Photosynthesis

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Photosynthesis

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This is the conversion of light (solar) energy to chemical energy. It is the most biological pathway. In photosynthesis, water is oxidized to oxygen while carbon dioxide is reduced to a carbohydrate the oxygen in water is given off in the form of oxygen

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Autotrophs

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Organisms that make organic compounds from inorganic compounds, such as water and Co2

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Heterotrophs

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Feed on organic compounds. Can't make their own.

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Light

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Sunlight is made up of three types of light: 4% ultraviolet (high energy), 53% infrared (low energy) and 44% visible light. Visible light provides just the right amount of energy for biochemical reactions; it contains just enough to excite or enegize molecules, it causes electrons to jump to higher energy levels or to jump out of the atom completely.

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Pigment molecules

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Organisms absorb light through pigment molecules. Pigments have a different colors because they transmit a particular wavelength of light.

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Chlorophyll a

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The primary photosynthetic molecule. It absorbs violet, blue, red, and transmit green wavelengths. It is responsible for the green color of plants. Has a long hydrocarbon chain and thus cannot dissolve water. Is found inside structure called grana which are stacked inside the chloroplast. It is in bedded in the thylakoid membrane of the chloroplast.

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Accessory pigments

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Plants have accessory pigments that absorb different wavelengths of chlorophyll a. These pigments become noticeable in the fall. Most plants regularly destroy and resynthesize chlorophyll. When plants break down chlorophyll faster than they resynthesize it, the green pigments cannot mask the other pigments producing the colors of autumn leaves.

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Carotenoid

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Absorb light in the violet blue green range

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Anthocyanins

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Absorb blue,blue green, green light; appears yellow orange

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Chloroplast

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Organelles in plants, it is the site of photosynthesis. It consists of two membranes that enclose a gelatinous matrix called stroma. suspended in the stroma are folded sacs of thylakoid membranes which enclose an area called thylakoid space. 10 to 20 thylakoids stack up into a structure, the grana; thylakoids and grana contain chlorophyll.

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Photochemical (light) reactions

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First stage of photosynthesis (light dependent). The photochemical reactions of photosynthesis oxidize water and release oxygen, produce ATP and reduce NADP+ to NADPH

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Biochemical reactions (Calvin Cycle)

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Second stage of photosynthesis. (light independent). The biochemical reactions incorporate (or fix) carbon from CO2 into organic compounds that cells use for storage.
• ATP and NADPH from light. reactions are needed

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P700

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Absorbs light at 700 nm and it is the reaction center for Photosystem 1

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P680

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Absorbs light by 680 nm and it is the reaction center for Photosystem 2

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Photosystems and Reaction Centers in Chloroplast

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A chlorophyll molecule can only absorb a very small amount of energy; but many chlorophyll molecules located near each other can capture far more energy. The light dependent reactions of photosynthesis depend on the light gathering units called photosystems; solar energy is passed on from one pigment to another until it is concentrated into one particular chlorophyll a molecule, the reaction center molecule; electrons in the reaction center molecule become so excited that they leave the pigment complex and move to a nearby electron acceptor molecule.

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Photosystem II

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The start of photosynthesis. Pigment molecules in Photosystem II absorb energy from the sun, and then transfer this energy to the P680 reaction center, where electrons become excited and then are ejected from the chlorophyll molecule in the reaction center. The reactive center is now empty; it replaces its lost electrons by obtaining electrons from water; WATER IS SPLIT INTO O2 GAS AND PROTONS, RELEASING ITS ELECTRONS. The ejected electrons are accepted by the electron transport chain and they are passed from carrier to carrier releasing enough energy to make 1 ATP

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Photosystem I

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Just like photosystem II, protons absorbed by chlorophyll a is passed to P700 reactive center, where electrons become excited and eject from the chlorophyll; they are then accepted by an electron acceptor that passes the electrons to NADP+; NADP+ becomes NADPH. The reactive center is now empty and it is filled by the electrons passing down the first electron transport chain.

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Noncyclic Pathway

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The two photosystems connected in a series. Produce more energy

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Cyanobacteria

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Some cyanobacteria utilize a cyclic electron pathway, which involves the actions of photosystem I only; This produces ATP but no carbohydrates

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Photophosphorylation

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This is the method used to produce ATP in the light dependent reactions. Water is present in the thylakoid space; when water is split giving off oxygen, the hydrogen ions remain in the thylakoid space; then, as electrons move from carrier to carrier in the electron transport chain, they give up energy which PUMPS HYDROGEN IONS FROM THE STROMA INTO THE THYLAKOID SPACE; thus, a very strong ion gradient is established, HIGH ION CONCENTRATION IN THE THYLAKOID SPACE AND LOW CONCENTRATIN OF IONS IN THE STROMA. The hydrogen ions flow down the gradient through the ATP SYNTHASE located on the thylakoid membrane PRODUCING 1 ATP.

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Algae and bacteria absorb CO2 from?

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The water that surrounds them

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Plants absorb CO2 from?

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The atmosphere through the stomata

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Stomata

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tiny leaf openings

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Phase 1 (Calvin Cycle)

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Carbon Fixation (RuBP+CO2). 3 CO2 react with 3 ribulose biphosphate (RuBP, 5C) to produce a 3 6C intermediate that quickly splits in half to produce 6 3-phosphoglycerate (3-PG, 3C). The enzyme Rubisco (RuBP carboxylase) catalyzes this reaction.

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Rubisco

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RuBP carboxylase. Most abundant and important proteins in the world.

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Phase 2 (Calvin Cycle)

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Reduction. 6 3-phosphoglycerate (3PG) become reduced to produce 6 glyceraldehydes-3-phosphate (G3P) using energy from ATP and NADPH; This redox reaction where CO2 is reduced and NADPH is oxidized; one G3P exits the cycle and is used to form GLUCOSE AND OTHER TYPES OF ORGANIC MOLECULES

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Phase 3 (Calvin Cycle)

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Regeneration. The rest (5 G3P) is used to re-form RuBP by using some of the ATP made in the light dependent reactions. For every three CO2 that enter the Calvin Cycle, one G3P leaves the pathway using 9 ATP and 6 NADH; two G3P (C3) molecules are needed to form glucose (C6) in plants.

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G3P

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Can be converted to form fatty acids and glycerol which are combined in plant oils. Also provides the hydrocarbon chain skeleton for amino acids and nucleotides

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The Calvin Cycle needs to have gone around _________ to?

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Twice to get 2 G3P C3 to make one glucose

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Photorespiration

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Where oxgen rather than CO2 is fixed during the Calvin Cycle. This is a wasteful process, ATP and NADPH are used but no glucose is formed

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C3 plants

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(Wheat, rice, oats) produce a 3-carbon molecule following CO2 fixation. On hot dry days C3 plants close their stomata to conserve water but they are now unable to take in CO2. The plant continues to fix CO2 until it runs out and then the plant will use O2.

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C4 Photosynthesis

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Plants fix CO2 in mesophylls by forming a C4 molecule, oxaloacetate. An adaptation called C4 photosynthesis enables plants to avoid photorespiration. Can survive in hot temperature temperarly, has two compartments. One for light reaction, one for Calvin Cycle so O2 doesn't get into the Calvin Cycle and the plant doesn't go through photorespiration

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CAM plants

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(Flowering succulent plants that live in arid and warm regions) fix CO2 by forming a C4 molecule but this occurs at night when their stomata remain open without much loss of water; during the day the CO2 is released to the Calvin Cycle within the same cell

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Photosystem

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each photosystem has closely packed chlorophyll a and b pigments along with accessory pigments such as the carotenoids that serve as an antenna for gathering solar energy