Test 3 Objectives Objectives for Lecture 11 BOT 3015 Spring 2014 You should be able to write a chemical equation that describes photosynthesis know that it occurs in two separate reactions the light rxn and the Calvin cycle Light RXN Light energy is converted into chemical energy in the thylakoid membrane Light captured by chlorophyll leads to electron transport and finally to the formation of ATP from ADP and the reduction of NADP to NADPH The electrons that are transferred in photosynthesis come from splitting water into oxygen plus electrons Calvin Cycle takes place in the stroma liquid portion of the chloroplast and fixes CO2 into carbohydrates using ATP and NADPH from the light reactions CO2 is converted into sugar using the chemical energy produced in the light reaction RuBP 5 carbon CO2 2 3carbon compounds The 3 carbon compounds are the reduced by the ATP and NADPH from the light reaction Two of the three carbon compounds can give off glucose 6 turns to give off one sugar Know the difference between and action spectrum and an absorption spectrum and what the roles of chlorophyll b and carotenoids are in photosynthesis Red and Blue wavelengths drive photosynthesis Action spectrum of photosynthesis wavelength that drives the process sum of absorption spectrum Absorption spectrum wavelength pigments absorb Chlorophyll a Chlorophyll b and carotenoids are accessory pigments that help to broaden the photosynthetic spectrum Chlorophyll that absorbs light is then excited and releases energy that is passed down an electron transport chain There are two photosystems II light hits the chlorophyll and this is transported in electrons to the electron transport chain and this creates ATP H2O is used to get the electrons back to chlorophyll and this produces O2 and I reduces NADP to NADPH ATP is made between the two photosystems Know that the enzyme that carries out CO2 fixation is Rubisco and this enzyme converts a 5 carbon sugar RuBP into two 3 carbon sugars PGA Six turns of the Calvin cycle are needed to make one glucose Excess glucose can be stored as starch Starch is always located in the plastids Know what photorespiration is why it is a problem and under what conditions it occurs C3 plant use this when the temperatures are high and CO2 levels are low This allows for O2 to bind to rubisco and eventually be turned into CO2 which is bad Plants start to use up carbohydrates and decrease efficiency of photosynthesis Be able to explain the differences between the photosynthetic schemes of C3 plants C4 plants and CAM plants and the advantages of each C4 they are more efficient than C3 plants at high temp and dry conditions They avoid photorespiration by fixing CO2 into a 4 carbon compound malate The compound that does this is not sensitive to O2 Malate acid is transported to bundle sheath cell and it is then broken back down to CO2 This is a bit more inefficient but makes up for it on hot dry day Tropical grasses corn sugar cane CAM This is an adaptation to dryness at night the stomates are open CO2 is fixed into malate Open their guard cells at night and close them in the day More to prevent water loss Chloroplast came from a eukaryotic cell that engulfed a bacterium that was about to Be able to explain the endosymbiotic hypothesis for the origin of chloroplasts and discuss the evidence that supports this hypothesis photosynthesis Chloroplasts grow and divide They also have 2 membranes from the engulfing They have their own DNA and if you compare this to photosynthetic bacteria it matches much better than eukaryotic organisms Evidence Arise by division of other plastids Contain DNA for making some of their own proteins and plastid is circular has operons and is close in sequence to bacterial DNA Know photosynthesis first evolved in the bacteria and that cyanobacteria are abundant modern day photosynthetic bacteria Oxygenic photosynthesis evolved about 2 5 billion years ago but was preceded by photosynthetic bacteria that use electron donors other than water for example the purple sulfur bacteria use H2S as the electron donor and elemental sulfur is the byproduct of photosynthesis rather than oxygen Objectives for Lecture 12 Know what transpiration is and why it is an inevitable aspect of photosynthesis in land plants Know what the cuticle is where it is located its composition and function and understand that transpiration occurs through pores stomates whose opening is regulated Movement of water is through the Xylem Transpiration loss of water by the plant Cells that are going to photosynthesis have to be wet Water loss helps to lower the temp of the plant making C3 more effective Xylem is comprised of tracheids skinny and vessel elements fatter Cuticle is a waxy covering that helps prevent water loss It is a layer of cutin on outer wall of epidermal cells Know that stomatal opening and closing is the result of osmotic swelling shrinking of the guard cells which is driven by the active uptake of potassium ions during opening and the passive efflux of potassium during closing Understand how the structure of the guard cell wall results in bending of the cells and opening of the stomatal pore when the guard cells undergo osmotic swelling opening intake of K ions and shrinking closing Inner wall ventral wall is thicker than the outer wall and the outer wall pulls the inner wall open when turgor pressure is high Each stoma has two guard cells that help it regulate the opening and closing By swelling Water is flowing passively by the water evaporating at the plants surface Water binds to itself Understand the Cohesion Tension Theory for the movement of fluid in the xylem know that the driving force is the difference in relative humidity between the inside of the leaf and the air the important role of hydrogen bonding between water molecules and the existence of negative pressures inside the xylem and if you have a standing column of water and the ones on the top evaporate and pull on the ones below them up Breaking of hydrogen bonds when it goes from liquid to gas phase is responsible for the movement Be able to cite two pieces of evidence which support the Cohesion Tension Theory 1 predicts that you will have negative pressure inside the Xylem 2 because water column is stretched you can expect the stem to be narrow when transpiration is high Humidity high transpiration is high and vice versa stem diameter shrinks during the day and increases at night Humidity high transpiration high
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