plant physiology

PLANT PHYSIOLOGYPLANT PHYSIOLOGY

Plants are dynamic!Plants are dynamic!

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 mineralsTransport of water and minerals 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 xylemWater movement in xylem Uptake from soil Conduction in the xylem Transpiration in the leaves

Transpiration Transpiration

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 StomaGuard Cells and Stoma

Guard Cell

Stoma (opening)

Open stomata permit transpirationOpen stomata permit transpiration

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

TranspirationTranspiration

Large amounts of water vapor are lost by transpiration– 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 Translocation of sugars in phloem Organic materials

are translocated by the sieve tube members of the phloem

Sieve tube members are living but highly specialized cells End wall

with sieveplate

Phloem translocationPhloem translocation

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 translocationPhloem translocation

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 Metabolism

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

EnergyEnergy 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 TransformationsCellular Energy Transformations

Transfer of electrons (or H atoms) ATP energy currency of all cells

– Cells use ATP when need energy– Cells make ATP when store energy

Other energy molecules – NADP--->NADPH– NAD--->NADH

Photosynthesis Photosynthesis

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 Light absorbing pigments

When light strikes an object it can– pass through the object – be reflected from the surface– be absorbed

For light to be absorbed, pigments must be present

Pigments in plants Pigments in plants 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

Granum

Thylakoid

Two stages of photosynthesis both occur in chloroplasts:Light Reactions and Calvin Cycle

Two stages of photosynthesis both occur in chloroplasts:Light Reactions and Calvin Cycle

Thylakoids location of pigments and Light Reaction Granum

Innermembrane

OuterMembrane

Stroma(Calvin Cycle)

Light reactionsLight reactions

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 ReactionsResults of the Light Reactions

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)Calvin Cycle (Dark reactions)

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 CycleEvents of the Calvin Cycle

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 CycleCarbon dioxide for Calvin Cycle

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 Overall Equation for Photosynthesis

CHLOROPHYLLCHLOROPHYLL

6CO6CO22 + 12H + 12H22O O + energy --------> + energy --------> CC66HH1212OO66 + 6O + 6O22 + 6H + 6H22OO

Oxygen release from light reactionOxygen release from light reaction 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 photosynthesisProducts of photosynthesis 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 Sugarcane

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

EuropeEurope

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 IslandsCaribbean Islands

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 LocationsOther New World Locations

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 SlaverySugar and Slavery

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 increasingSugar demand increasing

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 TradeTriangle Trade

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

SugarcaneSugarcane

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

ProcessingProcessing 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 beetSugar beet

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

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 Other plants store oils (triglycerides) and

proteins

Summary 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