Plant Tissues

Plant (Angiosperm) Tissues

-plants retain stem cells

>stem cells are undifferentiated cells (not specialized)

-totipotent stem cell: can become any type of cell (example: zygote)

-pleuripotent stem cell: can become one of a specific subset of cells (example: bone marrow cells)

plants retain totipotent stem cells in the apical meristem

woody plants have lateral meristems in addition to apical

>wood = lignified xylem (cell walls impregnated with lignin)

lateral meristem (cylinder around stem)

Differentiation

totipotent stem cells differentiate into pluripotent:

-epidermal

-vascular (xylem and phloem)

-ground

Epidermal Cell Types

-outer layer and specialized cells

guard cells (regulate water loss from stomata)

trichomes (stem and leaf "hairs")

root hairs (single cell thick)

Ground Tissue (filler)

-storage (large vacuoles), secretion, support

-parenchyma (most abundant), filler

-collenchyma: long, fibrous, support (example: strands in celery)

-sclerenchyma: tough, lignified cell walls, fibrous (example: flax --> linen), scleirids (example: pear grit)

Vascular Tissue

-xylem (water) and phloem (sugar)

xylem: only functional when dead

-moves water by evapotranspiration

phloem: only functional when alive

-moves sugar down a concentration gradient (diffusion through the cytoplasm)

Monocots vs Dicots

Monocots

-one cotyledon (seed leaf)

-parallel leaf variation

-fibrous roots

-flower petals in multiples of 3

-never have a woody stem

-vascular bundles scattered in stem

-vascular bundles arranged in a ring

Dicots

-two cotyledons

-branched leaf variation

-tap root (example: carrot)

-flower petals in multiples of 4/5

-may have a woody stem

-vascular bundles arranged in a peripheral ring in the stem

-single, central vascular cylinder (stele)

Leaf Section

-cuticle

-epidermis

-palisade mesophyll

-spongy mesophyll

-epidermis

-cuticle

stomata (openings in the spongy mesophyll) are flanked by guard cells

turgid (high water pressure)

flaccid (low water pressure)