1. Chapter 6 Let’s get into this

2. Every bit of energy you have had, have now or will have, comes from the sun. Defend this statement

3. Capturing the Energy in Light Photosynthesis The process by which solar energy is transferred into the chemical bonds of organic compounds Light energy 6H 2 O + 6CO 2 ----------> C 6 H 12 O 6 + 6O 2 chlorophyll Water + Carbon Dioxide ---------------> Glucose + Oxygen radiant energy food photoautotrophs Occurs in all photoautotrophs: Plants, algae and some bacteria

4. 2 biochemical pathways involved in the transfer of energy 1.Photosynthesis (Transfers the energy into the food) Only in the presence of light 2.Cellular Respiration (Releases the energy from food) Occurs all of the time

5. Photosynthesis Cellular Respiration Autotrophs Autotrophs & Heterotrophs

6. Role of Chloroplast - Site of photosynthesis. Structure double layer membrane "Grana" Thylakoid - composed of a double layer membrane (protein, carbohydrate, lipid) - inner membrane folds to form layers called "Grana" (sing., granum) where chlorophyll is concentrated each flattened sac is called a Thylakoid Stroma - surrounding the thylakoids is a fluid called the Stroma

8. Chloroplast

13. What is Light? White light contains all the wavelengths (colors) of the visible spectrum (ROYGBIV). Black light is the absence of all wavelengths Light particles (photons) travel in waves Wavelength is the distance from peak to peak

14. When visible light hits an object, some of the wavelengths are absorbed, reflected or transmitted. –The color of the object shows the wavelength that is reflected back Plants contain basically a green pigment called chlorophyll a or b. Since the pigments are green, the plant reflects back green light and does not absorb it. –Plants do not absorb green or yellow. –Love red and blue wavelengths

16. Chloroplast pigments Chlorophylls - a and b. Chlorophyll a absorbs less blue but > red. Chlorophyll b > blue but less red Neither absorb green & little yellow. Reflect green & yellow. Chlorophyll a is directly involved in the photosynthesis. Chlorophyll b acts as an accessory pigment

19. Accessory pigments – light absorbing pigment that transfer energy to chlorophyll a. Includes the Carotenoids – orange or red Xanthophyll- yellow Phaeophytin – brown Anthocyanins - blue In the fall, the amount of water available to the plant is <, cutting off water to produce pigments. Since chlorophyll is the densest (least soluble in water), plants lose it first leaving the other pigments, especially the carotenoids.

20. Photosystems – clustered groups of chlorophylls and carotenoids. 2 Types: Similar in pigments but different roles –Photosystem I –Photosystem II (Discovered after Photosystem I but is the most primitive and occurs first)

21. The Light Reaction!! Light Dependant Reaction Must occur in the presence of light Light energyLight energy is absorbed in both photosystems at the same time. Energy gets passed from 1 molecule to the next until it reaches a specific chlorophyll a pair. Animation

23. 1.Electrons in chlorophyll a are excited (raised to a higher energy level) in Photosystem II. Think of it like a red hot coal 2.Chlorophyll a’s excited electrons leave molecule (oxidation) & go to a primary electron acceptor (reduction) like a pan or bucket to carry the coals in the thylakoid. 3.Primary e- acceptor donates e- to the Electron Transport Chain (transfers energy from 1 molecule to the next). Energy is lost in each transfer. Lost energy is moved to protons in thylakoid Like dropping something down a set of steps. (Some herbicides interfere with the electron transport chain in PS II) 4.Light excites electrons in chlorophyll a of Photosystem I. Electrons move to a primary electron acceptor & are replaced by electrons from Photosystem II 5.Electrons from Photosystem I are passed through second electron transport chain 6.At end of electron transport chain, electrons combine w/ protons & NADP+ (Nicotinamide adenine dinucleotide phosphate) (Electron acceptor), reducing NADP + to NADPH. (Proton + electron = H) Another carrier molecule for the red hot coals

24. Light Dependant Reaction This one is my favorite! 2H 2 O 4e -, 4H + & O 2

25. If Photosystem I’s e- are replaced by e- from Photosystem II, how are the e- replaced in Photosystem II? 7.Enzymes in the thylakoid splits water into protons, electrons & oxygen. 2H 2 O 4H + + 4e - + O 2 8.Protons remain in the thylakoid while oxygen is released as a byproduct. Light Dependant Reaction

26. Chemiosmosis –Movement of protons into Stroma releases energy to produce ATP 1.Protons were produced from the photolysis of water in step 7 stay in the Thyakoid space 2.Protons (from Calvin Cycle) are pumped from the stroma to inside the thylakoids. Energy for pumping comes from excited electrons from the electron transport chain of photosystem II So the [ ] of protons is greater inside the thylakoid than outside in the stroma 3.Since there is now a higher [ ] of protons inside the thylakoids than outside, the protons move to a lower [ ] in the stroma. ATP synthase, another carrier protein (in the thylakoids) converts potential energy of protons into bonds of ATP. Light Dependant Reaction

27. 1 4 3 NADPH & ATP Go into the Calvin Cycle 2 Photosynthesis song

28. The Calvin Cycle – Carbon fixation (aka – The Dark Reaction) Light Independent Reaction Hydrogen atoms will combine with CO 2 to produce organic compounds »Melvin Calvin – 1911 – 1997 »Nobel Laureate »Identified The Path of Carbon in Photosynthesis). This reaction may occur in the presence or absence of light. It must follow the light reaction

29. The Calvin Cycle Takes place in the Stroma Animation

30. The Steps The Steps – Occurs in the Stroma The Steps 1.CO 2 combines w/ the phosphorylated 5-carbon sugar ribulose bisphosphate (RuBP). 6-carbon compound splits immediately into 2 molecules of 3 Carbon Phosphoglycerate (3-PGA). 2.The 2, 3-PGA molecules are phosphorylated (by ATP) and are reduced (by NADPH) to form… Glyceraldehyde-3- Phosphate (G3P). Phosphoglyceraldehyde (PGAL) or Glyceraldehyde-3- Phosphate (G3P). (ADP+ P and NADP+ result) G3P 3.10 molecules of PGAL (G3P) are converted back to 6 molecules of RuBP with the addition of a P from ATP G3P Some PGAL (G3P) serves as the starting material for the synthesis of glucose & fructose. Glucose & fructose make the disaccharide Sucrose, which travels in solution to other parts of the plant (e.g., fruit, roots). Glucose is the monomer for synthesis of the polysaccharides starch & cellulose.

33. Animation

34. Each turn of the Calvin Cycle fixes 1 CO 2 molecule. To produce 1 G3P, it takes 3 turns of the Cycle. For each turn, Step 2 uses 2ATP and 2 NADPH molecules. Step 3 uses 1 ATP molecule so after 3 turns, 9 ATP molecules are converted to ADP and 6 NADPH are converted to NADP+. Calvin Cycle song Let’s get into this

35. Alternative Pathways C 3 plants - fix CO 2 thru Calvin Cycle StomataNormal plants lose water thru pores on bottom of leaf called a Stomata The opening & closing of stomates regulates water lost, CO 2 entrance & O 2 release. When stomata is closed, CO 2 level drops off and O 2 level increases – No C fixation occurs 95% of plants use this pathway

36. C 4 Pathway These plants partiallyclose their stomates during hottest time of day. Enzymes allow CO 2 fixation to occur to produce 4-C compounds when CO 2 levels are low & O 2 levels are high Corn, Sugar cane & Crabgrass < by ½ the amount of water lost as with C 3 plants but same amt of carbohydrates

37. CAM Pathway Cacti, pineapples & succulents. Very Hot and Dry environments Open stomates at night & closed during day Take in CO 2 at night & fix it into other organic compounds. During day, CO 2 is released from those compounds & enters Calvin cycle Slow growers

39. Limiting Factors: 3 factors that limit the rate of photosynthesis:- Light CO 2 concentration Temperature As light intensity or [CO 2 ] >, the rate> until another factor limits the rate. Only by increasing that factor will the rate increase. As with light & [CO 2 ], rate > with increasing temperature until another factor limits it. The rate will also decline when enzymes denature.

42. 3PGA

44. 2H 2 O 4e -, 4H + & O 2