thick; provide flexible support in stalks and stems. Ex celery strings Sclerenchyma: lignin containing thick walls; gives strength, retains moisture—important in switching to land; stems, leaf veins, seed and nut coverings

Complex Tissues Xylem Phloem Epidermis includes specialized cells such as guard cells and sections of collenchyma and parenchyma

Xylem: a complex tissue Two types of cells: tracheids and vessels Both are dead at maturity The cytoplasm disappears, leaving the thick walls Water migrates through these tubes

Phloem: a complex tissue Phloem cells are alive at maturity Sieve cells are long narrow cells Alongside are nonconducting cells called companion cells

Vascular Bundles Xylem and phloem are usually together in vascular bundles Arranged differently in monocots and dicots in both the root and the stem Monocot: distributed throughout Dicot: arranged in a ring in stem

Monocots and Dicots One or two cotyledons Classes of flowering plants (angiosperms) Cotyledon is a seed leaf, part of the embryo

Cotyledons They look like leaves and they are the first plant part you see when a seedling pokes its head out of the ground. Cotyledons help keep the new seedling fed until it can make its own food. Sometimes cotyledons are called seed leaves.

Other mono vs dicot Monocots: flower parts in threes or multiples of three Parallel leaf veins Dicots: flower parts in fours, fives, or multiples of these Netlike veins in leaves

Meristems Localized regions of growth Dividing cells (onion root tip) Apical meristem: lengthens parts in shoots and roots (primary growth) Lateral meristem: increases in diameter (secondary growth) Vascular cambium adds secondary xylem and phloem Cork cambium produces sturdier periderm that replaces epidermis

Apical meristem Stem apical meristem Root apical meristem

Vascular Cambium Produces secondary xylem and phloem Adds diameter Wood is the accumulation of these secondary tissues, especially xylem

Wood Is an accumulation of secondary xylem Check pages in Chapter 29 Xylem is added on the inner surface; phloem is added on the outer surface

Vascular Cambium Is not active all year round Produces large cells with thin walls in the spring (early wood) Produces smaller cells with thick walls in the dry summer (late wood)

Growth Rings The sections of early wood and late wood reflect light differently They show up as light and dark These are growth rings on a tree