Tissues Chapter 4. Tissue a group of similar cells working together to perform a set of functions.

Tissues

Chapter 4

Tissue

• a group of similar cells working together to perform a set of functions

Plant Tissues

• Meristems

• Simple (Ground) Tissue

• Vascular Tissue

• Dermal Tissue

• Secretory Tissue

Meristems

• Apical Meristems – located at the ends of shoots, roots and in buds; produce primary growth – protoderm, ground meristem and procambium

• Lateral Meristems – located around the perimeter of shoots and roots; produce secondary growth

Primary and Secondary Growth

Your growth, typical of animals

infant child You, today

Plant Growth1st year – all primary growth

Primary growth – plant growth that produces an increase in length and new structures

Secondary growth – plant growth that produces an increase in diameter in existing plant parts in the second and any subsequent growing seasons

2nd year – only secondary growth, in blue, is shown below

2nd year primary (in green) and secondary (in blue) growth

3rd year’s growth, showing both primary (black) and secondary (red) growth

Woody dicot stem cross section showing growth rings

Apparent increase in limb height on many trees is due to loss of lower limbs

Lateral Meristems (cont.)

• Vascular Cambium – produce vascular tissue

• Cork Cambium – produces “bark”

Intercalary Meristems

• located near grass nodes

• produces an increase in stem and leaf length

• contributes to the grazing and cutting tolerance of grasses

Simple (Ground) Tissues

• Parenchyma

• Collenchyma

• Sclerenchyma

Parenchyma

• relatively spherical and thin walled

• alive at functional maturity

• perform a variety of functions

– photosynthesis (chlorenchyma)

– food and water storage

– pith

– wound healing

Collenchyma

• elongate with irregularly thickened cell walls

• provide flexible support; celery strings

• alive at functional maturity

Sclerenchyma

• elongate (fibers) to irregular shape (sclerids)

• very thick, lignified cell walls

• dead at functional maturity

Vascular Tissue

• Complex tissues since they include 2 or more kinds of cells

• Xylem

• Phloem

Xylem

• similar to straws• dead at functional maturity• vessels – composed of vessel elements

(cells); uniform tubes, open at both ends, relatively large diameter, may be relatively short

• tracheids – tapered at both ends, numerous pits rather than large openings between adjacent cells

• conducts water and minerals upwards

Xylem

Phloem

• alive at functional maturity

• consist of sieve tube members and companion cells

Sieve tube members – cylindrical, conduct organic molecules up

and down through plant

Companion cells – regulate activity of sieve tube members

Phloem

Xylem

Phloem

Dermal Tissue

• Epidermis – covers primary growth, single layer of cells; often secretes cutin

(lipid) forming cuticle (reduces transpiration and protection from pathogens)

• Periderm – covers secondary growth, many cell layers; becomes impregnated with lipids (suberin)

Epidermis (cont.)

• Root hairs - single cell extensions from the epidermis near root tips

• greatly increase surface area in contact with soil and thereby enhance water and mineral absorption

Stomata

• openings in epidermis

• surrounded by Guard Cells that regulate opening

Stomata from a epidermal peel of Commelina communis by Dr. J. Weyers

StomateStomate

Guard CellsGuard Cells

Lenticels

• regions of loosely packed cells in the periderm

• promote gas exchange with tissues below

Secretory Tissue

• produce a variety of products

• nectar in flowers

• oils in citrus and mints

• latex

• resins

• opium

• mucilage – e.g. for trapping insects