Plants II

1
Plants II

• Plant organs

2
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

3
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

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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

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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

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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 3s 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 4s, 5s
• Eudicots make up larger group and include most
  familiar flowering plants
• Monocots include grasses and most of food
  sources, like rice, wheat and corn

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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)

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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

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Ground tissue

• Bulk of a plant
• 3 types
• Parenchyma cells most abundant, found in all
  organs of plant, least specialized
• Collenchyma thick primary walls, flexible
  support to immature regions, celery strand
• Sclerenchyma thick secondary walls that contain
  lignin (make walls tough), support mature region
  of plant

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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

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Xylemfigure 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

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Phloem fig 25.7

• Sieve tube members continuous sieve tube no
  nucleus
• Companion cells have nucleus
• Connected to sieve tube member by plasmodesmata

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Root organization

• Root cap apical meristem, replaced often
• Zones
• Cell division primary meristem, mitosis
• Elongation cells lengthen and specialize
• Maturation root hairs, fully differentiated

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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

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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

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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)

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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

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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

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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

20
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

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Leaf organization

• Consist of blade and petiole
• Veins are netted in eudicots, parallel in monocot

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Cross section leaf

• Trichomes protective hairs
• Cuticle prevent desiccation but prevent gas
  exchange
• Stomata on underside
• Mesophyll tissue
• Palisade
• spongy

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Leaf diversity

• Simple
• Compound
• Pinnately compound
• Palmately compound
• Arrangement
• Alternate
• Opposite
• Whorled
• Leaves based on adaptation to environment