Creating glucose

Photosynthesis
 Is an anabolic reaction
 The main product is glucose
 It occurs in the chloroplasts of cells
 It is carried out by photosynthetic organisms (plants, algae, some protists and some bacteria)
 These organisms are autotrophic – they are able to create organic energy (glucose) from sunlight

The Equation
 Light is required to carry out the reaction
 The pigment (chlorophyll) is also necessary for the reaction to take place

Chloroplasts
 There are two components in chloroplasts:
 Stroma (the fluid part)
 Grana (stacks of thylakoids)
 The thylakoid stacks contain the chlorophyll

The phases of photosynthesis
 Light dependent phase (occurs in the grana)
 Light independent phase (occurs in the stroma)

The light dependent phase
Water splitting
 In the grana, water is split releasing the hydrogen ions.
 The oxygen atoms from two water molecules join together to make oxygen gas (O2) which is released as a by-product
 The hydrogen ions accumulate in the thylakoid stacks, eventually contributing to NADPH and ATP synthesis

The light dependent phase
At the same time…
 Photons (light) are absorbed into the grana and activate the chlorophyll molecules in the Photosystem II molecule
 Electrons are released by the chlorophyll molecule and passed along an electron transport chain via carriers
(plastoquinone to cytochrome to plastocyanin) to
Photosystem I
 This is where NADP is loaded to create NADPH

The light dependent phase
 ATP synthase uses the high number of hydrogen ions in the thylakoid stacks to generate ATP
 This ATP eventually goes on (with the
NADPH) to assist in the Calvin Cycle (the light independent phase)

The light dependent phase

Light dependent summary
Inputs
 Light energy
 Water
 ADP (Adenosine
Diphosphate )
 NADP (Nicotinamide
Adenine Dinucleotide
Phosphate)
 Oxygen
Outputs
 ATP
 NADPH

The light independent phase
 Occurs in the stroma
 Involves the reduction of carbon dioxide into glucose
 The light independent phase does not require light energy, however it does require the outputs of the light dependent phase
 The Calvin cycle produces PGAL (phosphoglyeraldehyde)
 PGAL is a 3 carbon compound. Two PGAL can join together to make a monosaccharide

The Calvin Cycle

The Calvin cycle
 This is the main part of the light independent phase
 It involves making glucose from carbon dioxide molecules
 The cycle involves several temporary molecules, including phophoglycerate (a 3 carbon molecule) and ribulose diphosphate (a 5 carbon molecule)
 The output is two PGAL molecules, which can join to make a sugar.
 The PGAL molecules are bonded in the cytosol of a cell

To make one glucose molecule
 6 carbon dioxide molecules must enter the Calvin cycle
 12 NADPH deliver 12 hydrogen ions
 This can be remembered by the formula C
6
H
12
O
6
 The Calvin cycle requires ATP to make the new bonds in the PGAL molecule
 The ATP is provided by the light dependent phase

Light independent summary
Inputs
 Carbon dioxide
 ATP*
 NADPH*
 Glucose
Outputs
 ADP*
 NADP*
*The ADP, ATP, NADP and NADPH are not included in the equation because they are not used up. They just keep getting recycled in the cell

Where does the glucose go?
 To the mitochondria for cellular respiration (the waste product of oxygen can also go here)
 The glucose can also form polymers to:
 create sugars for fruit formation (a part of plant reproduction)
 Create cellulose for cell walls
 Create starch for storage

Different types of plants
C3
 Slower carbon uptake
 Therefore slower fixation
 Photosynthesis happens only in mesophyll cells
 Needs a temperate environment
 Eg. Wheat
C4
 Rapid carbon uptake
 Therefore, faster fixation
 Photosynthesis occurs in more cells
 Can survive in hot, dry climates
 Eg. Sugar cane