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Photosynthesis

Photosynthesis. Ms. Napolitano & Mrs. Haas CP Biology. Recall:. Autotrophs – organisms that are able to make their own food (through sun or chemical energy) Heterotrophs – obtain energy from the foods they consume ATP – stores and releases energy

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Photosynthesis

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  1. Photosynthesis Ms. Napolitano & Mrs. Haas CP Biology

  2. Recall: • Autotrophs – organisms that are able to make their own food (through sun or chemical energy) • Heterotrophs – obtain energy from the foods they consume • ATP – stores and releases energy • Bonds broken = energy released (ATP  ADP) • Bonds formed = energy stored (ADP  ATP)

  3. Photosynthesis • Photosynthesis – plants use energy from the sun to convert water & CO2 into carbs • Divided into the Light Dependent Reactions & the Light Independent Reactions • Photosynthesis Equation: Sunlight + 6CO2 + 6H2O  C6H12O6 + 6O2

  4. Photosynthesis:

  5. Anatomy of a Leaf • Stoma (pl. stomata) – allows for CO2 & O2exchange • Mesophyll – layer of leaf where photosynthesis occurs • Vein – supplies H2O from roots (xylem) & delivers glucose to rest of plant (phloem)

  6. Anatomy of a Chloroplast • Thylakoids – photosynthetic discs • Site of light reactions • Photosystems made of pigments • Pigments absorb light • Chlorophyll – main pigment of plants • Grana – stacks of thylakoids • Stroma– space outside thylakoids • Site of dark reactions

  7. Electron (e-) Carriers • High-energy e-need special carriers • Electron transport – a carrier accepts a pair of e- and transfers them (with most of their energy) to another molecule • NADP+ accepts and holds e- with H+, eventually making NADPH • Transfers e- to other parts of the cell

  8. Light Dependent Reactions (LDR) • AKA “Light Reactions” • Occurs in the thylakoid membrane • Chemical Equation: Water + Light  O2 + ATP + NADPH • Divided into 2 parts – Photosystem II and Photosystem I

  9. LDR: Photosystem II • Discovered after photosystem I • Steps: • Chlorophyll & other pigments absorb light • e- become excited (energy level increases) & go to the electron transport chain • 2H2O  4H+ + O2 + 4e- • 4e- replace excited e- from sunlight • O2 gets released into air as byproduct

  10. LDR: Electron Transport Chain • Between photosystems II & I • Excited e- jump through electron transport chain and power proton pumps • Transfer H+ into thylakoid spaces

  11. LDR: Photosystem I • Pigments in photosystem I reenergize e- • e- continue through electron transport chain • NADP+ picks up high-energy e- and 2H+ • Becomes NADPH

  12. LDR: After Photosystem I • H+ are still being pumped into thylakoid spaces • Space = + charge, membrane = - charge • Difference in charges provides energy for ATP • ATP synthase (protein) allows for diffusion of H+ through the membrane • Rotates like a turbine & binds ADP + phosphate to make ATP

  13. Light Dependent Reactions

  14. WHEW!! One part left (& it’s much easier!)

  15. Light Independent Reactions (LIR) • AKA “Dark Reactions” or “The Calvin Cycle” • Light is NOT required • Occurs in stroma of chloroplasts • RECALL: ATP and NADPH were made from the LDR • High-energy sugars made (such as glucose) • Chemical equation: ATP + NADPH + CO2 Glucose

  16. The Calvin Cycle • Steps: • 6CO2 enters the cycle from the atmosphere • Energy is received from ATP and NADPH, making ADP & NADP+ • C from CO2 rearranged into glucose • Other C and more ATP is needed for next cycle

  17. The Calvin Cycle

  18. Let’s Sum It Up...

  19. Let’s Sum It Up...

  20. Factors Affecting Photosynthesis • Water availability • Temperature • Denatures necessary enzymes • Evaporation • Light intensity • Increases rate of photosynthesis(to a point) ...so take care of your plants!

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