Lecture 6

• Phloem transport moves sugar in solution
• Phloem transport occurs in sieve-tube elements
•  Phloem transport occurs by the pressure-flow hypothesis
• Phloem flow moves from source to sink
• Phloem transport starts when sugar is loaded by a companion parenchymal cell into the sieve-tube, water follows by osmosis. Higher water pressure sinks the phloem sap towards the sink cell where sugar is unloaded and water returns to the source through the xylem
• The phloem moves sugar from the leaf where it is created, to the roots where it is stored
• The phloem transports sap by bulk flow from positive pressure
• Phloem transport can happen in any direction
• In the summer and fall, phloem transport moves sugar from the leaves to the roots for storage
• In the winter, starch is stored in the roots and there is no phloem transport up or down
• In the spring, phloem transport moves sugar from the roots to budding leaves
• In plants, water spontaneously moves from regions of higher to regions of lower water potential energy
• Water potential is the sum of solute potential energy and pressure potential energy
• Solute potential energy is always 0 or a negative value
• Pressure potential energy can be any value
• There are two main tissues for transport: the xylem and phloem
• The xylem moves sap through tracheids and sometimes vessel elements
• The phloem moves sugar water through sieve-tube elements
• Photosynthesis is the source of oxygen in the atmosphere
• 50% of oxygen is made my terrestrial plants and 50% is made by marine phytoplankton and macroalgae
• Photosynthesis is the first step in moving energy into the living world
• Photosynthesis is the source of all energy in ecosystems
• Photosynthesis occurs in leaves
• The mesophyll cell is the main photosynthetic cell in plants
• Photosynthesis is the reaction of carbon dioxide and water to create glucose, oxygen and water
• Photosynthesis involves the transfer of electrons, it is a redox reaction
• In photosynthesis, water is split and loses electrons which are transferred along with hydrogen ions to carbon dioxide, reducing it to sugar
• Photosynthesis involves two stages: light reactions and the Calvin cycle
• Photosynthesis occurs in the chloroplasts of plant cells
• Light reactions occur in the thylakoid membrane of the chloroplast
• The Calvin cycle occurs in the stroma of the chloroplast
• Light reactions are when light energy is converted to chemical energy of NADPH and ATP
• Light reactions oxidize water and the molecule breaks apart by photolysis to release oxygen gas, its parts are combined with NADP+ to create NADPH
• Light reactions create ATP through photophosphorylation of ADP and Pi
• NADP+ and NAD+ are oxidizing agents which remove electrons from other molecules
• NADPH and NADH are reducing agents which place electrons on other molecules
• NADP+ and NADPH are used in photosynthesis
• NAD+ and NADH are used in respiration
• Chlorophyll a absorbs mostly violet-blue and red light wavelengths
• Chlorophyll a reflects or transmits green light which is why plants are green