Photosynthesis Ch. 7 Ms. Haut

1. PhotosynthesisCh. 7Ms. Haut

2. Light energy enzymes Basics of Photosynthesis • All cells need energy to carry out their activities • All energy ultimately comes from the sun • Photosynthesis—process in which some of the solar energy is captured by plants (producers) and transformed into glucose molecules used by other organisms (consumers). 6CO2 + 6H2O C6H12O6 + 6O2

3. Basics of Photosynthesis • Glucose is the main source of energy for all life. The energy is stored in the chemical bonds. • Cellular Respiration—process in which a cell breaks down the glucose so that energy can be released. This energy will enable a cell to carry out its activities. C6H12O6 + 6O2 6CO2 + 6H2O + energy enzymes

4. Basics of Photosynthesis • Autotroph—organisms that synthesize organic molecules from inorganic materials (a.k.a. producers) • Photoautotrophs—use light as an energy source (plants, algae, some prokaryotes) • Heterotroph—organisms that acquire organic molecules from compounds produced by other organisms (a.k.a. consumers) http://www.flatrock.org.nz/topics/animals/assets/conscious_animal.jpg

5. Leaf Anatomy

6. Photosynthesis: redox process • Oxidation-reduction reaction: • Oxidation-loss of electrons from one substance • Reduction-addition of electrons to another substance

7. A Photosynthesis Road Map • Photosynthesis is composed of two processes: • The light reactions convert solar energy to chemical energy. • The Calvin cycle makes sugar from carbon dioxide.

8. Figure 7.4

9. The Nature of Sunlight • Sunlight is a type of energy called radiation • Or electromagnetic energy. • The full range of radiation is called the electro-magnetic spectrum. • Light may be reflected, transmitted, or absorbed when it contacts matter

10. Chloroplasts: Nature’s Solar Panels • Chloroplasts absorb select wavelengths of light that drive photosynthesis. • Thylakoids trap sunlight

11. Photosynthetic Pigments • Pigments-substances that absorb light (light receptors) • Wavelengths that are absorbed disappear • Wavelengths that are transmitted and reflected as the color you see http://image.guim.co.uk/Guardian/environment/gallery/2007/nov/02/1/GD5161248@Autumn-colours-are-se-8810.jpg

12. Plant Pigments • Chlorophyll a – absorbs blue-violet and red light, thus appears green • Accessory pigments • Absorb light of varying wavelengths and transfer the energy to chlorophyll a • Chlorophyll b-yellow-green pigment • Carotenoids-yellow and orange pigments

13. Photosynthesis: 2 stages • Light reactions—convert light energy to chemical bond energy in ATP and NADPH • Occurs in thylakoid membranes in chloroplasts • Calvin Cycle—carbon fixation reactions assimilate CO2 and then reduce it to a carbohydrate • Occurs in the stroma of the chloroplast • Do not require light directly, but requires products of the light reactions

14. Light reactions produce: ATP and NADPH that are used by the Calvin cycle; O2 released Calvin Cycle produces: ADP and NADP+ that are used by the light reactions; glucose produced

15. How Photosystems Harvest Light Energy • Photosystem: assemblies of several hundred chlorophyll a, chlorophyll b, and carotenoid molecules in the thylakoid membrane • form light gathering antennae that absorb photons and pass energy from molecule to molecule • Photosystem I—specialized chlorophyll a molecule, P700 • Photosystem II—specialized chlorophyll a molecule, P680

17. Light Reactions • Light drives the light reactions to synthesize • NADPH and ATP • Includes cooperation of both photosystems, in • which e- pass continuously from water to • NADP+

18. When photosystem II absorbs light an e- is excited in the reaction center chlorophyll (P680) and gets captured by the primary e- acceptor. • This leaves a hole in the P680

19. To fill the hole left in P680, an enzyme extracts e- from water and supplies them to the reaction center • A water molecule is split into 2 H+ ions and an oxygen atom, which immediately combines with another oxygen to form O2

20. Each photoexcited e- passes from primary e- acceptor to photosystem I via an electron transport chain. • e- are transferred to e- carriers in the chain

21. As e- cascade down the e- transport chain, energy is released and harnessed by the thylakoid membrane to produce ATP • This ATP is used to make glucose during Calvin cycle

22. When e- reach the bottom of e- transport chain, it fills the hole in the reaction center P700 of photosystem I. • Pre-existing hole was left by former e- that was excited

23. When photosystem I absorbs light an e- is excited in the reaction center chlorophyll (P700) and gets captured by the primary e- acceptor. • e- are transferred by e- carrier to NADP+ (reduction reaction) forming NADPH • NADPH provides reducing power for making glucose in Calvin cycle

24. Chemiosmosis • Energy released from ETC is used to pump H+ ions (from the split water) from the stroma across the thylakoid membrane to the interior of the thylakoid. • Creates concentration gradient across thylakoid membrane • Process provides energy for chemisomostic production of ATP

25. Light reactions produce: ATP and NADPH that are used by the Calvin cycle; O2 released Calvin Cycle produces: ADP and NADP+ that are used by the light reactions; glucose produced

26. The Calvin Cycle: Making Sugar from Carbon Dioxide • Carbon enters the cycle in the form of CO2 and leaves in the form of sugar (glucose) • The cycle spends ATP as an energy source and consumes NADPH as a reducing agent for adding high energy e- to make sugar • For the net synthesis of this sugar, the cycle must take place 2 times

27. The Calvin Cycle: Carbon Fixation • 3 CO2 molecules bind to 3 molecules of ribulose bisphosphate (RuBP) using enzyme, RuBP carboxylase (rubisco) • Produces 6 molecules of 3-phosphoglycerate (3-PGA)

28. The Calvin Cycle: Reduction • 6 ATP molecules transfer phosphate group to each 3-PGA to make 6 molecules of 1,3-diphosphoglycerate • 6 molecules of NADPH reduce each 1,3-bisphosph. to make 6 molecules of glyceraldehyde 3-phosphate (G3P)

29. The Calvin Cycle: Regeneration of RuBP • One of the G3P exits the cycle to be used by the plant the other 5 molecules are used to regenerate the CO2 acceptor (RuBP): 3 molecules of ATP are used to convert 5 molecules of G3P into RuBP3

30. The Calvin Cycle: Regeneration of RuBP • 3 more CO2 molecules enter the cycle, following the same chemical pathway to release another G3P from the cycle. • 2 G3P molecules can be used to make glucose

31. Calvin Cycle

33. Special Adaptations that Save Water • C3 Plants=plants that only use Calvin Cycle to fix carbon • During dry conditions C3 plants conserve water by closing stomata • Plants then fix O2 to RuBP rather than CO2, since CO2 can’t enter the plant (photorespiration) • This yields no sugar molecules or ATP

34. How Photosynthesis Moderates Global Warming • Photosynthesis has an enormous impact on the atmosphere. • It swaps O2 for CO2. http://www.destination360.com/asia/malaysia/images/s/borneo-rainforest.jpg

35. How Photosynthesis Moderates Global Warming • Greenhouses used to grow plant indoors • Trap sunlight that warms the air inside. • A similar process, the greenhouse effect, • Warms the atmosphere. • Is caused by atmospheric CO2.

36. Global Warming • Greenhouse gases (CO2, CH4, CFC’s) are the most likely cause of global warming, a slow but steady rise in the Earth’s surface temperature. • Destruction of forests may be increasing this effect. • Combustion of fossil fuels

37. Global Warming Consequences • Polar ice caps melting • Rise in sea level and flooding of current coastline • New York, Miami, Los Angeles underwater • Change in types of plants—more adapted to warmer temps. and less water http://i.treehugger.com/images/2007/10/24/melting%20ice-jj-002.jpg

38. References • Unless otherwise noted, pictures are from Essential Biology with Physiology, 2nd edition. Campbell, Reece, and Simon. (2007).