Essential Guide to Photosynthesis in Plants

1. Ch 10 Photosynthesis Plants making their own food

2. Introduction • 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.

3. Role of Photosynthesis • 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 for forming fossil fuels • It removes carbon dioxide from the air

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

5. Photosynthesis produces • glucose • waste oxygen

6. oxygen Carbon dioxide glucose water How plants make their food Energy from sunlight, with chlorophyll as a catalyst, is used to combine CO2 and H2O to form glucose and release O2 chlorophyll

7. Balanced Equation for Photosynthesis 6CO2 + 6H2O + light C6H 12O6 + 6O2 carbon dioxide sunlight glucose + + water chlorophyll oxygen

9. Photosynthesis converts light energy chemical energy

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

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

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

13. Light Energises Electrons • 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.

14. Water is Split • Some of the trapped light energy is used to split water into oxygen gas (O2) protons (H+) and electrons (e-) • Summarised as 2H2O 4H+ and 4e- and O2

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

16. Glucose is formed • The trapped light provides the energy along with protons and carbon dioxide to form glucose (C6H 12O6 )

18. Learning Check • 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?

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

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

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

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

24. 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?

25. Syllabus Can you? • 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 , CO2 & water for photosynthesis. • Explain how human intervention can play a role in photosynthesis.

26. Photosynthesis Extended Study

27. Photosynthesis Light Stage Dark Stage 2 stages of Photosynthesis

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

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

30. Chloroplast Structure

31. http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.htmlhttp://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html

34. Light Stage Phosphorylation Making ATP Photolysis Splitting water Light stage

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

36. Cyclic Electron Transport – Pathway 1

37. Cyclic Electron Transport • 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.

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

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

41. ADP - adenosine diphosphate is a low-energy molecule • ATP - adenosine triphosphate is an energy-rich molecule.

42. ATP and ADP

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

45. ATP – The Unit of Energy

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

48. 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

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

50. NADP then receives another electron becoming NADP-. NADP + e- = NADP- • 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