Plant Tissues Chapter 28 Part 1. Impacts, Issues Drought Versus Civilization Without plants, we would die – prolonged drought can destroy crops and.
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Impacts, IssuesDrought Versus Civilization
Without plants, we would die – prolonged drought can destroy crops and civilizations
28.1 Components of the Plant Body
The unique organization of tissues in flowering plants is part of the reason why they are the dominant group of the plant kingdom
The Basic Body Plan
Shoots• Aboveground plant parts such as stems, leaves,
and flowers
Roots• Structures that absorb water and dissolved
minerals, store food, and support the plant• Usually grow down and outward in the soil
Plant Tissue Systems
Ground tissue system• Photosynthesis, storage, and structural support of
other tissues
Vascular tissue system• Distributes absorbed water and mineral ions and
products of photosynthesis
Dermal tissue system• Covers and protects exposed plant surfaces
Fig. 28-2, p. 476
shoot tip (terminal bud)lateral (axillary) bud young leaf
flower
nodeinternode
dermal tissuenode
vascular tissuesleaf
seeds in fruit
ground tissues withered seed leaf (cotyledon)stemSHOOTS
ROOTS
primary rootlateral root root hairs
root tiproot cap
Eudicots and Monocots
Flowering plants are divided into two classes with tissues organized into different patterns
Eudicots have two cotyledons (seed leaves)
Monocots have one cotyledon
Fig. 28-3, p. 477
A
Vascular bundles organized in a ring in ground tissue
In seeds, two cotyledons (seed leaves of embryo)
Flower parts in fours or fives (or multiples of four or five)
Leaf veins usually forming a netlike array
Pollen grains with three pores or furrows
B
Vascular bundles throughout ground tissue
In seeds, one cotyledon (seed leaf of embryo)
Flower parts in threes (or multiples of three)
Leaf veins usually running parallel with one another
Pollen grains with one pore or furrow
Introducing Meristems
All plants tissues arise at meristems (regions of rapidly dividing, undifferentiated cells)
Growth in apical meristems at tips of shoots and roots (primary growth) increases length
In some plants, growth in lateral meristems (secondary growth) thickens roots and shoots
Fig. 28-4a, p. 477
shoot apical meristem (new cells forming)
cells dividing, differentiating
three tissue systems developing
three tissue systems developing
cells dividing, differentiating
root apical meristem (new cells forming)
a Many cellular descendants of apical meristems are the start of lineages of differentiated cells that grow, divide, and lengthen shoots and roots.
Fig. 28-4b, p. 477
vascular cambium
cork cambium
thickening
b In woody plants, the activity of two lateral meristems—vascular cambium and cork cambium—result in secondary growth that thickens older stems and roots.
28.2 Components of Plant Tissues
Different plant tissues form just behind shoot and root tips, and on older stem and root parts
Tissue systems are organized as simple tissues (one cell type) or complex tissues (two or more cell types)
Simple Tissues
Parenchyma makes up most primary growth• Functions in secretion, storage, photosynthesis
(mesophyll), and tissue repair
Collenchyma supports growing plant parts• Pectin provides flexibility
Sclerenchyma contains lignin for support• Cells (fibers, sclereids) are dead at maturity
Complex Tissues: Vascular Tissues
Xylem carries water and ions through the plant• Consists of two types of cells that are dead at
maturity: tracheids and vessel members• Lignin-filled secondary walls
Phloem conducts sugars, other organic solutes• Sieve tubes connect end to end at sieve plates• Companion cells load sugars into sieve tubes
Fig. 28-8, p. 479
one cell’s wall
sieve plate of sieve-tube cell
pit in wall companion
cell
a b c
parenchyma vessel of xylem
phloem fibers of sclerenchyma
Complex Tissues: Dermal Tissues
Epidermis• Usually a single outer layer of cells that secrete a
waxy, protective cuticle• May contain specialized cells that form stomata
for gas exchange
Periderm• Replaces epidermis in woody stems and roots
28.1-28.2 Key Concepts Overview of Plant Tissues
Seed-bearing vascular plants have a shoot system, which includes stems, leaves, and reproductive parts; most also have a root system
Such plants have ground, vascular, and dermal tissues
Plants lengthen or thicken only at active meristems
28.3 Primary Structure of Shoots
Inside the soft, young stems and leaves of both eudicots and monocots, the ground, vascular, and dermal tissue systems are organized in predictable patterns
Behind the Apical Meristem
Terminal buds• Main zones of primary growth in shoots • Naked or encased in modified leaves (bud scales)• Form leaves at nodes
Lateral buds (axillary buds)• Dormant shoots in leaf axils• Form side branches, leaves, or flowers
Fig. 28-10 (a-c), p. 480
immature leaf
shoot apical meristem
a Sketch of the shoot tip in the micrograph at right, tangential cut. The descendant meristematic cells are color-coded orange .
b Same tissue region later on, after the shoot tip lengthened above it
cortex
c Same tissue region later still, with lineages of cells lengthening and differentiating
primary phloem
primary xylem pith
Fig. 28-10d (1), p. 480
immature leaf
youngest immature
leaf
apical meristem
epidermis forming
lateral bud forming
vascular tissues
forming
pith
Inside the Stem
Vascular bundles• Multistranded cords of vascular tissues threaded
lengthwise through ground tissues of all shoots
Two distinct patterns of vascular bundles• Eudicot stems: Cylinders run parallel with stem,
divide ground tissue into cortex and pith• Monocot stems: Bundles distributed throughout
ground tissue
Fig. 28-11a, p. 481
meristem cell
epidermis
cortex
vascular bundle
pith
sieve tube in phloem
companion cell in
phloemA Stem fine structure for alfalfa (Medicago), a eudicot
vessel in xylem
Fig. 28-11b, p. 481
collenchyma sheath cell
air space
vessel in xylem
epidermisvascular bundle
pith
sieve tube in phloem
companion cell in phloemB Stem fine structure for corn (Zea mays), a monocot
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