light-dependent reactions (i.e., light reactions)

Transcription

1 LEARNING OBJECTIVES By the end of this lecture you will be able to: 1. Understand that ENERGY can be transformed from one form to another. 2. Know that energy exist in two forms; free energy - available for doing work or as heat - a form unavailable for doing work. 3. Appreciate that the Sun provides most of the energy needed for life on Earth. 4. Explain why photosynthesis is so important to energy and material flow for life on earth. 5. Know why plants tend to be green in appearance. 6. Equate the organelle of photosynthesis in eukaryotes with the chloroplast. 7. Describe the organization of the chloroplast. 8. Understand that photosynthesis is a two fold process composed of the light-dependent reactions (i.e., light reactions) and the light independent reactions (i.e. Calvin Cycle or Dark Reactions). 9. Tell where the light reactions and the CO 2 fixation reactions occur in the chloroplast. 10. Define chlorophylls giving their basic composition and structure. 11. Draw the absorption spectrum of chlorophyll and compare it to the action spectrum of photosynthesis. 12. Define the Reaction Centers and Antennae and describe how it operates. 13. Describe cyclic photophosphorylation of photosynthesis. 14. Describe noncyclic photophosphorylation of photosynthesis.

2 THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

3 THE BASICS OF PHOTOSYNTHESIS Almost all plants are photosynthetic autotrophs, as are some bacteria and protists Autotrophs generate their own organic matter through photosynthesis Sunlight energy is transformed to energy stored in the form of chemical bonds (c) Euglena (d) Cyanobacteria (a) Mosses, ferns, and flowering plants (b) Kelp

4 Light Energy Harvested by Plants & Other Photosynthetic Autotrophs 6 CO H 2 O + light energy C 6 H 12 O O 2

5 Food Chain

6 THE FOOD WEB

7 WHY ARE PLANTS GREEN? It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that Kermit the Frog

8 Electromagnetic Spectrum and Visible Light Gamma rays X-rays UV Infrared & Microwaves Radio waves Visible light Wavelength (nm)

9 WHY ARE PLANTS GREEN? Different wavelengths of visible light are seen by the human eye as different colors. Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light Wavelength (nm)

10 The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. Reflected light Sunlight minus absorbed wavelengths or colors equals the apparent color of an object.

11 Why are plants green? Transmitted light

12 WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

13 THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light Absorbed light Transmitted light Chloroplast

14 AN OVERVIEW OF PHOTOSYNTHESIS Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS

15 AN OVERVIEW OF PHOTOSYNTHESIS The light reactions convert solar energy to chemical energy Produce ATP & NADPH The Calvin cycle makes sugar from carbon dioxide ATP generated by the light reactions provides the energy for sugar synthesis Light Light reactions Chloroplast NADP + ADP + P Calvin cycle The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose

16 Chloroplasts: Sites of Photosynthesis Photosynthesis Occurs in chloroplasts, organelles in certain plants All green plant parts have chloroplasts and carry out photosynthesis The leaves have the most chloroplasts The green color comes from chlorophyll in the chloroplasts The pigments absorb light energy

17 Photosynthesis occurs in chloroplasts In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts A chloroplast contains: stroma, a fluid grana, stacks of thylakoids The thylakoids contain chlorophyll Chlorophyll is the green pigment that captures light for photosynthesis

18 The location and structure of chloroplasts Chloroplast LEAF LEAF CROSS SECTION MESOPHYLL CELL Mesophyll CHLOROPLAST Intermembrane space Outer membrane Granum Inner membrane Grana Stroma Stroma Thylakoid Thylakoid compartment

19 Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a Chlorophyll b Carotenoids Figure 7.7

20 Chlorophyll a & b Chl a has a methyl group Chl b has a carbonyl group Porphyrin ring delocalized e - Phytol tail

21 Different pigments absorb light differently

22 Excitation of chlorophyll in a chloroplast Light Photon e - Excited state Heat Light (fluorescence) v Loss of energy due to heat causes the photons of light to be less energetic. v Less energy translates into longer wavelength. v Energy = (Planck s constant) x (velocity of light)/(wavelength of light) v Transition toward the red end of the visible spectrum. Chlorophyll molecule Ground state (a) Absorption of a photon (b) fluorescence of isolated chlorophyll in solution

23 Cyclic Photophosphorylation Process for ATP generation associated with some Photosynthetic Bacteria Reaction Center => 700 nm

24 Photon Two types of photosystems cooperate in the light reactions ATP mill Photon Water-splitting photosystem NADPH-producing photosystem

25 Noncyclic Photophosphorylation Photosystem II regains electrons by splitting water, leaving O 2 gas as a by-product Primary electron acceptor Primary electron acceptor Photons Energy for synthesis of PHOTOSYSTEM I PHOTOSYSTEM II by chemiosmosis

26 Plants produce O 2 gas by splitting H 2 O The O 2 liberated by photosynthesis is made from the oxygen in water (H + and e - )

27 How the Light Reactions Generate ATP and NADPH Primary electron acceptor NADP + Primary electron acceptor 2 Energy to make 3 Light Light Primary electron acceptor 1 Reactioncenter chlorophyll NADPH-producing photosystem Water-splitting photosystem 2 H / 2

28 In the light reactions, electron transport chains generate ATP, NADPH, & O 2 Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from the primary electron acceptor to electron transport chains Their energy ends up in ATP and NADPH

29 Chemiosmosis powers ATP synthesis in the light reactions The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H + through that membrane The flow of H + back through the membrane is harnessed by ATP synthase to make ATP In the stroma, the H + ions combine with NADP + to form NADPH

30 The production of ATP by chemiosmosis in photosynthesis Thylakoid compartment (high H + ) Light Light Thylakoid membrane Antenna molecules Stroma (low H + ) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

31 A Photosynthesis Road Map Chloroplast Light Stroma Stack of thylakoids Light reactions NADP + ADP + P Calvin cycle Sugar used for Cellular respiration Cellulose Starch Other organic compounds

32 Review: Photosynthesis uses light energy to make food molecules A summary of the chemical processes of photosynthesis Light Photosystem II Electron transport chains Photosystem I Chloroplast CALVIN CYCLE Stroma LIGHT REACTIONS CALVIN CYCLE Cellular respiration Cellulose Starch Other organic compounds

33 Unit 4 Photosynthesis and Cellular Respiration

34 Reading quiz (mitochondrion and chloroplast structure) Draw a LARGE, DETAILED, labeled sketch of a chloroplast Draw a LARGE, DETAILED, labeled sketch of a mitochondrion 1.25 point for having a drawing somewhat similar to below. ½ a point for each term labeled:. Chloroplast: Inner membrane outermembrane thylakoid Mitchondrion: outermembrane innermembrane Add any term not labeled to your diagram

35 Title each of the following pages Photosynthesis overview Plant pigments Reading quiz/light reactions Calvin Cycle Photosynthesis lab Reading quiz/cellular respiration overview Glycolysis and Krebs Cycle Electron Transport Chain and Fermentation Comparing Photosynthesis and Cellular Respiration

36 Photosynthesis overview Process of storing energy in sugar molecules from the energy initially in the sun (radiant energy) 1 st step: Capture radiant energy and use it to generate our energy currency 2nd step: Use energy currency to convert CO 2 to glucose Oxygen is released as a byproduct Happens in the chloroplast

37 Plant pigments Problem: How do plants utilize radiant energy to produce sugars? Properties of light While traveling, acts as a wave (properties depend on this wavelength) When interacting with matter (like your clothes) acts as a particle Photon: Discrete packet of light

38 Plant pigments Pigments are materials that absorb particular wavelengths of light and reflect others Why do your eyes have a color? When chlorophyll absorbs light, energy is transferred to electrons and boosts them to a higher state. Plant pigments

39 Reading quiz Where do the light reactions occur? Where does the Calvin cycle occur? What is the purpose of the light reactions? What is the purpose of the Calvin cycle?

40 Light reactions What you need to know: Location Input Output Purpose -

41 Light reactions Photosystem Role of chlorophyll: Capture energy from light Role of an electron carrier: transport electrons Tracking electrons and energy NADP + + 2e - + H + à NADPH

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44 Using Elodea to demonstrate Photosynthesis 6CO 2 + 6H 2 O light > C 6 H 12 O 6 + 6O 2

45 How can we determine if photosynthesis occurs? Measure How? CO 2 can turn into carbonic acid Bromothymol blue will be blue at ph around 7.6 and yellow-green at ph of 6 Some CO 2 will turn into Carbonic acid (so if enough CO 2 is present in a bromothymol blue solution, it will have a color.) If a initial color of yellow-green turns blue then what can you infer?

46 Calvin Cycle Location- Purpose- Input Output Tracing carbon Factors affecting photosynthesis

47 Reading quiz What organisms does cellular respiration occur in? Write the cellular respiration equation What are the inputs of glycolysis? Does aerobic respiration refer to having oxygen or lacking oxygen?

48 Cellular Respiration Overview (SG 4A, 4B, 4C) Process of forming ATP by breaking down glucose in the presence of oxygen 6O 2 + C 6 H 12 O 6 à 6CO 2 +6H 2 O + energy Why do we breathe (external respiration)? Why do we consume and digest carbohydrates? Does this happen in one step?

49 Glycolysis Series of chemical reactions that break down one molecule of glucose into pyruvate C 6 H 12 O 6 à 2C 3 H 6 O 3 Happens in cytosol of the cell Inputs Glucose 2 NAD+ 2 ADP + 2 P 2 ATP Outputs 2 pyruvate 2 NADH 4 ATP (net 2)

50 Draw this chart (under cell respiration overview) and fill in the following terms glycolysis, ATP, NADH, glucose, pyruvate

51 Photosynthesis lab continued (write analysis on a blank paper) Fill out the following chart 0 60 min. b.b. + light b.b. + elodea (dark) b.b. + elodea + light What color did the elodea + b.b. + light change to? What ph will bromothymol blue be green? When will it be blue? So, the color changed DIRECTLY due to a change in The change in was caused by a change in The change in was caused by a change in The change in was caused by a change in what process How can we get the b.b. in front of you back to green? Use all of this information to write a well coherent allows to support or not support the following hypothesis: Light will increase the rate of photosynthesis. My hypothesis was/was not supported. (restate hypothesis). Discuss color change in all 3 tubes. Discuss what chemical changes caused the color change. Speculate why light increased the rate of photosynthesis.

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53 Citric acid (Kreb) cycle Series of reactions that finishes glucose break down to carbon dioxide in the presence of oxygen (aerobic) Happens in matrix of mitochondria Inputs 2 pyruvate 2 ADP + 2 P 6 NAD + 2 FAD Outputs 4 CO 2 2 ATP 6 NADH 2 FADH 2

54 Cellular Respiration Electron Transport Chain Process that uses high energy electrons from Krebs cycle to convert ADP to ATP Location: cristae of mitochondria 32 total ATP

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56 Fill out the following chart to compare Photosynthesis and Cellular Respiration Photosynthesis Cellular Respiration Function Location Reactants Products Equation

57 Photosynthesis Cellular Respiration comparison Photosynthesis Cellular Respiration Function Energy capture Energy release Location Chloroplasts Mitochondria Reactants CO 2 and H 2 O C 6 H 12 O 6 and O 2 Products C 6 H 12 O 6 and O 2 CO 2 and H 2 O Equation 6CO 2 + 6H 2 O light > C 6 H 12 O 6 + 6O 2 6O 2 + C 6 H 12 O 6 à 6CO 2 +6H 2 O + energy

58 Fermentation (anaerobic respiration) Process that releases some energy from glucose when no oxygen is present Plants, yeast and few microbes Other organisms