chapter 8 photosynthesis - shaltry's biology...

Chapter 8 Photosynthesis

8-1 NRG and Living Things

n  Where does the NRG we use come from.

n  Directly or indirectly from the sun n  Plants get their NRG directly from the

sun n  How?

n  Plants use photosynthesis to convert light NRG into chemical NRG

n  Plants are autotrophs n  Autotrophs convert light NRG or inorganic

compounds to make organic compounds n  Photoautotrophs use the sun n  Chemoautotrophs use inorganic compounds

n  Heterotrophs must eat things to aquire NRG from organic compounds

n  Cellular Respiration is how most heterotrophs, and most autotrophs get their NRG from organic compounds

n  Similar to burning fuel (uses oxygen), to build ATP

n  Organisms get NRG from compounds by breaking chemical bonds

n  Some NRG gets released as heat when breaking chemical bonds

n  Most of the remaining NRG gets temporarily stored as ATP

ATP

n  ATP yields ADP + P + NRG n  Made of a nitrogen base, ribose sugar,

and three phosphate groups n  How is the NRG released? n  By breaking the chemical bond

between phophate groups

n  http://colorvisiontesting.com/ishihara.htm

Concepts

n Photosynthesis: CO2 + Water --> Sugar + O2

–  Photosynthesis is the production of sugar (stored energy) and oxygen using energy from the sun to combine carbon dioxide and water.

–  CO2 is brought into plants and O2 is released from plants through pores (stomata) in their leaves and other tissues.

–  RUBISCO is the enzyme plants use to undergo photosynthesis.

+ Solar Energy

Stomata

8-2, 8-3 Photosynthesis

n  Stage One (Light Dependent RXNS) n  Stage Two (Light Independent RXNS) n  Chloroplast contain pigments that

absorb solar NRG n  Primary pigment is called chlorophyll

and absorbs blue, red light waves n  Two types of chlorophyll a and b

n  Carotenoids are yellow and orange pigments

n  They absorb different wavelengths of light

Light Dependent Reactions

n  Pigments are located in chloroplast n  Embedded in the membranes of

thylakoids (disk shaped) n  When light hits them, NRG is

transferred to electrons n  Makes them “excited”

n  Excited electrons jump from chlorophyll molecules to other molecules in the thylakoid

n  These electrons fuel the second stage of photosynthesis

n  Plants must replace these lost electrons

n  Water molecules get spilt by an enzyme

n  Electrons are taken from hydrogen atoms, leaving H+

n  The oxygen is combined to form oxygen gas

Electron Transport Chain

n  Electrons are used to produce new molecules that store chemcal NRG

n  Electrons are passed between molecules in the thylakoid membrane

n  Called the Electron Transport Chain

n  One type of e- chain contains a protein that acts like a membrane pump

n  The e- lose their NRG as they pass through the protein

n  This NRG is used to pump H+ into the thylakoid

n  This creates a concentration gradient inside the thylakoid

n  The H+ then diffuse out the thylakoid through special carrier proteins

n  These carrier proteins function as enzymes and ion channels

n  These proteins catalyze a reaction that adds a phosphate group to ADP to create ATP

n  ATP used to fuel the Light Independent Reactions

n  Another e- transport chain makes NADPH

n  NADPH is an electron carrier that provides NRG to make carbon-hydrogen bonds in stage 3

n  NADP+ + Hydrogen ions=NADPH n  NADPH used to fuel the Light

Independent Reactions

Light Dependent RXNS Summary n  Pigments in thylakoids capture solar

NRG n  Electrons become excited and move

through the e- transport chain n  Electrons are replaced by splitting

water molecules n  H+ accumulate in thylakoid, helping to

create ATP and NADPH

n  http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

n  The Calvin cycle regenerates its starting material after molecules enter and leave the cycle.

n  CO2 enters the cycle and leaves as sugar. n  The cycle spends the energy of ATP and the

reducing power of electrons carried by NADPH to make the sugar.

n  The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P).

Light Independent Reactions (The Calvin Cycle)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

n  Each turn of the Calvin cycle fixes one carbon.

n  For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO2.

n  To make one glucose molecules would require six cycles and the fixation of six CO2 molecules.


n  The Calvin cycle has three phases. n  In the carbon fixation phase, each CO2

molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP). – This is catalyzed by RuBP carboxylase or

rubisco. – The six-carbon intermediate splits in half to

form two molecules of 3-phosphoglycerate per CO2.



Fig. 10.17.1

n  During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3 bisphosphoglycerate.

n  A pair of electrons from NADPH reduces each 1,3 bisphosphoglycerate to G3P. – The electrons reduce a carboxyl group to a

carbonyl group.



Fig. 10.17.2

n  If our goal was to produce one G3P net, we would start with 3 CO2 (3C) and three RuBP (15C).

n  After fixation and reduction we would have six molecules of G3P (18C). – One of these six G3P (3C) is a net gain of

carbohydrate. n This molecule can exit the cycle to be used by the

plant cell.

– The other five (15C) must remain in the cycle to regenerate three RuBP.


n  In the last phase, regeneration of the CO2 acceptor (RuBP), these five G3P molecules are rearranged to form 3 RuBP molecules.

n  To do this, the cycle must spend three more molecules of ATP (one per RuBP) to complete the cycle and prepare for the next.



Fig. 10.17.3

n  For the net synthesis of one G3P molecule, the Calvin recycle consumes nine ATP and six NAPDH. –  It “costs” three ATP and two NADPH per CO2.

n  The G3P from the Calvin cycle is the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.


chapter 8 photosynthesis - shaltry's biology...

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