PHOTOSYNTHESIS

Photosynthesis process by which green plants & some organisms seaweed, algae & certain bacteria use light energy to convert CO2 + water glucose all life on Earth, directly or indirectly, depends on photosynthesis as source of food, energy & O2

Autotrophs self feeders organisms that make their own organic matter from inorganic matter producers use inorganic molecules such as CO2, H2O & minerals to make organic molecules

Heterotrophs consumers other feeders depend on glucose as energy source cannot produce it obtained by eating plants or animals that have eaten plants

Carbon and Energy Flow Light energy Heat energy CO2 + H2O Photosynthesis Carbs Proteins Lipids + O2 Cellular (Aerobic) Respiration (ATP Produced)

Food Chain byproduct of photosynthesis is O2 humans & other animals breathe in oxygen used in cellular respiration

Other Benefits of Photosynthesis humans also dependent on ancient products of photosynthesis fossil fuels natural gas, coal & petroleum needed for modern industrial energy complex mix of hydrocarbons represent remains of organisms that relied on photosynthesis millions of years ago

Photosynthesis plants produce more glucose than can use stored as starch & other carbohydrates in roots, stems & leaves can draw on these reserves for extra energy or building materials as needed

Sites of Photosynthesis leaves & green stems in cell organelles chloroplasts concentrated in green tissue in interior of leaf mesophyll green due to presence of green pigment chlorophyll

Chloroplasts each cell has 40-50 chloroplasts oval-shaped structures with double membrane inner membrane encloses compartment filled with stroma suspended in stroma are disk-shaped compartments-thylakoids arranged vertically like stack of plates one stack-granum (plural, grana) embedded in membranes of thylakoids are hundreds of chlorophyll molecules

Chlorophyll light-trapping pigment other light-trapping pigments, enzymes & other molecules needed for photosynthesis are also found in thylakoid membranes

How Photosynthesis Works Requires CO2 Water Sunlight Makes O2 Glucose

How Photosynthesis Works CO2 enters plant via pores- stomata in leaves water-absorbed by roots from soil membranes in chloroplasts provide sites for reactions of photosynthesis chlorophyll molecules in thylakoids capture energy from sunlight chloroplasts rearrange atoms of inorganic molecules into sugars & other organic molecules

Photosynthesis redox reaction 6CO2 + 12H2OC6H12O6 + 6O2 + 6H2O in presence of light must be an oxidation & a reduction water is oxidized loses electrons & hydrogen ions carbon dioxide is reduced gains electrons & hydrogens

Photosynthesis 2 stages light-dependent reactions chloroplasts trap light energy convert it to chemical energy contained in nicotinamide adenine dinucleotide phosphate-(NADPH) & ATP used in second stage light-independent reactions Calvin cycle formerly called dark reactions NADPH (electron carrier) provides hydrogens to form glucose ATP provides energy

Light Energy for Photosynthesis sun energy is radiation electromagnetic energy travels as waves distance between 2 waves- wavelength light contains many colors each has defined range of wavelengths measured in nanometers range of wavelengths is electromagnetic spectrum part can be seen by humans visible light

Pigments light absorbing molecules built into thylakoid membranes absorb some wavelengths & reflect others plants appear green because chlorophyll-does not absorb green light reflected back. as light is absorbedenergy is absorbed chloroplasts contain several kinds of pigments different pigments absorb different wavelengths of light red & blue wavelengths are most effective in photosynthesis other pigments are accessory pigments absorb different wavelengths enhance light-absorbing capacity of a leaf by capturing a broader spectrum of blue & red wavelengths along with yellow and orange wavelengths

Pigment Color & Maximum Absoption Violet:   400 - 420 nm Indigo:   420 - 440 nm Blue:   440 - 490 nm Green:   490 - 570 nm Yellow:   570 - 585 nm Orange:   585 - 620 nm Red:   620 - 780 nm

Chlorophylls Chlorophyll A absorbs blue-violet & red light reflects green participates in light reactions Chlorophyll B absorbs blue & orange light reflects yellow-green does not directly participate in light reactions broadens range of light plant can use by sending its absorbed energy to chlorophyll A

Carotenoids yellow-orange pigments absorb blue-green wavelengths reflect yellow-orange pass absorbed energy to chlorophyll A have protective function absorb & dissipate excessive light energy that would damage chlorophylls

Photosynthesis Pigments Absorb light Excites electrons Energy passed to sites in cell Energy used to make glucose

Photosystems chlorophyll & other pigments clustered next to one another in a photosystem when photon strikes one pigment molecule energy jumps from pigment to pigment until arrives at reaction center

Reaction Center electron acceptor traps a light excited electron from reaction center chlorophyll passes it to electron transport chain which uses energy to make ATP & NADPH

Photosystems two photosystems participate in light reactions photosystems II & I

Light Reactions make ATP & NADPH electrons are removed from molecules of water oxygen escapes to air electrons are passed from photosystem II to photosystem I to NADP+ light drives electrons from H2O to NADP+ which is oxidized NADPH which is reduced

Photosystem II water is split oxygen atom combines with oxygen from another split water forming molecular oxygen-O2 each excited electron passes from photosystem II to photosystem I via electron transport chain

Photosystem I electron acceptor captures an excited electron excited electrons are passed through a short electron transport chain to NADP+ reducing it to NADPH NADP+ -final electron acceptor electrons are stored in high state of potential energy in NADPH molecule NADPH, ATP and O2 are products of light reactions

ATP Formation-Chemiosmosis uses potential energy of hydrogen ion concentration gradient across membrane gradient forms when electron transport chain pumps hydrogen ions across thylakoid membrane as it passes electrons down chain that connects two photosystems

ATP Formation-Chemiosmosis ATP synthase (enzyme) uses energy stored by H gradient to make ATP ATP is produced from ADP & Pi when hydrogen ions pass out of thylakoid through ATP synthase photophosphorylation

Calvin Cycle/Dark Reactions light independent reactions depend on light indirectly for inputs-ATP & NADPH occurs-stroma of chloroplast each step controlled by different enzyme cycle of reactions makes sugar from CO2 & energy ATP provides chemical energy NADPH provides high energy electrons for reduction of CO2 to sugar

Steps of Calvin Cycle starting material-ribulose bisphosphate (RuBP) first step-carbon fixation rubisco (an enzyme) attaches CO2 to RuBP Next-reduction reaction takes place to do this cycle uses carbons from 3 CO2 molecules to complete cycle must regenerate beginning component-RuBP for every 3 molecules of CO2 fixed, one G3P molecule leaves cycle as product of cycle remaining 5 G3P molecules are rearranged using ATP to make 3 RuBP molecules

Calvin Cycle regenerated RuBP is used to start Calvin cycle again process occurs repeatedly in each chloroplast as long as CO2, ATP & NADPH are available thousands of glucose molecules are produced used by plants to produce energy in aerobic respiration used as structural materials stored