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Plant Physiology

The study of the biochemical basis for plant physiology including hormones, water and sugar transport and the evolution onto land.

Claire Stubendorff

on 19 January 2017

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Transcript of Plant Physiology

Ch. 29-30, 35-39

Ch. 29-30 Plant Classification
Charophytes & Land Plants
Photosynthesis began in the water with algae then land became a new frontier with new resources but with the threat of drying out. This is the story of how plants moved onto land.
Walled Spores
Charophytes produce spores but not ones with walls so they'll dry out and be vulnerable to harm outside of the water.
Both moss & ferns produce spores with walls that are contained within a structure called a Sporangia in which diploid cells go through meiosis to produce haploid spores.
Alternation of Generations
Mosses & Ferns have a multicellular halpoid phase - a plant-like structure that goes through mitosis to create haploid spores. This is an extra step & leaves the haploid plant vulnerable to mutations by UV radiation.
Fern life cycle
Moss life cycle
Gametophyte (n) & Sporophyte (2n)
In ferns, gymnosperms & angiosperms
the Sporophyte is the dominant generation
Vascular Tissue - Xylem & Phloem
Xylem transports water to all parts of the plant, Phloem transports sugar made by photosynthesis.
Apical Meristems
Plants on land must extend roots down to find water and shoots upward to find light. The root tips and shoot tips are areas of rapid cell division called meristems.
Evolution of the Seed
From Ovule to Seed in a Gymnosperm
Gametophyte Life Cycle
Flower Structure
Angiosperm Life Cycle
Flowering Plants
Flowering Plants make up 95% of all land plants today. What does that tell you about this strategy of reproduction & survival?
Both Male & Female parts in one Structure plus adaptations to attract pollinators & seed dispersal animals.
Pollinator vs. Seed Disperser
What is their role in helping Angiosperms?
When do they participate in the process?
What type of evolution is this?
Yucca & Moth
The yucca can't survive without the moth and the moth can't survive without the yucca.
Seed Dispersal
Ch. 35 Plant Structure, Growth & Development
Types of Roots
Prop roots
Butress roots
Storage roots
Types of Leaves
Tendrils, spines, storage leaves, reproductive leaves, bracts (look like petals)
Types of Plant Tissues
Dermal tissue
Ground tissue
Vascular tissue
Dermal Tissue
Protective outer covering
In nonwoody plants, it's called the epidermis
In woody plants, it's
called the periderm
In leaves & most stems the
(waxy coating) covers the epidermis.
Ground Tissue
Vascular Tissue
Xylem (water transport) &
Phloem (sugar transport)
Pith and Cortex
- contain specialized cells for storage, photosynthesis & structure
Other types of Plant Cells
thin cell walls, photosynthetic, typical plant cell
thicker cell walls, flexible support as in leaf stems
thick cell walls reinforced with lignin, structural support
Lignin is the 2nd most common compound on the planet, second only to cellulose.
Primary vs. Secondary Growth
apical meristems
extend upward & downward (root & shoot tips).
- v
ascular & cork cambium
layers add girth to plant
(only present in woody
plants like trees).
Ch. 38 Seed Anatomy & Development
Casparian Strip
- waterproof barrier running along the
Suberin is the waxy substance that makes the strip waterproof.
Maturity of Seed (fertilized & fully developed)
Environmental cues (water, temp., light, fire, digestion, etc.)
Water absorption activates enzymes & cracks seed coat
Respiration begins (use of Oxygen & energy storage)
Radicle produces roots to anchor
Hypocotyl elongates to produce shoot
Germination (sprouting) of a Seed Requires:
Seed Coat - protection
Endosperm - 1 or 2 cotyledons
Embryo - several parts
Hypocotyl - stem
Epicotyl - top of stem that emerges first
Radical - roots
Monoecious vs Dioecious Reproduction
Flowers have both male & female parts on one plant and even in the same structure (Monoecious). However, some plants produce only male or only female parts (Dioecious). Advantages? Disadvantages?
carpellate flowers
staminate flowers
Vegitative Reproduction - asexual
Advantages to asexual reproduction for plants? Disadvantages?
In roots, the cortex absorbs & stores water too
Ch. 36 Resource Aquisition & Transport
movement of water and minerals up through the plant. Driven by the process of water loss through the leaves during transpiration.

Cohesion-tension Theory
– responsible for most of the water transport force up a plant.
creates negative pressure or tension at the top of the plant through loss of water by evaporation.
between water molecules is strong enough to form a polymer-like column of water that doesn’t break.
Bulk Flow
of water occurs when a single water molecule evaporates and pulls up the whole column of water behind it.
Capillary Action
– force that pulls liquids up small tubes by Adhesion (attraction to unlike surfaces), water sticks to the inside of the xylem.
Fern Sporangia
moss sporangia
Root Hairs
high surface area increases water absorption
capillary action
Apoplast vs. Symplast Pathways
apoplast - around cells
symplast - through semi permeable membrane
Symbiotic relationship between plant roots and fungi
increases surface area of roots, increasing water absorption, also increasing mineral & nutrient uptake (nitrates & phosphates)
Nitrogen-fixing bacteria
can also live symbiotically with plant roots increasing the amount of nitrogen absorbed by the plant
Water Potential
Remember solutes affect water potential & create a concentration gradient which causes water to move across a semi permeable membrane.
Absorbing nutrients
Storing sugar
Constant movement of water up toward the leaves (negative pressure)
Roots increase solute concentration by:
Stomata Control
stomata are the openings in the leaves that allow gas exchange for photosynthesis.
Guard Cells
Cells responsible
for opening and closing the stomata.
Water diffuses through the xylem (high conc.) into the leaf tissue (low conc.) where it is either used for photosynthesis or lost to evaporation, creating the transpirational pull.
Guard cells must be open for transpiration to occur
Potassium (K) influx (active), results in passive flow of water in also = guard cells bend, stomata open.
Sugar Transport
Source to Sink
Sugar is produced mainly in the leaves and stored mainly in the roots.
Pressure-Flow Hypothesis
Transport sugar into phloem (right next to xylem) causes water to diffuse over increasing pressure.
This pushes fluid downward in phloem. In roots, sugar is transported into root cells, causing water to diffuse back into xylem and decreasing pressure.
Selective Breeding
Advantages? Disadvantages?
Genetic Engineering
Inserting genes to increase production, pest resistance and resistance to other environmental issues (mold, frost, etc.)
Ch. 39 Plant Responses
to Internal & External Signals

The U.S. Food Market:
Most highly modified foods in the U.S. are soybeans (93%), cotton (93%), canola (93%) and corn (86%). Much higher compared to the rest of the world (because it's more expensive)
Why Modify?
Disease/Pest resistance
Higher nutrient value
Larger yeild/production
(IAA) Apical meristems (shoot tips) are the main source of auxin. Promotes growth upward and toward light by elongating the dark side of the shoot.

Acidification of cell walls
causes cellulose to loosen and water influx stretches fibers to cause cell to “grow.”
Polar transport – Auxin only moves from shoot tip down.
– made in roots, transported to places when needed.
– root growth & differentiation, stimulate cell division (cytokinesis) & germination, delay senescence (aging),
Usually works with (or counteracted by) other hormones especially Auxin. Counteracts Apical Dominance caused by Auxin.
Auxin inhibits axillary bud growth in favor of elongation of major shoot BUT Cytokinins come up from roots and counter act Auxin, that’s why many plants are triangle/ Christmas Tree shaped
Apical Dominance
– meristems of roots & shoots, embryo, young leaves.
– Promote germination, stem elongation, leaf growth, stimulate flowering & fruit dev., affect root growth & differentiation. 60 different types
- throughout plant
- promote cell growth & differentiation in xylem & inhibit it in phloem. Promote seed germination & pollen tube elongation.
Abscisic Acid
- throughout plant
- Inhibits growth (dormancy hormone), closes stomata during water stress, dormancy of plants, dormancy of seeds.
– tissues of ripening fruits, nodes of stems, aging leaves & flowers.
– cause fruits to ripen, influences leaf abscission (aging & dropping of leaves), oppose some affects of auxin, promotes or inhibits growth of roots, leaves, & flowers depending on species. Gas (H2C=CH2)
Tropisms - responses to environmental changes
Response to light
- auxin drives this response
plants grow toward light source. Cells on the dark side of the shoot elongate because auxin travels in higher concentration down that side.
Response to Touch - tendrils are especially sensitive to this but many plants will either grow toward another surface to climb up it or away from another surface to avoid competition.
Response to Gravity - roots and shoots must make sure they know up from down. Auxin travels down the root or shoot in different concentrations to make it turn up or down.
Can plants tell time? Yup!
Ch. 37 Plant Form and Function
Symbiosis and Plant Nutrition
Soil Bacteria
Nitrogen-Fixing bacteria
- takes N2 out of the air and converts it into NH3
Ammonifying bacteria
- takes nitrogen out of dead/decayed organic matter
Nitrify bacteria
- converts ammonium to Nitrate that can be absorbed by plants
Denitrifying bacteria
- converts Nitrates back into N2 in the air (cycle)
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