1 Unit 6- Photosynthesis & Cellular Respiration 6a- Photosynthesis
2 First Homework (New Semester) Bring a leaf to class tomorrow
3 Life RequirementsAll organisms need a constant source of energy to survive.The ultimate source of energy for most life on Earth is the Sun.
4 Trapping the Sun’s Energy Photosynthesis is the overall process by which solar energy is used to chemically convert water and carbon dioxide into chemical energy stored in simple sugars.Involves a complex series of chemical reactions in which the product of 1 reaction is a reactant in the nextBiochemical pathway
5 PhotosynthesisThe process of photosynthesis is generally represented using a balanced chemical equation. However, this equation does not represent all of the steps that occur.Sunlight6CO2 + 6H2O C6H12O6 + 6O2
6 Steps of Photosynthesis Photosynthesis can be divided into two stagesLight-dependent ReactionSolar energy is absorbed by chloroplasts and two energy-storing molecules (ATP & NADPH) are produced.Calvin Cycle (Light-independent reaction)Simple sugars (glucose) are formed using CO2 & the energy stored in ATP & NADPHPreviously, these reactions were called the light reaction and the dark reaction. While some text still refers to the Calvin Cycle as the dark reaction, most do not because it contributes to the misconception that the Calvin cycle occurs at night.
7 Structure of Chloroplasts Photosynthesis takes place in the chloroplastsEach chloroplast is surrounded by a pair of membranes.Inside the inner membrane is another system of membranes called thylakoids.Arranged as hollow disksConnected & layered to form stacks called granaSurrounding the grana is a solution called the stroma.Chloroplasts have 3 phospholipid bilayers
8 Where does each step take place? Light-dependent reactions take place in the membranes of the thylakoid disksCalvin Cycle takes place in the stroma
9 Review of Light Light from the sun- white light Can be separated into its component colors by passing the light through a prismResults in the visible spectrum (ROYGBIV)When white light strikes an object, its component colors can be reflected, transmitted, or absorbed.Pigments- compounds that absorb lightMost absorb certain colors more strongly than others, so the light that is reflected no longer appears white.
10 The Role of Chloroplasts and Pigments The thylakoid membranes contain the pigments that can absorb certain wavelengths of sunlight.The most important pigment is chlorophyll.Absorb most wavelengths of light except for green. Green is reflected making the plants appear green.In the fall, plants reabsorb chlorophyll leaving other pigments that reflect other wavelengths of light – making the leaves appear red, yellow, or orange.In leaves of plant, chlorophyll’s much more abundant and mask colors of other pigments. In the nonphotosynthetic parts like flowers, the other pigments are visibleDuring the growing season, chlorophyll is continually being produced and broken down & leaves appear green. As night length increases in the Fall, chlorophyll production slows down & then stops & eventually all the chlorophyll is destroyed.
11 Light-Dependent Reactions Sunlight strikes the chlorophyll molecules in the thylakoid membrane.Chlorophyll absorbs the light & the solar energy is used to split water molecules (photolysis)Results in the release of oxygen (O2) as a waste product.Allows for the temporary transfer of the solar energy to electrons released by the broken bondsElectrons are passed down an Electron Transport ChainPhoto- light…..lysis-splita water molecule is split (photolysis) into protons (H+), electrons, & oxygen.Electrons sent back to the chlorophyll, H+ left inside thylakoid, & the O2 diffuses out of the chloroplast & leaves the plant through stomataPhotolysis
12 Light Dependent Reactions The Electron Transport Chain is a series of proteins in the thylakoid membrane.As the electrons are transferred from one protein to another, some energy is released.This energy is used to make ATP & NADPH (electron carrier molecule)As the electrons are transferred from one protein to another, some energy is released which is used to…Join H+ and NADP+ (& 2e-) forming NADPH (electron carrier)Pump hydrogen ions into the center of the thylakoid disk to join ADP and an inorganic phosphate to form ATP (via ATP Synthase)ATP and NADPH will be used during the Calvin Cycle
14 Light-dependent Reactions Solar Energy absorbed by chloroplastsOxygen releasedATP ReleasedProducts of Light Reactions (ATP and NADPH) fuel the Calvin CycleNADPH released
15 Video https://www.youtube.com/watch?v=joZ1EsA5_NY (3:30) (7:35-8:20, end of light-dependent)
16 Calvin CycleA series of enzyme-assisted chemical reactions that produces 3-carbon sugarsOccurs in the stroma of the chloroplastUses the ATP & NADPH that was produced during the light reactions and CO2 from the atmosphere
17 Calvin CycleCarbon Fixation:An enzyme combines CO2 with a 5-carbon molecule called ribulose biphosphate (RuBP).6-carbon molecule is very unstable, so it immediately splits into two 3-carbon molecules called 3-phosphoglycerate (3-PGA or PGA)ReductionEach 3-PGA is converted into another 3-carbon molecule, PGAL (aka G3P) in 2 steps.1- receive a phosphate group from ATP; 2- receive a proton from NADPHADP & NADP+ will be used again in light reactionPGAL leaves & is used to build glucose (or other carbohydrates).RegenerationRemaining PGAL molecules converted back to RuBP by the addition of a phosphate group from ATP. Enter Calvin Cycle again.Students are not responsible for this information. All they need to understand is that the Calvin Cycle uses the products of the light reaction to produce 3-carbon sugars that will be recycled to keep the cycle going or will be used to produce glucose, other carbs, or other organic molecules
18 The Calvin Cycle Uses Carbon Dioxide from the air Uses ATP and NADPH from light reactions to build PGAL- a 3-carbon sugarUses another ATP to replenish RuBPOr the 3-carbon sugars can be recycled to keep the Calvin Cycle going.PGAL= G3P- glyceraldhyde 3-phosphateThe 3-carbon sugars can be used to build a glucose molecule
19 Photosynthesis Equation Light Energy6CO2 + 6H2O C6H12O6 + 6O2chlorophyllCarbon Dioxide from the air – Used in the Calvin CycleGlucose Made in the Calvin CycleOxygen Released during Photolysis in the Light ReactionsWater Split during Photolysis in the Light ReactionsPlants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose
21 3 Factors that Affect Photosynthesis Carbon Dioxide (CO2)Without CO2, the plant would not have one of the raw materials needed for photosynthesisCO2 is used in the first step of the Calvin CycleTemperatureThe temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur
22 3 Factors that Affect Photosynthesis Intensity of LightIf the intensity of light is lower, the available energy for photosynthesis is lower.In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occurIf light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the Calvin Cycle)
23 Video https://www.youtube.com/watch?v=joZ1EsA5_NY (3:30) (8:20, end of light-dependent)