Lab 14 Review: Roots, Stems, and Leaves

Roots

1. root system

fibrous root system, all the roots are basically the same size

• small-diameter roots have very high surface area (above ground) volume ratio (depth)

• absorbs lots of water quickly

tap root system

• large diameter

• divides into smaller and smaller branch roots

• can grow very deep all the way down to water table

2. root cross-section: monocot vs. dicot

common features

epidermis

• outer layer

• one-cell

• thick layer from which root hairs arise for water absorption

cortex

• wide layer

• beneath epidermis

  • parenchyma cells → large cells that store starch

  • endodermis → red stained ring of cells located towards the middle of the cross section

  • waterproofed by the Casparian strip - wax covered cells that force water to move along the endodermis until it encounters cells called passage cells that are adjacent: (junction between cells forming tissues that are subjected to stretching and pulling) to xylem vessels

  • water is channeled to xylem and carried upwards

• vascular stele (cylinder) → region just inside the endodermis

  xylem → large, red stained, hallow cells

  • angiosperm xylem has both tracheid and vessel

  • form secondary wall of lignin, and then die

  • cells connect end to end and serve as plumbing and move water up from the roots to the leaves

  • both vessels are large and main component of angiosperm xylem

    Phloem → tissue that stains blue green

  • found in exterior to the xylem towards outside the roof

  • 2 cells: sieve cells and have opening between cells that allow easy passage of dissolved sugar molecules

  • phloem is living tissue that carries sugar made by photosynthesis downward the roots and Non photosynthetic parts

differences

• monocot roots: xylem and phloem form ring inside endodermis

• pith

• starch storing parenchyma center of root

dicot roots: xylem branched pattern at center of root '

• patches of phloem between xylem branches

• no pith

Stems

common features

1. Stem cross - section

epidermis: outer one-cell

• thick layer

• produces waxy cuticle

• cuticle waterproofs all aboveground parts of the plant

vascular bundles:

• xylem towards inside

• phloem on the outside

• large parenchyma cells to store starch

differences

monocot stems → scattered vascular bundles

face of a monkey

• starch-storing parenchyma tissue

• sclerenchyma surrounds the vascular bundle

• no cortex or pith

dicot stems → vascular bindles arranged in a ring

• vascular bundle has wide cap which supports sclerenchyma tissue

2. 3-year stem, cross - section

perennial plants (living many years)

new layers of vascular tissue are added every year

• xylem → wood

• phloem → bark

Bark: replaces epidermis

• outside cross section

• consist of dead compressed cells

• functional phloem too

  • outer bark made of cork cambium protects phloem

vascular cambium: produces new phloem to the outside and xylem to the inside

wood: → xylem only outer ring functional

• spring wood

• summer wood

• annual ring

Leaves

Monocot leaves are long and narrow

• veins → vascular tissue are parallel and never branch

Dicot leaves are broad

• veins branch

palmate venation → more than one vein arising from base of the leaf with smaller veins branching from main veins (look like hands and fingers)

2. LEAF CROSS-SECTION: monocot versus dicot

common features

• epidermis → the outer layer of cells. The epidermis deposits a waxy cuticle to its outside to prevent water loss from the leaf.

(1) stomata → openings in the leaf epidermis for gas exchange

(2) guard cells → pair of cells that close a stoma during dry periods to prevent excessive water loss

mesophyll → the middle of the leaf that contains photosynthetic cells

veins → bundles of xylem and phloem supported by sclerenchyma tissue. On leaves, xylem is always positioned above the phloem.

differences

• monocot leaves → parallel venation

(1) Monocot leaves tend to be positioned somewhat vertically on the plant and have stomata on both surfaces.

(2) Scattered among the epidermal cells on one surface of a monocot leaf are large bulliform cells. On dry days, these collapse and cause the leaf to curl up, reducing water loss.

(3) Veins are regularly spaced, parallel veins visible externally.

• dicot leaves → branching venation

(1) dicot leaf has stomata only on its lower surface, away from direct sunlight.

(2) The mesophyll of a dicot has two areas of photosynthetic cells.

Palisade mesophyll consists of the upper layer of densely packed columnar cells.

Spongy mesophyll has spaces that allow the palisade mesophyll to exchange gases through the stomata.