Chapters 35 and 36

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Chapters 35 and 36

• Plant Structure and Growth
• Transport in Plants

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Genetics and Environment

• Genes ultimately determine the phenotypes of all
  organisms, including plants
• Environment can modify those phenotypes
• Long-term natural selection drives the evolution
  of a species based upon the environment (cacti)
• Short-term number of leaves around a tree
  exposed to prolonged periods of wind

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Genetics and Environment
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Ancestral plants
Vascular
Non-vascular
Seed-bearing
Spore-forming
Gymnosperms
Angiosperms
Ferns
Mosses
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Two types of angiosperms

• Monocots vs. Dicots

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Growth

• Plants grow by two types of cells doing mitosis
  apical and lateral meristems
• Primary growth is due to apical (tip) meristems
• Results in the elongation of the plant
• Secondary growth is due to lateral (side)
  meristems
• Results in the increase in diameter of stems and
  roots

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Plant Body Plans

• All plants exhibit structural and functional
  hierarchy
• Cells ? Tissues ? Organs ? Organ Systems ?
  Organisms
• Three basic organs
• Roots
• Stems
• Leaves

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Plant Body Plans

• Root system designed to access water and
  minerals from the soil
• Leaf system designed to access atmospheric CO2
  and sunlight, which doesnt penetrate very far
  into soil
• Stem system designed to connect the other two

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Roots

• Anchor the plant, store food, and absorb
  nutrients
• Monocots generally have fibrous roots
• Better anchorage and more potential absorption
• Dicots taproots
• Anchorage and food storage for flower and fruit
  production

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Roots

• Both mono- and dicots have root hairs,
  which increase surface area
  for better nutrient absorption

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Roots

• Plants can also create symbiotic relationships
  with fungi
• Mycorrhizae are made up of plant roots and fungal
  hyphae
• They create huge surface area for
  absorption

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Roots

• Adventitious roots (above ground)
  help support, or prop up, some
  plants
• Arenal, Costa Rica
• Woo hoo!!

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Modified Stems

• Often mistaken for roots
• Stolons, rhizomes, tubers, and bulbs
• Stolon surface runner that allows for asexual
  reproduction and area colonization
• Ex strawberries

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Modified Stems

• Rhizomes underground horizontal stems
  used for asexual reproduction
• Tubers swollen ends of rhizomes specialized
  for food storage
• Ex Potatoes

• Ex Ginger

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Modified Stems

• Bulbs vertical, underground shoots consisting
  mostly of the swollen bases of leaves that store
  food
• Ex Onions

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Leaves

• Main photosynthetic organ
• Green stems also do photosynthesis
• Consist mainly of a blade and petiole, which
  connects the leaf to the stem
• Monocots parallel veins
• Dicots branched veins

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Leaves

• Stomata regulate gas and water exchange
  with the environment
• Open and close due to ion pumping
• When Ks are pumped into the guard cells, they
  become hypertonic ? water diffuses into them,
  causing them to become turgid and swell stoma
  opens
• Vice versa

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Leaves

• Leaf hairs, trichomes, slow air movement over the
  leaf, reducing water loss via transpiration.

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Leaves modifications

• Tendrils cling for support
• Spines of cacti defend
• Leaves modified for water storage
• Flowers attract pollinators
• Insect trapping

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Tissues

• Each organ of a plant has three tissue systems
  the dermal, vascular, and ground
  tissue systems
• Each system is continuous throughout
  the plant body

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Dermal Tissue

• Also called epidermis
• Generally single layer of cells
• Protects what it covers
• Leaf epidermal cells secrete waxy, cuticle to
  help plant retain water

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Vascular Tissue

• Transports materials between roots and leaves
• Xylem transports water and dissolved minerals
• Phloem transports food to where its needed in
  the plant

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Vascular Tissue Xylem

• Made up of tracheids and vessel elements dead
  cells (at functional maturity) that form long
  tubes through which water and minerals can flow
• Tracheids long, thin cells with pits at ends
  (where water flows)
• 2O cell walls contain lignin tracheids aid in
  support as well as transport
• Vessel elements shorter, wider cells

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Vascular Tissue Xylem
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Vascular Tissue Phloem

• Made of chains of cells called sieve-tube members
  (alive at functional maturity)
• Lack nuclei and ribosomes
• Sieve plates are found at the ends of cells
• Sieve plates have pores through which organic
  materials can move
• Companion cells are nucleated

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Vascular Tissue Phloem
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Ground Tissue

• In dicot stems, ground tissue is divided into
  pith (internal to vascular tissue) and cortex
  (external to the vascular tissue)
• Functions photosynthesis, storage, and support

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Cells

• Recall differences between plant and animal cells
• Chloroplasts
• Central fluid-filled vacuole
• Cell wall

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Cells

• Recall differences between plant and animal cells
• Cells are often connected to each
  other by plasmodesmata
• Desmotubules plasmodesmata that
  has ER continuous throughout

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Transport

• Proton pumps very important
• Hydrolyze ATP to pump H out of the cell
• Creates a proton gradient
• Creates a membrane potential
• Both are potential E that can be used to pump
  solutes across the membrane

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Transport

• Proton pump example
• Membrane potential can drive K into root cells,
  creating a hypertonic environment
• Water then follows

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Transport

• Proton pump example
• Movement of H back into the cells can also bring
  in other solutes Cotransport

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Water Transport

• Osmosis passive movement of water across cell
  membranes
• Water potential (? Greek letter psi) solute
  concentration and physical pressure
• Determines the direction of water movement
• Water will move from the solution with high ? to
  the solution with low ?

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Water Transport

• Notice D a low ? can be created by a negative
  pressure or the creation of a vacuum
• Transpiration pull is based upon this concept
  (explained later)

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Water Transport

• When ? is higher inside the cell than outside,
  water moves out
• Plasmolysis

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Water Transport

• When ? is lower inside the cell than outside,
  water moves in
• Turgor pressure

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Water Transport

• A walled cell with a greater solute concentration
  than its surroundings will be turgid (firm)

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Water Transport

• Movement of water across a semi-permeable
  membrane occurs through channel proteins called
  aquiporins
• Aquiporins dont affect water potential, only the
  rate at which water will flow
• Therefore, aquiporins may function at different
  rates depending on different environmental
  factors (Ex to limit water loss from the cell)

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Transport

• Water and minerals in the root cannot be
  transported to the rest of the plant until they
  enter the xylem
• Any nutrients not yet moving from inside a cell
  to inside a cell will be forced into cells when
  they reach the endodermis
• Endodermis contains the Casparian strip
• A belt of suberin (waxy material that is
  impervious to water and dissolved minerals)

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Transport
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Water Transport Transpiration Pull

• Accumulation of minerals in the roots causes a
  lower water potential and draws more water into
  the roots, generating a positive pressure root
  pressure
• Root pressure forces water up the xylem and
  causes guttation formation of water
  droplets on the ends of some
  herbaceous leaves

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Water Transport Transpiration Pull

• Root pressure does not account for all upward
  movement of water in all plants
• Nor can it force water further than a few meters
• Water therefore must not only be pushed, but more
  importantly, it must be pulled
• Transpiration accounts for the majority of water
  movement up a plant, especially in very tall
  plants

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Water Transport

• Water evaporating through the surface of leaves
  is transpiration
• This reduces pressure in the leaf xylem
• This creates a tension that then pulls more water
  up from the roots (cohesion and adhesion)
• Bulk flow is the movement of a fluid driven
  by pressure

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Transport Translocation

• Movement of organics from photosynthesis
• Movement depends on concentration differences
• Sugar source an organ (especially mature leaves)
  in which sugar is being produced by either
  photosynthesis or the breakdown of starch
• Sugar sink an organ (such as growing roots,
  shoots, or fruit) that is a net consumer or
  storer of sugar

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Transport Translocation

• Phloem sap moves by bulk flow driven by pressure
• Higher levels of sugar at the source lowers the
  water potential and causes water to flow into the
  tube
• Removal of sugar at the sink increases the water
  potential and causes water to flow out of the
  tube
• The difference in hydrostatic pressure drives
  phloem sap from the source to the sink

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Transport Translocation
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