Transcript PLANT PHYSIOLOGY

PLANT PHYSIOLOGY
Plants are dynamic!
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Many physiological processes occur in
each part of the plant
Materials are transported through
specialized conducting systems
Energy is harnessed from the sun
through photosynthesis to forms
sugars and other storage products
Stored foods are broken down to yield
chemical energy through respiration
Transport of water and
minerals
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Occurs in the xylem
Tracheids and vessel elements conducting components
Source of water is the soil surrounding
the roots
Water moved up through plant to the
leaves often in excess of 300 ft
Water movement in xylem
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Uptake from soil
Conduction in the xylem
Transpiration in the leaves
Transpiration
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Transpiration is the loss of water vapor
from leaves
Occurs mainly through the stomata
(90%)
Driving force behind the movement of
water in xylem.
Guard Cells and Stoma
Guard Cell
Stoma (opening)
Open stomata permit transpiration
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Gas exchange can occur freely between
the leaf and the atmosphere
Water vapor and oxygen diffuse out of
the leaf
Carbon dioxide is able to diffuse into
the leaf
Transpiration
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Large amounts of water vapor are lost
by transpiration
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2 liters of water/day for a single corn plant
5 liters for a sunflower
200 liters for a large maple tree
450 liters for a date palm tree
Transpiration is a major component of
the global water cycle
Translocation of sugars in phloem
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Organic materials
are translocated by
the sieve tube
members of the
phloem
Sieve tube members
are living but highly
specialized cells
End wall
with sieve
plate
Phloem translocation
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Moves from source to sink.
In late winter, the source may be an
underground storage organ
translocating sugars to apical meristems
(the sink)
In summer the source is usually
photosynthetic leaves sending sugars
for storage to sinks such as roots or
developing fruits
Phloem translocation
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Sucrose in a watery solution
In a growing pumpkin which reaches a
size of 5.5 kg (11 lbs) in 33 days,
approximately 8 g of solution are
translocated per hour - small pumpkin
Record pumpkin over 1000 lbs
Metabolism
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Total of all chemical reactions occurring
in living organisms
Metabolic reactions that synthesize
compounds require an input of energy
Reactions which break down
compounds usually release energy
Energy
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All life process are driven by energy
A cell or an organism deprived of an
energy source will soon die
Among the forms of energy are radiant
(light), thermal (heat), chemical,
mechanical (motion), and electrical
One form of energy can be transformed
into another form
ATP energy currency of the cell
Cellular Energy Transformations
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Transfer of electrons (or H atoms)
ATP energy currency of all cells
– Cells use ATP when need energy
– Cells make ATP when store energy
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Other energy molecules
– NADP--->NADPH
– NAD--->NADH
Photosynthesis
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Transforms the energy of the sun into
chemical energy
Is the basis for life on Earth
Photosynthetic organisms are at the
base of all food chains
Without green plants and algae, life
could not survive
Light absorbing pigments
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When light strikes an object it can
– pass through the object
– be reflected from the surface
– be absorbed
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For light to be absorbed, pigments must
be present
Pigments in plants
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Leaf - the major organ of
photosynthesis
Chloroplasts within the mesophyll cells
are the actual sites of photosynthesis
The major photosynthetic pigments are
the green chlorophylls
Other pigments: Carotenoids
– Orange - carotenes
– Yellow - xanthophylls
– Normally masked by the chlorophylls
Thylakoid
Granum
Two stages of photosynthesis both
occur in chloroplasts:
Light Reactions and Calvin Cycle
Stroma
(Calvin Cycle)
Outer
Membrane
Inner
membrane
Granum
Thylakoids
location of
pigments and Light Reaction
Light reactions
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Photochemical phase of photosynthesis
Radiant energy is absorbed and then
converted into chemical energy
Occur extremely rapidly powered by
vast energy of the sun
Results of the Light Reactions
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Water molecules are split releasing
oxygen and electrons
Electrons used in a process that
ultimately results in the formation of two
energy molecules NADPH and ATP
Calvin Cycle (Dark reactions)
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Biochemical phase of photosynthesis
The pathway is named in honor of
Melvin Calvin who received a Nobel
Prize in 1961 for his work determining
the steps in the pathway
Events of the Calvin Cycle
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Transforms CO2 to form sugars
Uses ATP and NADPH produced in the
light reactions but doesn’t use light
energy directly
The end product of this pathway is the
formation of a six-carbon sugar which
requires the input of 6 molecules of
carbon dioxide
Carbon dioxide for Calvin Cycle
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From the atmosphere
Very small fraction (0.035%) of the
Earth's atmosphere
Enters the leaf by diffusing through the
stomata
Overall Equation for Photosynthesis
CHLOROPHYLL
6CO2 + 12H2O + energy --------> C6H12O6 + 6O2 + 6H2O
Oxygen release from light
reaction
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Oxygen released when water is split
Diffuses out of the leaves into atmosphere
Earth's only constant supply of oxygen
No oxygen in early Earth atmosphere
Current 20% oxygen atmosphere is the result
of three billion yrs of photosynthesis
Living organisms depend on oxygen for
cellular respiration
Products of photosynthesis
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Transported to growing fruits, storage
organs, other sinks
Sucrose is translocated in the phloem
After being unloaded, sugars are usually
converted to starch
Very few species store sucrose
Only sugarcane and sugar beet are
important sources of sucrose
Sugarcane
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Saccharum officinarum is a perenniel
member of the grass family
Native to the islands of the South Pacific
Grown in India since antiquity
Ancient civilizations in the Near East and
Mediterranean countries were acquainted
with sugar through Arab trading routes
7th century - grown in Mediterranean
Europe
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Honey remained the principal
sweetener until the 15th century
Sugar was an expensive luxury mainly
use in medicines to disguise the bitter
taste of herbal remedies
Early in the 15th century sugar
plantations were established on islands
in the eastern Atlantic
Caribbean Islands
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Columbus introduced sugarcane on his
second voyage in 1493
By 1509 sugarcane was harvested in
Santo Domingo and Hispaniola and
soon spread to other islands
Many Caribbean Islands were
eventually denuded of native forests
and planted with sugar cane
Other New World Locations
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Portuguese started sugar plantations in
South America in 1521
Spanish and Portuguese enslaved the
native populations to work in the fields
The first sugarcane grown in the
continental United States was in the
French colony of Louisiana in 1753
Sugar and Slavery
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Sugarcane was responsible for the
establishment of slavery in the Americas
Decimation of the native Indian populations
led to the need for workers on the sugar
plantations
By the early 16th century, sugar and the slave
trade became interdependent initially
established in Spanish and Portuguese
colonies
Sugar demand increasing
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Supplies of honey in Europe were
decreasing
Growing popularity of coffee, tea, and
cocoa in Europe accelerated the
demand for sugar
Sugar became the most important
commodity traded in the world
Triangle Trade
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First leg - England to West Africa with
trinkets, cloths, firearms, salt
Second leg - Africa to Caribbean Islands
with slaves
Third leg - Caribbean to England with
rum, molasses and sugar
10-20 million African slaves had been
brought to the New World
Sugarcane
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Provides over 50% of the world's sugar
supply
Canes are 15 to 20 ft tall with individual
stalks up to 6” in diameter
Moist lowland tropics and subtropics
Canes generally contain 12 to 15%
sucrose.
Sugarcane Field in Egypt
Processing
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Canes crushed to extract the sugary juice
Juice is concentrated and evaporated to form
a syrup
Sugar is crystalized and separated from thick
brown liquid (molasses)
Molasses is used in foods, or is fermented to
make rum, ethyl alcohol, or vinegar
The crystallized sugar (about 96-97% pure
sucrose) is refined
Sugar beet
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Beta vulgaris, a member of the
Chenopodiaceae is unrelated to
sugarcane
Same species as red beets which are
native to the Mediterranean region
Provide close to 40% of the world's
supply of table sugar
Other Storage Compounds in Plants
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Products of photosynthesis are stored
as various organic compounds
Starch - most common storage
compound
– Energy reserve for plants
– Energy source for the animals that feed on
the plants
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Other plants store oils (triglycerides)
and proteins
Summary
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Plants are dynamic metabolic systems
with hundreds of biochemical reactions
Life on Earth is dependent on the flow
of energy from the sun
Photosynthesis converts carbon
dioxide and water into sugar using
solar energy
Various compounds are stored by
plants including sucrose, starch, oils,
and proteins