Plant Form and Function

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Plant Form and Function
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General Plant Information

• Using CO2 and H2O (and a few others), plants
  synthesize carbohydrates, lipids, proteins, and
  nucleic acids
• Some plants can live for thousands of years, so
  the tissues produced must be durable
• Plants have indeterminate growth- continue to
  grow throughout their lifetime

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Plant Lifestyles

• Plants use light energy (sun), water (soil) and
  CO2 (air) to make carbohydrates
• Excess water is needed to fill vacuole
• To make other macromolecules, plants also need
• N, P, K, Mg, and a few other minor nutrients
• Most obtained from soil water

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Plant Organization

• Three basic organs evolved roots, stems, and
  leaves
• They are organized into a root system and a shoot
  system (consisting of stems and leaves)

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Root System

• Anchors, absorbs minerals and water, stores
  nutrients
• Root systems of trees can extend beyond the
  canopy
• Not unusual to have 80 of the biomass of a plant
  in root material
• Absorptive portion of a root is at the tip of any
  branch- root hairs

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Root Systems

• Dicots, gymnosperms taproot system
• Monocots, seedless vascular plants fibrous root
  system
• Roots arising from stem adventitious
• Many other modifications are possible

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Root Adaptations
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Shoot System

• An alternating system of
• nodes, the points at which leaves are attached
• Internodes, the stem segments between nodes
• In angle of each leaf is an axillary bud
• Terminal buds occur at tips of branches
• Apical dominance terminal bud (apical)
  suppresses growth in axillary buds

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Shoot Systems

• Shoots vary from a few mm to over 100 m
• Mass can vary from fractions of a gram to over 2
  million kg
• Different branching patters (tall, narrow, short,
  diffuse, etc.) allow light gathering variation
  that helps to prevent competition
• Adaptations include water storage, stolons,
  rhizomes, tubers, and thorns

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Shoot Adaptations
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Shoot Adaptations
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Leaves

• The leaf
• Is the main photosynthetic organ of most vascular
  plants
• Leaves generally consist of
• A flattened blade and a petiole, which joins the
  leaf to a node of the stem

Blade
Petiole
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Types of Angiosperms

• Monocots and dicots
• Differ in the arrangement of veins, the vascular
  tissue of leaves
• Most monocots have parallel veins
• Most dicots have reticulate veins

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dicot
monocot
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Simple
Compound
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Palmate
Pinnate
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Alternate Opposite Whorled
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Leaf Adaptations

• Some plant species have evolved modified leaves
  that serve various functions
• Climbing, pollinator attraction, storage,
  digestion, prevention of water loss, etc.
• Leaves may appear different based on whether they
  grow in shade or full sun

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Leaf Modifications
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Leaf Modifications
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Primary Growth

• Primary growth increases the length of plant
  organs (shoots, roots)
• Primary growth due to apical meristems
• Protoderm gives rise to the dermal tissue
• Ground meristem gives rise to ground tissue
• Procambium gives rise to vascular tissue

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The Three Tissue Systems Dermal, Vascular, and
Ground

• Each plant organ has dermal, vascular, and ground
  tissue

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Primary Growth of Roots

• The root tip is covered by a root cap, which
  protects the delicate apical meristem as the root
  pushes through soil during primary growth

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Root Zones

• Zone of cell division
• Actively dividing, including root apical
  meristem, produces root cap cells
• Zone of elongation
• Root cells elongate, pushes root tip further into
  soil
• Zone of maturation
• Cells complete maturation, become fully
  functional
• Roots hairs increase absorption, surface area

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Primary Growth of Shoots

• A shoot apical meristem
• Is a dome-shaped mass of dividing cells at the
  tip of the terminal bud
• Gives rise to a repetition of internodes and
  leaf-bearing nodes

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Primary Growth of Shoots

• In buds, leaf primordia jammed close together
  (short internodes)
• Below the shoot apex, elongation and division of
  cells causes the elongation in the stem
• Some species (think grasses) have meristems at
  the base of the leaves

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Bud Loctions

• An axillary bud
• Is a structure that has the potential to form a
  lateral shoot, or branch
• A terminal bud
• Is located near the shoot tip and causes
  elongation of a young shoot

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Closer Look at Plant Tissues

• All plant cells are surrounded by a
  cellulose-rich cell wall
• Plant-specific organelles
• Chloroplasts, vacuole
• Plasmodesmata link neighboring plant cells-
  continuous cytoplasm
• Plant cells do not change position once they are
  formed

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Conducting (Vascular) Tissues

• The vascular tissue system
• Carries out long-distance transport of materials
  between roots and shoots
• Consists of two tissues, xylem and phloem

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Types of Vascular Tissue

• Xylem
• Conveys water and dissolved minerals upward from
  roots into the shoots
• Phloem
• Transports organic nutrients from where they are
  made to where they are needed

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Dermal and Ground Tissues

• Dermal tissue
• Consists of the epidermis and periderm
• Ground tissue
• Includes various cells specialized for functions
  such as storage, photosynthesis, and support
• Basically everything other than dermal and
  vascular

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Cell Types

• Some of the major types of plant cells include
• Parenchyma
• Collenchyma
• Sclerenchyma
• Water-conducting cells of the xylem
• Sugar-conducting cells of the phloem

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Cell Types

• Parenchyma
• Primary walls (thin, flexible)
• Large central vacuole
• Function perform most metabolic functions of the
  plant many totipotent
• Collenchyma
• Support young parts of the plant shoot (growing
  regions)- petioles, young stems
• Thickened primary walls (uneven thickening)

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Cell Types, cont.

• Sclerenchyma
• Thick secondary walls, rich in lignin
• Cannot elongate at maturity, so usually found in
  part of the plant that have stopped growing
• Often dead at maturity
• Some schlerenchymous cells are for support only
  fibers, sclereids

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Xylem Cells

• Function water conduction
• Dead at maturity, columnar in shape
• Tracheids
• Found in xylem of all plants
• Long, thin, with tapered ends
• Pits in walls allow water flow
• Vessel Elements
• Wider, shorter, thinner walled
• Join together to form vessels
• End walls that are perforated, and have pits

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Phloem Cells

• Alive at maturity
• Function sugar conduction
• Sieve cells- small, independent
• Sugar conducting cells in gymnosperms and lower
  plants
• Sieve tube members- join to form sieve tubes
• Alive, but lack nucleus, ribosomes, and vacuole
• Sieve plates at ends like a strainer
• Companion cells
• Non-conducting cell connected to sieve cell by
  MANY plasmodesmata
• Loading and unloading of sugars happens here

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Figure. 35.9
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Other Specialized Cells

• Root Hairs In most plants, the absorption of
  water and minerals occurs near the root tips,
  where vast numbers of tiny root hairs increase
  the surface area of the root

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Other Specialized Cells, cont.

• Guard Cells regulate the opening and closing of
  stomata (pores)

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Other Specialized Cells, cont.

• Trichomes help to keep the leaf surface cooler,
  the air more humid, thwart herbivores,
  trap/digest insects

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Meristems

• Meristems generate cells for new organs
• Apical meristems
• Are located at the tips of roots and in the buds
  of shoots
• Elongate shoots and roots through primary growth
• Lateral meristems
• Add thickness to woody plants through secondary
  growth
• Vascular and cork cambiums

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Secondary Growth- Lateral Meristems

• Secondary growth adds girth to stems and roots in
  woody plants
• Secondary growth
• Occurs in stems and roots of woody plants but
  rarely in leaves
• The secondary plant body
• Consists of the tissues produced by the vascular
  cambium and cork cambium

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Lateral Meristems

• Vascular cambium
• Produces secondary phloem and secondary xylem
• Cork cambium
• Produces cork cells

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The Vascular Cambium and Secondary Vascular Tissue

• The vascular cambium
• Is a cylinder of meristematic cells one cell
  thick
• Develops from parenchyma cells
• Produces secondary xylem to the interior of the
  stem
• Produces secondary phloem to the exterior of the
  stem

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Vascular Cambium in Woody Plants
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Vascular Cambium Contributions

• Viewed in transverse section, the vascular
  cambium
• Appears as a ring, with interspersed regions of
  dividing cells called fusiform initials and ray
  initials

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Aging of Woody Plants

• As a tree or woody shrub ages
• The older layers of secondary xylem, the
  heartwood, no longer transport water and minerals
• The outer layers, known as sapwood
• Still transport materials through the xylem

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Figure 35.20
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Cork Cambia and the Production of Periderm

• The cork cambium
• Gives rise to the secondary plant bodys
  protective covering, or periderm
• Periderm
• Consists of the cork cambium, phelloderm, and the
  layers of cork cells
• Bark
• Consists of all the tissues external to the
  vascular cambium, including secondary phloem and
  periderm

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Annual Rings in Wood