Photosynthesis

1. Photosynthesis

2. Essential knowledge 2.A.1: • All living systems require constant input of free energy • a. Life requires a highly ordered system. • b. Living systems do not violate the second law of thermodynamics, which states that entropy increases over time. • c. Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway. • d. Organisms use free energy to maintain organization, grow and reproduce. • e. Changes in free energy availability can result in changes in population size. • f. Changes in free energy availability can result in disruptions to an ecosystem.

3. Essential knowledge 2.A.2: • Organisms capture and store free energy for use in biological processes. • a. Autotrophs capture free energy from physical sources in the environment • b. Heterotrophs capture free energy present in carbon compounds produced by other organisms. • c. Different energy-capturing processes use different types of electron acceptors. • d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

4. Essential knowledge 2.A.2: • Organisms capture and store free energy for use in biological processes. • e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis. • f. Cellular respiration in eukaryotes involves a series of coordinateenzyme-catalyzed reactions that harvest free energy from simple carbohydrates. • g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes. • h. Free energy becomes available for metabolism by the conversion of ATP→ADP, which is coupled to many steps in metabolic pathways.

5. Essential knowledge 4.C.1: • Variation in molecular units provides cells with a wider range of functions. • a. Variations within molecular classes provide cells and organisms with a wider range of functions. • b. Multiple copies of alleles or genes (gene duplication) may provide new phenotypes.

6. 7.1 Photosynthetic Organisms All life on Earth depends on solar energy. Photosynthetic organisms (algae, plants, and cyanobacteria) transform solar energy into the chemical energy of carbohydrates. Photosynthesis: • A process that captures solar energy • Transforms solar energy into chemical energy • Energy ends up stored in a carbohydrate

7. Plants and other autotrophs are the producers of the biosphere • Plants make organic food molecules from simple raw materials, so are called producers • Photosynthesizers produce food energy. • Feed themselves as well as heterotrophs • Heterotrophs are also known as consumers.

8. Plants are photoautotrophs • They use the energy of sunlight to make organic molecules from water and carbon dioxide

10. Photosynthesis • Occurs in plants, algae, certain other protists, and some prokaryotes

11. Heterotrophs • Obtain their organic material from other organisms

12. Photosynthesis converts light energy to the chemical energy of food

13. Chloroplasts: The Sites of Photosynthesis in Plants • The leaves of plants are the major sites of photosynthesis, but all green parts of plants can photosynthesize

14. Chloroplasts are the organelles in which photosynthesis occurs • Contain thylakoids and grana

15. CHLOROPLASTS • Chloroplasts are concentrated in the mesophyll cells of leaves • Chloroplasts have a double membrane - inner membrane encloses compartment filled with stroma • Chlorophyll molecules are found within the thylakoid membranes

16. Tracking Atoms Through Photosynthesis: Scientific Inquiry • Photosynthesis is summarized as: 6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O The equation for photosynthesis is a simple summary of a very complex process or metabolic pathway

17. Reactants: 12 H2O 6 CO2 6 O2 6 H2O C6H12O6 Products: Figure 10.4 The Splitting of Water • Chloroplasts split water into • Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules

18. Photosynthesis as a Redox Process • Photosynthesis is a redox process • Water is oxidized, carbon dioxide is reduced ------------reduction------------> 6 CO2 + 12 H2O -------> C6H12O6 + 6 H2O + 6 O2 -------------------------------oxidation-------------------------->

19. Redox rxns of photosynthesis involve an uphill climb • Electrons gain energy by being boosted up an energy hill • Light energy captured by chlorophyll molecules in the chloroplasts provides boost for electrons

20. The Two Stages of Photosynthesis: A Preview • Photosynthesis consists of two processes • The light reactions • The Calvin cycle

23. Energy is shuttled between light rxns and Calvin cycle by ATP and NADPH • The conversion of low-energy CO2 to high-energy organic compounds involves carbon fixation

24. The Nature of Sunlight • Light • Is a form of electromagnetic energy, which travels in waves

25. The electromagnetic spectrum • Is the entire range of electromagnetic energy, or radiation

26. visible • The light spectrum • Includes the colors of light we can see • Different colors of light are made up different wavelengths

27. Photosynthetic Pigments: The Light Receptors • Pigments are substances that absorb visible light of certain wavelengths, while reflecting or transmitting other wavelengths

28. Pigments reflect light, which include the colors we see

29. The spectrophotometer • Is a machine that sends light through pigments and measures the fraction of light transmitted at each wavelength

30. An absorption spectrum • Is a graph plotting light absorption versus wavelength

31. The absorption spectra of chloroplast pigments • Provide clues to the relative effectiveness of different wavelengths for driving photosynthesis

32. Chlorophyll is green because it absorbs much of the reds and blues of white light and reflects green light. • Carotenoids are accessory pigments which absorb light in the violet-blue-green range and reflect yellow and orange light.

33. Chlorophyll a • Is the main photosynthetic pigment • Chlorophyll b • Is an accessory pigment

34. Other accessory pigments (carotenoids) • Absorb different wavelengths of light and pass the energy to chlorophyll a

35. Light also behaves as packets of energy called photons • When a pigment moleculeabsorbs a photon, the energyis passed on to an electron in the pigment molecule which is said to become excited • The excited electron is passed to a neighboring molecule, the primary electron acceptor (the start of the electron transport chain) • This redox rxn is the first step of the light rxns

36. Excitation of Chlorophyll by Light • When a pigment absorbs light • It goes from a ground state to an excited state, which is unstable

37. If an isolated solution of chlorophyll is illuminated • It will fluoresce, giving off light and heat

38. A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes • Pigments chlorophyll a & b and the carotenoids are found in clusters of 200-300 pigment molecules known as antenna pigment molecules (light-harvesting complexes) • Only 1 specific chlorophyll a molecule actually donates electrons to the primary electron acceptor, together they form the reaction center

39. A photosystem • Is composed of a reaction center surrounded by a number of light-harvesting complexes

40. The light-harvesting complexes • Consist of pigment molecules bound to particular proteins

41. When a reaction-center chlorophyll molecule absorbs energy • One of its electrons gets bumped up to a primary electron acceptor

42. The thylakoid membrane • Is populated by two types of photosystems, I and II • Photosystem Iabsorbs red light with a wavelength of 700 nm best (p700 reaction center)

43. Plants Convert Solar Energy-2

44. Light Reactions • Key events are 1) absorption of light energy 2) excitation of electrons by that energy 3) production of ATP & NADPHfrom electron transport chain • As electron pass down the ETC, they lose energy • This energy is temporarily stored in ATP or NADPH

45. Electrons are donated to NADP+(ox) to become NADPH (re) • These electrons originally come from chlorophyll a pigment molecule of p700 rxn center of photosystem I • When p700 chlorophyll molecule gives up its electrons, they are replaced with electrons from the ETC

46. Electrons to replace those lost to ETC by p680 chlorophyll come from the splitting of water • Water is split into 2 H+, 1/2 O2 (O), and two electrons (photolysis) • O combines with another O to form O2which is released as a waste product • Electrons replace those lost by p680 chlorophyll

48. Noncyclic Electron Flow • Noncyclic electron flow • Is the primary pathway of energy transformation in the light reactions

49. Produces NADPH, ATP, and oxygen

50. Cyclic Electron Flow • Under certain conditions • Photoexcited electrons take an alternative path