Topic 9

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Topic 9 Plant Science
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Introduction to Plants

• Plants make up over 50 of the living organisms
  on this planet
• They belong to the kingdom Plantae
• There are five phylum
• Bryophyta
• Filicinophyta
• Coniferophyta
• Angiospermophyta

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Introduction to Plants (cont)

• Angiosperms are the most dominant phylum
• Angiosperms, or flowering plants, produce seeds
  enclosed inside fruits.
• Angiosperm comes from the word
• angerion a container
• sperma a seed
• phyton a plant.

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Introduction to Plants (cont)

• Angiosperms are divided into two large groups 
• Monocotyledons (Monocots)
• Dicotyledons (Dicots)
• These names refer to the number of leaves
  contained in the embryo, called cotyledons.

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Typical Monocot
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Monocots vs. Dicots
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Typical Dicot
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Shoot Apical Meristems
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Lateral Meristems
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Comparison of Growth for Apical and Lateral
Meristems

• Apical Meristems

• Lateral meristems

• Primary growth
• Allows plant to grow longer (upwards)
• Forms leaves and branches
• Increases photosynthetic capacity
• Found in both monocots and dicots

• Secondary Growth
• Allows plant to grow in width
• Widening of main trunk for support and depositing
  of vascular tissue and bark
• Found only in dicots

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Stems

• Supports the leaves for photosynthesis
• Transports water and nutrients from roots to
  leaves
• Support is achieved by
• Tugor
• Cellulose walls
• Lignin reinforcing the xylem

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Stems

• Consist of an epidermis which surrounds the
  vascular tissue, composed of xylem (water
  transport, up the stem) and phloem (mineral and
  sugar transport, up and down the stem to sinks
  for storage)
• Meristems deposit secondary xylem and phloem,
  which will grow outwards to become primary xylem
  and phloem.

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Plan Diagram of the Stem
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Leaf Structure

• Consists of a
• Leaf Blade
• Leaf stalk
• Leaves have a large surface area and a small
  space between layers
• Designed for photosynthesis

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Leaf Structure (cont)

• Leaves consist of
• Outer structure - Epidermis
• Tough, transparent layer
• Upper waxy Cuticle
• Lower specialized cells called guard cells,
  that form openings in the bottom, called Stoma
• Inner Structure Specialized Cells
• Mesophyll cells

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Leaf Structure (cont)

• Upper Surface Palisade Mesophyll
• Tightly packed
• Contain chloroplasts
• Lower Surface Spongy Mesophyll
• Loosely packed with air spaces
• Vascular Bundles
• Consist of xylem and phloem
• Bring water to and transport sugars and minerals
  away and to leaves
• Support the leaves along with cellulose and turgor

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Plan Diagram of the Leaf
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Roots

• First stage of development for the seed when it
  germinates
• Tap Roots
• Lateral Roots
• Roles
• Absorption
• Anchors
• Support
• Storage

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Roots (cont)

• Roots have an outer coat, called the epidermis,
  and the inner portion is called the cortex
• In the root, there is a vascular bundle, of xylem
  and phloem
• Branching of roots allow for a greater surface
  area
• Root hairs off of growing roots, increase the
  surface area as well.

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Diagram of Roots and tissue Plan Diagram
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Modifications of Stems, Roots and Leaves

• Roots
•  
• Prop Roots
•  
• Storage Roots
•  
• Pneumatophores
• Buttress Roots

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Examples of Root Modifications
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Modifications of Stems, Roots and Leaves

• Stems
•  
• Bulbs
• Tubers
• Rhizomes
• Stolons

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Examples of Stem Modifications
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Modifications of Stems, Roots and Leaves

• Leaves
•  
• Tendrils
• Reproductive Leaves
• Bracts or floral leaves
• Spines

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Control of Plant Growth - Phototropism

• Plant growth is controlled by gravity and light
• Plant grows against gravity
• Plants grow towards the light
• Responses to the above stimuli, called tropisms
• Growth towards light called phototropism
• Controlled by a hormone called auxin
• Produced in the tip of the shoot

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Control of Plant Growth - Phototropism

• Steps of phototropism
• Photoreceptors in the tip of the plant sense the
  light
• Stimulate the production of auxin
• Auxin will travel to the shady side of the
  plant, as detected by the phototropins
• Promotes the elongation of cells in stems, by
  loosening the connections between the cell walls
  and cellulose microfibrils
• Promotes the stem to grow more on the shadier
  side and go towards the light.
• Allows the leaves on the sunny side to get more
  light and photosynthesize at a greater rate.

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Control of Plant Growth - Phototropism
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Transport in Angiosperms

• Root System
• Transpiration
• Water uptake
• Factors affecting Transpiration
• Translocation

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Transport in Angiosperms

• Roots Absorption and uptake
• Provide large surface area for uptake of water
  and minerals
• Water is absorbed by osmosis
• Amount of water absorbed is increased by root
  hairs, on ends of growing roots
• Minerals absorbed by active transport

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Water uptake

• Occurs by osmosis
• Flows through epidermis, into cortex by mass
  flow, as the cells are interconnected
• Three possible routes for uptake of water
• Apoplast Pathway (Mass Flow)
• Symplast Pathway
• Vacuolar Pathway

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Water uptake

• Apoplast Pathway (Mass Flow)
• Most common way for water to move (faster)
• Water does not enter the cell
• Moves through the cell walls until it reached the
  endodermis
• Cells of the endodermis have a Casparian Strip
  around them that is impermeable to water
• The water is diverted to the spaces of dead
  cells, eventually to the xylem

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Water uptake

• Symplast Pathway
• Water enters the cytoplasm but not the vacuole
• It passes from cell to cell via connections
  between cellular cytoplasm of adjacent cells,
  called plasmodesmata
• The organelles are packed together in cells, and
  as a result, block significant progress of water
• It is not the major pathway for water. Minerals
  mainly move through this pathway.

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Water uptake

• Vacuolar Pathway
• Water enters the cell and move into the vacuole
• It can be stored in the cells
• It can also travel through the cytoplasm and the
  cell wall to the next cell, to move into cortex
• Once in the endodermis, water can move into the
  xylem and pulled via transpiration forces.

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Pathways for water uptake
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Uptake of Minerals

• Minerals are important to build cells walls,
  carbohydrate storage and protein synthesis
• Processes for mineral uptake
• Active transport
• Mass flow (in water)
• Fungal hyphae

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Transpiration

• Transpiration
• the loss of water vapour from the leaves and
  stems of plants.
• Like perspiration
•  
• As water is lost, the amount of water in the
  plant decreases. A pull is created in the plant
  to pull water up the plant. This is similar to
  maintaining homeostasis.

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Transpiration (cont)

• Water moves from root to leaf by transpiration
  pull
• Water moves up the stem to leaves in the xylem
• Dead material
• Made of tracheids and xylem vessels

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Xylem Tissue
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Mechanism of Movement of Water Transpiration
Pull

• Controlled by stomata
• Stomata open and close depending on the amount of
  water in the plant
• If there is a lot of water high turgor pressure
  in guard cells and stomata are open
• If there is a deficiency of water low turgor
  pressure in guard cells and stomata close
• If water drops, abscisic acid is released,
  overriding all variables and stomata close

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Mechanism of Movement of Water Transpiration
Pull

• When stomata are open, water vapour is lost to
  the external environment
• Concentration gradient is created
• The lost water needs to be replaced
• Water moves from the high concentration (roots)
  to lower concentration (leaves) and moves up the
  plant
• Cohesive forces of water allow water to move in a
  continuous flow

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Transpiration
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Factors that affect Transpiration

• Biotic Factors
• Size of the plant
• The thickness of the cuticle
• How widely spaced the stomata are
• Whether the stomata are open or closed

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Factors that affect Transpiration

• Abiotic Factors
• Temperature
• Humidity
• Wind
• Light
• All of these can be over ridden by abscisic acid

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Translocation

• Movement of manufactured food (sugars and amino
  acids).
• Occurs in the phloem tissues of the vascular
  bundles.
• Moves sugars from source to sink (leaves to
  storage) and from source to areas of new growth,
  like ends of shoots and new leaves.
• Phloem tissue allows movement up and down the
  stem of the plant

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Translocation

• Phloem Tissue, is living tissue, and consists of
• Sieve tubes
• Flow of sugars and minerals
• Companion cells
• Control flow / Active transport
• Theory of Translocation is by mass flow, from
  source to sink
• Source and sink can change, depending on use and
  season

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Translocation
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Transpiration and Adaptations of Xerophytes

• Small, thick leaves
• Reducing the number of stomata
• Stomata located in crypts or pits on the leaf
  surface
• Thickened, waxy cuticle
• Hair-like cells on the surface to trap water
  vapour
• Become dormant in the dry months
• Store water in the fleshy stems and restore the
  water in the rainy season
• Using alternative photosynthetic processes called
  CAM photosynthesis (Crassulacean acid metabolism)
  and C4 photosynthesis

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Reproduction in Flowering Plants

• Parts of the flower
• Pollination
• Fertilization
• Seed formation and dispersal
• Seed germination
• Control of flowering - Photoperiodism

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Typical Dicotyledonous Flower

• Sepal
• enclose and protect the flower in the bud, and
  are small, green and leaf like.
• Petals (together called the corolla)
• coloured and used to attract insects or other
  small animals to pollinate the flower.
• Stamen male part of the flower, which consists
  of
• Anthers produces the male sex cells house the
  pollen grains
• Filament or stalk holds up the anther

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Typical Dicotyledonous Flower

• Carpels female part of the flower, and they may
  be on their own or fused together. Each carpel
  consists or
• Ovary at the base of the carpel which contains
  the female sex cells (containing many ovules)
• Stigma sticky top of the carpel (to receive the
  pollen)
• Connecting style supports the stigma

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Pollination and Fertilization

• Pollination
• the transfer of pollen from a mature anther to a
  receptive stigma.
• Fertilization
• occurs after the pollen grain has landed on a
  stigma, and germinated there. It is the fusion
  of the male and female gametes.

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Pollination and Fertilization

• Process of Fertilization
• The pollen produces a tube, which grows down
  between the cells of the style, and through the
  ovule.
• The pollen tube delivers two male nuclei.
• One of these male nuclei then fuses with the egg
  nucleus in the embryo sac, forming a diploid
  zygote.
• The other fuses with the other nucleus, which
  triggers formation of the food store for the
  developing embryo.

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Seed Formation and Dispersal

• Seed contains the developing embryo and the food
  store
• The zygote grows by mitosis, forming the
  embryonic plant, consisting of an embryo root and
  stem.
•  
• A seed leaf or cotyledon forms. The seed leaf
  has two forms, as angiosperms have two classes.
• Monocotyledons have a single seed leaf
• Dicotyledons have two seed leaves
• The formation of stored food reserves is
  triggered. In many seeds the food store is
  absorbed into the cotyledons.

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Seed Formation and Dispersal

• The outer layers of the ovule become the
  protective seed coat, or testa.
• The micropyle is a small hole through the testa,
  where it was attached to the parent plant.
• The whole ovary develops into the fruit.
• The water content decreases and the seed moves
  into a dormancy period, assisted by the formation
  of abscisic acid.

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Seed Formation and Dispersal

• Seeds are dispersed when fruit ripens
• Seeds are dispersed in such a way as to eliminate
  many seeds in one place and around the base of
  the parent plant (population dynamics)
• Dispersed by
• Wind
• Animals
• Explosive

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Seed Germination

• Seeds are in suspended animation
• When metabolic activity starts, this is
  germination
• Seeds are dormant because
• Incomplete seed development
• Presence of a plant growth regulator abscisic
  acid
• Impervious seed coat

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Seed Germination

• In order for germination to occur, the proper
  conditions are needed
• Water hydrates plant and activates amylase and
  removes the abscisic acid
• Oxygen for Cellular respiration
• Period of warm temperatures as this is important
  for enzyme production.

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Seed Germination

• The metabolic processes during the germination of
  a seed are as follows
• The seed absorbs water.
• Gibberellin, or gibberellic acid, is released
  after the uptake of water and is a plant hormone
• Gibberellin triggers the production of amylase.
• Amylase causes the hydrolysis of starch into
  maltose. The starch is present in the seeds
  endosperm or food reserve.
• Maltose is then further hydrolysed into glucose
  that can be used for cellular respiration or may
  be converted into cellulose by condensation
  reactions.
• Cellulose is used to produce the cell walls of
  new cells.
• The seed coat cracks and out comes the plant.

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Control of Flowering of Angiosperms -
Photoperiodism

• Photoperiodism
• Plants response to light involving the lengths
  of day and night. It is the length of day and
  night that controls flowers
• Plants that respond to large amounts of sunlight,
  and short periods of darkness are called long
  day plants (late spring, summer)
• Plants that respond to small amounts of sunlight,
  and long periods of darkness are called short day
  plants (early spring, late fall)

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Control of Flowering of Angiosperms -
Photoperiodism

• It is actually the length of night that controls
  the flowering process
• The control by light is brought about by a
  special blue-green pigment called phytochrome.
• Phytochrome is a large protein that is not a
  plant growth hormone, but a photoreceptor
  pigment.

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Control of Flowering of Angiosperms -
Photoperiodism

• There are two forms of phytochrome
• inactive form Pr
• active form Pfr
• In light, the Pr is converted to Pfr.
• In darkness, the active form (Pfr) slowly
  converts back to Pr
• The slow conversion allows the plant to time the
  dark period and controls the flowering in
  short-day and long-day plants.

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Process of Photoperiodism

• A long day in the summer
• A lot of Pr is made into Pfr during the day.
• In the night, because the night is short, little
  Pfr is converted back to Pr, and when the sun
  rises, there is still a lot of active phytochrome
  (Pfr) left
• This signals a long day, short night, and
  promotes flowering in long day plants
• This does not signal a short day, long night and
  inhibits flowering in short day plants

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Process of Photoperiodism

• A short day in the spring or fall
• A small amount of Pr is made into Pfr during the
  day.
• In the night, because the night is long, almost
  all Pfr is converted back to Pr, and when the sun
  rises, there is minimal active phytochrome (Pfr)
  left and lots of inactive (Pr)
• This does not signal a long day, short night,
  and inhibits flowering in long day plants
• This does signal a short day, long night and
  promotes flowering in short day plants

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Summary of Photoperiodism

• Long day plants need active phytochrome (Pfr)
• Pfr acts as a promoter
• Need a short night
• Short day plants do not need active phytochrome
  (Pfr)
• Pfr acts as an inhibitor
• Need a long night

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Experiment for Photoperiodism