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 & CO 2 into carbs  Divided into the Light Dependent Reactions & the Light Independent Reactions  Photosynthesis Equation: Sunlight + 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

4. Photosynthesis:

5. Anatomy of a Leaf  Stoma (pl. stomata) – allows for CO 2 & O 2 exchange  Mesophyll – layer of leaf where photosynthesis occurs  Vein – supplies H 2 O 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  O 2 + 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  2H 2 O  4H + + O 2 + 4e -  4e - replace excited e - from sunlight  O 2 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 2 high-energy e - and H +  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 + CO 2  Glucose

16. The Calvin Cycle  Steps :  6CO 2 enters the cycle from the atmosphere  Energy is received from ATP and NADPH, making ADP & NADP +  C from CO 2 rearranged into glucose  Other C and more ATP is needed for next cycle

17. The Calvin Cycle

18. Let’s Sum It Up... Light Dependent ReactionsLight Independent Reactions

19. Let’s Sum It Up... Light Dependent ReactionsLight Independent Reactions Requires: Light & H 2 O Products: O 2 (released into atmosphere), ATP, NADPH Occurs in thylakoid Divided into photosystem II & I Electron Transport Chain between II & I and after I ATP Synthase makes ATP at the end Requires: CO 2 (as well as ATP & NADPH from LDR) Products: sugar (glucose) Occurs in stroma ATP becomes ADP and NADPH becomes NADP +

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!