The process that occurs in green plants, wherebysolar energy is converted into chemical energyand stored as organic molecules by making useof carbon dioxide, sunlight, and water. Waterand Oxygen are formed as byproducts Photosynthesis can be summarized in thefollowing equation: 6 CO2 + 12 H2O + Lightenergy C6H12O6 + 6 O2 + 6H2O (glucose)WHAT IS PHOTOSYNTHESIS?
Photoautotrophs can photosynthesize.Include: Green plants, algae, cyanobacteriaand green protists.WHO OR WHAT CAN PHOTOSYNTHESIZE?PlantsGreen protistsCyanobacteriaAlgae
To provide nutrients and oxygen forheterotrophs.Heterotrophs are dependent onautotrophs, because they cannot producethere own food.WHY DO PLANTS PHOTOSYNTHESIZE?
Photosynthesis occurs in the chloroplasts ofplant cells. The chloroplasts are mainly concentrated inthe mesophyll cells of leaves. Chloroplast contain chlorophyll – greenpigment that absorbs sunlight. Chlorophyll fill the space in the thylakoidmembrane.WHAT PART OF THE PLANT ISRESPONSIBLE FOR PHOTOSYNTHESIS?
RAW MATERIALS OFPHOTOSYNTHESIS• The raw materials ofphotosynthesis are: water,carbon dioxide andsunlight.
HOW RAW MATERIALS REACHTHE CHLOROPLASTS Water is absorbed through the root hair into thexylem of the roots, into the xylem of the stem,through the xylem of the leaves into the mesophyllcells and finally into the chloroplasts. Carbon dioxide diffuses from the atmospherethrough the stomata, into the intercellular airspacesin the leaves, and finally into the chloroplasts of themesophyll cells. The chlorophyll and other pigments in thethylakoid membrane absorb the solar energy todrive photosynthesis
LIGHT REACTION PHASE(Dependent on light)DARK PHASE/ CALVIN CYCLE(Light independent)PHOTOSYNTHESIS CONSIST OF 2STAGES:
Takes place in the thylakoids of the chloroplasts.Chlorophyll absorbs solar energy from the sun.When a chlorophyll pigment absorbs light(photon of energy), it excites the electrons, whichgoes from ground state to an excited state, whichis unstable, but can be used as potential energy.When unused excited e- fall back to the groundstate, photons and heat are given off.LIGHT REACTION PHASE
The electrons are excited in thephotosystems fount in the thylakoidmembrane.This potential energy is then used firstly tosplit water – into hydrogen & oxygen. 2H2O 2H2 + O2 Oxygen is released as a byproduct – diffusethrough stomata into atmosphere.The hydrogen reduces NADP+ to NADPHSome energy is then used tophotophosphorylate ADP to generate ATP. ADP + P ATP
Carbon dioxide diffuses through thestomata of the leave and finally into thestroma of the chloroplast. The carbon dioxide is accepted by a 5Cmolecule called ribulose biphosphate(RuBP) which then forms an unstable 6Ccompound. 6C compound dissociates into 2 x 3Ccompounds called phosphoglycerate(PGA)CALVIN CYCLE
PGA is then reduced to phosphoglyceraldehyde(PGAL/ G3P) by accepting a phosphate from ATPand a hydrogen electron from NADPH.Thus changing ATP back to ADP and NADPH toNADP. PGAL are now used for the following reactions: Some PGAL are used to make RuBP again, sothat the cycle can start over again. Some PGAL are used to form hexose sugars likeglucose and fructose. Which combine to formdisaccharides and polysaccharides.* The carbohydrates can then be converted toother biological compounds like proteins or fatsby adding mineral salts like nitrates andphoshates.
CO2 + RuBP(5C) 6Ccompound2x PGA (3C) PGALATP = ADP + PNADPH = NADP + H
.Fig. 10-21LightReactions:Photosystem IIElectron transport chainPhotosystem IElectron transport chainCO2NADP+ADPPi+RuBP 3-PhosphoglycerateCalvinCycleG3PATPNADPHStarch(storage)Sucrose (export)ChloroplastLightH2OO2
Light is a form of energy =ELECTROMAGNETIC ENERGY/ELECTROMAGNETIC RADIATION The electromagnetic energy travel in waves. Distance between crests of electromagneticwaves = WAVELENGTH Wavelength range from ≤ 1nm (gamma rays) – ≥ 1 km (radio waves) The entire range of radiation wavelengths =ELECTROMAGNETIC SPECTRUMTHE NATURE OF SUNLIGHT
The most important part for life is the visiblelight (380nm – 750nm)We can see this light as various colours.Light consist of particles = PHOTONSPhotons have energy- The shorter the wavelength the greater the energy of the photon.Therefore violet light has more energy than redlight.Photosynthesis are driven by visible light of thesun.
Chlorophyll a – Absorb violet, blue and red light.Reflects and transmits green light (that is why plantleaves appear green) Chlorophyll b – Absorb violet, blue and red light.Reflects and transmits green light (that is why plantleaves appear green). Carotenoids – Play an accessory role inphotosynthesis. They are shades of yellow andorange and able to absorb light in the violet-blue-green range. These pigments become noticeable inthe fall when chlorophyll breaks down.MAIN PIGMENTS USED DURINGPHOTOSYNTHESIS:
The thylakoid membrane of a chroloplastcontains several photosystems. A photosystem consist of a protein complexcalled a reaction-centre complex surrounded byseveral light harvesting complexes. Study the diagram to understand the process oflight harvesting.HOW A PHOTOSYSTEM HARVESTSLIGHT
THYLAKOID SPACE(INTERIOR OF THYLAKOID)STROMAe–PigmentmoleculesPhotonTransferof energySpecial pair ofchlorophyll amoleculesThylakoidmembranePhotosystemPrimaryelectronacceptorReaction-centercomplexLight-harvestingcomplexes
The Importance of Photosynthesis: A ReviewEnergy entering chloroplasts as sunlight getsstored as chemical energy in organic compoundsSugar made in the chloroplasts supplies chemicalenergy and carbon skeletons to synthesize theorganic molecules of cells.Plants store excess sugar as starch in structuressuch as roots, tubers, seeds, and fruitsIn addition to food production, photosynthesisproduces the O2 in our atmosphere