1 / 36

Photosynthesis

Photosynthesis. Bio 391 – Ch4 How Exactly is Sunlight captured and converted into Food?. What are autotrophs?. Obtains energy from nonliving sources Two types Photoautotrophs Photosynthesis Sun energy converts CO 2 into sugars

ling
Télécharger la présentation

Photosynthesis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photosynthesis Bio 391 – Ch4 How Exactly is Sunlight captured and converted into Food?

  2. What are autotrophs? • Obtains energy from nonliving sources • Two types • Photoautotrophs • Photosynthesis • Sun energy converts CO2 into sugars • Enzymes convert sugars into amino acids and other needed compounds • Chemoautotrophs • Specialized bacteria • No sunlight – use energy of inorganic substances (Fe, S, etc.)

  3. Electromagnetic Spectrum • Wide range of energy types – travels in waves – energy is defined by their wavelength • λ = wavelength = distance between two adjacent wave crests or wave troughs • Visible Light • Very small section of the electromagnetic spectrum • ROYGBIV

  4. Rainbows are separated white light* white reflects all light* black absorbs all light* color seen is that color reflected

  5. Chloroplasts • Structure • Thylakoids • Highly folded inner membrane • surface area • Holds pigments • Granum • Stack of thylakoid membranes • Stroma • Liquid between thylakoid and outer membrane of chloroplast • Have their own DNA & RNA

  6. Chlorophyll & Accessory Pigments • Pigments = light absorbing molecules • Found on the thylakoid membrane • Chlorophyll • Two types – “a” and “b” • Absorbs violet-blue and orange-red colors • ~ 350-500 nm & 650-700 nm • Reflects green  plants have green color • Accessory Pigments • Absorb other colors of light and transfer Σ to chlorophyll-a • Most noticeable in the fall months • EX: carotenoids

  7. Absorption Spectrums of Pigments

  8. Photosynthesis Simplified • Can be broken down into two steps: • Light Reactions • Pigments in thylakoids absorb light • Light converted into chemical energy • Calvin Cycle (a.k.a. “Dark Reactions”) • Chemical energy from light reactions used to make 3 carbon sugars from CO2 • Used to make more complex sugars or other biochemical molecules • Overall Reaction • 6CO2 + 6H2O C6H12O6 + 6O2

  9. Light Dependent Reactions • Broken into Photosystem II and Photosystem I • Reactants: • light, water • Use: • ADP and Pi to make ATP • NADP+ to make NADPH (similar to NAD+/NADH) • Happens on the thylakoid membrane

  10. Light Dependent Reactions • Photosystem II • Light hits the chlorophyll molecules and excites them – releasing two high energy electrons • Electrons are used to create a H+ gradient across the thylakoid membrane • This gradient drives the formation of ATP (similar process to the ETC in respiration) • Photophosphorylation

  11. Light Dependent Reactions • Photosystem I • Light hits the chlorophyll molecules and excites them – releasing two high energy electrons • Electrons from Photosystem II replace the electrons that leave chlorophyll molecule • Electrons are captured by NADP+ to make NADPH

  12. Light Dependent Reactions • ATP and NADPH are used in the light independent reactions • How are electrons from Photosystem II replaced? • Water is split • O2 – waste product – released by the plant • Electrons – go into chlorophyll to replace lost e’s • H+ - used to make gradient to help make ATP

  13. LIGHT DEPENDENT REACTIONS

  14. Cyclic v. Noncyclic Photophosphorylation • Cyclic – photosystem I only – electrons are recycled (use no NAPDH) • Chemiosmosis – process of using proton movement to join ADP and Pi • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter39/cyclic_and_noncyclic_photophosphorylation.html • Simple vs. Complex Autotrophs • Generates ATP but not NADPH. Why?

  15. Light Independent Reactions • Also called the Calvin Cycle • Reactants: • ATP, NADPH, and CO2 • Use: • ATP to make ADP and Pi • NADPH to make NADP+ • Sugars are created • Happens in the stroma

  16. Calvin Cycle • Keys to understanding…. • It’s all about rearrangement of carbon atoms • CO2 enters cycle by attaching to RuBP • RuBP is a 5-carbon molecule • Similar to Acetyl CoA entering Krebs cycle • Creates 2 PGA • PGA is a 3-carbon molecule • PGA turns into PGAL • PGAL is a PGA molecule that has been energized by the ATP and NADPH

  17. Calvin Cycle Summary • Each turn fixes 1 CO2 to a RuBP • Rubisco • Enzyme that catalyzes CO2 fixation • Activated by light thus Calvin cycle requires some level of light to occur • Can bind O2 if present • 3 turns = 1 PGAL • “C3 plants” – those that fix 3 CO2 into 1 PGAL

  18. Calvin Cycle Summary RuBP unstable 6C sugar (5C) CO2 PGA PGA (3C) (3C) ATP ATP 5 PGAL to regenerate PGAL (3C) NADPH NADPH 1 PGAL released for growth PGAL (3C) 6 PGAL 3x

  19. PGAL

  20. Light Reactionhttp://vcell.ndsu.edu/animations/photosynthesis/movie.htm Calvin-Benson Cycle http://www.youtube.com/watch?v=mHU27qYJNU0

  21. Light- dependent reactions Calvin cycle Energy from sunlight Thylakoid membranes ATP Stroma NADPH High-energy sugars ATP NADPH O2 Chloroplasts Concept Map Section 8-3 Photosynthesis includes takes place in uses use take place in to produce to produce of

  22. Factors Effecting the Rate of Photosynthesis

  23. More light = higher rate Reaches saturation point Enzymes of light reaction going as fast as possible Higher than saturation point  PS declines Chlorophyll accumulates light faster than it can transfer it to ETS Extra energy goes to oxygen producing OH- when reaction w/H2O OH- or H2O2 damages chloroplasts Light Intensity PHOTOINHIBITION

  24. Similar to light intensity Hits a saturation point Does not decline after saturation CO2 Concentration

  25. Optimal temperature range If too high… Proteins denature If too low… Molecular movement is slower High Temps = cause stomata to close Prevents water loss Increases photorespiration C4 and CAM adaptations Temperature A metabolic pathway in plants that consumes oxygen, produces carbon dioxide, generates no ATP, and reduces photosynthesis

  26. O2 Concentration / Photorespiration • REMEMBER  Rubisco binds CO2 and O2 equally as well • Molecular shapes are similar • Halves productivity of PGA • Carbon fixation = 2 PGA • Photorespiration = 1 PGA • Glycolate = toxic to plant • Benefits of photorespiration? • Occurs when stomata close • Dry and hot • Evolutionary of C4 and CAM plants • Still makes some CO2 and thus some sugars

  27. C3 vs C4 vs CAM http://wc.pima.edu/~bfiero/tucsonecology/plants/plants_photosynthesis.htm

  28. Leaf Anatomy – C3 vs. C4 • C3 plants • CO2 pulled through stomata and immediately goes to mesophyll cells to complete photosynthesis • Called C3 because it makes PGA (3-Carbon molecule) • Stomata open during day • Efficient in cool and moist envir. • C4 plants • CO2 pulled through stomata and immediately goes to mesophyll cells then to the bundle sheath cells to complete photosynthesis • Called C4 because it makes a 4-carbon molecule first (using PEP carboxylase • Stomata open during day • Efficient in higher temps and higher light intensity

  29. Reducing Photorespriation:CAM plants • CAM plants • Crassulacean Acid Metabolism • CO2 pulled through stomata and stored as an acid. During the day, stomata close, CO2 is released, then the cell goes through the Calvin cycle • Stomata open during night • Close during the day to prevent water loss • Efficient in extremely hot and dry environments

  30. Photosynthesis Song 1: The Light Reactions Song Photosynthesis Song 2: The Calvin Cycle

More Related