Chapter 6 Photosynthesis. Capturing Light Energy All energy needed by living things comes directly...
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Transcript of Chapter 6 Photosynthesis. Capturing Light Energy All energy needed by living things comes directly...
Chapter 6
PhotosynthesisPhotosynthesis
Capturing Light Energy• All energy needed by living things comes
directly or indirectly from the Sun
• Energy moves through organisms in a living system
• Autotrophs vs. Heterotrophs
• Energy is released as bonds are broken.
• Some as heat the rest is stored, temporarily, as ATP.
• Energy is stored when bonds are made.
ATP• Energy storing compound
• Nucleotide structure
• As phosphate is removed, energy is released from ATP.
• ATP--> ADP + P---> AMP + P
• As phosphate is added, energy is stored in ATP.
• AMP + P ---> ADP + P ---> ATP
Photosynthesis Intro.• Example of a biochemical pathway
• 6CO2 + 6H20 + Sunlight---> C6H12O6 + 6O2 + Energy
• Reverse reaction is Cellular Respiration (chapter 7)
• Use of sunlight (radiant energy) to make chemical energy (ATP)
• Involves Chloroplasts located in the leaves of plants
• 2 types of reactions take: Light and Dark reactions
Chloroplasts• Light reactions begin with the absorption of
light
• Contain a double membrane like mitochondria
• Thylakoids are individual sacs stacked to form a grana and are surrounded by the stroma
• Thylakoids contain pigments that absorb the different wavelengths of light
• Chlorophyll a and b
• Accessory pigments (carotenoids, xanthophylls)
Physics of Light• White light contains different wavelengths of color
• Visible spectrum (light) is what is seen by the eye
• ROY G BIV
• red region has long wavelengths
• blue region has short wavelengths
Light Reaction• AKA: Light Dependent Reaction
• Photosystems II and I are involved
• Light excites molecules in Photosystem II causing them to move to an electron acceptor which then passes them through an ETC to replace ‘lost’ electrons in photosystem I
• Light also excites molecules in Photosystem I causing them to move to an electron acceptor which then passes them through an ETC to form NADPH
• Hydrolysis of water allows for electrons to replace ‘lost’ electrons in photosystem II. Hydrogen atoms stay inside the thylakoid while Oxygen diffuses out of the chloroplast.
• 2H20---> 4H+ + 4e’ + O2
Chemiosmosis
• Concentration of protons across the thylakoid causes ATP to form
• ATP synthase (protein located in the thylakoid membrane) harnesses energy from concentration gradient causing ADP to add another P to make ATP
• ATP synthase also acts like a carrier protein and an enzyme
http://youtu.be/Oi2_n2wbB9o
Recap of Light Rx
• Light Dependent Reactions absorb light energy in structures called thylakoids, which contain pigments.
• Electrons in photosystems II and I are excited and move via the ETC
• Water is split to replace ‘lost’ electrons for PS2
• NADPH and ATP are made
Calvin Cycle• AKA: Light Independent Reaction or Dark
Reaction
• Products made during the Light Reaction start the Dark Reaction (biochemical pathway)
• Dark Reaction takes place in the stroma
• Carbon Dioxide is used to make organic compounds (carbon fixation) by enzyme controlled reactions
• CO2 joins a 5-carbon sugar called RUBP making a 6-carbon sugar
• 6-carbon sugar splits into 2 3-carbon sugars PGA
• ATP and NADPH from the light reaction are used to convert PGA into PGAL
• PGAL is converted back into RUBP using more ATP and into organic molecules
http://youtu.be/o1I33Dgcc_M
Recap of Dark Rx
• ATP and NADPH from Light Reaction are used in the Dark Reaction
• RUBP combines with a CO2 to make 2 PGA molecules
• ATP then NADPH rearrange PGA into PGAL
• Some PGAL is used to make organic compounds; the rest to remake RUBP so cycle can continue
Alternative Pathway
• C3 plants use Calvin cycle to fix Carbon Dioxide
• C4 plants covert CO2 into a 4-carbon compound before going to calvin cycle (corn, sugar cane, crabgrass)
• CAM plants close stomata during day and open them at night fixing CO2 into organic compounds to use during the day in the calvin cycle (pineapple, cactuses)
Rate of Photosynthesis
• Rate at which a plant carries out photosynthesis is affected by the environment
• Light intensity
• Carbon Dioxide levels
• Temperature