Photosynthesis is the process by which plants use sunlight (light energy) to produce glucose from carbon dioxide and water, with oxygen as a byproduct. This process occurs LIGHT in the in a plant cell and has DEPENDENT Cytochrome b f Reduced REACTIONS two stages – the light-dependent reactions 6 NADP NADP + 1. Light activation of and the light-independent reactions.  H ATP  synthase photocentres It all starts with the sunlight hitting  e- PSII 2. Photolysis of water - + the fi rst photocentre (PSII). (P68  e PSI H e- (P 3. Electron transport e- ATP e- +  4. Pumping H into the + O H space  ADP + Pi H O +  + H 5. Synthesis of ATP H  6. Reduction of NADP Photolysis THYLAKOID SPACE

CO OXYGEN Thylakoid membrane GLUCOSE REDUCED NADP & ATP

Glucose is used in respiration for energy. Glucose is converted to: 1. Cellulose for cell walls 2. Sucrose for transport 3. Starch for storage ADP + Pi & NADP + Pi ADP

CHLOROPLAST

CALVIN C LIGHT CO YCL  E ( Six INDEPENDENT RuBisCO tu rn enzyme BON FIXAT s CAR ION to REACTIONS p  ro d u c Calvin cycle e

RuBP GP g l 1. Carbon fi xation u Ribulose bisphosphate Glycerate phosphate c o

s e

) 2. Reduction

P

B 3. Regeneration of RuBP

u

R ATP

F ADP + Pi O

N ADP + Pi

O

R

I ATP 

E T

D A

R

Reduced NADP U

E C

N

T

E I

O

G NADP

N E R

 GALP Glyceraldehyde phosphate Hexose Glucose

LAMELLA

THYLAKOIDS

STROMA KEY TO SYMBOLS INNER MEMBRANE Carbon atom: Electron transport: e- OUTER H+ movement:

GLOSSARY

ATP synthase: An enzyme that catalyses the Ferrodoxin: An electron carrier sitting just Light-dependent reactions: The fi rst stage Photosystem I (PSI): The second photosystem Plastoquinone: A molecule that is reduced Regeneration of RuBP: The third stage of Stroma: The aqueous solution that fi lls the synthesis of ATP from ADP and inorganic outside the thylakoid in the chloroplast of photosynthesis. These reactions take in the of the light- by taking two electrons from photosystem II, the Calvin cycle. Glyceraldehyde phosphate inner chloroplast membrane, suspending the phosphate (Pi). stroma. In the poster, this is the small light place in the thylakoid membrane, forming an dependent reactions (but named because it before picking up two hydrogen ions from the molecules are converted into ribulose chloroplast’s contents. The light-independent green oval. electron transport chain that creates ATP and was discovered fi rst). chloroplast stroma and passing the electrons monophosphate (which has fi ve carbon atoms reactions of photosynthesis take place here. Carbon fi xation: The fi rst stage of the Calvin reduced NADP. and protons to cytochrome b f. and one phosphate), which are then converted cycle. The enzyme RuBisCO catalyses a Glucose: A hexose sugar and the product of Photosystem II (PSII): The fi rst photosystem 6 Sucrose: A disaccharide sugar composed into ribulose biphosphate (RuBP) by reacting reaction between ribulose biphosphate (RuBP) photosynthesis. It is one of the main sources Light-independent reactions: Also known as in the electron transport chain of the light- Reaction centres: Complexes of proteins, of two monosaccharide sugars: glucose with ATP. This RuBP then relaunches the cycle and carbon dioxide, producing glycerate of chemical energy used in cellular respiration. the Calvin cycle, these three reactions – carbon dependent reactions (but named because it each containing a special pair of chlorophyll and fructose. with new carbon dioxide molecules. phosphate (GP), thus fi xing inorganic carbon fi xation, reduction and regeneration of ribulose was discovered second). It uses light energy to molecules, that sit at the heart of Hexose: A six-carbon sugar formed as the : Disc-shaped compartments, into an organic compound. biphosphate (RuPB) – form the second stage of emit excited electrons sourced via photolysis photosystems. Regular chlorophyll molecules Ribulose biphosphate (RuBP): A molecule product of six turns of the Calvin cycle. enclosed by their own membranes, present photosynthesis, in which glucose is produced. of water. channel light energy to these special with fi ve carbon atoms and two phosphates Chlorophyll: A family of green pigments Glucose is a hexose. inside the chloroplast. Much of the light- They occur in the chloroplast stroma. chlorophyll pairs (called P680 in photosystem that reacts with carbon dioxide to fi x carbon in found in and around the photosystems Plastocyanin (PC): An electron carrier in dependent reactions of photosynthesis take Inorganic phosphate (Pi): A molecule II, P700 in photosystem I), which then, the Calvin cycle. of chloroplasts. NADP (nicotinamide adenine dinucleotide the thylakoid membrane, sitting between place in the membranes of thylakoids. that plays a key role in respiration and when su ciently excited, shed a highly phosphate): A coenzyme that acts as an photosystem II and cytochrome b f. In the RuBisCO: Ribulose bisphosphate carboxylase Chloroplasts: The pigment-rich organelles photosynthesis and which, among its 6 energised electron. Thylakoid space: The compartment enclosed electron acceptor in photosynthesis. poster, this is the medium-sized purple oval. oxidase; an enzyme that catalyses a reaction where photosynthesis takes place in plant cells. functions, combines with ADP to create ATP. by the thylakoid membrane. Hydrogen ions Reduction: The donation of an electron to between carbon dioxide and ribulose Photolysis: A chemical reaction in which a concentrate inside this space, creating an Cytochrome b f: An enzyme in the thylakoid Lamella: An extension connecting two a molecule. biphosphate (RuBP). 6 compound is broken down using light energy. electrochemical gradient across the thylakoid membrane that acts as an electron carrier. thylakoid discs arranged in diff erent stacks Photosystem II uses water photolysis to replace membrane that powers ATP synthase. A within a chloroplast. the electrons emitted from its reaction centre. stack of thylakoid discs is known as a granum (plural: grana).

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The Wellcome Trust is a charity registered in England and Wales, no. 210183. Its sole trustee is The Wellcome Trust Limited, a company registered in England and Wales, no. 2711000 (whose registered o ce is at 215 Euston Road, London NW1 2BE, UK). PU-6461.3/40K/04–2016/BS

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