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Ch. 10 part 1 The light reaction

Ch. 10 part 1 The light reaction. I. Autotrophs- Organisms that make their own food (convert light energy to chemical energy) A. Plants require only CO2 , H2O and minerals. B. Known also as Photoautotroph . 1. Photoautotroph- Convert light energy

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Ch. 10 part 1 The light reaction

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  1. Ch. 10 part 1The light reaction

  2. I. Autotrophs- Organisms that make their own food (convert light energy to chemical energy) • A. Plants require only CO2, H2O and minerals. • B. Known also as Photoautotroph. • 1. Photoautotroph- Convert light energy • 2. Chemoautotroph-Obtain energy from inorganic substances • 3. Heterotrophs- must eat other organisms to obtain energy

  3. II. Chloroplasts • A. Chlorophyll – A green pigment found in photosynthetic organisms, that captures light. • B. Found in chloroplasts and photosynthetic bacteria • C. Pores in leaf were gases pass through are called stomata. • D. Intermembrane space- separation between the two membranes of the chloroplast. • E. Thylakoid space- thylakoids are disks inside the chloroplasts, where chlorophyll is found. Grana are a stack of these thylakoids • F. Stroma – Conversion of Carbon dioxide happens here. It is the fluid (cytoplasm) of the chloroplast.

  4. III.Pathways of Photosynthesis • A. Chloroplasts splits water • 6CO2 + 12H2O + LIGHT ENERGY -> C6H12O6 + 6O2 + 6H2O • The net equation is? • 6CO2 + 6H2O + LIGHT ENERGY -> C6H12O6 + 6O2 • The simplest form of the equation is? • CO2 + H2O -> CH2O + O2

  5. B. The splitting of water • 1. The electrons associated with hydrogen have more potential energy in organic molecules than in water. • 2. Energy can then be stored in glucose. • C. Redox process • 1. Photosynthesis is anabolic; energy is required to reduce carbon dioxide • 2. Light is the energy source. • 3. When water is split the electrons are transferred to carbon dioxide making sugar.

  6. B. The light reaction • 1. Light reaction – Conversion of light to chemical energy of ATP and NADPH. • 2. Occurs in the thylakoid membranes of the chloroplast. • 3. Reduce carbondioxide to sugar • a. Hydrogens are added to it • 4. O2 released as waste from water being split. • 5. ATP generated.

  7. . How it happens • a. Photons of light boost the pigment molecule’s electron to a higher orbital • b. Electrons fall back giving off energy. • c. Photosystems- pigments are arranged within thylakoid membrane • 1. Antenna complex – Absorb photon and pass energy to other pigment molecule. • 2. Reaction center- Chlorophyll a transfers excited electron. • 3. Primary electron acceptor- traps excited electron, powering the synthesis of ATP and NADPH. • 4. Photosystem 1 – P700 • 5. Photosystem 2 _ P680

  8. 6. Noncyclic – involves both photosystems, electrons are passed from water to NADP+. ATP, NADPH and oxygen are produced.

  9. . An electron transport chain is used where each link in the chain passes an electron to the next link until it reaches the next photosystem. • c. NADP+ is the last link in the chain and becomes reduced. • d. Chemiosmosis produces ATP; see 10.14, Basically an electrochemical gradient has been created. While the electrons have been passed along H+ have been pumped across the membrane, building up in the thylakoid space. These H+ want to come back into the stroma. They are ions so they cannot pass without help. Facilateddiffusion is used to bring them back. The protein involved is ATP synthase. All the H+ coming back generates energy allowing for ATP to be made.

  10. I. Calvin Cycle • A. Carbon Fixation- the conversion of CO2 to an organic compound. • 1. This happens to 3 CO2to form one 3 carbon sugar (G3P) in the Calvin Cycle • 2. Rubisco (the most plentiful enzyme in the world) attaches the CO2 to a 5C sugar called RuBP (this happens 3 at a time) • 3. RuBP is like the cart on a roller coaster- CO2comes on for a ride and gets off forming G3P ( 1for every 3 CO2 ), leaving the RuBP to go back to pick up a new CO2. • 4. So it takes a total of 2 turns of the cycle to get 2 G3P, the equivalent of a glucose molecule.

  11. B. Reduction- this is a reduction of CO2to sugar • 1. ATP is used to make the reactions spontaneous- in other words the phosphates are moved on and off the intermediate sugars to make the ultimate conversion to G3P- It is a coupling of the ATP reaction to the formation of G3P. • 2. NADPH gives the hydrogens over to the sugar as well- those are the original hydrogens from water. What happened to the water in the light reaction?

  12. C. Photorespiration- Its not respiration, what is it? • 1. C3 plants- a C3 plant does photosynthesis as just discribed- its called C3 because a 3C sugar is made • a. On hot days the plant closes its stomata (pores), trapping oxygen and water in and CO2out. • b. oxygen competitively inhibits Rubisco, binding it when there is low CO2. This is not a good thing,it wastes O2 and generates no ATP. • 2. C4 plants- they still do photosynthesis the same way but there is a step added to the process. • a. These plants storeCO2in cells called mesophyll, in the form of a 4 carbon sugar (Malate). • b. The enzyme PEP carboxylase does this in the mesophyll cells • c. This allows plants to keep the levels of CO2high at all times and minimize photorespiration. Calvin cycle takes place in the bundle sheath cell of these plants

  13. 3. CAM plants- work on the same principles as C4 • a. The stomates are closed during the day and open during the night. • b. At night organic acids are made, in the day they are converted back to CO2and put into the Calvin cycle

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