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Chapter Six

Chapter Six. How Cells Acquire Energy. Summary of the Reaction. light 12 H 2 0 + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O. Photosynthesis. The process of converting sunlight energy into chemical energy.

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Chapter Six

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  1. Chapter Six How Cells Acquire Energy

  2. Summary of the Reaction light 12 H20 + 6CO2 6O2 + C6H12O6 + 6H2O

  3. Photosynthesis The process of converting sunlight energy into chemical energy. The sun is the primary source of energy – either directly or indirectly. It is used by plants, protists, algae, and some bacteria.

  4. Photosynthesis performance depends on the earth’s atmosphere and climate. CO2 buildup could have a profound impact on PS in the future.

  5. A Brief History Joseph Priestly showed that plants release air that allows combustion Jan Ingenhousz showed that sunlight was necessary for photosynthesis and that only the green parts release oxygen. Jean Senebier showed that CO2 is required for growth

  6. Light • To understand photosynthesis, you must first understand light. • We are only able to perceive light within the visible spectrum: Red, Orange, Yellow, Green, Blue, Indigo, and Violet. (ROYGBIV)

  7. Above it (with longer wavelengths) are infrared (heat), microwaves, and radio waves

  8. Below it (with shorter wavelengths) are UV, Xrays, and Gamma rays

  9. Visible Spectrum

  10. Light is seen as a reflection off of an object. The object will absorb all colors, and the one that is not absorbed is the one that can be seen.

  11. Chlorophyll and other pigments are designed to use the light it absorbs, and reflect light that cannot be used effectively

  12. Pigments in Chloroplasts Chlorophyll a – appears green. Absorbs blue-violet and red. Chlorophyll b – appears green. Absorbs red-orange and blue. Carotenoids – appear red, orange, and yellow. Absorbs blue-violet and blue-green.

  13. Chloroplast • Found in plant cells • Stroma: fluid that fills inside • Thylakoids: disk-shaped interconnected sacs • Grana: stacks of thylakoids

  14. Photosynthesis • 2 reactions • Light Dependent • Photosystem II • Photosystem I • Light Independent (Calvin Cycle)

  15. Light Dependent Reactions Occur in the thylakoids of the chloroplasts during times of light Purpose is to absorb sunlight and convert it to ATP that can be used in the Calvin cycle.

  16. Light Dependent Reactions The pigments in the thylakoid space organize themselves into PHOTOSYSTEMS

  17. Photosystems contain combinations of chlorophyll a and b and also other pigments called phycobilins, and carotenoids (they help pick up other wavelengths of light)

  18. Photosystem II Photons split water molecules producing O2 When chlorophyll is hit by light, the electron produced from the split is elevated to a higher energy level (it is "excited")

  19. The excited electron is then passed to a PRIMARY ELECTRON ACCEPTOR of the Electron Transport Chain as begins to travel down the ETC. Energy provided in the ETC is used to make ATP from ADP

  20. Photosystem I Photons (again) boost electrons to a higher energy state electrons travel down another electron transport chain, Energy is used to make NADPH from NADP.

  21. Summary of Light Dependent Sunlight enters the chloroplast in the thylakoids. Pigments absorb the light energy and release excited electrons. Water molecules are split, ATP and NADPH are formed, and oxygen is released

  22. And now what…. The ATP and the NADPH of the light dependent reactions are used for the next main step, the Calvin cycle (Light independent reactions)

  23. Light Independent Reactions Calvin Benson Cycle The enzymes that catalyze the reactions of the Calvin Benson Cycle USE the energy in ATP and NADPH, produced in the thylakoids by the light reactions, to reduce CO2 to sugars.

  24. Occurs in the stroma in the chloroplast The Calvin Cycle is named after Melvin Calvin the American scientist who worked out the details of the pathway.

  25. Calvin Benson Cycle The function of this pathway is to produce a single molecule of glucose (C6H12O6) To accomplish this, the CB cycle must repeat 6 times and use 6 CO2 molecules.

  26. 3 phases: • Carbon Fixation • Reduction • Regeneration of RuBP

  27. Carbon Fixation • Carbon dioxide is fixed or attached to a 5-carbon sugar called RuBP, producing a 6-carbon compound rubisco. • Each unstable 6 carbon molecule splits into 2 (3 Carbon compounds) known as PGA.

  28. Reduction ATP and NADPH are then used to convert PGA to PGAL. PGAL is VERY energy rich!

  29. 2 PGAL can be removed from the cycle at this point and used for the formation of larger carbohydrates such as glucose, sucrose, and starch. The other 10 PGAL are kept in the cycle for the next step….regeneration

  30. Regeneration ATP used to convert PGAL to RuBP – which is what we need to start the Calvin Benson Cycle again.

  31. Summary of Light Independent Reactions Enzymes attach CO2 to RuBP (5 carbon compound) to make rubisco (6 carbon compound) Rubisco is unstable and splits into 2 PGA (3 carbon compound)

  32. PGA accepts a phosphate from ATP to make PGAL 2 PGAL combine to make glucose 10 PGAL recycled to form RuBP to start cycle over.

  33. Environmental factors that affect photosynthesis are: Light quality Light intensity Light Period Carbon dioxide availability Water availability

  34. Works Cited http://www.sciencebuddies.org/mentoring/project_ideas/HumBeh_img019.gif http://www.daviddarling.info/images/chloroplast.jpg http://www.biologycorner.com/resources/light-dependent.gif http://www.biologycorner.com/bio4/notes/photosynthesis.html http://www.biologycorner.com/bio4/notes/photosynthesis.html

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