STRUCTURE OF HIGHER PLANTS

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Chapter 2

• STRUCTURE OF HIGHER PLANTS

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Gymnosperms and angiosperms

• Gymnosperms have naked seed
• Most gymnosperms are narrow-leaved evergreen
  trees like pines, spruces and firs
  
• http//nature.snr.uvm.edu/www/mac/plant-id/gymnosp
  erms/gymnosperms.html
  
• Angiosperms have seeds enclosed within an ovary
• Most angiosperms are broad-leaved flowering
  plants
  

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Monocots and dicots

• Monocots or monocotyledonous plants have an
  embryo with only one seed leaf.
  
• Other characteristics of monocots are
• 1) Parallel veins
• 2) Diffuse vascular bundles
• 3) Flower parts usually in multiples of three.

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Monocot stem
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Dicots

• Dicots or dicotyledonous plants have embryos with
  2 seed leaves.
  
• Other characteristics of dicots are
• 1) Leaves have net shaped venation
• 2) Vascular bundles are distributed around a
  central vascular cambium
  
• 3) Flower parts are usually in multiples of four
  or five
  

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Dicot stem
7
Fromhttp//www2.cdepot.net/walser/worldofscience
/Biology/Pictorial20Help/Botany/monocots_dicots.h
tm
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From http//gened.emc.maricopa.edu/bio/bio181/BIO
BK/BioBookPLANTANATII.html
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Monocot germination- Corn
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Dicot germination- Bean
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Major parts of the plant cell

• The protoplast includes
• plasma membrane
• the cytoplasm
• the nucleus
• the vacuole
• Plasma membrane plasmalemma
• a double membrane, actually a lipid bilayer,
  surrounding the cytoplasm and cell organelles.

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Major parts of the plant cell

• The cytoplasm thick liquid within the
  plasmalemma containing endoplasmic reticulum and
  plastids of various types.
  
• The endoplasmic reticulum membranes where
  proteins are synthesized on ribosomes.

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Major parts of the plant cell

• Plastids capsule-like organelles bound by a
  double membrane.
  
• Plastid types
• Chromoplasts - contain pigments like chlorophyll
  (chloroplasts) and several others.
  
• Leucoplasts - colorless and serve as storage
  bodies for oil, starch and proteins.

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Major parts of the plant cell

• Mitochondria - smaller than plastids, double
  membrane bound.
  
• Powerhouse of the cell - involved in
  respiration and ATP production.
  
• ATP-an energy rich compound.
• Mitochondria -also involved in protein synthesis.

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Major parts of the plant cell

• The nucleus the organelle which contains
  chromosomes long lengths of DNA containing the
  genetic code.
  
• Vacuoles - surrounded by a membrane called the
  tonoplast.
  
• Vacuoles serve as storage for the cell.
• Vacuoles also regulate turgor (keep cells
  inflated)
  

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Major parts of the plant cell

• The primary cell wall - composed mainly of
  cellulose, pectic substances and lingins.
  
• provides protection for the protoplast and
  structure for the plant.
  
• The middle lamella -lies between adjacent cells
  holding them together.
  
• The secondary cell wall - lies inside the primary
  wall and is composed of cellulose, lignins,
  suberins and cutins.

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Major parts of the plant cell

• Plasmodesmata - strands of cytoplasmic tissue
  connecting individual cells to each other.
  
• http//www.cellsalive.com/cells/plntcell.htm
• http//koning.ecsu.ctstateu.edu/cell/cell.html

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Plant tissues

• Plant tissues large tracts of organized cells
  of similar structure that perform a collective
  function.
  
• Meristematic tissue or meristem actively
  dividing cells which can differentiate into other
  tissues and organs.
  
• Permanent tissues fully differentiated tissues
  developed from meristems.

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Meristematic Tissues

• Apical meristems
• 1) shoot apical meristems-
• Determine leaf patterns and branching habit -
  opposite, alternate, spiral
  
• Produce primary vascular tissues and stem tissue
• May produce terminal flowers or remain vegetative
  and continue to grow producing flowers on lateral
  growth depending on the plant
  

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Meristematic Tissues

• 2) root meristems-
• Found at the root tips
• Some plants have a dominant taproot which
  develops mainly downward with little lateral
  growth.
  
• Examples include carrots, beets, oaks and
  pecans.
  

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Meristematic Tissues

• Many plants lack a strong tap root and so they
  develop a well branched fibrous root system.
  
• Grasses, grains and shallow rooted trees are
  examples.
  
• http//koning.ecsu.ctstateu.edu/Plant_Biology/meri
  stems.html

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Subapical meristems

• Subapical meristem -produces new cells a few
  millimeters behind an active apical meristem.
  Cells also expand in this area increasing
  internode length.
• Plants that bolt like mustard, and lettuce do so
  because of the activity of the subapical meristem.

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Intercalary meristems

• Intercalary meristems meristems separated from
  other meristematic tissues by older more mature
  or developed tissue.
  
• Intercalary meristems are located just above the
  leaf sheath of grasses and many other monocots.

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From http//www.puc.edu/Faculty/Gilbert_Muth/art0
037.jpg
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Lateral meristems

• Lateral meristems cylinders of actively
  dividing cells somewhat below the apical or
  subapical meristem continuing through the plant
  axis and producing secondary growth.
• May be referred to as vascular cambium
• produces new xylem and phloem tissue
• the cork cambium produces mainly bark.

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Lateral meristems

• The continued increase in diameter of trees and
  other woody perennials - lateral meristems.
  
• The growth rings that are produced in woody
  plants which allow determination of plant age are
  created by this lateral growth.

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Woody Stem Cross Section
Insert drawing from page 21


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From Champion Paper Co.
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Permanent tissues

• Simple tissues permanent tissue composed of
  only one cell type.
  
• Examples epidermis, collenchyma, parenchyma,
  sclerenchyma and cork.
  
• Complex tissues -composed of of more than one
  cell type.
  
• Examples are xylem and phloem.

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Simple tissues

• The epidermis single exterior layer of cells
  that protects plant parts.
  
• The epidermis is often covered with cutin, a
  waxy substance that prevents water loss.
  
• Parenchyma tissue -made of living thin walled
  cells with large vacuoles and flattened sides.
  
• Parenchyma cells retain the ability to become
  meristematic and can heal wounds and regenerate
  other types of tissues.

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Simple tissues

• Sclerynchyma tissue - composed of thick walled
  cells found throughout the plant as fibers and
  sclerids.
  
• The protoplasts in these cells die eventually.
  Sclerynchyma cells are common in bark, stems and
  nut shells.
  
• Collenchyma tissue- gives support to young
  petioles, stems and veins of leaves.
  
• Cell walls of collenchyma are thickened cells
  mainly made up of cellulose.
  
• A living tissue

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Simple tissues

• Cork tissue occurs mainly in the bark, stems, and
  trunks of trees.
  
• The cell walls are suberized (suberin is a waxy
  substance), and the protoplasts are short lived.
  
  
• As a result cork tissue is mostly dead.

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Complex tissues

• Xylem a complex tissue that conducts water and
  dissolved minerals in plants.
  
• Xylem can be composed of vessels, tracheids,
  fibers and parenchyma.
  
• Vessels long tubes made up of short vessel
  members .

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Complex tissues

• Tracheids long, tapered dead cells that conduct
  water through pits.
  
• Fibers thick walled sclerenchyma cells that
  provide support to plants.
  
• Most xylem tissue is missing one or two of these
  cell types.

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Xylem
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From http//www.iacr.bbsrc.ac.uk/notebook/courses
/guide/xylem.htm
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Complex tissues

• Phloem -a complex tissue which conducts
  metabolites (food) from the leaves to stems,
  flowers, roots and storage organs.
  
• comprised of sieve tubes, sieve tube members,
  companion cells, fibers and parenchyma.

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Phloem

• Sieve tube members long slender cells with
  porous ends called sieve plates and are found
  only in angiosperms.
  
• Gymnosperms have sieve cells which are similar
  but lack the sieve plate.
  
• Companion cells -closely associated with sieve
  tube members and aid in metabolite conduction.
  

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Phloem

• Phloem fibers - thick walled cells that provide
  stem support.
  
• Parenchyma cells in the phloem serve as storage
  sites.

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Phloem
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THE PLANT BODY

• Roots-
• conduct water and mineral nutrients
• support and anchor the plant
• May serve as storage organs for photosynthesized
  food.

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THE PLANT BODY

• The root cap - a layer of cells that covers the
  root tip and protects the procambium as the root
  pushes through the soil.
  
• Cells of the root cap are continually sloughed
  off and replaced by new cells to keep the
  protective layer intact.

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Root cross section
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From http//www.puc.edu/Faculty/Gilbert_Muth/phot
0027.jpg
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More roots.

• The endodermis a single cell layer found only
  in the root.
  
• Each cell in the layer is encircled by a
  waterproof band called the Casparian strip which
  does not let water and nutrients between the
  cells.
• In order for the soil solution to get in to the
  xylem it must travel through the cell itself
  (protoplasm).

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Casparian strip
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And still more roots...

• The procambium layer produces
• A) The pericycle - the outermost layer of the
  cells found just inside the endodermis.
  
• The pericycle is the area where lateral roots are
  formed and in some instances the vascular and
  cork cambium are produced here.
  
• B) The vascular cambium also produces primary
  xylem and phloem,and in some plants pith.

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Adventitious roots

• Roots arising from any location other than the
  primary root (radicle) adventitious roots.
  
• Adventitious root formation is the basis for
  producing many new plants from cuttings .
  

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Stems

• From the outside in
• Epidermis - a single layer of cells which is
  usually cutinized to keep it from drying out.
  
• Stomata are also in this layer to allow for gas
  exchange.
  
• The cortex lies just inside the epidermis and is
  made up of collenchyma, parenchyma, sclerenchyma,
  and secretory cells.

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Stems continued...

• Collenchyma cells lie just below the epidermis
  and add strength to the stem.
  
• Sclerenchyma cells serve a similar purpose.
• Parenchyma cells may continue to divide and and
  form new tissue to heal the stem if it is
  wounded.
  
• Primary phloem is the next layer in dicots
  followed by the procambium, xylem and pith.

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Stems continued...
From http//www.ualr.edu/botany/monocotstem.jpg
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Woody dicot stem
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Early wood vs. late wood
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Herbaceous Dicot Stem
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Herbaceous Monocot Stem
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Leaves

• Monocot - parallel veins.
• Dicot - veins organized in a net like pattern.
• Leaves primary function is photosynthesis.
• Leaves secondary function is transpiration.

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Leaf structure

• Epidermis is present on the upper and lower leaf
  surfaces.
  
• usually covered with a waxy cuticle to prevent
  tissue desiccation.
  
• Hairs may also be present on the surface to
  reduce wind velocity and create a boundary layer.

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Leaf structure

• Guard cells specialized cells which occur in
  pairs forming stomata which open and close
  allowing for gas exchange and transpiration.
  
• Stomata are more abundant on the lower leaf
  surface in most plants.

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Guard cells
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Leaf structure

• Transpiration the loss of water from the plant
  which helps to regulate leaf temperature.
  
• The palisade and spongy mesophyll layers contain
  chlorophyll for photosynthesis.

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Leaf structure

• The palisade layer of parenchyma cells lies
  directly below the epidermis
  
• The spongy mesophyll layer of parenchyma cells
  lies directly below the palisade layer and
  contains spaces which allow for gas movement.
  

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Buds

• A bud is generally defined as an undeveloped
  shoot or flower composed mainly of meristematic
  tissue.
  
• Buds may be
• 1)vegetative- producing shoots
• 2) flower
• 3) mixed- producing both shoots and flowers.
• Adventitious buds are buds arising in places buds
  dont normally form.
  
• This allows for propagation by root cuttings in
  some plants like sumac.

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Flowers and flower structure

• Angiosperms
• specialized leaves born on and arranged on the
  stem adapted for sexual reproduction flowers.
  
• Inflorescences more than one flower attached to
  the same stalk.
  
• Flowers may be at the top of the stem or in the
  axils of the leaves farther down the stem.
  
• Flowers can be very useful in plant ID.

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Flowers and flower structure

• Complete flowers have four parts
• sepals
• petals
• stamens
• pistil(s)

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Flowers and flower structure

• Sepals are the leaf like scales that encircle the
  other flower parts.
  
• Sepals are usually green, but may also be
  colored.
  
• All the sepals together on the flower are termed
  the calyx.

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Flowers and flower structure

• Petals are the next whorl of leaves in from the
  sepals.
  
• Petals are usually brightly colored and often
  contain nectaries which secrete nectar and
  attract insects.

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Flowers and flower structure

• The term for all the petals together is corolla.
• The corolla and the calyx together are called
  the perianth.

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Flowers and flower structure

• The next whorl of parts found inward from the
  petals are the male flower parts known as the
  stamens.
  
• Each stamen consists of the filament and anther.
  
  
• The filament is a stalk-like structure supporting
  the anther.
  
• The anther produces pollen.
• All the stamens together in the flower form the
  androecium.

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Flowers and flower structure

• The pistil is the female flower structure.
• The three parts of the pistil are
• 1) stigma- the receptive sticky end that
  receives the pollen
  
• 2) style- the tube connected to the stigma
• 3) ovary- the flask shaped structure at the base
  of the style.

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FROM http//www.csdl.tamu.edu/FLORA/301Manhart/re
pro/Flower20diagram/flower_diagram.htm
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Floral Structure
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Fromhttp//www.biologie.uni-hamburg.de/b-online/e
02/02d.htm
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Flowers and flower structure

• Incomplete flowers are flowers that lack one or
  more of the four parts (sepals, petals, stamens,
  or pistils.)
  
• Flowers that lack stamens but have pistils are
  termed pistillate flowers.

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Flowers and flower structure

• Similarly, flowers that lack pistils but have
  stamens are termed staminate flowers.
  
• Imperfect flowers lack either male (stamens) or
  female (pistils) flower parts.
  
• Both staminate and pistillate flowers are
  imperfect flowers.
  

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Flowers and flower structure

• Plants with staminate and pistillate flowers on
  the same plant are known as monoecious.
  
• Corn is an example of a monoecious plant.

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Flowers and flower structure

• Plants with staminate and pistillate flowers on
  the different plants are known as dioecious.
  

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Buffalograss-dioecious
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Fruits

• A Fruit is a matured ovary and its associated
  parts.
  
• Most fruits bear seeds, except for those termed
  parthenocarpic fruits like seedless oranges.

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Fruits

• The pericarp or ovary wall can develop into
  peels, shells or even the fleshy part of fruit
  depending on the plant.
  
• http//www.ibiblio.org/botnet/glossary/a_xi.html

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Fruits

• Simple fruits are fruits which are formed from a
  single ovary from one flower.

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Fruits

• Most commonly simple fruits are classified as
  fleshy, semi-fleshy or dry depending on the
  texture of the mature pericarp.
  
• Aggregate or multiple fruits are formed from
  several ovaries.
  
• The true fruit is attached to or contained within
  a receptacle or accessory structure.

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Fruits

• Aggregate fruits are formed from one flower with
  many pistils on the same receptacle, strawberries
  are an example.
  
• Multiple fruits are formed from many flowers that
  occur in cluster, pineapples are an example.
  
• http//www.orst.edu/extension/mg/botany/fruit.html
  
  

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Seeds

• A seed is a mature ovule with three basic parts
  
  
• the embryo
• the food storage tissue (endosperm, cotyledons or
  perisperm)
  
• seed coats (also known as testa)

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Seeds

• The embryo is a plantlet formed within the seed
  during fertilization.
  
• The embryo has two growing points the radicle,
  which is the embryonic root and the plumule (or
  coleoptile) which is the embryonic shoot.
  
• One or two cotyledons (seed leaves) are located
  between the radicle and plumule.
  

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Seeds

• Albuminous seeds store most of their food in the
  endosperm.
  
• Exalbuminous seeds store most of their food in
  fleshy cotyledons (like the bean), or
  occasionally in the perisperm.
  
• Food reserves are in the form of starch, fat, or
  protein.

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Seeds

• Seed coats also known as testa are generally
  tough to protect the embryo. They are formed from
  the integuments which are the outer layers of the
  ovule.
• The hilum is a scar left on the seed where it was
  attached to the stalk.

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Seeds

• The micropyle is a small opening near the hilum.
• The raphe is the ridge on the seed.

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Seed parts
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Presentation adapted from
Hartman, et al 1988. Plant Science, Second
Edition, Englewood Cliffs, N.J. Prentice- Hall.