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Photosynthesis Plants and other photoautotrophs use the following reaction to make food:

Photosynthesis Plants and other photoautotrophs use the following reaction to make food: 6 CO 2 + 6 H 2 O + Energy C 6 H 12 O 6 + 6 O 2 In plants, the reactions take place in the chloroplast: cross-section of a leaf. chloroplast.

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Photosynthesis Plants and other photoautotrophs use the following reaction to make food:

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  1. Photosynthesis Plants and other photoautotrophs use the following reaction to make food: 6 CO2 + 6 H2O + Energy C6H12O6 + 6 O2 In plants, the reactions take place in the chloroplast: cross-section of a leaf chloroplast

  2. The energy in the equation is provided by light from the sun. • light strikes the leaf of a plant and is absorbed by pigments (called chlorophylls) in the chloroplast. • the chlorophylls absorb certain wavelengths of light, and as a result, photosynthesis occurs best at these wavelengths.

  3. The chlorophyll molecules are embedded in the thylakoid membrane, arranged into a network called a photosystem. Chlorophyll molecules are called antenna pigments because they anchor themselves into the membrane here… and stick out to absorb light energy using electrons in a porphyrin ring (up top).

  4. Photosynthesis takes place in 2 stages: The light dependent reactions - where energy from the sun is converted into chemical energy (in the form of ATP and NADPH - a mobile electron carrier). The light independent reactions - where the energy made in stage 1 is used to make organic compounds (glucose) from CO2 photosynthesis movie

  5. The Light Dependent Reactions • 3 parts: • a photon is absorbed by a chlorophyll electron • electron transport - the excited electron is moved through membrane carriers, pumping H+ to create a gradient and eventually reduces NADP+ to NADPH. • H+ moves through ATP synthase to drive the formation of ATP from ADP.

  6. Photosystems • the primary light harvesting units of chloroplasts. • in the chloroplast, chlorophyll molecules are found in clusters called photosystems. • a photosystem consists of an antenna complex and a reaction centre - embedded in the thylakoid membrane. • an antenna pigment absorbs a photon and transfers the energy from pigment to pigment until it reaches a chlorophyll a molecule in the reaction centre. • the chlorophyll a molecule transfers this electron to a primary electron acceptor.

  7. Electron Flow and Chemiosmosis • Two photosystems (1 and 2) are used to make ATP and NADPH. • photosynthesis starts when a photon strikes PS II. • Z-protein splits water into 2 H+ , O2 and electrons. • protons are pumped into the lumen (middle) of the thylakoid and eventually make ATP. • the electrons leave the ETC by reducing NADP+ to form NADPH.

  8. Light Independent Reactions (the Calvin Cycle) • ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose. • called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose) • occurs in the stroma • don’t require light • also known as C3 Cycle

  9. An overview – Don’t copy this – we’ll use the handout I already gave you.

  10. Steps in Light Independent Phase: • Carbon Fixation • An enzyme, RuBisCo, combines a CO2 molecule with a 5C molecule called RuBP (ribulose biphosphate) to produce 2, 3C molecules called 3-PGA (3-phosphoglycerate). 2. Reduction Reactions • 3-PGA phorphorylated by ATP then reduced by NADPH to produce G3P (glycerate 3-phosphate). 3. RuBP Regeneration • G3P phosphorylated by ATP to re-create RuBP to restart the cycle. For every 2 G3P, 1 molecule glucose is removed from cycle, so need 6 CO2 to create 1 glucose.

  11. Other Methods of Carbon Fixation

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