Photosynthesis bio 1

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Published on December 30, 2007

Author: Olivia

Source: authorstream.com

Slide1:  Photosynthesis Slide2:  Basic Photosynthesis Photosynthesis – the process by which autotrophs use light energy to turn carbon dioxide and water into glucose and oxygen The basic equation for photosynthesis is as follows: 6CO2 + 6H2O C6H12O6 + 6O2 *** It actually takes 12 water molecules to react, and 6 water molecules are produced, but the net loss is 6 water molecules Photosynthesis takes place in the chloroplast Light energy Slide3:  The Process of Photosynthesis Using the pigments of chlorophyll and the membranous structure of the chloroplasts to their advantage, plants can take carbon dioxide and water, and using sunlight, can produce glucose. The process of photosynthesis consists of two parts: The Light-Dependent Reaction, which takes place in the thylakoid membrane The Light-Independent Reaction (also called Dark Reaction or Calvin Cycle), which takes place in the stroma Slide4:  Steps of the Light-Dependent Reaction Along the thylakoid membrane, there are areas of pigments known as photosystems, and areas of proteins known as electron transport chains Photosystems – their job is to absorb light energy from the sun, causing electrons to be released Electron Transport Chains – their job is to move the electrons released from the photosystem, causing energy to be released slowly and moving hydrogen ions inside the thylakoid Slide5:  Step 1 -- The Job of Sunlight Sunlight contains energy This energy hits the pigments (chlorophyll) of an area in the membrane known as Photosystem II (it was discovered second) Photosystem II releases two electrons that gained too much energy to stay in a molecule of chlorophyll So, what now? -- the electrons move to the electron transport chain -- Photosystem II needs to replace the lost electrons Slide6:  Step 2 -- The Splitting of Water Along the thylakoid membrane, enzymes (and sunlight) split molecules of water. When a water molecule splits, it breaks into 5 parts: 2 electrons (e-) H2O 2 hydrogen ions (H+) 1 oxygen atom (O) The electrons go into Photosystem II to replace the lost electrons The hydrogen ions go inside the thylakoid The oxygen atom goes into the stroma, where it combines with another oxygen atom to form oxygen gas (O2), which is released into our atmosphere Slide7:  Step 3 -- Electron Transport The two original electrons from Photosystem II travel down the electron transport proteins in the thylakoid membrane -- as they travel, each protein gains a slight negative charge -- these proteins are unhappy, so they gain a hydrogen ion to counterbalance the charge -- when the electron moves to the next protein, the protein is now positively charged (unhappy), so it releases the hydrogen ion into the thylakoid Slide8:  Step 4 -- The Electrons Get Their Energy Back After traveling down the electron transport chain, the electrons have lost most of their energy that they gained in Photosystem II Eventually, the electrons reach another collection of pigments known as Photosystem I In Photosystem I, sunlight gives energy back to the electrons that were lost traveling down the electron transport chain Slide9:  Step 5 -- Making NADPH The two electrons are picked up from Photosystem I by a molecule in the stroma called NADP+ -- with two electrons, NADP+ becomes NADP- -- NADP- gains a hydrogen ion to become NADPH NADPH is used in the light-independent reaction of photosynthesis Slide10:  Step 6 -- Making ATP Electron transport has moved a whole bunch of hydrogen ions inside the thylakoid. All of these positive charges are unhappy together inside the thylakoid together, so they move out into the stroma through a protein called ATP synthase As the hydrogen ions move through the protein, the protein attaches phosphate groups to ADP, forming ATP ATP is now in the stroma, and available to be used in the light-independent reaction. Slide11:  Summary of Light-Dependent Reaction The light-dependent reaction: -- Uses water and sunlight -- Creates the products of ATP and NADPH -- Gives off oxygen as a waste product -- Is all about the movement of electrons Slide12:  Summary Chart of Light-Dependent Reactions Slide13:  The Light-Independent Reaction The light-independent reaction is also called the dark reaction or the Calvin Cycle -- named after Melvin Calvin who discovered it The light-independent reaction takes place in the stroma of the chloroplast Uses carbon dioxide from the air Uses ATP and NADPH from the light-dependent reaction This is what produces glucose Slide14:  Steps of the Calvin Cycle 3 molecules of carbon dioxide enter the stroma -- each molecule contains one carbon The 3 carbon dioxide molecules combine with 3 molecules of a 5-carbon molecule called RuBP -- forms three 6-carbon molecules The three 6-carbon molecules split into six 3-carbon molecules The six 3-carbon molecules gain energy from ATP and NADPH One of the high-energy 3-carbon molecules leaves the cycle, leaving five high-energy 3-carbon molecules Slide15:  Calvin Cycle Continued The five remaining 3-carbon molecules use the energy of ATP to turn back into three 5-carbon molecules of RuBP -- the cycle can start again! 7. Every time the cycle turns, one high-energy 3-carbon molecule leave, every two times the cycle turns, these high-energy 3-carbon molecules join together to form glucose Slide16:  Drawing of Calvin Cycle (turns twice) Slide17:  Schematic Drawing of Photosynthesis Light Dependent Reaction Sunlight Water Oxygen gas ATP NADPH Light Independent Reaction Carbon dioxide Glucose

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