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Photosynthesis

Photosynthesis. Even SpongeBob does it!!! http://www.youtube.com/watch?v=lqEDz2vfhpQ&feature=emai l. Why is energy needed within cells?. Allows chemical reactions to take place BUILD UP (synthesis) or BREAKDOWN of molecules In order to do this, energy is required to make and break bonds.

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Photosynthesis

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  1. Photosynthesis Even SpongeBob does it!!! http://www.youtube.com/watch?v=lqEDz2vfhpQ&feature=email

  2. Why is energy needed within cells? • Allows chemical reactions to take place • BUILD UP (synthesis) or BREAKDOWN of molecules • In order to do this, energy is required to make and break bonds

  3. Where does the energy come from? • The SUN is the ultimate source of energy for nearly all living organisms (the exceptions being a few deep sea chemosynthetic bacteria) • Autotrophs make their own food (organic compounds) using carbon dioxide • Heterotrophs assimilate energy by consuming plants or other animals

  4. What provides the energy within cells? • ATP…Adenosine Tri Phosphate • Common to ALL living things • Any chemical that interferes with the production or breakdown of ATP is fatal to the cell and therefore the organism • Chemical energy is stored in the phosphate bonds

  5. How does ATP provide the energy? • Chemical energy is stored in the phosphate bonds, particularly the last one • To release the energy, a HYDROLYSIS reaction takes place to break the bond between the last two phosphate molecules • Catalyzed by ATP-ase • ATP is broken down into ADP and Pi • For each mole of ATP hydrolyzed, about 34kJ of energy is released • Some is lost, but the rest is useful and is used in cell reactions

  6. Where does the energy to synthesise ATP come from? • Catabolic (breakdown) reactions • Redox (reduction/oxidation) reactions • The main way in which ATP is synthesised is by the removal of hydrogen atoms from intermediate compounds in a metabolic pathway • When two hydrogen atoms are removed from a compound, they are picked up by a HYDROGEN CARRIER or ACCEPTOR • We say the hydrogen carrier is reduced • Electrons from the hydrogen atoms are passed along carriers (Electron Transfer Chain) • When a component of the chain receives one of the hydrogen atoms, we say it is REDUCED • When a component passes an electron on, we say it is OXIDISED • Each of these redox reactions releases a small amount of energy and this energy is used to synthesise ATP

  7. What does this have to do with photosynthesis? • ATP is both synthesised and broken down during photosynthesis! 6CO2 + 6H2O = C6H12O6 + 6O2 • Light energy is required • Chlorophyll • Stored within chloroplasts • 10-50 chloroplasts per plant cell

  8. Evolution of the chloroplast • It is believed that photosynthetic bacteria were acquired by eukaryotic cells • By endocytosis (engulfing) • To produce the first algal/plant cell • This is called the “endosymbiont theory” • They were then passed on to the next generation

  9. Intergranal lamellae

  10. Size and Shape • Can vary • Usually between 2-10µm in length • Usually disc shaped

  11. Membranes Double membrane; • Outer membrane – permeable to many small ions • Inner membrane – less permeable and has transport proteins embedded in it Intermembrane space is 10–20nm wide between the inner and outer membrane

  12. Lamellae and thylakoids • The inner membrane is folded into lamellae (thin plates) aka thylakoids • The lamellae (thylakoids) are stacked in piles called granum • Between the grana are intergranal lamellae

  13. Stroma • Fluid-filled matrix • The light-independent stage of photosynthesis occurs here • Contains starch grains, oil droplets, DNA and ribosomes

  14. Grana • Contains stacks of thylakoids • Where the light-dependant stage of photosynthesis takes place • Absorb light and make ATP

  15. How chloroplasts are adapted

  16. Pigments and photosystems Chloroplasts contain photosynthetic pigments to absorb the light energy Pigments are chlorophyll a, chlorophyll b and carotene The pigments are found in the thylakoid membranes attached to proteins. The protein and pigment are called a photosystem Two photosystems used by plants to absorb light are PSI ( 700nm wavelength) and PSII ( 680nm wavelength)

  17. Chlorophylls • Chlorophyll a • Is in the “Primary pigment reaction centre” • Two forms • P680 – in photosystem 2 • P700 – in photosystem 1 • Appears yellow-green • Absorbs red light (and blue at 450nm) • contains a Mg atom – when light hits this, a pair of electrons become excited http://www.youtube.com/watch?v=0W6JgnCFezo&feature=related http://www.youtube.com/watch?feature=endscreen&NR=1&v=qfw5-wCVMNM

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  19. Accessory pigments • Chlorophyll b • Absorbs light at wavelengths between 500-640nm • It appears blue-green • Is one of the accessory pigments • Carotenoids • Absorb blue light • Reflects yellow (xanthophyll) and orange (carotene) light • They absorb light not normally absorb by chlorophylls

  20. A quick review of visible light Visible light is a mixture of wavelengths Each wavelength appears as a different color Different colors of light can be absorbed by an object. If they are not absorbed, they are reflected Go to

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