Roots, Stems, and Leaves

Specialized Tissues In Plants

A.Seed Plant Structure1. Roots2. Stems3. Leaves

B.Plant Tissue SystemsC.Dermal TissueD.Vascular Tissue

1. Xylem2. Phloem

E. Ground TissueF. Plant Growth and Meristematic Tissue

Seed Plant Structure• The cells of seed plants are organized into

tissues and organs.• The three main plant organs are roots,

stems, and leaves.– Roots absorb water and dissolve

nutrients and anchor plants in the ground.

– Stems support the plant body and transport materials throughout the plant.

– Leaves are the main organs of photosynthesis. They also function in gas exchange.

Dermal tissue

Vascular tissue

Ground tissue

Stem

Root

Leaf

Root, Stem, and Leaf Tissues

Plant Tissue Systems• Within the roots, stems, and leaves are specialized tissue

systems. The three main tissue systems:– Dermal tissue is like the skin of a plant. It protects the

plant and prevents water loss.– Vascular tissue consists of xylem (move water

throughout the plant) and phloem (moves sugars and other materials throughout the plant).

– Ground tissue is made up of all of the cells that lie between dermal and vascular tissues. (made up of 3 kinds of cells)• Parenchyma cells: function in photosynthesis and

storage• Collenchyma cells: help support larger plants• Sclerenchyma cells: make ground tissue tough and

strong

Plant Tissue Systems Cont.• A fourth kind of tissue, meristematic tissue, is responsible for

plant growth.– Meristematic tissue is the only plant tissue that produces

new cells by mitosis.– The tips of stems and roots are made of meristematic

tissue.

Concept Map

include

includes includes includes

includes includes

Plant Tissues

Dermaltissue

Meristematictissue

Vasculartissue

Groundtissue

Epidermalcells Xylem Phloem Parenchyma

cellsCollenchyma

cellsSchlerenchyma

cells

Tracheids Vesselelements

Sieve tubeelements

Companioncells

Roots

• The two main types of roots are taproots and fibrous roots.• Taproots: the primary root grows long and thick, while the

secondary roots stay small.• Fibrous roots: secondary roots that grow and branch out • Roots have two main functions– To anchor a plant in the ground– To absorb water and dissolved nutrients form the soil

Taproots and Fibrous Roots

• Taproots (Carrots) Fibrous Roots (Grasses)

Epidermis

Ground tissue(cortex)

VascularCylinder

Cross Section of Plant Root(magnification: 40x)

Ground tissue (cortex)

Epidermis

Endodermis

Vascular cylinder

Root hairs

Phloem

Xylem

Apical meristem

Root cap

Zone of maturation

Zone of elongation

Endodermis

The Structure of a Root

Stems• Stems have three important functions– To produce leaves, branches, and flowers– To hold leaves up to the sunlight– To carry water and nutrients between the roots and leaves

Comparing Primary and Secondary Growth of Stems

Characteristics

Where It Occurs

Effect on Plant

How It IsProduced

Primary Growth Secondary Growth

Plant stems grow in two ways

At ends of plants

Increases plant length

By cell division in the apical meristem

In stem

Increases stem width

By cell division in meristems other thanthe apical meristem

Leaves

• The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

• To collect sunlight, most leaves have thin, flattened sections called blades.

• Plants can lose water out of their leaves as they exchange gases with the air (transpiration).– To prevent major water loss plants allow air in and out of

their waterproof covering only through small openings called stomata.

– Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.

Evaporation of water molecules out of leaves.

Pull of water molecules upward from the roots.

A B

Transpiration

Blades On Leaves

Veins

XylemPhloem

Vein

Cuticle

Epidermis

Palisademesophyll

Epidermis

Stoma

Guardcells

Spongymesophyll

The Internal Structure of a Leaf

Transport in Plants

• Forces of Attraction• Molecules of a similar substance are attracted to one

another by a force called cohesion.

• Molecules of different substances are attracted to one another by a force called adhesion.

Movementof water

Movementof sugar

Sugarmolecules

Source cell

Sink cell

Phloem Xylem

Transport In Plants