CHAPTER 6 PHOTOSYNTHESIS

1. CHAPTER 6PHOTOSYNTHESIS BIOLOGY LECTURE

2. ENERGY FOR LIFE PROCESS • All organisms require a constant supply of energy • Energy does not recycle; almost all energy is from the sun 3. Organisms capture the energy of light and store it in organic compounds

3. ENERGY FOR LIFE PROCESS • Classifying Organisms By How They Get Their Energy: • Autotrophs – manufacture their own food from inorganic substances and energy • Heterotrophs – cannot manufacture their own organic compounds from inorganic substances

4. AUTOTROPHS MAKE FOOD: Use photosynthesis to convert light energy from the sun into chemical energy They store the chemical energy in organic compounds (carbohydrates) Examples are plants, algae, and cyanobacteria

5. HETEROTROPHS • Take in food • They eat autotrophs or other heterotrophs • A caterpillar (H) feeds on grass (A) • A bird (H) feeds on the caterpillar (H) • Examples are animals, most bacteria, fungi, and protozoa

6. All fuel originates with the Autotrophs

7. Energy Transfer Compounds Photosynthesis – a biochemical pathway that converts solar energy to chemical energy (STORE ENERGY = FOOD) Autotrophs manufacture organic compounds from carbon dioxide and water and oxygen is released 6CO2 + 6H2O + LIGHT = C6H12O6 + 6O2

8. How Do We Get Energy? Cellular Respiration – A biochemical pathway that breaks down chemical energy for use by the cell (RELEASE ENERGY) In both autotrophs and heterotrophs, organic compounds are combined with oxygen to produce ATP, carbon dioxide and water C6H12O6 + 6O2 = 6CO2 + 6H2O + ENERGY (ATP)

10. Energy Transfer Compounds Adenosine Triphosphate – molecule of stored energy Energy stored in bonds between phosphate (A M P ~ P ~ P) AMP, ADP, ATP Nicotinamide Adenine Dinucleotide Phosphate - molecule that transports energy NADP+ to NADPH

11. Do Now • 1. What is the difference between autotrophs and heterotrophs? • 2. What is photosynthesis? • 3. What is cellular respiration? • 4. What are the 2 energy transfer compounds we talked about?

12. LIGHT ABSORPTION IN CHLOROPLASTS Chloroplasts - membrane bound organelles that contain: 1. the pigment chlorophyll 2. enzymes for photosynthesis *Both light and dark reactions take place here

13. Chloroplasts • Inner/outer membrane • Thylakoids: flattened sacs where photosynthesis takes place • Granum (pl. grana): stack of thylakoids • Stroma: liquid solution that surrounds the thylakoids

14. CHLOROPLASTS IN PLANT CELL

15. Light • A. White light composed of visible spectrum • ROY G BIV • B. Light travels in energy waves • C. Wavelength (λ) determines color of light • D. UV → violet → red • Short λ → Long λ • E. Pigment: compound that absorbs light • F. Ex. Green pigment absorbs colors other than green & reflects/transmits green

16. Chloroplast Pigments • There are several different pigments in the thylakoid membranes • Chlorophyll is a pigment that absorbsred and blue light and reflectsgreen light • Chlorophylla is directly involved with the light reaction

17. Chloroplast Pigments • Accessory pigments trap wavelengths of light that can not be absorbed by chlorophyll a (help capture more light) a. Chlorophyll b – also reflects green, but absorbs more blue than red b. Carotenoids – reflect orange, yellow, and brown and absorbs green and blue c. Phycobilins – reflect violet & blue and absorb orange, brown and green

21. Do Now • 1. What important process occurs in chloroplasts? • 2. What are the flattened sacs in chloroplasts called? • 3. What is a pigment and what important pigment is found in the chloroplast?

22. Electron Transport Chain (ETC) • Photosystem: a cluster of pigment molecules found in the thylakoid membrane • 2 Photosystems – each has different roles in photosynthesis • Photosystem I • Photosystem II

23. Electron Transport Chain (ETC) • Light Reaction – Photosystem II 1. Light energy absorbed by pigments and transferred to chlorophyl a . Electron from chlorophyl a gets “excited” & enters a higher energy level 2. Electron leaves chlorophyl a & enters primary e- acceptor 3. Primary e- acceptor transfers e- to series of molecules (electron transport chain) & loses Energy (E used to move p+ into thylakoid)

24. Electron Transport Chain (ETC) • Light Reaction – Photosystem I • 4. Light is absorbed by photosystem I, electrons move from chlorophyll a molecules to another primary electron acceptor. These e- are replaced with those from photosystem II • 5. e- used to make NADPH from NADP+ (NADP+ & H+ NADPH)

25. Water’s role • e- from splitting of H2O replaces lost e- in photosystem II • 2 H2O → 4 H+ + 4 e- + O2 • O2 leaves plant or used for cellular respiration • H+ stays in thylakoid → concentration gradient

26. Electron Transport Chain

27. E. Biochemical pathways – series of biochemical reactions

28. Chemiosmosis - Make ATP • Concentration gradient causes protons (H+) to move from thylakoid (high conc) to stroma (low conc) • ATP synthase uses movement of protons/change in potential energy to make ATP • Converts potential E to chemical E • ATP synthase (multifunctional protein) • Carrier protein – carries protons across thylakoid membrane • Enzyme – catalyzes synthesis of ATP from ADP

30. Calvin cycle • Uses ATP & NADPH from the light reaction as energy to make organic compounds • Carbon from CO2 “fixed” into organic compounds • Each cycle uses 3 ATP & 2 NADPH • Occurs in stroma of chloroplast • Called the Dark Reaction

32. Photosynthesis Balance Sheet • 3 turns of the Calvin Cycle are required to produce each molecule of PGAL • This uses up 9 molecules of ATP and 6 molecules of NADPH • Most of the molecules made in the Calvin Cycle are built up into: • Amino Acids • Lipids • Carbohydrates • Heterotrophs use the energy in these organic compounds for living

33. Photosynthesis Equation 6CO2 + 6H2O + Light Energy = C6H12O6 + 6O2

34. Do Now • 1. What is a photosystem? • 2. What is the electron transport chain? • 3. What is the purpose of the Calvin cycle? • 4. What is the equation for photosynthesis?

35. C3 Plants & Alternative Pathways • Plants that use Calvin cycle are called C3plants because they fix CO2 into a 3C compound PGA • Stomata (pl.) - small pores on the underside of a leaf where water, CO2, and O2 pass through • Plants can partially close stomata to minimize water loss • Plants open stomata during day & close @ night

37. C3 Plants & Alternative Pathways • When stomata close up, CO2 can’t get into the plant and O2 can’t get out of the plant • This inhibits carbon fixation by the Calvin Cycle in the plant • Plants have to find other ways to fix carbon and make food

38. C4 Plants • Partially close stomata during hottest part of day • Certain cells have enzymes that can fix CO2 into 4C compound even when CO2↓, O2↑ • Lose ½ the amount of water as C3 plants but produce the same amount of carbs • Ex. Corn, sugar cane, crab grass

39. CAM Plants • Open stomata @ night & close during day • B/C of this CO2 enters when colder → slower growth, less water loss • Fix CO2 into a variety of diff. C comp. at night, use for Calvin Cycle during day • Cactuses, pineapple, and others with different adaptations to hot climate

40. Rate of Photosynthesis • Effected by the Environment: • Light Intensity – as light increases – rate of photosynthesis increases and then levels off when available electrons are already excited • CO2 – as CO2 levels increase – rate of photosynthesis increases and then levels off • Temperature – raising the temp. speeds up chemical reactions and increases the rate of photosynthesis, but soon the temp gets too high and photosynthesis rate decreases

41. Rate of photosynthesis • 1. Light, CO2: eventually level off @ maximum • 2. Temperature: reach a maximum & decrease • Enzymes begin to become unstable & ineffective • Stomata close & limit water loss & CO2 entry

44. Cellular Respiration Chapter 7

45. Cellular Respiration Overview A. Releases energy from organic molecules (sugars) to make ATP (available cell energy) B. Done by autotrophs and heterotrophs C. Aerobic respiration – organic molecules broken down with oxygen – yields a lot of ATP D. Anaerobic respiration – organic molecules broken down without oxygen – little or no ATP. E. Living organisms could specialize in one, or switch depending on available oxygen.

46. Glycolysis • All organisms begin respiration with glycolysis (to break glucose) = small amount of energy (net 2 ATP produced), but makes energy carrying (electron) molecule NADH and pyruvic acid (organic product) • Anaerobic in nature • Products can either be fermented (recycle NADH) or aerobically broken (lots of ATP) • Takes place in cytoplasm • Reactions in the biochemical pathway:

47. Glycolysis • 2 phos. groups attach to glucose from 2 ATPs to form a new 6 C compound • 6 C comp. splits into 2 PGAL molecules (3 C) • 2 phos. groups attach to PGALs and PGALs oxidized. NAD+ reduced to NADH. • Phos. groups removed and combine with ADPs → ATP. 2 pyruvic acid molecules formed.

48. Do Now • 1. What is cellular respiration? • 2. What is anaerobic respiration? • 3. What is aerobic respiration? • 4. What is glycolysis?

49. Fermentation • Performed in the absence of oxygen • Makes no ATP, occurs in cytoplasm • Regenerates NAD+ which can keep glycolysis going • Types: 1. Lactic Acid 2. Ethyl alcohol

50. Lactic Acid Fermentation • Enzyme converts pyruvic acid into lactic acid • Some bacteria & fungi do this → yogurt, cheese • Animal cells (Muscle cells w/o oxygen)