PLANT FORM AND FUNCTION

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PLANT FORM AND FUNCTION

• Chapter 27

Fiddlehead of a fern.
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• A. Plant Tissues
• Gymnosperms Angiosperms consist of 4 basic
  tissue types.
• 1. Meristems
• Regions of active cell division contain
  undifferentiated cells.
• Apical meristems
• located near tips of shoots roots in all plants

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• allow shoots roots to lengthen (primary growth)
• Shoot root apical meristems give rise to 3
  types of meristems (protoderm, procambium
  ground meristem).
• give rise to
• protoderm ? forms dermal tissue
• procambium ? forms vascular tissue
• ground meristem ? forms ground tissue

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• Lateral meristems
• located in older roots shoots of woody dicots
  gymnosperms
• allow shoots roots to increase in diameter
  (secondary growth)
• Intercalary meristems
• located in bases of grass leaves
• allow rapid regrowth

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• 2. Ground Tissue
• Makes up the bulk of plants interior consists
  of 3 cell types.
• Parenchyma cells

• relatively unspecialized
• thin primary cell walls
• function in cellular respiration, photosynthesis
  storage of metabolic products
• Stored products include starch, fragrant oils,
  salts, pigments, citric acid, crystals.

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• Collenchyma cells

• unevenly thickened primary cell walls
• function to support growing regions of plant

• Sclerenchyma cells
• thick secondary cell walls
• usually dead at maturity

• function to support non growing regions of plant
• Two types of sclerenchyma cells
• sclereids fibers
• Sclereids responsible for gritty
• texture of pears form hulls of peanuts.
• Fibers of hemp plants are used to
• make rope.

sclereids
fibers
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• 3. Dermal Tissue
• Single layer of tightly packed cells (epidermis)
  covering plant.

• Dermal Specializations
• Cuticle - waxy coating produced by epidermis of
  stems leaves
• Functions to protect plant conserve water.

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• Stomata - pores extending through epidermis
• Regulate gas water exchange with environment.

• Trichomes - epidermal outgrowths
• Root hairs increase surface area for absorption.
• Leaf hairs slow air movement over leaf, reducing
  water loss.

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• 4. Vascular Tissue
• Specialized conducting tissue in plants xylem
  phloem.
• Xylem
• transports water dissolved minerals from roots
  to shoots1

• consists of tracheids vessel elements
• dead at maturity
• Tracheids - long, narrow cells.
• Water moves from one cell to
• the next through thin areas (pits).
• Vessel elements - short, barrel-
• shaped cells more specialized
• than tracheids. Water moves
• directly from one cell to the next
• because the end walls usually
• disintegrate. Water moves faster
• through vessel elements because
• of their larger diameter direct
• water movement.

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• Phloem
• transports organic compounds throughout plant

• consists of sieve cells or sieve tube members
  companion cells
• alive at maturity

Compounds found in phloem sap include
carbohydrates, hormones, alkaloids, viruses
inorganic ions. Sieve cells - long, tapering
cells usually found in gymnosperms seedless
vascular plants. Sieve tube members - specialized
cells usually found in angiosperms lose nucleus
at maturity. Companion cells - transfer
carbohydrates to/from sieve tube members.
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• B. Plant Anatomy
• Basic parts of a flowering plant include stems,
  leaves, roots, flowers fruits.

• 1. Stems - central axes of shoots.
• Function to
• support plant
• transport nutrients/water
• produce/store nutrients
• Consist of nodes, internodes
• axillary buds.
• Flowers fruits will be discussed in chapter 28.
• Nodes - areas of leaf attachment.
• Internodes - portions of stem between the nodes.
• Axillary buds - underdeveloped shoots that form
  in leaf axils. Axillary buds can elongate to
  form a branch or flower.

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Comparison of monocot dicot stems. Both
surrounded by epidermis that secretes a
cuticle has few stomata. Monocots vascular
bundles scattered throughout ground tissue
each vascular bundle somewhat resembles a
monkey face note phloem forms on outer
portions of the bundles. Dicots vascular
bundles form a ring around outer edge of stem
here again, phloem forms on outer portions of
the bundles. Pith centrally located ground
tissue. Cortex ground tissue located between
epidermis vascular tissue.
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• Modified Stems

stolons
tendrils
thorns
rhizomes
fleshy stems
tubers
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• Stolons (runners)
• stems that grow along the soil surface.
• Ex. Strawberries
• Thorns
• outgrowths that provide protection.
• Ex. Honey locust
• Tendrils
• support plants by coiling around objects.
  tendrils may also be modified leaves Ex.
  Grapevines bean plants
• Fleshy stems
• store large quantities of water. Ex. Cacti
  (spines of cacti are modified leaves, not stems)
• Tubers
• swollen regions of underground stems that store
  nutrients. Ex. Potato tubers store starch
• Rhizomes
• underground stems that produce roots new
  shoots. Ex. Iris ginger

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• 2. Leaves - primary photosynthetic organs of most
  plants.

• Most consist of
• flattened blade
• stalk-like petiole
• central midrib
• numerous veins
• Leaves are shed from an abscission zone at
• base of petiole.
• Petiole - attaches leaf to stem.
• Midrib - large vein
• Veins - strands of vascular tissue
• Separation layer forms in abscission zone
• in response to environmental cues
• (shortening days / cooler temps).
• Abscission zone minimizes risk of infection
  nutrient loss when leaf is shed.

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• Leaves are classified based on form type of
  venation.

Leaf Forms
? simple
? palmate compound
? pinnate compound
Leaf Venation
? netted
parallel?
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• Simple leaves have flat, undivided blades.
• Ex. Elm maple
• Compound leaves have divided blades divisions
  are called leaflets.
• Palmate compound leaves - leaflets all attach to
  one point at the top of the petiole, like fingers
  on a hand. Ex. Horse chestnut (5 leaflets)
  clover (3 leaflets)
• Pinnate compound leaves - leaflets are paired
  along a central line. Ex. Mimosa, rose walnut
• Netted venation - minor veins branch off from
  larger, prominent midveins. Ex. Most dicots
• Parallel venation - several major parallel veins
  connected by smaller minor veins.
• Ex. Most monocots

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Vein
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• Epidermis surrounds outer portion of leaf. It
  typically secretes a cuticle contains numerous
  stomata.
• - stomata of horizontal leaves concentrated
  on bottom
• - stomata of aquatic lily pads concentrated
  on top
• - stomata of vertical leaves evenly
  distributed
• Portion of leaf sandwiched between epidermal
  layers is called mesophyll (ground tissue,
  primarily parenchyma cells). Horizontally
  oriented leaves usually have two types of
  mesophyll cells
• palisade mesophyll cells - column shaped cells
  specialized for light absorption contain large
  numbers of chloroplasts.
• Spongy mesophyll cells - irregularly shaped cells
  specialized for gas exchange contain fewer
  chloroplasts than palisade cells.

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• Modified Leaves
• Tendrils
• Spines
• Bracts
• Storage leaves

• Cotyledons

• Insect-trapping leaves

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• Tendrils - support plants by coiling around
  objects. tendrils may also be modified stems
  Ex. Pea plants
• Spines - leaves modified to protect plant from
  predators. Ex. Cacti
• Bracts - floral leaves that protect developing
  flowers. Ex. Poinsettia flower.
• Storage leaves - fleshy leaves that store
  nutrients. Ex. Onion bulbs
• Cotyledons - embryonic leaves. (monocot seeds
  have one small cotyledon dicot seeds have two
  relatively large cotyledons). Cotyledons supply
  energy for germination in dicots (endosperm
  supplies energy for germination in monocots).
• Insect-trapping leaves - attract, capture
  digest prey. Ex. Venus flytrap, sundew pitcher
  plant

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• 3. Roots
• Underground part of a plant.
• Function to
• anchor plant
• absorb, transport, store water and minerals
• absorb oxygen
• Two main types
• taproots

• fibrous roots

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• Tap roots - embryonic root (radicle) enlarges to
  form a major root that persists throughout life
  of the plant lateral roots develop from major
  root.
• Tap roots are deep roots most dicots have tap
  roots.
• Fibrous roots - radicle is short-lived replaced
  by roots which form on stems (adventitious
  roots).
• Fibrous roots are shallow prevent soil erosion
  most monocots have fibrous roots.

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• Growth in length occurs near the roots tip.
• Zone of cell division - contains apical meristem,
  which forms
• root cap - protects apical meristem produces
  mucigel (a lubricant)
• protoderm - future dermal tissue
• ground meristem - future ground tissue
• procambium - future vascular tissue
• Zone of elongation - cells lengthen, pushing root
  tip through soil.
• Zone of maturation - cells complete
  differentiation become functionally mature.
  Outer epidermal cells form root hairs.

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Monocot root
Dicot root
(stele)
Enlargement of dicot stele
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• Both monocot dicot roots possess
• Epidermis (dermal) - single layer of cells that
  produce root hairs unlike epidermis of stems
  leaves, does not produce cuticle.
• Cortex (ground) - region of root between
  epidermis stele.
• Endodermis (ground) - innermost layer of cortex
  single layer of tightly packed cells, whose walls
  possess a band of suberin (waxy, waterproof
  material). This waxy barrier is called the
  Casparian strip (blocks movement of materials
  between endodermal cells).
• Vascular cylinder or Stele (vascular) - includes
  pericycle (thin layer of cells beneath
  endodermis produces lateral roots), xylem
  phloem.
• Monocot stele - ring of vascular bundles
  surrounds the pith (parenchyma tissue).
• Dicot stele - phloem located between arms of
  xylem core.

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• Modified Roots
• Storage roots
• Pneumatophores
• Aerial roots

• Buttress roots

• Prop roots

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• Storage roots - store carbohydrates (beets,
  carrots, sweet potatoes) or water (desert
  plants).
• Pneumatophores - form on plants that live in
  oxygen poor environments (swamps) allow oxygen
  to diffuse inward. Ex. Black mangrove trees
• Aerial roots - roots that form grow in the air.
  Ex. Banyan tree, mistletoe, orchids
• Buttress roots - large roots that form at base of
  a tree provide support. Ex. Tropical fig tree
• Prop roots - roots that arise from the stem
  provide support. Ex. corn

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• C. Secondary Plant Growth (growth in diameter)
• Lateral meristems (vascular cork cambia)
  increase diameter of stems roots in woody
  dicots gymnosperms.
• 1. Vascular Cambium
• Ring of meristematic tissue that produces
  secondary xylem phloem.

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Vascular cambium will produce secondary xylem
toward the inside secondary phloem toward
the outside.
Woody stem secondary growth
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• 2. Cork Cambium
• Ring of meristematic tissue that produces
  phelloderm cork.
• phelloderm - parenchyma cells alive at maturity
• cork - waxy, densely packed cells insulates,
  waterproofs, protects underlying tissues dead
  at maturity
• Periderm cork cork cambium phelloderm
• Cork used to stopper wine bottles comes from a
  cork oak tree that grows in the Mediterranean.

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Woody stem secondary growth
Bark - everything external to the vascular
cambium (phloem, phelloderm, cork cambium
cork)
Bark periderm phloem
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Woody stem secondary growth
Note oldest xylem is innermost, while oldest
phloem is outermost.
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Growth rings occur as result of differences in
available soil moisture when wood forms in
spring and summer. Spring - soil moisture is
high large diameter cells are produced, giving
wood a lighter color. Summer - soil moisture is
low small diameter cells are produced, giving
wood a darker color. Sapwood - functioning wood
(transports water dissolved minerals) located
nearest the vascular cambium. Heartwood -
nonfunctioning wood located in center of tree.