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What is photosynthesis?

What is photosynthesis?. The process in which plants use the energy of the sun to convert water and carbon dioxide into high-energy carbohydrates (sugars and starches) and oxygen (a waste product). chloroplast. leaf cell. leaf. Chlorophyll is a molecule that absorbs light energy.

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What is photosynthesis?

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  1. What is photosynthesis? • The process in which plants use the energy of the sun to convert water and carbon dioxide into high-energy carbohydrates (sugars and starches) and oxygen (a waste product).

  2. chloroplast leaf cell leaf • Chlorophyll is a molecule that absorbs light energy. • In plants, chlorophyll is found in organelles called chloroplasts.

  3. grana (thylakoids) chloroplast stroma Photosynthesis in plants occurs in chloroplasts. • Photosynthesis takes place in two parts of chloroplasts. • grana (thylakoids) • stroma

  4. The light-dependent reactions capture energy from sunlight. • take place in thylakoids • water and sunlight are needed • chlorophyll absorbs energy • energy is transferred along thylakoid membrane then to light-independent reactions • oxygen is released

  5. The light-independent reactions make sugars. • take place in stroma • needs carbon dioxide from atmosphere • use energy to build a sugar in a cycle of chemical reactions

  6. granum (stack of thylakoids) 1 chloroplast sunlight 6H2O 6O2 2 energy thylakoid stroma (fluid outside the thylakoids) 6CO2 1 six-carbon sugar C6H12O6 3 4 • The equation for the overall process is: 6CO2 + 6H2O  C6H12O6 + 6O2

  7. Light Energy Chloroplast CO2 + H2O Sugars + O2

  8. Light and Pigments • Photosynthesis requires: • water • carbon dioxide • light • chlorophyll (a pigment molecule in chloroplasts; two types) • chlorophyll a • chlorophyll b

  9. ROYGBIV • Sunlight is perceived as white light, but is really a mixture of different wavelengths of light (like a rainbow). The visible light we can see is a very small portion of the electromagnetic spectrum. • Red Orange Yellow Green Blue Indigo Violet Red: long wavelength, less energy Violet: Short wavelength, high energy

  10. Pigments are molecules that absorb light at different wavelengths. • Chlorophyll absorbs light in the visible spectrum, except the green wavelengths. • Green light is reflected by the leaves making plants look green. • The high energy that is absorbed makes photosynthesis work.

  11. Factors affecting photosynthesis • Shortage of water • Temperature (0-35 degrees Celsius) • Intensity of light

  12. Inside a Chloroplast • Photosynthesis takes place inside chloroplasts. • Chloroplasts contain: • thylakoids: saclike photosynthetic membranes containing pigments • grana (singular: granum): stacks of thylakoids • stroma: region of chloroplasts outside of the thylakoid membranes • inner membrane • outer membrane

  13. Photosystem II captures and transfers energy. • chlorophyll absorbs energy from sunlight • energized electrons enter electron transport chain • water molecules are split • oxygen is released as waste • hydrogen ions are transported across thylakoid membrane

  14. Electron Carriers • Sunlight excites electrons in chlorophyll, causing them to gain energy. • An excited electron is like a hot coal, and cannot be easily carried from one place to another- a protein called an electron carrier is required to transport excited electrons.

  15. Electron transport: An electron carrier molecule can accept a pair of high-energy electrons and transfer them to another molecule. • Electron transport chain: Series of electron carriers • Example: NADP+ (nicotinamide adenine dinucleotide phosphate) NADP+ + 2 electrons + H + NADPH • NADPH can carry high-energy electrons to other chemical reactions in the cell that need energy

  16. Photosystem I captures energy and produces energy-carrying molecules. • chlorophyll absorbs energy from sunlight • energized electrons are used to make NADPH • NADPH is transferred to light-independent reactions

  17. Light Dependent Reactions • The light-dependent reaction splits water, produce oxygen gas as waste, and converts ADP and NADP+ into ATP and NADPH.

  18. The second stage of photosynthesis uses energy from the first stage to make sugars. • Light-independent reactions occur in the stroma and use CO2 molecules.

  19. A molecule of glucose is formed as it stores some of the energy captured from sunlight. • carbon dioxide molecules enter the Calvin cycle • energy is added and carbon molecules are rearranged • a high-energy three-carbon molecule leaves the cycle

  20. A molecule of glucose is formed as it stores some of the energy captured from sunlight. • two three-carbon molecules bond to form a sugar • remaining molecules stay in the cycle

  21. Light Dependent Reactions • Light hits Photosystem II in the thylakoid membranes. Two electrons are excited and these excited electrons are passed onto the electron transport chain • To replace the lost electrons, the thylakoid membrane obtains low-energy electrons by splitting water 2H2O  4H+ + O2 + 2 e- • The O2 is released as waste • The hydrogen ions (4H+) are released inside the thylakoid membrane

  22. Light Dependent Reactions 2. Electron transport chain (ETC) • Electrons are passed from Photosystem II to Photosystem I from one electron carrier to the next until they reach Photosystem I • Energy from the electrons is used by the electron carriers in the ETC to force H+ ions from the stroma into the inner thylakoid space- build up of H+ will be used to drive ATP synthase

  23. Light Dependent Reactions 3. Light hits Photosystem I • Pigments in Photosystem I use energy from light to energize two electrons, making them high-energy • They are passed to NADP+ Reductase which catalyzes the reaction of NADP+ take combining with the high-energy electrons and hydrogen ions (H+) to become NADPH

  24. Light Dependent Reactions 4. Hydrogen Ion Movement • The inside of the thylakoid membrane fills up with positively charged hydrogen ions (H+) as electrons are passed from Photosystem II to I • ATP synthesis • The thylakoid membrane contains a protein called ATP synthase that spans the membrane and allows H+ ions to pass through it • As H+ ions pass through ATP synthase, the protein rotates and binds ADP and a phosphate group to produce ATP.

  25. Light-independent reactions (The Calvin Cycle) • During the Calvin cycle, plants use ATP and NADPH from the light-dependent reactions to produce high-energy sugars for long-term storage. • The Calvin cycle does NOT require light.

  26. H2O CO2 Sugars O2 light Chloroplast Chloroplast NADP+ Chloroplast ADP + P Light- Dependent Reactions Calvin Cycle Thylakoids ATP NADPH

  27. The Calvin Cycle: (4 Steps) • CO2 enters the cycle • Six carbon dioxide molecules enter and combine with six 5-Carbon molecules. • Result: 12 3-carbon molecules

  28. The Calvin Cycle • Energy input • The 12 3-carbon molecules are converted into high energy forms using ATP and NADPH • During this process, 12 ATP  12 ADP • During this process, 12 NADPH  12 NADP+

  29. The Calvin Cycle • 6-carbon sugar produced from two 3-carbon molecules removed to produce sugar • 5-carbon molecules regenerated • 10 remaining 3-carbon molecules converted into six 5-carbon molecules • This requires 6 ATP  6 ADP • These 5-carbon molecules can be reused in step A.

  30. The Calvin Cycle CO2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced

  31. Photosynthesis includes Light- dependent reactions Calvin cycle takes place in uses use take place in H2O and Energy from sunlight NADPH and ATP Thylakoid membranes CO2 Stroma to produce to produce of High-energy sugars ATP NADPH O2 Chloroplasts

  32. Photosynthesis includes Light- dependent reactions Calvin cycle takes place in uses use take place in Energy from sunlight Thylakoid membranes ATP Stroma NADPH to produce to produce of High-energy sugars ATP NADPH O2 Chloroplasts

  33. Photosynthesis is important for almost all life on Earth because it — A produces oxygen B uses simple elements C is responsible for most decay D releases usable forms of nitrogen

  34. A B • What is this picture showing? • What is letter A? __________ • What is letter B? __________ chloroplast stroma thylakoid

  35. CO2 Sugars H2O Light Chloroplast Chloroplast NADP+ Chloroplast ADP + P Light- Dependent Reactions Calvin Cycle Thylakoids ATP NADPH O2

  36. Light Dependent or Calvin Cycle? Calvin Cycle • Occurs in the stroma • Needs CO2 • Produces ATP and NADPH • Occurs in the thylakoid membranes • Needs sunlight • Can occur in the dark • Uses ATP and NADPH • Produces a 6-Carbon Sugar Calvin Cycle Light Dependent Light Dependent Light Dependent Calvin Cycle Calvin Cycle Calvin Cycle

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