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  1. 1. What do you conclude? 90.72kg 90.20kg soil soilIn the 17th Century, A Belgian physician, van Helmont, set up anexperiment in which he planted a willow sapling in a weighedamount of soil.The soil was watered but nothing else was added. After 5years, the tree had gained 74kg in weight but the soil had lostonly 52g. The soil is not providing the plant with materials for growth.
  2. 2. Photosynthesis is the build up of sugars from carbon dioxide and water by green plants using energy from sunlight by means of chlorophyll
  3. 3. Balanced Equation: sunlight6CO2 6H 2O chlorophyll C6 H12O6 6O2 Word Equation: sunlightcarbon dioxide + water chlorophyll glucose + oxygen
  4. 4. Explain the results of each experiment.Candle burning in an A mouse dies when A mouse lives if aairtight jar went out. kept in an airtight jar. plant is placed inside an airtight jar.
  5. 5. Site of Photosynthesis: any green part of the plant, but mostly the leaves
  6. 6.  the whole process of photosynthesis takes place inside chloroplasts
  7. 7. Name the pigment inside chloroplastsFunction of chlorophyll is to……………............
  8. 8. Name two gases that diffuse out of the leaf during the day stoma1. Water vapour2. O2
  9. 9. Adaptations of leaves for photosynthesis1) Broad, flat shape:  a large surface area to absorb light & CO2.2) Thin leaves:  diffusion of gases is fast.3) Large air spaces:  quick diffusion of gases.
  10. 10. 4) Numerous stomata:  allow exchange of gases.5) Many chloroplasts in palisade cells:  to absorb light.6) The branching veins:  provide a good supply of water to the photosynthesising cells.
  11. 11. Question: SEP, 2011In a long-term investigation onphotosynthesis, plant scientists observed thatplants growing in reduced atmospheric carbondioxide (amount of carbon dioxide is less than thatfound in air) responded by developing greaternumber of stomata per unit leaf area.List TWO features of the leaf that affect the rate ofphotosynthesis. (2) 1. Surface area 2. Number of stomata per unit area 3. Amount of chloroplasts
  12. 12. Explain why plants growing in conditions ofreduced carbon dioxide levels have anincreased number of stomata per unit area. (4)Stomata open to allow CO2 to enter the leaf forphotosynthesis.An increase in the number of stomata meansthat more CO2 enters. This makes up for thereduced CO2.
  13. 13. Experiments to study: sunlight6CO2 6H 2O chlorophyll C6 H12O6 6O21. Is chlorophyll is necessary for photosynthesis?2. Is light necessary for photosynthesis?3. Is CO2 necessary for photosynthesis?4. Is O2 produced during photosynthesis?
  14. 14. Leaves used in these experiments MUST NOT contain starch at the start. Why? 1. Is chlorophyll is necessary for photosynthesis? 2. Is light necessary for photosynthesis? 3. Is CO2 necessary for photosynthesis? So that one can tell whether it has formed during the experiment.
  15. 15. These 3 experiments : 1. Is chlorophyll is necessary for photosynthesis? 2. Is light necessary for photosynthesis? 3. Is CO2 necessary for photosynthesis?…………involve: 1. Destarching the plant 2. Testing a leaf for starch
  16. 16. What is a ‘destarched’ plant? A plant without starch Starch in cells. No starch in cells.
  17. 17. How is a plant destarched? by leaving it in the dark for 2-3 days What happens to the starch in the dark?
  18. 18. How can you tell whetherphotosynthesis has occurred or not?By testing for starch using iodine solution. No starch Has starch
  19. 19. Can you test a leaf for starch bypouring iodine solution onto a leaf? NO. Iodine solution runs off the leaf surface due to the waxy cuticle.
  20. 20. 4 steps in testing a leaf for starch Boil leaf1 Dip leaf in boiling water for 30 seconds. 2 in alcohol. Spread leaf on a white tile Dip leaf in boiling 4 and place iodine solution3 water. on the leaf.
  21. 21. Boiling in alcohol removes chlorophyll Precaution: Switch off bunsen burner.
  22. 22. Why is a white tile used?Colour changes are seen better on a white background.
  23. 23. 1. Plant with variegated leaves is destarched.2. Left in sunlight for 2-3 hours.3. Outline of leaf is drawn.4. Leaf is tested for starch using those 4 steps explained previously.CONTROL
  24. 24. Result & Conclusion Yellow: no starch Blue black: has starchChlorophyll is needed for photosynthesis.
  25. 25. 1. Plant is destarched.2. A black paper is placed on one of the leaves.3. Plant is left in sunlight for 2-3 hours.4. Leaf is tested for starch using those 4 steps explained previously. CONTROL
  26. 26. Result & Conclusion Blue black: has starch Yellow: no starchLight is needed for photosynthesis.
  27. 27. 1. Two plants are destarched.2. The plants are watered and set up as shown.3. Plants are left in sunlight for 2-3 hours.4. A leaf from each plant is tested for starch. CONTROL
  28. 28. What is the function of: Soda lime Sodium hydrogen[sodium hydroxide] carbonate Absorbs CO2 Releases CO2 - CO2 + CO2
  29. 29. Result & Conclusion - CO2 + CO2 Yellow: Blue black:no starch has starch CO2 is needed for photosynthesis.
  30. 30. Canadian pondweed (Elodeacanadensis)
  31. 31. 1. The funnel is raised to allow water to circulate.2. A control is set up and placed in the dark.3. When enough gas is collected, the test tube is removed and a glowing splint inserted to test for oxygen.
  32. 32. Test for O2: Relights a glowing splint
  33. 33. Result Glowing splint relighted. ConclusionGas collected was rich in O2.
  34. 34. Count number of bubbles released in 1 minute
  35. 35. What does the graph show?
  36. 36. When do plants respire? All the time.
  37. 37. Gaseous exchange in plantsDARKNESS DIM LIGHT BRIGHT LIGHT O2RespirationCO2
  38. 38. Ann has many plants in her room. Explain why she wakes up feeling dizzy.Plants use up O2 atnight.Not enough O2 forAnn.
  39. 39. Gaseous exchange in plantsDARKNESS DIM LIGHT BRIGHT LIGHT O2 O2 PhotosynthesisRespirationCO2 Respiration CO2
  40. 40. Gaseous exchange in plantsDARKNESS DIM LIGHT BRIGHT LIGHT O2 O2 Photosynthesis PhotosynthesisRespiration CO2 O2CO2 Respiration Respiration Rates are equal. CO2
  41. 41. Compensation pointRate of photosynthesis = Rate of respiration sunlight 6CO2 6H 2O chlorophyll C6 H12O6 6O2 C6 H12O6 6O2 6CO2 6 H 2O energy
  42. 42. When is compensation point reached in nature? Dawn / dusk
  43. 43. Finding the compensation point
  44. 44. According to formula, what is needed for photosynthesis? sunlight6CO2 6H 2O chlorophyll C6 H12O6 6O2 + Temperature A limiting factor is the factor in shortest supply.
  45. 45. The limiting factors are: Light Temp. CO2 PHOTOSYNTHESIS Chlorophyll H2O
  46. 46. Effect of light intensity on the rate ofphotosynthesis - temperature & CO2 were kept constant
  47. 47. Question: SEP, 2010Give a biological explanation for each of thefollowing statements.It is possible to grow plants in a closed glass bottlebut a goldfish bowl must be open to air for thegoldfish to survive. (4) Oxygen from air diffuses into water. Plants release O2 during Fish thus can respire. the day which is used for respiration all the time. Respiration releases CO2 which is used for photosynthesis by day.
  48. 48. What is the limiting factor between A-B?CO2
  49. 49. Why is the rate higher at 25 C? Enzymes work faster. Rate ofphotosynthesis 25 C 10 C CO2 concentration
  50. 50. The glucose formed: is rapidly changed into STARCH to be stored for a short period in the leaf SUCROSE carried in phloem both up & down
  51. 51. other sugars fruits energye.g. seed germination protein GLUCOSE starch cytoplasm cellulose cell wallsstorage e.g. starch in potato
  52. 52. Glucose (C6H12O6) is used to formproteins, but three other elements are needed. Name the elements.  nitrogen  sulfur  phosphorus
  53. 53. Mineral ions are absorbed from the soil in the form of salts e.g. a plant absorbs potassium nitrate (KNO3) to use potassium and nitrogen
  54. 54. Sources of mineral ions1. Rock erosion 1. Fertilisers
  55. 55. Salts are lost from the soil:1. absorption by plants 2. leaching
  56. 56. Element & Use in plant Effect ofSource deficiencyNitrogen: To form proteins Lack of growthnitrates +ammoniaSulfur: To form certain Yellowing ofsulfates amino acids & so young leaves proteins
  57. 57. Element & Use in plant Effect ofSource deficiencyMagnesium: Forms the centre of Yellowing ofas salt in chlorophyll older leavesfertiliser moleculesIron: fertiliser Essential for Yellowing ofsalt chlorophyll young leaves formation
  58. 58. Question: MAY, 2011Give a biological explanation for each of thefollowing statements.The process of photosynthesis is vital for allliving things. (6)
  59. 59. Photosynthesis is important not only to green plants butto all living organisms. It is the basic reaction that bringsthe energy of the sun into ecosystems. 1 markThe flow of energy in ecosystems is one way so there is aconstant need for replenishment from the energy sourceand therefore a constant need for photosynthesis. 2 marksPhotosynthesis is important for the formation ofbiomass – this acts as a food reservoir for herbivores. 1markPhotosynthesis is also essential for maintaining aconstant level of oxygen and carbon dioxide. The oxygengiven off is available for respiration while the carbondioxide is used for photosynthesis. This prevents thelevel of carbon dioxide from rising. 2 marks
  60. 60. Question: MAY, 2012Comment on the biological significance of each ofthe following statements.It is advantageous for a farmer to grow crops suchas celery, lettuce and tomatoes in glasshouses. (6)
  61. 61.  Keep off frost and extremely wet conditions in winter Shield plants from wind Keeps a warm temperature – higher rate of photosynthesis Prevents excessive water loss Protect from pests Lights can be left on – plants photosynthesise during the night
  62. 62. Question: MAY, 2006The following diagram shows lettuce under cloches.Cloches are movable tent-like covers of transparentpolythene (plastic) which farmers put over soil andplants, in open fields.Suggest TWO advantages that cloches have overglasshouses. (2) 1. Cheaper to set up and maintain 2. Can be easily removed 3. Need fewer people to look after them
  63. 63. YES
  64. 64. Plants are grown in a salt solution rather than soil
  65. 65. Advantages of growing plants without soil:1. Less water used
  66. 66. Advantages of growing plants without soil 2. No pests
  67. 67. Kew Gardens, London