Plant Tissue Growth

Key Concepts

• Overview of Plant Tissues

• Seed-bearing vascular plants have a shoot system with

stems, leaves, and reproductive parts

• Most also have a root system

• These systems consist of ground, vascular, and dermal

tissues

• Plants lengthen or thicken at meristems

Introducing Meristems

• Plant tissues originate at meristems, which are regions of

undifferentiated cells that retain their ability to divide

• Primary growth (or lengthening) arises from apical

meristems

• Secondary growth (or thickening) arises from lateral

meristems

Key Terms

• meristem

• Zone of undifferentiated plant cells

• Cells of meristem tissue can divide rapidly

• primary growth

• Plant growth from apical meristems in root and shoot tips

• secondary growth

• Thickening of older stems and roots

• In woody plants, secondary growth occurs when cells of a

thin cylindrical layer of meristem divide

A

B

B

C

D

25.3 Components of Plant Tissues

• Simple tissues consist primarily of one type of cell

• Examples: Parenchyma, collenchyma, and sclerenchyma

• Complex tissues have two or more cell types

• Examples: Xylem, phloem, and epidermis

Simple Tissues

• Parenchyma cells are typically thin-walled, flexible, and are

alive in mature tissue

• Function in storage, secretion, wound repair, photosynthesis,

and other specialized tasks

• Mesophyll is photosynthetic parenchyma

• parenchyma

• Simple plant tissue made up of living cells

• Main component of ground tissue

Simple Tissues

• Collenchyma cells have thick, flexible walls that support fast-

growing plant parts, and are alive in mature tissue

• collenchyma

• Simple plant tissue composed of living cells with unevenly

thickened walls

• Provides flexible support

Simple Tissues

• Cells in sclerenchyma die at maturity, but their lignin-

reinforced walls remain and support the plant

• sclerenchyma

• Simple plant tissue that is dead at maturity

• Its lignin-reinforced cell walls structurally support plant

parts

Complex Tissues

• Complex tissues consist of simple tissues in varying

arrangements and proportions

• Complex tissues:

• Dermal

• Ground

• Vascular

Dermal Tissues

• The first dermal tissue to form on a plant is epidermis, which

is usually a single layer of cells on the plant’s outer surface

• Epidermal secretions form a cuticle that helps the plant

conserve water and repel pathogens

• epidermis

• Outermost tissue layer of a plant

Some Dermal Tissues

• Dermal tissues include specialized cells, hairs, and other

epidermal cell outgrowths

• Pairs of specialized epidermal cells form stomata, which

control diffusion of water vapor, oxygen, and carbon dioxide

gases across the epidermis

• Periderm replaces epidermis in woody stems and roots

Vascular Tissues

• Xylem and phloem are vascular tissues composed of

elongated conducting tubes often surrounded by

sclerenchyma fibers and parenchyma

• Xylem conducts water and dissolved mineral ions

• Consists of dead tracheids and vessel members with

perforated, interconnected walls

• Phloem conducts sugars and other organic solutes

• Consists of live sieve-tube members interconnected to

form sieve tubes

• Companion cells load sugars into sieve tubes

Fig. 25.7, p. 401

fibers of

sclerenchyma

companion

cell

sieve plate

of sieve-

tube cell

pit in

wall

one

cell’s

wall

parenchyma vessel

of xylem

phloem

A B C

Vascular

Tissues

Simple Graphic

Ground Tissues

• Ground tissue (everything other than dermal and vascular

tissue) makes up the bulk of a plant

• Consists mostly of parenchyma, but can also include other

simple tissues

• mesophyll

• Photosynthetic parenchyma

Overview

Key Terms

• xylem

• Complex vascular tissue of plants; its tracheids and vessel

members distribute water and mineral ions

• tracheid

• Tapered cell that forms water-conducting tubes in xylem

• Dead at maturity

• vessel member

• Cell that forms water-conducting tubes in xylem

• Dead at maturity

Key Terms

• phloem

• Complex vascular tissue of plants; distributes sugars

through its sieve tubes

• sieve tube

• Conducting tube of phloem

• companion cell

• In phloem, parenchyma cell that loads sugars into sieve

tubes

Complex Tissues in a Sunflower

Overview of Flowering Plant Tissues