Photosynthesis Energy & Life 1

Overview of Photosynthesis 2

Autotrophs Plants and some other types of organisms that contain chlorophyll are able to use light energy from the sun to produce food. 3

Autotrophs  Autotrophs include organisms that make their own food  Autotrophs can use the sun’s energy directly 4 Euglena

Heterotrophs  Heterotrophs are organisms that can NOT make their own food  Heterotrophs can NOT directly use the sun’s energy 5

Energy  Energy Takes Many Forms such as light, heat, electrical, chemical, mechanical  Energy can be changed from one form to another  Energy can be stored in chemical bonds & then released later 6

ATP – Cellular Energy  Adenosine Triphosphate  Contains two, high-energy phosphate bonds  Also contains the nitrogen base adenine & a ribose sugar 7

ADP Adenosine Diphosphate Adenosine Diphosphate ATP releases energy, a free phosphate, & forms ADP ATP releases energy, a free phosphate, & forms ADP 8 One phosphate bond has been removed

Sugar in ADP & ATP  Called ribose  Pentose sugar  Also found on RNA 9

Importance of ATP Principal Compound Used To Store Energy In Living Organisms 10

Releasing Energy From ATP  ATP is constantly being used and remade by cells  ATP provides all of the energy for cell activities  The high energy phosphate bonds can be BROKEN to release energy  The process of releasing ATP’s energy & reforming the molecule is called phosphorylation 11

Releasing Energy From ATP  Adding A Phosphate Group To ADP stores Energy in ATP  Removing A Phosphate Group From ATP Releases Energy & forms ADP 12 Loose Gain

Cells Using Biochemical Energy Cells Use ATP For:  Active transport  Movement  Photosynthesis  Protein Synthesis  Cellular respiration  All other cellular reactions 13

More on ATP  Cells Have Enough ATP To Last For A Few Seconds  ATP must constantly be made  ATP Transfers Energy Very Well  ATP Is NOT Good At Energy Storage 14

Glucose  Glucose is a monosaccharide  C 6 H 12 O 6  One Molecule of glucose Stores 90 Times More Chemical Energy Than One Molecule of ATP 15

History of Photosynthesis & Plant Pigments 16

Photosynthesis  Involves the Use Of light Energy to convert Water (H 2 0) and Carbon Dioxide (CO 2 ) into Oxygen (O 2 ) and High Energy Carbohydrates (sugars, e.g. Glucose) & Starches 17

Investigating Photosynthesis Many Scientists Have Contributed To Understanding Photosynthesis Many Scientists Have Contributed To Understanding Photosynthesis Early Research Focused On The Overall Process Early Research Focused On The Overall Process Later Researchers Investigated The Detailed Chemical Pathways Later Researchers Investigated The Detailed Chemical Pathways 18

Early Questions on Plants Several Centuries Ago, The Question Was: Does the increase in mass of a plant come from the air? The soil? The Water? 19

Van Helmont’s Experiment 1643  Planted a seed into A pre-measured amount of soil and watered for 5 years  Weighed Plant & Soil. Plant Was 75 kg, Soil The Same.  Concluded Mass Came From Water 20

Priestley’s Experiment 1771  Burned Candle In Bell Jar Until It Went Out.  Placed Sprig Of Mint In Bell Jar For A Few Days.  Candle Could Be Relit And Burn.  Concluded Plants Released Substance (O 2 ) Necessary For burning. 21

Ingenhousz’s Experiment Repeated Priestly experiment with & without sunlight

Results of Ingenhousz’s Experiment  Showed That Priestley’s Results Only Occurred In The Presence Of Sunlight.  Light Was Necessary For Plants To Produce The “Burning Gas” or oxygen 23

Julius Robert Mayer 1845 Proposed That Plants can Convert Light Energy Into Chemical Energy 24

Samuel Ruben & Martin Kamen 1941 Used Isotopes To Determine That The Oxygen Liberated In Photosynthesis Comes From Water 25 KAMEN RUBIN

Melvin Calvin 1948  First to trace the path that carbon (CO 2 ) takes in forming Glucose  Does NOT require sunlight  Called the Calvin Cycle or Light Independent Reaction  Also known as the Dark Reaction 26

Rudolph Marcus 1992  Studied the Light Independent Reactions  First to describe the Electron transport Chain 27

The Photosynthesis Equation 28

Pigments In addition to water, carbon dioxide, and light energy, photosynthesis requires Pigments Chlorophyll is the primary light-absorbing pigment in autotrophs Chlorophyll is found inside chloroplasts 29

Light and Pigments  Energy From The Sun Enters Earth’s Biosphere As Photons  Photon = Light Energy Unit  Light Contains A variety of Wavelengths  Different Wavelengths Have Different Colors 30

Light & Pigments  Different pigments absorb different wavelengths of light  Photons of light “excite” electrons in the plant’s pigments  Excited electrons carry the absorbed energy  Excited electrons move to HIGHER energy levels 31

Chlorophyll There are 2 main types of chlorophyll molecules: Chlorophyll a Chlorophyll b A third type, chlorophyll c, is found in dinoflagellates 32 Magnesium atom at the center of chlorophyll

Chlorophyll a and b 33

Chlorophyll a  Found in all plants, algae, & cyanobacteria  Makes photosynthesis possible  Participates directly in the Light Reactions  Can accept energy from chlorophyll b 34

Chlorophyll b  Chlorophyll b is an accessory pigment  Chlorophyll b acts indirectly in photosynthesis by transferring the light it absorbs to chlorophyll a  Like chlorophyll a, it absorbs red & blue light and REFLECTS GREEN 35

The Biochemical Reactions 36

It Begins with Sunlight! 37

Photoautotrophs Absorb Light Energy 38

Inside A Chloroplast 39

Structure of the Chloroplast  Double membrane organelle  Outer membrane smooth  Inner membrane forms stacks of connected sacs called thylakoids  Thylakoid stack is called the granun (grana-plural)  Gel-like material around grana called stroma 40

Function of the Stroma  Light Independent reactions occur here  Location of the Calvin Cycle 41

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Thylakoid membranes  Light Dependent reactions occur here  Photosystems are made up of clusters of chlorophyll molecules  Photosystems are embedded in the thylakoid membranes  The two photosystems are: Photosytem I Photosytem I Photosystem II Photosystem II 43

Photosynthesis Overview 44

Energy Carriers  Nicotinamide Adenine Dinucleotide Phosphate (NADP + )  NADP + = Reduced Form  Picks Up 2 high-energy electrons and H + from the Light Reaction to form NADPH  NADPH carries energy to be passed on to another molecule 45

NADPH 46

Light Dependent Reactions  Occurs across the thylakoid membranes  Uses light energy  Produce Oxygen from water  Convert ADP to ATP  Also convert NADP + into the energy carrier NADPH 47

Light Dependent Reaction 48

Light Dependent Reaction 49

Photosystem I Discovered First Discovered First Active in the final stage of the Light Dependent Reaction Active in the final stage of the Light Dependent Reaction Made of 300 molecules of Chlorophyll Made of 300 molecules of Chlorophyll Almost completely chlorophyll a Almost completely chlorophyll a 50

Photosystem II Discovered Second Discovered Second Active in the beginning stage Of the Light Dependent Reaction Active in the beginning stage Of the Light Dependent Reaction Contains about equal amounts of chlorophyll a and chlorophyll b Contains about equal amounts of chlorophyll a and chlorophyll b 51

Photosynthesis Begins 52 Photosystem II absorbs light energy Electrons are energized and passed to the Electron Transport Chain Lost electrons are replaced from the splitting of water into 2H +, free electrons, and Oxygen 2H + pumped across thylakoid membrane

Photosystem I High-energy electrons are moved to Photosystem I through the Electron Transport Chain Energy is used to transport H + from stroma to inner thylakoid membrane NADP+ converted to NADPH when it picks up 2 electrons & H+ 53

Phosphorylation Enzyme in thylakoid membrane called ATP Synthase As H+ ions passed through thylakoid membrane, enzyme binds them to ADP Forms ATP 54

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Light Reaction Summary Reactants: H2OH2OH2OH2O  Light Energy Energy* Products:  ATP  NADPH  *Oxygen also product but not an energy product 56

Light Independent Reaction  ATP & NADPH from light reactions used as energy  Atmospheric C0 2 is used to make sugars like glucose and fructose  Six-carbon Sugars made during the Calvin Cycle  Occurs in the stroma 57

The Calvin Cycle 58

The Calvin Cycle  Two turns of the Calvin Cycle are required to make one molecule of glucose  3-CO 2 molecules enter the cycle to form several intermediate compounds (PGA)  A 3-carbon molecule called Ribulose Biphosphate (RuBP) is used to regenerate the Calvin cycle 59

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Factors Affecting the Rate of Photosynthesis  Amount of available water  Temperature  Amount of available light energy 61