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Photosynthesis

Photosynthesis. Photosynthesis in Overview. Process by which plants and other autotrophs store the energy of sunlight into sugars. Requires sunlight, water, and carbon dioxide. Overall equation: 6 CO 2 + 6 H 2 0  C 6 H 12 O 6 + 6 O 2

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Photosynthesis

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  1. Photosynthesis

  2. Photosynthesis in Overview • Process by which plants and other autotrophs store the energy of sunlight into sugars. • Requires sunlight, water, and carbon dioxide. • Overall equation: 6 CO2 + 6 H20  C6H12O6 + 6 O2 • Occurs in the leaves of plants in organelles called chloroplasts.

  3. Leaf Structure • Most photosynthesis occurs in the palisade layer. • Gas exchange of CO2 and O2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. Palisade Spongy

  4. Chloroplast Structure • Inner membrane called the thylakoid membrane. • Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana) • Stroma is a liquid surrounding the thylakoids.

  5. Pigments • Chlorophyll A is the most important photosynthetic pigment. • Other pigments called antenna or accessory pigments are also present in the leaf. • Chlorophyll B • Carotenoids (orange / red) • Xanthophylls (yellow / brown) • These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

  6. Pigment Absorption

  7. This is an ocean plant. Seaweed

  8. Photosynthesis: The Chemical Process • Occurs in two main phases. • Light reactions • Dark reactions (aka – the Calvin Cycle) • Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. • Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.

  9. BIG PICTURE

  10. Light Reactions • Light-dependent reactions occur on the thylakoid membranes. • Light and water are required for this process. • Energy storage molecules are formed. (ATP and NADPH) • Oxygen gas is made as a waste product.

  11. Dark Reactions • Dark reactions (light-independent) occur in the stroma. • Carbon dioxide is “fixed” into the sugar glucose. • ATP and NADPH molecules created during the light reactions power the production of this glucose.

  12. The Minor Details :P

  13. Photosystem I & II

  14. Non-cyclic Electron Flow • Uses photosystem I (P700) and Photosystem II (P680) • Electrons from water replace e- lost from PSII • Electrons lost from chlorophyll in PSII replace e- lost in PSI • ATP and NADPH are made

  15. Cyclic Electron Flow • Uses PSI • Produces ATP but not NADPH • Electron is passed back to the chlorophyll that it left when excited

  16. Light Independent ReactionsAKA – Dark Reactions (not really – just don’t need light)Also called Calvin Cycle • 1. Occurs in the stroma of the chloroplast • 2. Uses ATP and NADPH from the Light Reactions • 3. Accepts carbon from carbon dioxide – this is called carbon fixation to make sugar. It reduces CO2. • 4. Produces Glyceraldhyde 3- Phosphate which is a 3-C sugar and is used to make glucose

  17. Details • 1. Carbon dioxide enters the Calving cycle and become attached to a 5-C sugar – ribulose biphosphate (RuBP). This reaction is catalyzed by Rubisco enzyme. • 2. 6-C intermediate breaks apart into two 3-C molecules of 3-phosphoglycerate (3-PGA) • 3. Converted to phosphoglyceraldehyde which is used to make glucose. Uses ATP and NADPH. • 4. RuBP is regenerated using ATP from Light reactions.

  18. CO2 is a substrate in an enyme-catalysed light-dependent reaction. At low CO2 concentration, rate is positively correlated with concentration

  19. plateau At Low Light Intensity Rate is Proportional to Light Intensity

  20. Optimum temperature Above the optimum temp., enzymes are denatured and rate drops steeply. Increased temp. gives increased energy and increased rate of photosynthesis Which enzymes are used in respiration?

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