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Plants II
Plant organs
Plant organs
 Root system – roots
 Shoot system – stem and leaves
 Vegetative organs – (allow to live and
grow): roots, leaves, stem
 Reproduction: flowers, seeds and fruits
Roots
 Underground, usually equal to shoot
system in size
 Anchors and gives support
 Absorbs water and minerals
 Penetrates soil as it grows
 Root hairs increase surface
area
 Produce hormones
stems
 Main axis of plant
 Support leaves so that leaves are
exposed to as much light as possible
 Node – where leaf is attached
 Internode – space between nodes
 Vascular tissue used in transport
 Can store nutrients and water and
conduct photosynthesis
leaves
 Photosynthesis
 Size, shape and texture vary and is used
in identification
 Blade – wide portion of leaf
 Petiole – stalk, attaches blade to stem
 Axillary bud – where branch or flower
may originate
Monocot vs Eudicot
fig 25.3
 Compare seed leaf, root, stem, leaf and flower
 Monocot – 1 seed leaf, xylem and phloem in a
ring, vascular bundles scattered, leaf veins
parallel, flower parts in 3’s and multiples of 3
 Eudicot – 2 seed leaves, phloem between
arms of xylem, vascular bundles in ring, leaf
veins in net pattern, flower parts in 4’s, 5’s
 Eudicots make up larger group and include
most familiar flowering plants
 Monocots include grasses and most of food
sources, like rice, wheat and corn
Plant tissues
 Meristematic tissue = embryonic
 Apical meristem – located on tip of stem and
roots, growth
 produces 3 types of meristem
 Protoderm epidermis
 Ground meristem  ground tissue
 Procambium  vascular tissue
 Woody (non herbaceous), non woody
(herbaceous – perennial, dies back in winter)
Epidermal tissue
 Forms outer protective covering of plant
 Walls of epidermal cells exposed to air are covered
with a waxy cuticle
 Roots – form root hairs
 Stems and leaves – trichomes – hairs that protect
form too much sun and moisture reserve
 Leaves – guard cells, stomata
 Periderm – old woody plants, replaces epidermis
 Cork cells – protection
 Cork cambium – new cork cells made from
 Lenticels – areas of overproduction of cork cells, gas exchange
Ground tissue


Bulk of a plant
3 types:
1. Parenchyma cells – most abundant, found
in all organs of plant, least specialized
2. Collenchyma – thick primary walls, flexible
support to immature regions, celery strand
3. Sclerenchyma – thick secondary walls that
contain lignin (make walls tough), support
mature region of plant
Vascular tissue
 Xylem – water and minerals, roots to leaves
 Phloem – sucrose and organic molecules
(hormones) form leaves to roots
 Complex tissues – contain 2 or more kinds of
cells
 Both extend from roots to leaves
 Roots- located in vascular cylinder, stem – vascular
bundles, leave – leaf veins
Xylem
figure 25.6
 2 types of conducting cells, hollow and
non-living
 Tracheids – tapered ends, contain pits
where secondary wall does not form
 Vessel elements – larger, perforation plates
 Parenchyma cells that store substances
Phloem –
fig 25.7
 Sieve tube members – continuous sieve
tube – no nucleus
 Companion cells – have nucleus
 Connected to sieve tube member by
plasmodesmata
Root organization
 Root cap – apical meristem, replaced
often
 Zones
 Cell division – primary meristem, mitosis
 Elongation – cells lengthen and specialize
 Maturation – root hairs, fully differentiated
Eudicot root tissue
 Epidermis – single outer layer, root hairs
 Cortex – thin walled parenchyma, food storage
 Endodermis – boundary between cortex and
vascular tissue
 Casparian strip – prevents water and mineral ions
between cell walls
 Vascular tissue – xylem and phloem
 Pericycle – first layer of cells
 Monocots similar, differ in arrangement of
xylem and phloem in a ring, ground tissue is
pith
Root diversity
 Taproot – grows straight down, fleshy, stores
food, carrot, beet
 Fibrous root system – in monocots – seen in
grasses, strong anchorage
 Adventitious roots – develop from shoot
system instead of root system, seen in corn,
can come above soil line
 Root nodules – beans, peas…, nitrogen
fixation
 Mycorrhizae – plant roots and funugs
Stem organization
 Terminal bud – shoot tip protected by bud scales
 Leaf and bundle scars – location of leaves that have
dropped
 Axillary buds – give rise to branches or flowers
 Bud scale scar – indicates age of stem, one for each
year of growth
 Primary meristem  primary tissues
 Protoderm  epidermis
 Ground meristem  pith (ground tissue)
 Procambium  cortex (vascular tissue)
Herbaceous stems
 Non woody, die off in winter, perennial
 Only primary growth
 Eudicot, vascular bundle in rings, cortex
separate from pith
 Monocot – vascular bindles scattered, no
well defined cortex or pith
Woody Stems
 Primary (length) and secondary (girth of
trunks) tissues
 Secondary tissues form from lateral
meristem: vascular cambium and cork
cambium
 Vascular cambium produces new xylem and
phloem each year
 3 distinct areas: bark, wood and pith
Bark and Wood
 Contains periderm
 when stem becomes woody, replaces
epidermis
 Cork, cork cambium and phloem
 Removing bark and be fatal to tree
 Wood is secondary xylem, girth
 Vascular cambium is dormant in winter
 Annual ring – sapwood, inner rings heartwood
Stem diversity
 Stolons – aboveground horizontal
stems, reproduce where nodes touch
ground, runners, strawberries
 Rhizomes – underground, horizontal
stems, some contain tubers (food
storage) like potatoes
 Corm – bulbous underground stems,
gladiolus
Leaf organization
 Consist of blade and petiole
 Veins are netted in eudicots, parallel in
monocot
Cross section leaf
 Trichomes – protective hairs
 Cuticle – prevent desiccation but prevent
gas exchange
 Stomata on underside
 Mesophyll tissue
 Palisade
 spongy
Leaf diversity
 Simple
 Compound
 Pinnately compound
 Palmately compound
 Arrangement
 Alternate
 Opposite
 Whorled
 Leaves based on adaptation to environment