Summary of photosynthesis

Two Main Processes of Photosynthesis

1) Light dependent stage

2) Light independent stage

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Main summary of photosynthesis

1) Light and H2O enter

2) Photolysis of water

3) Light dependant reaction

4) Reduced NADP and ATP are made

5) O2 is released

6) The reduced NADP and ATP move to the light independant stage

7) CO2 enters the light independant stage

8) The energy from reduced NADP and ATP are used to make sugar

9) C6H12O6 is made (glucose)

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Light Dependent Stage

1) Pair of electrons from chlorophyll boosted to higher energy level by light energy it has trapped (photosystem 2 involved)

2) Here they are accepted by electron acceptor and then passed along chain of carriers

3) Energy released is used to convert ADP and Pi into ATP - this process is called photophosphorylation

4) The electrons then enter another chlorophyll molecule (photosystem 1 involved)

5) Electrons eventually pass to NADP w/ hydrogen from water to form reduced NADP

6) The ATP and reduced NADP are then used in the light independent reactions to make carboyhydrate from carbon dioxide

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Light Independent Stage (Calvin Cycle)

1) CO2 combines w/ RuBP (5 carbon compound) - reaction is catalysed by enzyme RuBISCO

2) The 6 carbon compound formed is unstable and immediately breaks down into two 3 carbon molecules, GP

3) GP is reduced to form GALP (3 carbon sugar phosphate) - the hydrogen from the reduction comes from the reduced NADP in the LDR, ATP provides the energy for this reaction

4) 2/12 GALPs formed are involved in the creation of hexose (6 carbon suagr) - this can be converted into other organic compounds such as amino acids or lipids

5) 10/12 GALPs are involved in the regeneration of RuBP - the 10 GALP molecules rearrange to form six 5 carbon compounds, followed by phosphorylation using ATP which forms RuBP

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Full Names

  • RuBP = ribulose bisphosphate
  • RuBISCO = bisphosphate carboxylase
  • GP = glycerate-3-phosphate
  • GALP = glyceraldehyde-3-phosphate
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Parts of Chloroplast

Thylakoid membranes: system of interconnected flattened fluid-filled sacs - contains proteins, photosynthetic pigments and electron carriers

DNA loop: chloroplasts contain genes for some of their proteins

Stroma: fluid surrounding thylakoid membranes - contains all enzymes needed to carry out L-IR

Thylakoid space: fluid within the thylakoid membrane sacs - contains enzymes for photolysis

Granum: stack of thylakoids joined to each other (pl. grana)

Smooth inner membrane: contains many transporter molecules - these are membrane proteins which regulate the passage of substances in and out of chloroplast, such as sugars and proteins

Smooth outer membrane: this is freely permeable to molecules such as CO2 and H2O

Starch grain: stores the product of photosynthesis

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Locations of Processes

Absorption of light by chlorophyll: thylakoid (membrane)

Photolysis of water: thylakoids

Production of ATP: thylakoids

Use of ATP: stroma

Reduction of CO2: stroma

Synthesis of starch: stroma

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Structure and Functions

Thylakoid (membrane) => light dependent reactions

Thylakoid (space) => photolysis of water

Granum => provides a site for light dependent reactions

Stroma => light independent reactions

Outer membrane => fully permeable

Inner membrane => permeable to many substances which need to enter/leave the chloroplast

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