Monday, Jan. 9 AIM: How do plants grow? DO NOW: What are the differences between monocots and dicots? HW: Read Ch. 35, pp Study notes and diagrams. Multiple Choice packet, Ch. 35

Life span of a plant vs. an animal Indeterminate growth – meristematic tissue

Annuals –one year (i.e., germinate, flower, produce seeds, die) (wildflowers, food crops like cereal grains and legumes) Biennial – life span of 2 years (beets, carrots) Perennials – life span of many years (trees, shrubs, some grasses like Buffalo grass)

411 Some Buffalo grass has been growing for 10,000 years from seeds that sprouted at the end of the last Ice Age.

Meristematic Tissue Capable of perpetual embryonic growth Apical meristem  primary growth in tips of youngest parts of plant (i.e., 1 0 xylem & 1 0 phloem) Lateral meristem  secondary growth (girth) (eg. 2 0 xylem and 2 0 phloem in woody plants)

Roots: Primary Growth

Primary growth in roots 3 zones of cells in root meristem: 1.Zone of cell division 2. Zone of elongation 3. Zone of maturation

Primary Structure of a Root

Primary Structure of Roots 1.Epidermis –  root hairs 2.Cortex – main part of root – stores starch in plastids 3.Endodermis -- tightly packed cells surrounding vascular cylinder  Each cell wrapped in suberin which leads to water-impermeable barrier called casparian strip  NB: CASPARIAN STRIP FOUND ONLY IN ROOTS. 4.Stele – AKA vascular cylinder

Dicot Root

Suberin & Casparian strip

Stems Consist mainly of vascular bundles

Dicot vs. Monocot Stems

Dicot Stem Vascular bundles arranged in a ring Phloem external to xylem Vascular cambium between xylem & phloem

Monocot Stem Vascular bundles scattered throughout the ground tissue

Do not confuse monocot and dicot roots with monocot and dicot stems.

Growth of Stems Primary growth (apical dominance) Secondary growth (girth) (Secondary growth occurs in all gymnosperms, but takes place only in angiosperms that are dicots.)

2 Lateral Meristems that lead to lateral growth 1.Vascular cambium – give rise to secondary xylem and phloem  Wood = accumulation of secondary xylem 2.Cork cambium – gives rise to periderm (bark)

Secondary Structure of Stems & Roots Cells on inside of vascular cambium differentiate into secondary xylem which increases girth of tree Cells on outside differentiate into secondary phloem

Annual Growth Rings Produced by cambium dormancy, early wood production, and late wood production each year

Sapwood – recent xylem that remains active in transporting water Heartwood – older xylem in center of stem that functions only in support

What happened here?