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Tissues Chapter 4
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
