Plant
Growth and Structure
Chapter
35
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Angiosperms
Most diverse and
widespread group of plants - 275,000 species worldwide
Adaptations to
terrestrial environment - root system, shoot system, vascular tissues (xylem
& phloem)
Two classes - Monocots
& Dicots
Characteristics of
Monocots Dicots
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Root
System
Tap root - vertical,
with lateral roots - serves to anchor plant - present in dicots
Fibrous root - lateral,
matlike - present in monocots
Adventitious - above
ground - serves as prop for support
Root hairs on both types
- increases surface area
Shoot
System
Vegetative - consists of
stem and attached leaves
Alternating system of
nodes (points where leaves attached) and internodes (segment between nodes)
Growth usually
concentrated at apex - presence of terminal bud usually inhibits growth of
axillary buds (apical dominance)
Leaves
Main photosynthetic
organ of most plants
Consists of blade &
petiole (absent in some monocots)
Simple - single undivided blade
Compound - blade divided into leaflets
Doubly compound - leaflets subdivided
Many leaves modified -
e.g., cactus spines
Cell
Types in Plants -
1) Parenchyma
Primary cell walls thin
and flexible (secondary walls lacking in most)
Large central vacuole
generally present
Perform most of
metabolic functions of plant (e.g., photosynthesis)
Occur in leaves, stems
& roots
Most developing cells of
this type before becoming specialized
Cell
Types in Plants -
2) Collenchyma
Thicker primary walls -
lack secondary walls
Usually grouped in
strands or cylinders in zones of growth
Cells living - lignin
absent
Provide support without
restraining growth
Cell
Types in Plants -
3) Sclerenchyma
Secondary walls usually
thick - rigid - strengthened with lignin
At maturity, may lack
protoplast (dead cells)
Function in support -
two types
Fibers - usually occur
in bundles (hemp)
Sclereids - scattered
among parenchyma cells - gritty texture (nutshells & seed coat)
Cell
Types of Plants -
4) Xylem
Elongated - rigid -
strengthened with lignin - cells dead at maturity
Function in water
conduction
Two types - tracheids
& vessel elements
What we normally call
wood
Cell
Types in Plants -
5) Phloem
Chains of tubes formed
by sieve-tube members - alive at functional maturity, but lack
organelles (e.g., nucleus, ribosomes)
Function in conduction
of nutrients
Serviced by companion
cells connected by plasmodesmata
Tissue
Systems
Dermal tissue (epidermis) - generally single layer - tightly packed
- covers & protects
Vascular tissue - continuous throughout plant - arranged differently
in each organ - functions in water and nutrient transport
Ground tissue - located between dermal and vascular tissues -
responsible for most metabolic functions
Plant
Growth
Generally
indeterminate - continues throughout life (note: animals determinate)
Meristems - perpetually
embryonic tissues - make indeterminate growth possible
Primary growth - increase in length - apical meristems (tips of
roots and buds of shoots)
Secondary growth - increase in girth - lateral meristems (cylinders of
cells)
Primary
Growth
Apical meristems extend roots & shoots - give rise to primary
plant body
Primary meristems (protoderm, procambium & ground meristem) give
rise to 3 primary tissues respectively (dermal, vascular & ground)
Three zones of growth -
zones of cell division, elongation & maturation
Secondary
Growth
Lateral meristems -
produce secondary vascular tissue & periderm
Vascular cambium -
develops into meristematic cylinder - produces secondary xylem & phloem
Cork cambium - gives
rise to periderm (protective covering)
Secondary tissues
external to vascular cambium
Anatomy of a Leaf