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Chpt . 11: Photosynthesis

Chpt . 11: Photosynthesis. Autotrophic Organisms: are organisms that make their own food – producers. Majority of autotrophs are green plants and they make their food by a process called photosynthesis.

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Chpt . 11: Photosynthesis

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  1. Chpt. 11: Photosynthesis

  2. Autotrophic Organisms: are organisms that make their • own food – producers. • Majority of autotrophs are green plants and they make • their food by a process called photosynthesis.

  3. Photosynthesis: is the process by which plants make food and oxygen using carbon dioxide from the atmosphere, water from the soil and energy from the sun. • Equation for photosynthesis: • 6CO2 + 6H2O + Light C6H12O6 + 6O2 • Carbon Water Glucose Oxygen • Dioxide Chlorophyll

  4. Photosynthesis: • cells need energy to carry out their reactions • light (sun) provides this source of energy. • energy provided by the breakdown of Adenosine • TriPhosphate (ATP). • Light Energy ATP Glucose

  5. Role of Photosynthesis: • plants use photosynthesis to make food. • animals get their food from plants. • photosynthesis produces oxygen (O2)needed for • respiration. • responsible for forming fossil fuels.

  6. Priestly’s experiment. A plant in a closed jar died and a mouse in another closed jar died, but when plant and mouse were put together, both lived. Role of photosynthesis:

  7. Location of Photosynthesis: • Photosynthesis depends on chlorophyll which is located • in structures called chloroplasts. • Chloroplasts concentrated in cells in the upper surfaces • of leaves. • Chloroplasts are also present in the green stems of • some plants.

  8. Factors necessary for photosynthesis: Chlorophyll: - green pigment found in grana of chloroplasts. - made with magnesium. - absorbs light and converts it into glucose. 2. Light: - comes directly from the sun. 3. Carbon Dioxide (CO2): - comes from the atmosphere through the stomata of the leaf. - also comes from plant during respiration.

  9. Factors necessary for photosynthesis: • 4. Water: • comes from the soil. • taken up through the roots and transported via the xylem to the leaves. • 5. Temperature: • - Photosynthesis is controlled by enzymes that work best at 25oC. • at approx. 50oC most enzymes are denatured.

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

  11. 1. CHLOROPHYLL ABSORBS THE LIGHT ENERGY CAUSING ELECTRONS TO LEAVE THE CHLOROPHYLL AND TO PASS THROUGH A SERIES OF ELECTRON CARRIERS 2. WATER MOLECULES SPLIT INTO H+ IONS (PROTONS) AND OH- IONS. THE H+ IONS ACCEPT THE ELECTRONS TO BECOME H ATOMS, THIS PROCESS IS REFERRED TO AS PHOTOLYSIS 3. THE OH- IONS RELEASE THEIR ELECTRONS, WHICH ARE CARRIED BACK TO THE CHOLROPHYLL

  12. 4. THE OH GROUPS COMBINE TO FORM H20 AND 0 ATOMS. THE OXYGEN ATOMS ESCAPE FROM THE LEAF INTO THE ATMOSPHERE AS 02 MOLECULES, OR USED INSIDE THE LEAF FOR RESPIRATION 5. THE HYDROGEN ATOMS ARE COMBINED WITH CO2 TO FORM GLUCOSE Products of photosynthesis: Glucose - food Oxygen – used for respiration

  13. 4. 0 OH (+OH) EC4 EC3 E- sunlight H20 OH- 3. EC5 H2O 2. E- Chlorophyll molecule 1. H+ E- E- E- glucose Electron carrier 1 EC2 5. CO2

  14. CATALYSTS • SUNLIGHT 6CO2 + 6H20 -------------- C6H12O6 + 602 CHLOROPHYLL

  15. What happens to the glucose? • Can be converted to starch and stored for later • use • Moved to another part of the plant to give • energy( respiration) • Changed to lipids or protein • Can be used to make cellulose for new cell • walls for growth

  16. Environmental Factors Environmental factors effecting the rate of photosynthesis are: Light intensity* Temperature CO2 concentration * need to know experiment

  17. Experiment: To investigate the influence of light intensity on the rate of photosynthesis. • Plants can only photosynthesise in the light • At night photosynthesis cannot take place • By using artificial light at night we can increase the hours • of photosynthesis • In winter daylight is often weak , artificial lamps can • supplement the light and increase the rate of • photosynthesis • Example – in green houses

  18. Experiment: To investigate the influence of light intensity on the rate of photosynthesis. • As the light intensity increases the rate of photosynthesis will also increase provided there is no shortage of CO2 and if the temperature is maintained at approx 250C • If you vary the light intensity (by moving the light) the other factors are kept constant because CO2 concentration and temp also effects the rate of photosynthesis Keep CO2 conc constant by adding sodium bicarbonate Keep temp constant by using a water bath

  19. Experiment: To investigate the influence of light intensity on the rate of photosynthesis. Elodea ( Canadian pondweed ) used, the rate of photosynthesis is measured by the number of oxygen bubbles produced per unit time ( must allow time for plant to adjust to each condition)

  20. Experiment: To investigate the influence of light intensity on the rate of photosynthesis.

  21. Experiment: To investigate the influence of light intensity on the rate of photosynthesis. Light saturation pt Sodium bicarbonate runs out No of bubbles light * Note: see experiment pg 107/108

  22. Biochemistry of Photosynthesis (Higher Level) Structure of Chloroplast: LAMELLA INNER MEMBRANE OUTER MEMBRANE DNA

  23. Photosynthesis takes place in 2 stages: • - the LIGHT STAGE( light dependent) occurs in the • GRANA of chloroplast • - the DARK STAGE ( light independent—occurs • whether light is present or not) occurs in STROMA of chloroplast

  24. LIGHT STAGE Events in the Light Stage: A) Light absorption B) Light energy transferred to electrons C) Electron flow – Pathway 1 D) Electron flow – Pathway 2

  25. Light Absorption: Light is absorbed by a range of pigment clusters found in the chloroplast (almost all colours of light are absorbed but green is normally reflected) Each cluster consists of: - a variety of pigments - a chlorophyll molecule *(specially placed) - an electron acceptor Electron acceptor Chlorophyll molecule Pigments Pigment Cluster

  26. B. Light Energy Transferred to Electrons: The pigment cluster absorbs as much light energy as possible and passes it to the reaction centre chlorophyll molecule. This light energy is trapped by the chlorophyll molecule and passed to an electron. This energy causes the electron to become energised. The energised electron is passed to the electron acceptor which can then send it on one of two pathways.

  27. C. Electron Flow – Pathway 1: In pathway 1 the electrons pass from the first electron acceptor to a series of other electron acceptors (electron carriers) and back again to the chlorophyll As the electrons are passed around they lose energy This energy is used to join a phosphate (P) to ADP to form high energy ATP and water (Chpt. 10: energy carriers): ADP + Energy + P ATP + Water The addition of phosphate to ADP in this way is called photophosphorylation Because the electron travels in a cycle and returns to its original chlorophyll this process is called Cyclic Photophosphorylation(e- recycling)

  28. D. Electron Flow – Pathway 2: 2 high energy electrons at a time are passed from chlorophyll to the electron acceptor and then along another series of electron acceptors (electron carriers) 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 Eventually the 2 electrons are passed to combine with NADP+ to form NADP- : NADP+ + 2 electrons (2e-) NADP-

  29. D. Electron Flow – Pathway 2: The chlorophyll molecule is now short of electrons and gains more from the splitting of water. Electrons pass, two at a time, from a water molecule to chlorophyll 2H2O 4H+ + 4e- + O2 The splitting of water using light energy is called Photolysis Light Energy The H+ ions are attracted to NADP- and combine with it to form NADPH which is used in the DARK stage of photosynthesis. 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 (no e- recycling)

  30. Photolysis The splitting of water

  31. End Products of the Light Stage There are 3 end products of the light stage ATP - this will provide energy for the dark stage 2. NADPH - this will provide protons and energised electrons for the dark stage Oxygen is made when water is split – can be used for respiration or be released into the atmosphere * Note: water is also produced to hydrate cytoplasm of cells

  32. Light Stages ATP ADP + P ATP CE 3 CE 2 CE 1 O2 ADP + P 4OH- ions CE 2 ATP Chlorophyll molecule CYCLIC PHOTOPHOSPHORYLATION 2H2O NON-CYCLIC PHOTOPHOSPHORYLATION CE I ADP + P e- 4H+ ions Electron acceptor NADP+ 2e- NADPH (used in dark stage) NADP- excited e- Pathway 2 (non-cyclic) e- start with water and end up with NADPH Pathway 1 (cyclic) e- flow from chlorophyll back to chlorophyll

  33. DARK STAGE (Calvin Cycle) This may also be called the light independent stage as it can occur in the light but does not need to use it It takes place in the stroma of the chloroplast It is controlled by enzymes and therefore can be affected by temperature

  34. Carbon dioxide from the air enters the chloroplast where it combines with protons (H+) and electrons to form glucose. This process requires energy, protons and electrons: - it obtains energy from the breaking down of: ATP (produced in light stage) into ADP + P - it obtains hydrogen ions and electrons from the breaking down of: NADPH (produced in light stage) into NADP+ + 2 electrons + H+ Remember the addition of electrons to anything is known as reduction Carbon Dioxide is reduced to glucose

  35. Remember the addition of electrons to anything is known as reduction, thus, Carbon Dioxide is reduced to glucose The NADP+ , the ADP and P return to the light stage to reform NADPH and ATP for the dark stage

  36. ATP NADP+returns to light stage ADP + P + ENERGY The Dark Stage NADPH From light stage C6H1206 Carbohydrate is formed CO2 from atmosphere

  37. Summary 2 stages The light dependent stage which converts H2O, NADP+, ADP + P into NADPH, ATP and O2 using chlorophyll and sunlight The light independent stage which converts CO2 into glucose using NADPH and ATP. This process generates NADP+, ADP + P which can be reused in the light dependent stage

  38. Differences between the light and dark stage LIGHT STAGEDARK STAGE • Occurs in the grana Occurs in stroma • Light dependent Light independent • ATP produced ATP used up • NADPH produced NADPH used up • O2 is produced CO2 is used up • Chlorophyll molecule Chlorophyll not involved • is involved

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