Leaves have many functions

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					                    Leaves
           have many functions
1. Leaves are the photosynthetic organ of a plant; usually
   they are composed of 2 parts: the blade and petiole.
2. leaves are the main site of evaporation of water
   from the plant.
3. gas exchange carbon dioxide for photosynthesis
   and oxygen from photosynthesis and for
   respiration are usually exchanged through the leaves.
Parts of a Typical Leaf
          Function of Leaf Tissues

•   Cuticle – waxy covering which prevents water loss
•   Upper and Lower Epidermis - Protection
•   Palisade Mesophyll Cells – main photosynthetic tissue
•   Bundle Sheath Cells - The sheath cells primarily function to
    give some rigidity and protection to the enclosed vascular
    tissue.
•   Xylem – transports water
•   Phloem – transports sugars
•   Spongy Mesophyll Cells – create spaces for gas exchange
•   Guard Cells – regulate the flow of water
•   Stomata – openings in the leaf, allow the exchange of gases
•   Vein (Vascular bundle)– transportation of water and sugars
•   Sclerenchyma – strength and support
 Most of the photosynthesis takes
place in the palisade cells… in the chloroplasts.
                      Stomata
are the "pores" in leaves
   (and stems) through
  which CO2 is taken in
    and O2 is released
 during photosynthesis.
   Plants control when
   stomata are open or
 closed and the width of
 the opening (formed by
   two guard cells that
 expand and contract to
    open and close the
  space between them).
Leaf Types
Leaf Margins
Leaf Arrangements
                                       Flowers
           are the reproductive structures of the plant.
                                            - Attract pollinators, and protects the reproductive
                                                                  structures




                                                      - Protects young flower
Site where the eggs are produced -

              base of the flower   -
  The Male Reproductive Structures
      are called the Stamens.
They consist of two parts:
• The anther -- a small
  case in which the pollen
  grains form
• The filament -- a slender
  stem that supports the
  anther
      The Female Reproductive
    Structure is called the Pistil.
It consists of three parts:
• The stigma -- the pollen
    grains stick to this
    small sticky pad
• The style -- the pollen
    grains grow down
    through this stem-like
    cylinder
• The ovary -- this is
                               also called a Carpel
    where the young seeds
    (eggs) wait for the
    chromosomes in the
    pollen (sperm), and
    where they grow into
    mature seeds…. Which
    contain the embryos.
                Pollination
is the transfer of pollen from the male part of the
       plant to the female part of the plant.
      Insect Pollination
The pollen is transferred
  to the stigma by an
         insect.
                Water Pollination
 orchids are usually water-pollinated plants.


 The pollen is transferred
(washed) to the stigma by
       water (rain).
             Wind Pollination
conifers are usually wind-pollinated plants.




 The pollen is transferred (blown) to the stigma by wind.
              Self-Pollination

Pollen from plant
A pollinates plant
A… the offspring
now is composed
 of the DNA from
 only one parent.
 Self-pollination
 ensures genetic
  continuity…..
every generation
  is genetically
     identical.
              Cross-Pollination

 Pollen from plant B is
transferred to plant A…
  the offspring now is
 composed of the DNA
of both parents. Cross-
   pollination creates
        diversity.
           Germination
a plant starts to grow…. Germination is
         triggered by Cytokinin.
Gymnosperms (cone-bearing plants)
         Gymnosperms
  reproduce using cones
  • The Female cone is
   called the “Seed” cone…
      it contains the eggs
    (which become seeds
        after fertilization)



 • The Male cone is called
    the “Pollen” cone… the
   pollen contains the sperm
              cells.
               Double Fertilization
each pollen grain contains two sperm cells….. One sperm cell fertilizes
the egg (2n - which becomes the embryo), the other fertilizes the polar
       nuclei. (3n – which eventually becomes the endosperm)
                              Seeds
                                   - Store and digest foods




                                Hypocotyl - Embryonic Stem


Embryonic leaves - Epicotyl
                                                     - Opening for sperm tube
     Embryonic root -
                                               - Attachment point to Ovule




                                                               - Protection
         Monocot and Dicot Seeds
Monocots have one cotyledon (seed leaf), Dicots have two cotyledons (seed leaves)
                         Fruit
a mature plant ovary that encloses a seed, or seeds, and provides
                  nourishment and protection




          Pericarp


         Floral Tube
                                                                Endocarp

         Mesocarp

             Exocarp



                                 Seed
                         Fruit
a mature plant ovary that encloses a seed, or seeds, and provides
                  nourishment and protection

				
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posted:9/16/2012
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