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Photosynthesis Light-Dependent Reaction By: Naweed Zamani What is Photosynthesis? • The process of transforming radiant energy of sunlight into the chemical energy of high-energy compounds Equation of Photosynthesis • 6CO2 (g) + 6H2O (l) + Energy C6H12O6 (s) + 6O2 (g) • Main reactions that make up Photosynthesis are – Light-Dependent – Light-Independent Light-Dependent Reaction • The main function of this reaction is to provide a source of ATP and reduced NADP for the dark side reaction • Involves light energy, CO2 and water • Water enters through the roots, travels up to the leaves • CO2 enters through openings in the leaf called Stomata • Both diffuse into the cells of the leaves which then enter the chloroplasts • Light is absorbed by molecules inside the Thylakoids of chloroplasts Plant diagram K, S. (n.d.). Photosynthesis Diagram. Retrieved November 24, 2014, from http://www.buzzle.com/articles/photosynthesisdiagram.html Leaf cross section Leaves and Leaf Anatomy - EnchantedLearning.com. (n.d.). Retrieved November 24, 2014, from http://www.enchantedlearning.com/subjects/plants/leaf/ Chloroplast Shmoop Editorial Team. (2008, November 11). The Light-Dependent and Light-Independent Reactions - Shmoop Biology. Retrieved November 24, 2014, from http://www.shmoop.com/photosynthesis/light-independent-reactions.html Visible Light Spectrum • The visible spectrum is the portion of the electromagnetic spectrum can be seen by human eye. • The colours are Red, Orange, Yellow, Green, Blue, Indigo and Violet • Each wavelength (color) of visible light varies in energy – Long wavelength = small amount of energy – Short wavelength = large amount of energy Electromagnetic Spectrum Shmoop Editorial Team. (2008, November 11). Inputs and Architecture of Photosynthesis - Shmoop Biology. Retrieved November 24, 2014, from http://www.shmoop.com/photosynthesis/inputs-architecture.html Absorption of Light • Within thylakoid membrane are pigments which absorb wavelengths of visible light • Chlorophyll is the main type of photosynthetic pigments in plants and it is green, it does not absorb green wavelengths of light thus it will reflect it • A reason why leaves appear to be green is due to the dominance of the green chlorophyll pigment which reflects green light • Chlorophyll a is the main pigment, chlorophyll b and carotenoids are accessory pigments. accessory pigments help broaden the absorption spectrum Photosystems • There are two Photosystems – Photosystem II 680 – Photosystem I P700 • Made up of clusters of chlorophyll, accessory pigments embedded in the thylakoid membrane • Protein based complexes • Photons are absorbed when shown onto leaf and then passed on through antenna complexes until it reaches the reaction centre • This causes the electrons of the reaction centre to become excited then leave the centre and attach itself to the electron carrier Photosystem Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-andtransport-of-solutes.html Noncyclic Photophosphorylation Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-andtransport-of-solutes.html Noncyclic Photophosphorylation • Step 1: Light is absorbed in Photosystem II then transferred to the reaction center, electron becomes excited then attaches to electron acceptor • Reaction center grabs a pair of electrons from water to stabilize • Oxygen is produced when two water molecules lose their pairs of electrons • Process keeps on repeating each time an electron becomes excited and leaves the reaction center Noncyclic Photophosphorylation • Step 2: electron acceptor passes the electrons through a electron transport chain, energy is released as passed along • Protein complex B6-F uses this energy to pump hydrogen ions from stroma into the thylakoid space creating a proton gradient to aid in ATP creation Noncyclic Photophosphorylation • Step 3: light energy is also shown into photosystem II and undergoes the same process of photosystem I. • The electron of the P700 reaction center is energized then attaches itself to an electron acceptor • The P700 molecule’s lost electrons are then replaced by the electron from the P680 molecule which was passed on through the electron transport chain until it reached photosystem II, thus becoming stable again • An electron carrier carries the electrons to NADP reductase • NADP is then reduced into NADPH and then used for the Light-Independent reaction Making ATP by Chemiosmosis • The proton gradient in the Thylakoid space is created by positively charged hydrogen ions pumped by the B6-F complex • Hydrogen ions cannot diffuse out of the space due to it being to large to diffuse through membrane • Hydrogen ions travel through ATP synthase, its energy is used to synthesis ADP-> ATP Chemiosmosis Photosynthesis. (n.d.). Retrieved November 24, 2014, from http://kensieandhuntersproject.blogspot.co.uk/2013/05/describe-processof-chemiosmosis-in.html Cyclic Phosphorylation Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-andtransport-of-solutes.html Noncyclic Photophosphorylation Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-andtransport-of-solutes.html Cyclic and Noncyclic Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-andtransport-of-solutes.html References Leaves and Leaf Anatomy - EnchantedLearning.com. (n.d.). Retrieved November 24, 2014, from http://www.enchantedlearning.com/subjects/plants/leaf/ K, S. (n.d.). Photosynthesis Diagram. Retrieved November 24, 2014, from http://www.buzzle.com/articles/photosynthesis-diagram.html Photosynthesis and transport of solutes. (n.d.). Retrieved November 24, 2014, from http://biology4isc.weebly.com/3-photosynthesis-and-transport-of-solutes.html Photosynthesis. (n.d.). Retrieved November 24, 2014, from http://kensieandhuntersproject.blogspot.co.uk/2013/05/describe-process-of-chemiosmosis-in.html Shmoop Editorial Team. (2008, November 11). Inputs and Architecture of Photosynthesis - Shmoop Biology. Retrieved November 24, 2014, from http://www.shmoop.com/photosynthesis/inputsarchitecture.html Shmoop Editorial Team. (2008, November 11). The Light-Dependent and Light-Independent Reactions Shmoop Biology. Retrieved November 24, 2014, from http://www.shmoop.com/photosynthesis/lightindependent-reactions.html
