Part 2: Tissues, Roots, Stems & Leaves Unit 7 Plants Part 2: Tissues, Roots, Stems & Leaves

Plant Tissues – 1. Dermal Tissue Outer covering Made of epidermal cells Waxy coating: cuticle Accessories: Trichomes (“fuzz”) Root hairs (absorption) Guard cells (regulate water/gas movement at surface)

Plant Tissues – 2. Vascular Tissue Transport system – Moves water/nutrients Xylem: water-conducting tissue Tracheids Vessel elements Phloem: food-conducting tissue Sieve tube elements Companion cells Tracheid cells connect with one another to form tubes. They “hollow out” after they mature, die, and their cytoplasm disintegrates. All represent modified cells that either die and form a shell that is used or that lose their organelles and only function in transport

Plant Tissues – 3. Ground Tissue Everything else Three types Parenchyma (majority)  Thin cell walls; functions include storage & photosynthesis Collenchyma  Strong, flexible cell walls; functions include support Sclerenchyma  Extremely thick/rigid; extra support/toughness Tracheid cells connect with one another to form tubes. They “hollow out” after they mature, die, and their cytoplasm disintegrates. All represent modified cells that either die and form a shell that is used or that lose their organelles and only function in transport

Plant Growth Indeterminate (never stop) Meristem  Tissue clusters where new growth occurs via mitosis Cells produced in meristem = undifferentiated (not yet specialized) Apical meristem = at end of root or stem; responsible for increased length Cells gradually differentiate

Plant Roots: 1. Types Taproots  Long, thick primary root; mainly in dicots Fibrous roots  Branching system, no primary; mainly in monocots

Plant Roots: 2. Structure/Growth Root hairs: tiny projections; absorption. Epidermis (exterior layer). Cortex (ground tissue). Vascular cylinder (xylem/phloem) surrounded by endodermis. Apical meristem (new growth). Root cap: protects new growth as it pushes through ground.

Plant Roots: 3. Functions Anchor Uptake nutrients from soil (N, P, K, Mg, Ca) Active transport of mineral ions  Leads to osmosis of water One-way movement into vascular cylinder and up (capillary action) Generates root pressure to move water/nutrients from roots all the way up plant Active transport  uses ATP (energy) to pump mineral ions from soil into plant which then forces water to move into the plant via osmosis

Stems: 1. Structure/Function Three functions: Produce leaves/branches/flowers Hold leaves up to sun Transport substances between roots + leaves Node (where leaves attach); internode (area between nodes); bud (developing tissue)

Stems: 2. Primary Growth Primary growth: New cells only produced at root + shoot tips (ends) Cell division in apical meristem

Stems: 3. Secondary Growth Stems grow thicker/wider Dicots and conifers Division of the vascular cambium (a different kind of meristem) Produces more xylem + phloem Grows from inside - outward Protected by cork cambium

Stems: 3. Secondary Growth Leads to formation of wood Wood = layers of xylem Center = oldest, eventually non-functional xylem (heartwood) Exterior layer = sapwood (active)

Why do you see rings? In the spring, there is rapid growth which produces are large, light colored ring followed by slower growth in the late summer and early fall (cells get smaller and more compact in the slower growth period due to less water availability). Each annual ring is actual comprised of a light and dark subring. To count age, go from dark to dark.

Leaves: 1. Structure Blades: flattened; collect sunlight Petiole: stem

Leaves: 2. Function A. Photosynthesis Special ground tissue: mesophyll palisade + spongy) Stomata (pores; gas movement) Guard cells (regulation)

Stomata on underside of leaf

Leaves: 2. Function B. Transpiration C. Gas exchange Loss of water Replaced by water drawn up from roots C. Gas exchange Take in CO2, give off O2 Guard cells regulate movement in response to environment