PLANT SCIENCE

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• PLANT SCIENCE

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• Plant Classification
• Examples 4 common plant divisions
• -Bryophyta mosses and liverworts
• -Filicinophyta ferns
• -Coniferophyta coniferous plants
• -Angiospermatophyta flowering plants

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• A. Bryophytesmosses, liverworts, hornworts
• 1. have no true roots, leaves or stems
• 2. have structures called rhizoids
• (rhizoids are root like structures that look
  like long hairs)

rhizoids
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• 3. mosses have simple leaves and stems
• 4. liverworts consist of a flattened thallus
• 5. a thallus is a plant body not divided into
  true roots, stems and leaves

6. bryophytes can grow up to 0.5 m 7. they do not
produce flowers
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• 8. bryophyte reproduction
• -can be sexual or asexual
• -often involves alteration of generations
• -spores are developed in capsules that are
  found at the end of stalks
• 9. bryophytes are often homosporous (the
  gametophytes contain male and female sex organs)
• 10.most common in damp habitats

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• B. Filicinophytes (ferns)
• 1. have, roots, leaves and short non-woody stems
• 2. leaves are often curled up in buds and are
  often pinnate
• 3. pinnateleaves divided into pairs

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• 4. ferns are vascular plants
• -they have transport tissue called vascular
  bundles (xylem and phloem)
• 5. can grow up to 15m
• 6. filicinophyte reproduction-
• -spores are produced by sporangia, usually
  found on the underside of the leaves
• 7. ferns can be heterosporous or homosporous
• 8. ferns do not produce flowers

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• C. Coniferophytes (conifers)
• 1. conifers are shrubs of trees with roots,
  leaves and woody stems
• 2. leaves are often narrow with thick, waxy
  cuticles
• 3. they are vascular plants
• 4. can grow up to 100m

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• 5. reproduction-
• -seeds are produced
• -they develop in the ovules on the surface of
  the scales of the female cones
• -male cones produce pollen
• 6. coniferophyta are heterosporous
• 7. they do not produce flowers

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Immature female cone
Mature female cone
Male cone
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• D. Angiospermatophyta-flowering plants
• 1. usually have true roots, leaves and stems
• 2. stems that develop into shrubs and trees are
  woody
• 3. can grow up to 100m

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• 4. reproduction
• -seeds are produced
• -they develop in the ovary
• -ovaries are part of the flowers
• -fruits develop from ovaries to disperse the
  seeds
• 5. angiospermatophytes are heterosporous

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• Xerophyte adaptations
• A. Xerophytes are plants adapted to dry
  environments
• --their adaptations allow them to obtain the
  maximum amount of water from their environment
• B. Xerophytedry plants

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• Xerophytes (cont)
• C. The adaptations
• 1. reduced leaves (reduced surface area)
• 2. thick waxy cuticle
• -reduces water loss
• 3. reduced number of stomata
• -reduces water loss, gas exchange and
  photosynthesis
• 4. Water storage tissue
• -helps in long dry periods

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Xerophyte adaptations (cont) 5. Stomata in pits
and/or surrounded by hair -reduces air flow past
pore -water that has diffused out will stay
near -this reduces the concentration gradient
and reduces the diffusion of water out of the
plant
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• Xerophyte adaptations (continued)
• 6. Vertical stems
• -allow absorption of light early and late in the
  day (not at midday when light is most intense)

-reduces transpiration
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• Xerophyte adaptations (cont.)
• 7. Wide-spreading shallow root network
• -allow immediate absorption of extensive
  amounts of water immediately after rain
• 8. CAM physiology
• -stomata open at night and stay closed during
  the day

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• Hydrophyte Adaptations
• A. Hydrophyte water plant
• B. The adaptations
• 1. Air spaces
• -allow the plant to float on top of the
  water to absorb the most sunlight
• 2. Stomata found in upper epidermis (not in
  lower epidermis)
• -open to air

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• Hydrophyte adaptations (continued)
• 3. Small amount of xylem in stems and leaves
• -xylem conducts water
• 4. Surrounded by water
• -roots serve mainly as anchorage (not water
  absorption

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• Plant Leaf Structure and Function
• A. Leaf functionto produce food via
  photosynthesis (C3, C4, CAM)
• B. Leaves are adapted to their environments (C3,
  C4, CAM)
• C. Photosynthesis depends on gas exchange over a
  moist surface

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• Plant Leaf Structure and Function
• D. Cross section of a leaf

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• Plant Leaf Structure and Function
• E. Leaf anatomy
• 1. Upper epidermis-layer of cells covered by a
  thick waxy cuticle
• -prevents water loss from the upper surface
• 2. Palisade mesophyll-densely packed cylindrical
  cells
• -contain many chloroplasts
• -main photosynthetic tissue
• -positioned near top of leaf for maximum light
  absorption

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• Plant Leaf Structure and Function
• E. Leaf anatomy
• 3. Xylem-vascular tissue responsible for water
  transport
• -replaces water lost during transpiration
• 4. Phloem-vascular tissue that transports
  minerals
• -transports photosynthetic products out of
  leaves
• 5. Spongy mesophyll-cells that provide a means
  for gas exchange
• -have fewer chloroplasts than the palisade
  mesophyll
• -found near stomata and lower epidermis

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• Plant Leaf Structure and Function
• E. Leaf anatomy
• 6. Stoma (stomata pl.)
• -pore that allows carbon dioxide to diffuse in
  and oxygen to diffuse out
• -also responsible for water loss
• 7. Guard cells-cells that open and close the
  stomata
• -control transpiration

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• Stem anatomy
• (dicot)

Epidermis
Cuticle (outside layer)
Xylem
Pith of parenchyma cells
Phloem
Cortex of Parenchyma cells
Cambium
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13.2 Transport in Angiosperms

• Roots
• A. Plants take in water and minerals through
  their roots
• B. Roots have large surface area to allow for
  adequate uptake of water and minerals
• -they are branched and they have root hairs
• C. Function of the cortexto facilitate water
  uptake
• D. Roots also act as anchorage to ground

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• Roots and active transport
• A. Mineral concentrations are often higher in
  the root than in the soil
• B. This suggests active transport (going against
  the concentration gradient)
• C. Cortex cells can absorb ions that are
  dissolved in the water that is drawn by capillary
  action through the cortex cell walls

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• Water Uptake By Roots
• A. Roots take in water via osmosis
• -Water in the soil contains a lower
  concentration of solutes than the cytoplasm of
  root cells
• -This causes water to diffuse in to the roots

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Water Uptake by Roots
Root cell
Soil
High solute
Low solute
H2O
H2O
Water diffuses (osmosis) to an area of high
solute concentration to reach equilibrium between
the roots and the soil Minerals are taken in
via active transport because the roots have
higher solute concentration than the soil
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• Water Uptake By Roots (continued)
• B. Most absorbed water is eventually drawn to
  the rest of the plant because of transpiration
• -as water leaves the leaves it must be
  replaced
• C. To get water from the root hairs to the
  xylem, there are three possible methods
• -apoplast, symplast or vacuolar pathways

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• Water Uptake By Roots (continued)
• D. Apoplast pathway
• -water does not enter the root cells
• -it travels by capillary action through the cell
  walls of the cortex until it reaches the
  endodermis
• -cells of the endodermis have Casparian strips
  around them that are impermeable to water
• -to pass through the endodermis the water must
  follow the symplast pathway (the apoplast pathway
  stops at the endodermis)

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• Water Uptake By Roots (continued)
• E. Casparian Strips
• -found in endodermis
• -thought to be a protective measure
• -prevent water from seeping between cells
• -forces water to enter the endodermis before
  passing to the vascular tissue
• -forces water to go through cell walls (not
  between them

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Water flow with Casparian strips
Cell wall
Casparian strip
Cell membrane
Vacuole
Water flow (cannot flow between cells when
Casparian strips are present)
Water flow without Casparian strips
Cell wall
Cell membrane
Vacuole
Water flow
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• Water Uptake By Roots (continued)
• F. Symplast Pathway
• -water enters the cytoplasm of the cells, but
  not the vacuole
• -water passes from cell to cell via the
  plasmodesmata (connections of cytoplasm between
  cells)
• -the water eventually enters the xylem

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Movement Through Roots
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• Water Uptake By Roots (continued)
• G. Vacuolar Pathway
• -water enters the cells and moves to the vacuole
• -when necessary the water will travel through
  the cytoplasm and cell wall to the vacuole of the
  next cell

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• Assignment Make a chart to compare apoplast,
  symplast and vacuolar pathways

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• The Xylem
• A. Function-to transport water and dissolved
  minerals from the roots to other parts of the
  plant
• B. Mature xylem cells are dead
• C. Made of two components
• 1. tracheids
• 2. xylem vessels

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• The Xylem (continued)
• D. Tracheids
• -narrow cells, arranged in columns
• -overlap at tapered ends
• -function as support
• -overlapping ends have pits that allow water
  to move rapidly between cells
• -all plants have tracheids
• -not as efficient as xylem vessels

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• The Xylem (continued)
• E. Xylem vessels
• -most water travels through vessels
• -composed of columns of cells
• -when the cells die the walls between them
  disappear partly or completely (leads to more
  efficient transport)
• -diameter is wider than tracheid diameter
• -side walls are reinforced with lignin (this
  helps with structural support)

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Tracheid
Xylem vessel
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• Water Transport Through Plant Tissue
• A. Transpirationloss of water vapor from leaves
  and stems
• B. Transpiration causes water flow from roots,
  through stems and to the leaves
• C. Transpiration stream describes the
  transpiration flow through the plant
• D. The process begins with evaporation of water
  from the leaves (through the spongy mesophyll)

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• Water Transport Through Plant Tissue
  (continued)
• E. Evaporated water is replaced with more water
  from the xylem
• F. Capillary action allows the water to move
  from the xylem to the spongy mesophyll
• G. The capillary action creates transpiration
  pull
• -transpiration pull low pressure or suction
  within the xylem
• H. Water molecules have strong cohesion forces

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• Water Transport Through Plant Tissue
  (continued)
• I. As water moves out of the vessel, other
  molecules will want to replace it
• J. All water will move up a little (toward the
  leaves), at the other end of the plant (the
  roots) water will move from the soil to the plant

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• Water Cohesion
• A. Water molecules are attracted to each other
• B. These are intermolecular forces
• C. This is created by hydrogen bonding
• The whole point
• EVAPORATION CAUSES TRANSPIRATION PULL. THIS
  PULLS WATER INTO THE ROOTS AND TO THE REST OF
  THE PLANT BECAUSE OF THE STRONG COHESION OF WATER
  MOLECULES.

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• Phloem
• A. Primary function translocation
• B. Translocation-movement of substances from
  one part of a plant to another in the phloem
• C. Sugars, amino acids and other organic
  compounds produced by photosynthesis are
  transported away from the leaf
• -materials sprayed on the plant can also be
  transported from the leaves via the phloem

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• Phloem
• D. Found in all leaf veins
• E. Materials can be transported in both
  directions
• Remember xylem only transports one way (up)
• Ex In summer trees transport sugars from
  leaves to roots
• -In spring transport sugar from roots
  (where it is stored) to the new branches

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• Food storage in plants
• A. Many perennial plants have food storage for
  dormant seasons
• B. The food is transported when necessary by the
  phloem from the root to the rest of the plant for
  new growth
• C. Examples
• 1. Carrots-carrots store food in the
  cortex of their roots
• -may be used to allow the
  growth of stems and leaves after winter

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• Food storage in plants
• C. Examples (continued)
• 2. Seeds
• -seeds need a certain amount of food to allow
  them to grow a stem
• and a few leaves
• -this food usually lasts until
• photosynthesis takes over
• 3. Tubers (potatoes)
• -tubers are swollen
• underground stems
• that store food

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Other plant modifications

• Tendrils-used for climbing
• -modified leaves or stems
• -Example grape vine or ivy
• B. Bulb - any plant that stores its complete life
  cycle in an underground storage structure
• -usually perennial flowers have this type of
  structure

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Classwork (in your notebook)

• Explain the relationship between the distribution
  of tissues in the leaf and the functions of these
  tissue. 8
• Draw and annotate a diagram showing the structure
  of a dicotyledonous animal-pollinated flower.
• -Include 1. sepal 2. petal 3. anther 4.
  filament
• 5. stigma 6. style 7. ovary
• Draw and annotate a diagram showing the external
  and internal structure of a named dicotyledonous
  seed.
• -Include 1. testa 2. micropyle 3. embryo root
  4. embryo shoot 5. cotyledons

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• Plant support
• A. No skeleton
• B. Xylem vessels have some support tissue that
  help keep the plant upright
• -xylem alone is inefficient (think about
  wilting plants)
• C. Trees and shrubs have woody stems
• D. Herbaceous (non-woody) plants use turgor for
  support

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• Plant support
• E. Turgor
• -vacuoles take up water
• -the cell swells up
• -the cell wall is stretched to the limit
• -the vacuole still has less water
  potential than the cytoplasm and continues
  to draw in water
• -the force of the cell wall forces water out
  at the same rate

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• More on guard cells
• A. Plants maintain large surface areas to
  capture sunlight
• B. To avoid water loss their surfaces are
  covered with waxy cuticle layers
• -cuticle also is impermeable to gases
• (oxygen and carbon dioxide)
• C. Pores in the cuticle and lower epidermis
  allow gas exchange within the spongy mesophyll

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More on guard cells D. When the plant is at risk
of drying out the guard cells lose turgor and sag
together, closing the stomata E. This reduces
water loss and photosynthesis F. Because
photosynthesis is reduced guard cells only close
the stomata when the plant is at risk G.Guard
cells regulate transpiration by opening and
closing the stomata. -A plant hormone called
abscisic acid causes the stomata to close. (This
is helpful during times of drought or stress.)
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Anatomy of stomata and guard cells
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Pea leaf stomata and guard cells
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• Four abiotic factors that affect the rate of
  transpiration in typical mesophytes
• Mesophytes-plants adapted to conditions of
  average water supply (not xerophytes or
  hydrophytes
• A. Light
• -plants generally open stomata in day to allow
  carbon dioxide to diffuse in and allow
  photosynthesis to occur
• -this increases transpiration

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• Four abiotic factors that affect the rate of
  transpiration in typical mesophytes
• B. Temperature
• -as temperature increases transpiration also
  increases because high temperatures increase the
  rate of diffusion and decrease relative humidity
• -the rate of transpiration doubles for every 10
  degree C increase in temperature

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• Four abiotic factors that affect the rate of
  transpiration in typical mesophytes
• C. Humidity
• -Decrease in humidity increase in
  transpiration
• -Increase in humiditydecrease in transpiration
• This is directly related to concentration
  gradients

Plant Increase transpiration
Air Low humidity Low moisture
Plant Decrease transpiration
Air High humidity High moisture
H2O
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• Four abiotic factors that affect the rate of
  transpiration in typical mesophytes
• D. Wind
• -High winds increase transpiration
• -When the wind blows it moves moist air away
  from the stomata
• -When the air is still there is no current to
  move the water saturated air away from the
  stomata (moist air stays above the stomata and
  reduces transpiration)

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• Questions to Consider
• 1. When a farmer sprays a chemical on to crop
  plants, how does the chemical travel to the roots
  of the plants?
• a. In the phloem, by active translocation
• b. In the phloem, by transpiration pull
• c. In the xylem, by active translocation
• d. In the xylem, by transpiration pull
• 2. Roots take up minerals from the soil by
• a. osmosis b. facilitated diffusion
• c. active transport d. diffusion
• 3. What causes movement of water through the
  xylem?
• a. active transport in the root tissue c. active
  translocation
• b. evaporation of water from the leaves d.
  gravity
• 4. Describe how water is transported in a plant.
  4

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• Questions to consider (and turn in)
• 1. Draw a labeled diagram to show the arrangement
  of tissues in a leaf.
• 2. Explain how roots absorb water and then
  transport it to the xylem, noting any special
  adaptations that help these processes to occur.

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• Reproduction in flowering plants
• Pollination, fertilization and seed dispersal
• A. Pollination -the transfer of pollen grains
  from the anther to the stigma
• 1.self pollination
• -the plant pollinates itself
• 2. cross pollination
• -one plant pollinates another
• -the plants genes are spread
• 3. Male gametes must use an external force to
  transfer the pollen (wind, animals)

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• Pollination, fertilization and seed dispersal
• B. Fertilization
• 1. The fusion of male and female gametes to form
  a zygote (happens inside the ovule)
• 2. Pollen develops from the anthers (male
  gamete)
• 3. Female gametes are found in the ovules in the
  ovaries of the flowers
• 4. Ovules that become fertilized develop into
  seeds
• 5. Ovaries with fertilized ovules develop into
  fruits
• Pollination does not always lead to
  fertilization

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Path of pollen to fertilization
Anatomy of a flower
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Draw, Label and Annotate
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Anatomy of a flower
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• Pollination, fertilization and seed dispersal
• C. Seed dispersal
• 1. One of the primary functions of fruits is
  seed dispersal
• 2. Seeds are often dispersed by animals or
  insects
• -Ex The seeds pass through animal intestines
  and are released
• 3. Seeds can be carried by wind
• 4. Fruits can explode and disperse the seeds
• 5. Seeds can be dispersed by moving water

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This plant grows near water. The fruit bursts,
the seeds fall in the water and the river carries
them away.
Wind dispersal
Pond Iris
Exploding fruit
Carduus nutans (nodding plumeless thistle)
Impatiens capensis (orange spotted touch me not)
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• Dicotyledonous and monocotyledonous seed
  structure
• A. Dicots-have 2 seed leaves(two cotyledons)
• 1. Mature plants have broader and shorter
  leaves with net-like veins
• 2. Examples Oak trees Buttercups

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• 3. Dicotyledonous seed internal anatomy
• Phaseolus multiflorus (a bean seed)

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DICOT SEED ANATOMY
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• B. Monocots -have one seed leaf (one cotyledon)
• 1. Mature plants tend to have long, narrow
  leaves with parallel veins
• 2. Examples
• Grasses Palm trees

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A typical monocot seed
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• Required conditions for seed germination
• A. Seeds are normally in a dormant condition
• (they grow in the parent plant and become
  dormant when they leave)
• B. The dormancy must be broken for the seed to
  germinate
• C. Germinationthe resuming of growth or
  development from the seed

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• Required conditions for seed germination
• D. Breaking the dormancy
• -water must be available for hydration of
  tissues inside the seed
• -oxygen must be available for cellular
  respiration
• -suitable temperatures (seeds stay dormant at
  temperatures that are too low or too high because
  enzyme activities are altered)
• -ideal light conditions (to ensure
  photosynthesis will be possible)
• -wearing down of the testa (seed coat)

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• Metabolic events during germination
• A. Absorption of water
• -presence of water activate hydrolytic enzymes
• -the seed will become metabolically activated
• B. Gibberellins are produced
• - Gibberellins are plant growth hormones
  produced by the cotyledons
• -Gibberellins stimulate the production of
  amylase which breaks down stored starches into
  maltose

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• Metabolic events during germination
• D. Maltose is moved to the embryo and eventually
  converted into glucose
• E. Glucose is used in cellular respiration to
  produce energy or it is used to make cellulose
  for cell walls
• F. Stored proteins and lipids are hydrolyzed
• -The amino acids produced will be used to make
  new proteins or used as enzymes
• -The fatty acids and glycerol produced will be
  used in the cell membrane as phospholipids

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• Metabolic events during germination
• F. Continued
• -The food reserves are stored as large insoluble
  macromolecules in seed.

Useful
Not useful
G. When the leaves of the seedlings reach
sunlight photosynthesis will begin to supply the
necessary nutrients (seed energy stores are no
longer needed
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Phaseolus multiflorus seedling (after about two
weeks)
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Work ahead

1. Explain how flowering is controlled in plants.
2. What is a photoperiod?
3. Distinguish between long and short day plants.
4. Explain the experiment dealing with red and far
   red light and plant flowering.

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Flowering in plants

1. Phytochrome-a photoreceptor that plants use to
   detect light
2. Photoperiod-relative lengths of night and day
3. Photoperiodism-physiological response to
   photoperiods
4. Flowering in plants is related to A, B and C

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Flowering in plants

• Three types of plants (you should be able to
  figure out which plants need longer/shorter
  photoperiods)
• -short-day (ex poinsettas)
• -long day (ex spinach)
• -day neutral (ex tomatoes)
• Each type of plant has a defined photoperiod

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During the 1940s, researchers conducted
experiments in which periods of darkness were
interrupted with brief exposure to light to test
how the light and dark portions of a photoperiod
affected flowering in short-day and long-day
plants.
EXPERIMENT
Critical dark period
RESULTS
(b) Long-day plantsflowered only if aperiod
of continuousdarkness was shorterthan a
critical darkperiod for thatparticular species
(13hours in this example).
Darkness
(a) Short-day plantsflowered only if a period
ofcontinuous darkness waslonger than a critical
darkperiod for that particularspecies (13 hours
in thisexample). A period ofdarkness can be
ended by abrief exposure to light.
Flash oflight
24 hours
Light
CONCLUSION
The experiments indicated that flowering of each
species was determined by a critical period of
darkness (critical night length) for that
species, not by a specific period of light.
Therefore, short-day plants are more properly
called long-night plants, and long-day plants
are really short-night plants.
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Flowering in plants

• There are two types of red light
• -Pfr-far red absorbing
• -Pr-red absorbing
• B. Pfr promotes flowering in short-day plants
• C. Pr promotes flowering in long-day plants

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• Action spectra and photoreversibility experiments
• Show that phytochrome is the pigment that
  receives red light, which can interrupt the
  nighttime portion of the photoperiod

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FR
EXPERIMENT
R
R
20
FR
FR
FR
Critical dark period
R
R
R
R
A unique characteristic of phytochrome is
reversibility in response to red and far-red
light. To test whether phytochrome is the pigment
measuring interruption of dark periods,researchers
observed how flashes of red light and far-red
light affected flowering in short-day and
long-day plants.
16
Hours
12
8
RESULTS
4
0
Short-day (long-night) plant
Long-day (short-night) plant
CONCLUSION
A flash of red light shortened the dark period. A
subsequent flash of far-redlight canceled the
red lights effect. If a red flash followed a
far-red flash, the effect of the far-red light
was canceled. This reversibility indicated that
it is phytochrome that measures the interruption
of dark periods.
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Distinguishing between monocots and dicots
Monocots Dicots
Leaf venation Parallel Net-like
Vascular tissue distribution
Number of cotyledons
Floral organs
Root types Adventitious roots Tap roots w/ lateral branching
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Apical vs. Lateral Meristems in Dicots

• Apical meristems allow primary growth
• -found in buds and tips of shoots
• -allows plants to grow organs and develop the
  shape of a plant
• B. Lateral meristems are responsible for
  secondary growth
• -make the stem grow thicker and/or develop new
  vascular bundles
• -found in cambium

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Auxin and plant growth

1. Auxin-a plant growth hormone
2. Best known auxin is IAA
3. Produced by apical buds and transported down stem
   (towards the end)
4. Accumulates at shaded side of plant
5. Stimulates cell divisions and stretching
6. Activity is related to phototropism (growth
   response in response to light)
7. Auxin allows positive photropism (the plants grow
   towards the light
8. Read p. 152 of the green IB textbook.

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• Compare growth due to apical and lateral
  meristems in dicotyledonous plants. 6
• Explain the role of auxin in phototropism as an
  example of the control of plant growth. 6
• Distinguish between monocots and dicots.

Monocots Dicots
Leaf venation
Vascular tissue distribution
Number of cotyledons
Floral organs
Root types
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• Review
• Draw and label a flowering plant (from memory).
• Describe the metabolic events of germination in a
  starchy seed.
• Explain how abiotic factors affect the rate of
  transpiration.