Ch 10 Photosynthesis Plants making their own food

Ch 10 Photosynthesis Plants making their own food 1

Introduction n Photosynthesis is the production of sugars (glucose) from Carbon Dioxide and Water using light energy trapped by chlorophyll. Energy for this reaction comes from the sun. The sun’s energy is converted to chemical energy using molecules of ATP. 2

Role of Photosynthesis 1. 2. 3. 4. 5. Plants use it to make food Animals get their food from plants It produces oxygen which is needed to release energy in respiration It is responsible forming fossil fuels It removes carbon dioxide from the air 3

Photosynthesis requires: carbon dioxide, n water, n light energy, n chlorophyll. u 4

Photosynthesis produces § § glucose waste oxygen 5

How plants make their food Energy from sunlight, with chlorophyll as a catalyst, is used to combine CO 2 and H 2 O to form glucose and release O 2 chlorophyll w at er glucose oxygen Carbon dioxide

Balanced Equation for Photosynthesis 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 carbon dioxide sunlight + water chlorophyll glucose + oxygen 7

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Photosynthesis converts light energy chemical energy 9

Learning Check What is photosynthesis? 2. Why is it important to all life? 3. What do plants require for photosynthesis? 4. What do plants produce in photosynthesis? 5. What kind of energy is light energy changed into in photosynthesis? 1. 10

Stages in Photosynthesis Light is absorbed 2. Light energises electrons 3. Water is split 4. Products are produced (4 protons, 4 electrons and oxygen) 5. Glucose is formed 1. 11

Light is Absorbed The light that reaches a plant is trapped by chlorophyll n Chlorophyll is found in the chloroplasts of plant cells n Therefore photosynthesis occurs in chloroplasts – mainly in the upper half of the leaf in the palisade layer. n 12

Light Energises Electrons n n n Light energy is absorbed by electrons in the chlorophyll The trapped light energy changes them into high energy electrons An energised electron escapes the chlorophyll molecule. 13

Water is Split Some of the trapped light energy is used to split water into oxygen gas (O 2) protons (H+) and electrons (e-) n Summarised as 2 H 2 O 4 H+ and 4 e- and O 2 n 14

What happens to these Products? Some electrons are passed back to the chlorophyll 2. The protons are stored in a proton pool for later use 3. The oxygen may pass out of the leaf into the atmosphere or else may be used for plant respiration 1. 15

Glucose is formed n The trapped light provides the energy along with protons and carbon dioxide to form glucose (C 6 H 12 O 6 ) 16

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Learning Check 1. 2. 3. 4. What are the main stages in photosynthesis? What is water split into? What happens to each of there products? What is the trapped light energy used for? 18

Promoting Crop Growth in Greenhouses Artificial Lighting n Increase light intensity and duration to increase the rate of photosynthesis Increase Carbon Dioxide Concentration: n Increase the rate of photosynthesis = more food produced. 19

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Sources of light for plants Sunlight is the natural source of light for plants but they can use artificial light for photosynthesis n Artificial light is often used in greenhouses to stimulate growth n Increasing light can increase growth up to a certain saturation point where no more light can be absorbed and photosynthesis will level off n 21

Sources of carbon dioxide for plants Plants have 2 sources of carbon dioxide one is external the other is internal n Plants get most of their carbon dioxide from the atmosphere this is external n Plants get carbon dioxide internally from their own cellular respiration n Sometimes artificial sources of carbon dioxide are used to stimulate growth e. g. burning gas in a green house n 22

Sources of water for plants Water is absorbed from the soil by the roots of plants n This water passes up the stem and is used for photosynthesis n 23

Learning Check 1. Where do plants get (a) Light, (b) carbon dioxide and (c) water from? 2. How can humans increase photosynthesis? 3. Why would humans want to do this? 24

Syllabus Can you? n n n n Define the term: photosynthesis. Express photosynthesis as a balanced reaction. State the nature of photosynthesis from the syllabus – what are the main events? State the role & location of chlorophyll. Explain the nature of electron carriage. Identify the sources of light , CO 2 & water for photosynthesis. Explain how human intervention can play a role in photosynthesis. 25

Photosynthesis Extended Study 26

2 stages of Photosynthesis Light Stage Dark Stage 27

Chloroplasts Chlorophyll is found in the internal green membranes of the chloroplast. Chloroplast Structure: n Double outer membrane – inner membrane is smooth, not folded n Green internal membranes n 28

Two stages in Photosynthesis: Light Stage in the green internal membranes / granum 2. Dark Stage in the liquid portion/ stroma of the chloroplast 1. 29

Chloroplast Structure 30

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Light stage Light Stage Phosphorylation Making ATP Photolysis Splitting water 34

The Light Phase 1. 2. Cyclic Electron Transport – Pathway 1. Non-cyclic Electron Transport – Pathway 2 or Non cyclic photophosphorylation. 35

Cyclic Electron Transport – Pathway 1 36

Cyclic Electron Transport 1. 2. 3. Light energy is absorbed by chlorophyll in the green internal membranes of the chloroplast. An ‘excitable’ electron in chlorophyll absorbs light energy. The energised electron escapes the chlorophyll molecule. 37

4. 5. An electron acceptor molecule picks up this energised electron. The electron is passed along an ‘electron carrier system’ where its ‘excess’ energy is released. 38

4. The excess energy is used to produce ATP by the phosphorylation of ADP + P = ATP 39

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n n ADP - adenosine diphosphate is a lowenergy molecule ATP - adenosine triphosphate is an energyrich molecule.

ATP and ADP 42

5. The electron then returns to chlorophyll after all the excess energy has been given off. 43

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ATP – The Unit of Energy 45

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Non-cyclic Electron Transport – Pathway 2 or Non cyclic photophosphorylation. 47

1. 2. 3. 4. Light energy is absorbed by chlorophyll electrons in the green internal membranes of the chloroplast. An electron acceptor picks up these energised electrons and then passes them along a series of electron acceptors In this case the electrons do not return to the original chlorophyll They lose energy as they pass from electron acceptor to electron acceptor and this energy is used to make more ATP 48

5. The electron acceptor passes this electron to NADP+ becoming NADP (neutral) - Nicotinamide adenine dinucleotide phosphate. 49

6. NADP then receives another electron becoming NADP-. NADP + e- = NADP- 7. 8. The chlorophyll molecule is now short of electrons and gains more from the splitting of water The splitting of water using light energy is called Photolysis 51

§ NADP+ - is a low-energy molecule § NADPH - is a high-energy molecule § Both molecules are involved in photosynthesis § NADP+ and NADPH are interconvertible i. e. § NADP+ + energy (high-energy electrons) + H+ → NADPH § NADPH → NADP+ + energy (high-energy electrons) + H+

Photolysis The splitting of water Water H 2 0 Hydrogen ions H+ Used to convert NADP To NADPH Electrons E- Oxygen 02 Go back to chlorophyll By product Excreted through leaf 53

Water breaks up into oxygen, protons (hydrogen ions) and electrons. 10. The oxygen passes out of the chloroplast by diffusion. 11. The protons pass into the general pool of protons in the chloroplast. 12. The electrons pass to chlorophyll as replacement for those lost to NADP-. 13. The electrons from water pass through an electron transport chain resulting in ATP formation. 9. n http: //www. fw. vt. edu/dendro/forestbiology/photosynthesis. swf 54

n ATP is the source of energy used for most cell reactions. n ADP and ATP are interconvertible, i. e. n ADP + energy + P → ATP + water n ATP + water → ADP+ energy + P n Phosphorylation is the addition of phosphate to a molecule.

14. The protons that were stored in the proton pool are attracted to NADP- and combine with it to form NADPH 56

14. n Because the electrons start at a chlorophyll and finish at NADPH and form ATP on their way this pathway is known as Non cyclic photophosphorylation http: //www. compulink. co. uk/~argus/Dreambio/photosynthesis%20 a nimation%20 gif. gif 57

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Phosphorylation 1: 5: Chlorophyll traps sunlight Hydrogen ions join with NADPTo form NADPH 4: Other electrons join with NADP To form NADP- 2: Electrons are energised 3: Electrons lose energy to ADP Which joins with P to form ATP 59

Learning Check 1. 2. 3. 4. 5. 6. Where do the electrons move to from the chlorophyll in pathway 2? What happens to the electrons as they are moved around? What is the final destination of the electrons and what does this form? What is attracted to NADP-? What was the original source of these substances? What is photolysis? 60

End Products of the Light Stage (HL) There are 3 end products of the light stage 1. ATP this will provide energy for the dark stage 2. NADPH this will provide protons + energised electrons for the dark stage 3. Oxygen is made when water is split 61

Learning Check 1. 2. 3. What are the 3 end products of the light stage? Where do each of these products come from? What will happen to each of these products? 62

Photosynthesis – The Light Stage To Dark Stage NADPH H+ NADP- NADP+ Non - Cyclic Electron Transport Electron Acceptor H+ H+ H+ Proton Pool Electron Emitted H+ Electron Emitted Electron’s excess energy released by Electron Transport Chain Chlorophyll Molecule O 2 ADP + P Light Water H 2 O splits Electron Start Here ATP To Dark Stage 63

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The Dark Stage n n n Also called the Light Independent Phase Does not require light. Occurs in light and also in darkness as long as the products of the light phase are still available. The dark stage runs if ATP, NADPH and carbon dioxide are present. Takes place in the liquid portion/ stroma of the chloroplast. Carbohydrate is the crucial product of the dark 65 stage.

Carbon dioxide from the air enters the chloroplast where they combine with electrons + protons to form glucose n NADPH delivers electrons and a proton to CO 2 (NADPH NADP+ + 2 e- + H+) n n n The energy needed for this reaction is supplied by the break up of ATP into ADP +P NADP+, ADP and P pass back to the light stage. 66

n n Remember the addition of electrons to anything is known as reduction Carbon Dioxide is reduced to glucose 67

Dark Stage CO 2 is reduced Oxygen atom is removed Hydrogen ions are added Electrons are added Glucose is formed C 6 H 1206 68

Learning Check 1. 2. 3. 4. 5. 6. Why can the dark stage more accurately be called the light independent stage? What part of the chloroplast does the dark stage take place in? Why is the dark stage affected by temperature? What gas is reduced to glucose? Where does the energy for this come from? What else is needed to reduce the gas? Where do these items come from? 69

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NADP+ n n n NADP+: Nicotinamide adenine Dinucleotide Phosphate Function: to transfer energy for the formation of complex organic compounds. The energy is in the form of energy-rich electrons that came from light activated chlorophyll. NADP+ becomes NADPH in the light stage. NADPH transfers electrons and protons to carbon dioxide reducing it to carbohydrate. NADP+ is regenerated when NADPH passes 71 on the electrons and proton.

Photosynthesis – The Dark Stage CO 2 AT P ADP + P Protons Energy for reaction NADPH H+ NADPElectrons NADP+ C 6 H 12 O 6 72

Affect on Light Intensity on Rate of Photosynthesis 1. 2. 3. 4. 5. Place a funnel over Elodea, pondweed, in a beaker of pond water at 25°C. The funnel is raised off the bottom on pieces of blue-tack. This allows continuous free diffusion of CO 2 to Elodea. Invert a test tube full of water over the stem of the funnel to collect any gas from the Elodea. Place the beaker on a hot plate at 25°C. Maintain and monitor the temperature of the 73 water with a thermometer.

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Affect on Light Intensity on Rate of Photosynthesis 1. 2. 3. 4. 5. Excess sodium bicarbonate is placed in the water to give a constant saturated solution of CO 2. Place the lamp (the only light source) at a predetermined distance from the plant. Use a light meter to measure the light intensity at this distance. Record the light intensity. Allow the plant five minutes to adjust to the new conditions. Count the number of oxygen bubbles given off by the plant in a five-minute period. 75

Affect on Light Intensity on Rate of Photosynthesis Repeat the count twice more and calculate the average of the three readings. 7. This is the rate of photosynthesis at that particular light intensity. 8. The gas should be checked to prove that it is indeed oxygen — it relights a glowing splint. 9. Repeat at different light intensities by moving the lamp to different distances. 10. Graph the results placing light intensity on the x-axis. 76 6.

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Light Released Chlorophyll Electron Deficient Chlorophyll High Energy Electrons Water Protons + electrons + oxygen ADP Proton Pool ATP NADP+ 78 NADPH

Outline of Photosynthesis Light Stage n Light energy used to make ATP. n Light energy used to produce NADPH from NADP-. n Oxygen gas as a by-product. n Half of the water used as a hydrogen source is recycled Dark Stage n Carbon dioxide and hydrogen are used to make carbohydrate. n The energy to drive this process comes from ATP. 79

Syllabus Can you? . . . Explain the role of ATP n Explain the production of ATP from ADP n Explain the role of NADP+ in trapping & transferring electrons & H ions. n Explain the Light Stage/Dark Stage n State the two-pathway system of electron carriage. 1. Direct to chlorophyll 2. Trapped by NADP+ n 80