Plant Tissues

Cells of a vascular plant are organized into different tissues and organs Three major organs are: roots, stems, and leaves Dermal tissue Vascular tissue Ground tissue Stem Root Leaf

Plant Organs Roots – absorb water and nutrients from soil, anchor plant, hold plant upright Stems – supports plant, transports water and nutrients Leaves – carry out photosynthesis, have adjustable pores to help conserve water, allow O 2 to leave and CO 2 to enter

Tissue Types Three tissue types: –D–Dermal –V–Vascular –G–Ground Dermal tissue Vascular tissue Ground tissue Stem Root Leaf

Dermal Tissue Dermal Tissue – outermost layer of cells covered with a waxy cuticle to protect against water loss

Vascular tissue Vascular tissue – transports water and nutrients through plant by xylem and phloem –Xylem – conducts WATER throughout the plant –Phloem – conducts NUTRIENTS throughout the plant

Ground Tissue Ground Tissue – cells that lie between dermal and vascular tissues; site of photosynthesis

Roots Two main types – taproots (found in dicots) and fibrous roots (found in monocots –Taproots – long primary root like that of carrots or trees –Fibrous roots – branching root system with no single root growing larger than the rest (many plants, such as grasses)

Root Function Anchors plant Absorbs water and nutrients –Active transport proteins in the root pump minerals and nutrients into the plant (moves from low to high concentration and requires ATP/energy to do so) –Water then moves into the roots by osmosis (high to low concentration and NO energy required) – capillary action!

Stems Vary greatly in size and shape Three important functions: –Produce leaves, branches, and flowers –Hold leaves up in sunlight –Transport substances between roots and leaves

Growth in Stems Primary growth of stems –For the life of the plant, new cells are produced at the tips of the roots –Plant gets taller Secondary growth of stems –Stem increases in thickness/width

Formation of Wood in Trees Actually layers of xylem that build up year after year Tree growth is seasonal –In spring, light-colored xylem cells with thin cell walls form –In fall/winter, xylem cells becomes dark and have thicker cell walls –This light and dark pattern is called tree rings. Each ring is composed of a band of light wood and dark wood

Formation of Wood in Trees (continued) –One ring = one year of growth –Counting rings = approximate age of tree –Thick rings = favorable conditions/good growing season –Thin rings = less favorable conditions/bad growing season

Layers of a Tree Trunk WoodBark Cork Cork Cambium Phloem Vascular Cambium Xylem: Sapwood Xylem: Heartwood

Leaves Main organ of photosynthesis Leaves vary in shape, but all collect sunlight on flattened sections called blades Epidermis of leaves covered by a waxy cuticle to prevent water loss

Leaf Functions Photosynthesis – bulk of leaf tissue is called mesophyll, where many chloroplasts are Gas exchange – leaves take in CO 2 and give off O 2 during photosynthesis

Leaf Functions (continued) –Leaves have stomata – pore-like openings on the underside of the leaf that allow gas exchange to occur –Stomata are open just enough to allow photosynthesis to occur, but not so much that they lose excess amounts of water –Guard cells surrounding the stomata control the opening/closing of the stomata and thus regulate the movement of gases into and out of the leaf –In general, stomata open during the day and close at night

Function of Guard Cells Stoma OpenStoma Closed Guard cells Inner cell wall Stoma Guard cells Inner cell wall

Function of Guard Cells Stoma OpenStoma Closed Guard cells Inner cell wall Stoma Guard cells Inner cell wall

The Internal Structure of a Leaf Veins Xylem Phloem Vein Cuticle Epidermis Palisade mesophyll Epidermis Stoma Guard cells Spongy mesophyll