Photosynthesis

1. Photosynthesis “Life on Earth is solar-powered” - Campbell, Biology

2. Where we begin…. • Autotrophs- a.k.a. producers - organisms which can make their own food • Producers turn light energy into chemical energy using pigments.

3. Chlorophyll - green pigment; the main pigment found in most producers Two types: a and b absorbs red and violet light; reflects greens and yellows located in the chloroplasts of plants and algae Carotenoids - accessory pigments, yellow and orange absorbs other colors of light and transfers the energy to chlorophyll Pigments - substances that absorb visible light

5. Chlorophyll

6. Remember… CHLOROPLASTS? • All green parts of a plant have chloroplasts, but the leaves are the major sites of photosynthesis.

7. History of Chloroplasts • Double membrane bound organelle • Contains the pigment chlorophyll • Has its own DNA and can replicate independently! • Thought to once have been a free-living organism that became a part of a larger cell and eventually the two cells became interdependent.

8. Structure of a Chloroplast • Granum - (pl. grana) whole stack of membranes (pancakes) • Thylakoid - individual membrane of a granum • Stroma – fluid filled space between the grana

9. Review of Chloroplast Structure • Chlorophyll - found in the membranes of the thylakoids; traps light for photosynthesis

10. Anatomy of a leaf • The leaf is the major site of photosynthesis • One leaf has tens of thousands of cells and each cell contains 40 to 50 chloroplasts.

11. Relationship:

12. Electromagnetic Spectrum • Light is measured in wavelengths. Visible light = 400 to 700 nm. • ROY G. BIV • Chlorophyll best absorbs blue & red. It appears green b/c it reflects green light. • Photons - energy of light

13. What does the dip in the graphs between 500 -600 nm tell you?

14. Figure 7.3a

15. Overview

16. What is photosynthesis? • To use the energy from the sun, cells must trap light energy and store it in a form that can be used by cell organelles. • Photosynthesis is the process plants, algae and some bacteria use to trap the sun’s energy & build a carbohydrate, called glucose, that stores energy.

18. General Equation

19. This is a coupled reaction…called a redox reaction. This is also an endergonic reaction.

20. Requirements • Light Energy (Sun) • Chlorophyll a,b and accessory pigments (these absorb wavelengths of light) and accessory pigments • Raw materials (CO2 and H2O ) • Enzyme: NADP+ (Little yellow bus with a P!)

21. Figure 7.4

22. Stages of Photosynthesis • Light Reactions (occurs in thylakoid) • Calvin Cycle or Dark Reaction (occurs in stroma)

23. Light Reactions Overview: 1. Light energy (photons) is absorbed in the THYLAKOID 2. Water is split apart: 2H+ + 1/2O2 + 2e- 3. ATP and NADPH are formed 4. Reactants: chlorophyll a & b, accessory pigments, light energy, water, ADP, Pi and NADP+ • CO2 is NOT involved

25. Details of Light Reactions 1. Light energy is absorbed by chlorophyll a in the reaction center of the 2 photosystems. (The energy can come from the accessory pigments!) 2. Magnesium electrons in chlorophyll become “excited” (high energy) and leave the molecule, moved by a series of electron acceptors 3. The electrons lost by the chlorophyll in P680 are replaced by electrons from water as it is split apart by an enzyme (Z). H2O → H++2e-+1/2O2 4. The electrons “lost” from P680 go down the ETC until they reach P700. On the way down the ETC, the energy is used to pump a H+ across the thylakoid membrane. The electrons replace the electrons “lost” by the chlorophyll a in P700. 5. The electrons lost by P700 join H+ and NADP+ to make NADPH

26. Light Reactions • The ETC has added 3 H+ ions inside the thylakoid space to create the concentration gradient needed for the phosphoralation of ADP to ATP. • 3 H+ will pass through the ATP synthase to allow for the photophosphorylation of ADP to ATP. • To have enough high E molecules (ATP and NADPH), this entire process must occur 12 times producing: 12 NADPH and 12 ATP (and used 12 H2O) • This is still not enough ATP! Photosystem I will generate an additional 6 ATP (using an alternative pathway) for a total of 18 ATP! • Now we have enough energy to make a glucose!

28. ETC in photosynthesis

30. Products of Light Reactions • 6 O2 are released into the air via stomata (simple diffusion!). What molecule were they a part of originally? • 12 NADPH and 18 ATP: go to the stroma for the Calvin Cycle. Question: How did the plant get the water in the first place?

31. Let’s Watch… • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html# • http://instruct1.cit.cornell.edu/Courses/biomi290/MOVIES/OXYGENIC.HTML • http://www.web.virginia.edu/gg_demo/movies/figure18_12b.html

32. Calvin Cycle or Dark Reaction (or Light Independent Reaction) Overview • Reactants: • ATP and NADPH from Light Reactions • 6 CO2 • 6 RuBP • Products: Glucose (C6H12O6) and 6 RuBP (and NADP+ and ADP) • Takes place in the stroma

33. Steps of the Calvin Cycle 1. CO2 Fixation: CO2 combines with RuBP, a 5 carbon compound. 2. The resulting 6C compound is unstable and immediately splits into 2-3C compounds. 3. A series of steps take place which ultimately replenish the RuBP, using 3 ATP and 2 NADPH. 4. The cycle occurs 3 times in order to produce a molecule of PGAL, a 3C compound. It takes 9 ATP and 6 NADPH to make one PGAL (a.k.a. G3P). 5. Two PGAL will be joined outside of the Calvin Cycle to make one glucose molecule. *Ultimately, it takes 18 ATP and 12 NADPH to make one molecule of glucose. To produce one glucose: 6CO2 + 6RuBP + 12 NADPH + 18 ATP  2 PGAL (1 Glucose) Question: What happens to the NADP+ and ADP?

34. Calvin Cycle Con’t. • Formation of glucose: PGAL + PGAL Glucose C3H6O3 + C3H6O3  C6H12O6 Recall: PGAL is a 3- Carbon molecule and is also known as G3P.

35. Calvin Cycle

36. Figure 7.8

37. Importance of Photosynthesis • Forms glucose which is necessary for cellular respiration • Forms the source of oxygen we breathe • The G3P (a.k.a. PGAL) is very versatile and also forms other very important biological molecules.

38. Figure 7.9

39. Factors that Affect Photosynthesis 1. Amount of water 2. Temperatures 3. Light Intensity 4. Amount of CO2

40. Summary of Photosynthesis

42. Can you fill this out?

43. Check your answers… Water Carbon dioxide ADP + P NADP+ NADPH ATP Oxygen Carbohydrate

44. Good website… • http://www.cix.co.uk/~argus/Dreambio/photosynthesis/photosynthsis%20animation.htm

45. Picture it happening... • CO2 is taken in and O2 is released. • H2O is absorbed by the roots • Glucose (sugar ) is made and used or stored by the plant.

46. History with important information... • At first it was believed that the O2 given off by plants was derived from CO2. Later scientists discovered that the O2 comes from the splitting of H2O (known as hydrolysis). • The CO2 is used for the glucose as well as the H from water. The O from water is given off as a by-product. • From what molecule does the O2 you breath originally come?

47. Gas Exchange • Gas exchange, CO2 enters and O2 exits, through specialized structures known as stomata of a leaf. • stoma; plural = stomata; Greek for mouth (hole) • flanked by two guard cells which regulate the opening

48. Photosynthetic Variations Location, location, location… Adaptations to the environment

49. Variations • Based on how carbon is “trapped” and the molecule that is formed when CO2 is incorporated.

50. C3 Plants • C3 plants- ex. roses, oak trees, peas, sunflowers, beans, peanuts • C3 plants must capture their CO2 while the sun shines. They open their stomata to get the CO2 during the day . As a result, the heat and wind may dry them out and they are more likely to die. • Advantageous in moderate weather.