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Chapter 24
PLANT
STRUCTURE
and
FUNCTION
Reproductive shoot (flower)
Overview of
PLANT
STRUCTURE
Terminal bud
Node
Internode
Terminal
bud
Shoot
system
Vegetative
shoot
• Vegetative organs are
concerned with growth
and nutrition
• Flowers, seeds, and
fruits are structures
involved in
reproduction.
Leaf
Blade
Petiole
Axillary
bud
Stem
Taproot
Lateral roots
Root
system
Flowering Plants:
Monocots or Eudicots
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Root
Stem
Leaf
Vascular bundles
scattered in stem
Leaf veins form
a parallel pattern
Flower
Monocots
Seed
Root xylem and
phloem in a ring
Flower parts in threes
and multiples of three
Eudicots
One cotyledon in seed
Two cotyledons in seed
Root phloem between
arms of xylem
Vascular bundles
in a distinct ring
Leaf veins form
a net pattern
Flower parts in fours or
fives and their multiples
10
ROOTS
• Roots
– Generally, the root system is at least
equivalent in size and extent to the shoot
system
• Anchors plant in soil
• Absorbs water and minerals
• Produces hormones
– Root hairs:
• Projections from epidermal root hair cells
• Greatly increase absorptive capacity of root
4
Roots
1
• Roots anchor plant in soil, absorb
minerals & water, & store food
– fibrous roots (1)
• mat of thin roots that spread out
• monocots
– tap roots (2)
• 1 large vertical root
• also produces many small lateral,
or branch roots
• dicots
– root hairs (3)
• increase absorptive
surface area
2
3
Shoots
• Shoots consist of stems, leaves & buds
• Stems
– nodes = points at which
leaves are attached
– internodes = stem
segments between nodes
• Buds
– growth of shoot
• terminal or apical bud = at tip of plant
• axillary bud = in nodes on stem
STEMS
– Support for the plant body
– Carries nutrients throughout
plant
– Defense system to protect
against predators and infection
– Few millimeters to 100 meters
LEAVES
• Leaves are the major part
of the plant that carries on
photosynthesis
– Foliage leaves are usually
broad and thin
• Blade - Wide portion of
foliage leaf
• Petiole - Stalk attaches blade
to stem
• Leaf Axil - Axillary bud
originates
– Tendrils - Leaves that
attach to objects
–
Bulbs - Leaves that store
8
food
Modified leaves
tendrils (peas)
succulent leaves
spines (cacti)
colored leaves (poinsetta)
Interdependent systems
• Both systems depend
on the other
sugars
– roots receive sugars &
other nutrients from
photosynthetic parts
– shoot system depends
on water
& minerals absorbed
from the soil by roots
water
Putting it all together
• Obtaining raw materials
– sunlight
• leaves = solar collectors
– CO2
• stomates = gas exchange
– H2O
• uptake from roots
– nutrients
• uptake from roots
•
TISSUES OF FLOWERING
PLANTS
Dermal
– “skin” of plant
– single layer of tightly
packed cells that
covers & protects
plant
• Vascular
– transport materials
between roots &
shoots
– xylem & phloem
• Ground
– everything else:
storage,
photosynthetic
DERMAL TISSUE
• Dermal Tissue
– Outer covering
– Single layer of cells
consisting of
• Cuticle – waxy coating
• Hairs
• Guard Cells that
surround stomata
Cells of GROUND TISSUE
Those would’ve
been great names
for my kids!
• Parenchyma
– “typical” plant cells = least specialized
– photosynthetic cells, storage cells
– tissue of leaves, stem, fruit, storage roots
• Collenchyma
– unevenly thickened primary walls = support
• Sclerenchyma
– very thick, “woody” secondary walls (lignin) = support
– Fibers (rope); Schlereids (grittiness, hardness of nuts,
peach pit)
– rigid cells that can’t elongate
– dead at functional maturity
VASCULAR TISSUE
• Transports materials in roots, stems &
leaves
• Xylem
– carry water & minerals up
from roots
– tube-shaped dead cells
• only their walls provide a system
of microscopic water pipes
• Phloem
– carry nutrients throughout plant
• sugars (sucrose), amino acids…
– tube-shaped living cells
Xylem
• Dead at functional maturity
• Cell elongated into tubes
– tracheids
• long, thin cells with tapered ends
• walls reinforced with lignin = support
• thinner pits in end walls allows water
flow
– vessel elements
• wider, shorter, thinner walled & less
tapered
• perforated ends walls allows free
water flow from one hole to the next
Aaaaah…
Structure-Function
again!
Phloem
• Living cells at functional maturity
– lack nucleus, ribosomes & vacuole
• more room: specialized for
liquid food (sucrose) transport
• Cells
– sieve tubes
• end walls, sieve plates, have pores to
facilitate flow of fluid between cells,
pump sugars
– companion cells
• nucleated cells connected to the sievetube
• Surround sieve tubes; support phloem
cells
Aaaaah…
Structure-Function
again!
Phloem: food-conducting cells
 sieve tube elements & companion cells
Vascular tissue in herbaceous stems
dicot
monocot
trees & shrubs
grasses & lilies
• What I should eat….
What I actually eat….
Root structure: dicot
phloem
xylem
Root structure: monocot