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Photosynthesis: Where it all begins!

Photosynthesis: Where it all begins!. AP Biology. Us versus Them. Autotrophs make their own food (self-nourishing) Photoautotrophs use sunlight as the energy source Heterotrophs must feed on autotrophs, one another, or waste. Photosynthesis.

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Photosynthesis: Where it all begins!

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  1. Photosynthesis: Where it all begins! AP Biology

  2. Us versus Them • Autotrophs make their own food (self-nourishing) • Photoautotrophs use sunlight as the energy source • Heterotrophs must feed on autotrophs, one another, or waste

  3. Photosynthesis • Is the main pathway by which carbon and energy enter the web of life. • Where do we find carbon in living things?

  4. An overview 12 H2O + 6 CO2 6O2 + C6H12O6 + 6H2O Sunlight Two divisions: Light dependent reactions, which yields ATP and H+ Light independent reactions, which uses the products of the light dependent reactions to make glucose

  5. An Overview • Takes place in the chloroplasts • Two outer membranes surrounding a mostly fluid interior called the stroma • Another folded membrane is stacked in the stroma. • The stacks of thylakoid discs are grana (granum) Stroma Double membrane Thylakoids

  6. Light Dependent Reactions • Sunlight splits water molecules • Oxygen diffuses away • Its electrons flow through electron transfer chains • This forms ATP • Coenzyme NADP picks up the electrons and hydrogen

  7. Light Dependent Reactions

  8. One Needs the Other

  9. Light Independent Reactions • Occur in the stroma • Does not require light • ATP gives up energy • Coenzyme NADPH gives up electrons and hydrogen • CO2 is dismantled for its C and O atoms • Glucose is made

  10. Not Really Glucose • Glucose is quickly changed to sucrose, cellulose, or starch

  11. Properties of Light • Light travels in waves • The distance between two crests is a wavelength • The shorter the wavelength, the higher the energy • All wavelengths combined appear as white

  12. Photons • The energy of light has a particle-like quality • Energy, when absorbed, can be measured as packets called photons • Each photon has a fixed amount of energy

  13. Pigments • Absorb wavelengths of light • Most absorb only certain wavelengths • Reflect back or transmit the others • Chlorophyll looks green because it does NOT absorb green wavelengths

  14. Accessory Pigments • Carotenoids • Phycobilin • Phycoerythrin • Phycocyanin • Anthocyanins

  15. Light Dependent Reactions A Closer Look Produces ATP and NADPH

  16. Photosystems • In the thylakoid membrane, pigments are organized in clusters called photosystems • Photons of light are absorbed by pigment, and the pigment’s electrons get “excited.”

  17. Excited Electrons • When electrons of an atom absorb energy, they move to a higher energy level • Energy entering a pigment destabilizes the arrangement of electrons. (They jump around)

  18. Excited Electrons • The excited electrons quickly return to a lower energy level, stabilizes, and some energy is released in the form of light or heat. (fluorescence.) • In photosynthesis, this releasing energy gets passed on to another pigment in a random “walk” Some is lost as heat. The remaining energy matches to a wavelength that the photosystem’s reaction center can trap. • The reaction center passes the energy in the form of excited electrons to an electron transport chain

  19. The Photosystems • P700 is photosystem I, and can be cyclic. P700 can cycle alone, or can receive electrons from P680 as part of a non-cyclic pathway. • When it cycles alone, light energy excites electrons, boosting them to a higher energy level, and sending them through an electron transport chain. The end product of the electron transport chain is ATP.

  20. Photosystems • P680 is photosystem II and is non-cyclic. It receives energy from light, boosting electrons to a higher energy level and sending them through an electron transport chain to P700. The electrons it gives up from the pigments are replaced by the splitting of water (constant supply) p114

  21. Photosystems • Both electron transport chains use the energy from the “falling” electrons to pump H ions to the inside of the thylakoid membrane, resulting in a concentration gradient • When H ions move through ATP synthase, the energy is used to attach ADP to P, making ATP, needed for the light indep.

  22. How ATP is made • Hydrogen ions from the splitting of water accumulate in the thylakoid membrane. • Electron transport chains build up even more hydrogen ions in the thylakoid. • Ions are pumped from the stroma into the thylakoid. • Sets up a concentration gradient • When they flow into stroma, they are used to form ATP from ADP and P (ATP synthase enzyme required)

  23. This method of making ATP • Is called the chemiosmotic model for ATP production • Will also happen in the mitochrondria • In which place do you think more ATP will be made?

  24. Light Independent Reactions A Closer Look: takes the ATP and NADPH from light dependent and makes glucose

  25. A Cycle • Called the Calvin-Benson cycle. • ATP drives the reactions • NADPH delivers hydrogen and electrons • CO2 provides the carbon

  26. Photophosphorylation • Is a specific type of Chemiosmosis • Chemiosmotic theory refers to the method of building up H+ concentration gradient to make ATP.

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