7 - Photosynthesis Light Reactions & Calvin Cycle PDF

7 – Photosynthesis Light Reactions & Calvin Cycle MHR Grade 12 Biology Textbook: 4.1: Capturing Solar Energy: The Light Dependent Reactions (pg. 156 – 165) Guiding Questions: 1. How are the light & light- independent reactions connected? 2. What are the molecules involved with li...

7 – Photosynthesis Light Reactions & Calvin Cycle MHR Grade 12 Biology Textbook: 4.1: Capturing Solar Energy: The Light Dependent Reactions (pg. 156 – 165) Guiding Questions: 1. How are the light & light- independent reactions connected? 2. What are the molecules involved with light reactions? 3. What are the stages and molecules in the Calvin Cycle?  Photosynthetic Organisms Plants are not the only organisms that photosynthesize! cyanobact Euglena eria phytoplank Kelp (algae)  Leaves Leaves are the photosynthetic organ of plants! Structure allows for maximum exposure to sunlight Water enters through roots and is transported to leaves through the veins Carbon dioxide enters through openings called stomata Reece et. al (2017)  Carbon dioxide and water diffuse into the mesophyll cells and enters the chloroplasts ~40-200 chloroplasts per mesophyll cell Thylakoid - one of many interconnected sac-like membranous disks within the chloroplast, containing the molecules that absorb Reece et. al (2017) energy from the sun  Stomata Allows CO2 to diffuse into the leaf Open and close due to osmosis Stomata cover 1- 2% of leaf’s surface  Chloroplast Location of photosynthesis Double membrane organelle  Notice that the membranes within the thylakoids of the chloroplasts have chlorophyll embedded within them, which is what allows photosynthesis to happen! https://www.carlsonstockart.com/photo/chlorophyll-complex-structure-  Chlorophyll Green coloured pigment Pigment = compound that absorbs certain wavelengths of visible light while reflecting others Chlorophyll in the thylakoid membrane absorbs light energy to begin process of Reece et. al (2017) photosynthesis  The Absorption of Light Energy Light is absorbed in the form of packets of energy called photons Photons carry specific amounts of energy An electron will only absorb the energy from a photon if it provides enough energy to excite the photon to the next energy level Reece et. al (2017)  Visible Light Spectrum Longer wavelength = relatively ↓ energy in the photon Shorter wavelength = relatively ↑ energy in the photon Wavelength corresponds to a colour on the visible spectrum  Why do Plants Appear Green? Plants contain chlorophyll a and chlorophyll b Each of these pigments absorb slightly different frequencies of light In general, the pigments absorb light in the violet- blue region and red regions of the Reece et. al (2017) Photosystems Capture Energy Photosystems = protein based complexes made of clusters of pigments that absorb light energy Photosystem I (P700) – contain specialized chlorophyll a molecules that absorb light optimally at wavelength 700 nm Photosystem II (P680) – absorb optimally at 680 nm Antenna complex = web of chlorophyll molecules that transfer energy to reaction centre Overview of Photosynthesis Overall Chemical Equation of Photosynthesis: chloroph yll 6CO2 + 6H2O + sunlight 🡪 C6H12O6 + 6O2 Light-Dependent Reactions (Photochemical) Where: Thylakoid What Happens: Photons excite electrons in the chlorophyll (in the thylakoid membrane) Reactants: H2O, NADP+, ADP + Pi Products: O2, NADPH, ATP Role: Chemiosmotic ATP synthesis and formation of NADPH (a coenzyme)  Light-Independent Reactions (Biochemical) a.k.a. – The Calvin Cycle Where: Stroma What Happens: Incorporation of CO2 into organic compounds such as glucose (called carbon fixation) Reactants: CO2, NADPH, ATP Products: Sugar, NADP+, ADP + Pi Role: To create sugar molecules Light-Dependent Reactions (Photochemical)  Light-Dependent Reactions 1. Photosystem (Photochemical) II (P680) Enzyme splits water (photolysis) H+ and electrons released; O2 is generated 2. Plastoquinone (Pq) Electron acceptor 3. Cytochrome Complex (aka B6-f complex) Proton pump (active) Moves H+ into thylakoid space, generating proton gradient  Light-Dependent Reactions 4. Plastocyanin (Pc) (Photochemical) Protein e- carrier Carries electrons to PSI 5. Photosystem I (P700) Absorbs light, energizes e Passes e- to ferredoxin 6. Ferredoxin (fd) Electron acceptor Reduces FNR 7. NADP reductase (FNR) Transfers e- to NADP to create ADP  Light-Dependent Reactions (Photochemical) 8. ATP Synthase Protons pass down gradient into stroma Synthesize ATP in a process called photophosphorylation  Noncyclic Photophosphorylation The pathway of an electron from Photosystem II to I and ending at NADPH is referred to as the Z- scheme This is the Linear Pathway and is referred to noncyclic photophosphorylation  Cyclic Photophosphorylation The light independent reaction requires a 3:2 ratio of ATP to NADPH When ATP is insufficient, the electron can get passed back to the b6-f complex to create a greater H+ ion gradient to generate more ATP This is the nonlinear pathway and is referred to as cyclic