PHOTOSYNTHESIS

PHOTOSYNTHESIS Process that converts light energy to chemical energy Occurs in chloroplasts of green plants (mostly in leaves) Contains pigment called chlorophyll Gives chloroplasts their green color

Chloroplast Thylakoid stacks are connected together Organelle where photosynthesis takes place. Stroma Outer Membrane Thylakoid Granum Inner Membrane Thylakoid stacks are connected together

CHLOROPLAST STRUCTURE Enclosed by two membranes Inner membrane encloses a thick fluid called stroma Disk-shaped sacs called thylakoids are suspended in stroma Granum: stack of thylakoids

PHOTOSYNTHESIS EQUATION SUN 6 CO2 + 6 H2O  C6H12O6 + 6 O2 6 carbon dioxide + 6 water  glucose + 6 oxygen Occurs in two main stages: 1. light reactions: happens in thylakoid membranes 2. Calvin cycle: happens in the stroma

C6H12O6 + 6 O2  6 CO2 + 6 H2O + ATP Photosynthesis Equation: sunlight 6CO2 + 6 H2O  C6H12O6 + 6 O2 6 Carbon Dioxide + 6 Water  Glucose + 6 Oxygen Cellular Respiration Equation: C6H12O6 + 6 O2  6 CO2 + 6 H2O + ATP Glucose + 6 Oxygen  6 Carbon Dioxide + 6 Water

The Light Reactions Convert energy in sunlight to chemical energy Chlorophyll molecules capture light energy (units called photons) Captured energy is used to split water molecules  photolysis H2O  O2 and H+ ions produced

The Light Reactions O2 escapes from leaf as waste product H+ bonds to NADP+ (electron carrier molecule) forming NADPH NADPH moves to stroma ATP is produced by light energy

The Calvin Cycle Glucose made from atoms of CO2, hydrogen, ATP, and electrons carried by NADPH Enzymes for Calvin cycle reactions are located outside thylakoids  dissolved in stroma ATP from light reactions provides energy to make glucose

The Calvin Cycle Calvin cycle reactions are also called the light-independent or dark reactions (can occur without direct light) Cannot continue indefinitely without two inputs supplied by light reactions: 1. ATP 2. NADPH

LIGHT ENERGY & PIGMENTS Visible light: part of the electromagnetic spectrum our eyes detect as different colors Pigments: chemicals that absorb, transmit, or reflect different wavelengths of light

CHLOROPLAST PIGMENTS Absorb blue-violet & red-orange light Convert absorbed light energy to chemical energy Green pigments do not absorb green light well: reflect or transmit it back makes leaves look green

LIGHT REACTIONS & PHOTOSYSTEMS Photosystems: clusters of chlorophyll and other molecules in thylakoid membranes of the chloroplast Two photosystems involved in light reactions Each photosystem uses a different chlorophyll molecule and performs a different task Electron transport chain connects the two photosystems and produces ATP

PHOTOSYSTEM 2 “Water-splitting” photosystem Produces hydrogen ions (H+) and releases oxygen (O2) as a waste product Electrons released in splitting H2O are used to make ATP

PHOTOSYSTEM 1 “NADPH producing” photosystem Light striking another chlorophyll molecule causes electrons to gain energy and leave the molecule These electrons along with H+ ions from water are added to NADP+ to produce NADPH

What you need to know about the light reactions Occur on thylakoid membranes Get energy from photons of light Reactants: H2O, light End products: O2, NADPH, ATP Destination of end products: ATP and NADPH go to stroma (Calvin cycle) O2 leaves as waste product

What you need to know about the Calvin Cycle Uses CO2 and a 5-carbon sugar (RuBP) along with molecules from the light reactions (ATP & NADPH) to produce glucose—the main cellular fuel Occurs in the stroma of chloroplast Where do the reactants come from? RuBP  present in stroma CO2  from atmosphere NADPH, ATP  from light reactions

CALVIN CYCLE What are the end products? 3-carbon sugar G3P  used by plant cells to produce more complex carbohydrates Glucose starch cellulose Where does energy for Calvin cycle come from? ATP produced in light reactions Where does the Calvin cycle occur? stroma of chloroplast

SUMMARY OF PHOTOSYNTHESIS

THE CARBON CYCLE Process by which carbon moves from inorganic to organic compounds and back Photosynthesis converts inorganic carbon dioxide to organic compounds Consumers eat producers and return carbon dioxide to the atmosphere via cellular respiration

CARBON CYCLE

PHOTOSYNTHESIS & GLOBAL CLIMATE Photosynthesis uses CO2 to make sugars Most organisms give off CO2 in cellular respiration Total effect of all the organisms on Earth has a large effect on the amount of CO2 in the atmosphere

Greenhouse Effect Amount of CO2 in atmosphere has been increasing rapidly greenhouse effect: CO2 traps heat from the sun that would otherwise escape into space Increased CO2—mainly from fossil fuels—traps more heat leading to global warming

GREENHOUSE EFFECT