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PLANT PHYSIOLOGY 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 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 xylem Uptake from soil Conduction in the xylem Transpiration in the leaves 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 Stoma Guard Cell Stoma (opening) Open 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 Transpiration 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 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 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 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 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 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 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 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 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 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 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 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) 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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