Capturing sunlight to provide energy for life on earth Photosynthesis http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html Capturing sunlight to provide energy for life on earth

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

The Electromagnetic Spectrum The ES describes all of the various types of radiation. Radiation is energy that travels and spreads out as it goes– visible light that comes from a light bulb or radio waves that come from a radio station are two types of electromagnetic radiation. Other examples of EM radiation are microwaves, infrared and ultraviolet (UV) light.

Visible Light The portion of the ES that can be seen by animals is called Visible Light. Light is given off by the sun in waves. The waves determine the color and energy.

Wavelengths The length of the waves determines the energy and the light’s color. The shorter the wave, the greater its energy.

Why are plants green? Chlorophylls and accessory pigments ABSORB blue/violet and orange/red light REFLECT green light Makes chlorophyll in plants appear green

Two accessory pigments Chlorophyll The primary pigments for photosynthesis Captures sunlight energy Two accessory pigments Carotenes Xanthophyll absorb light transfer energy to chlorophyll

Pigments absorb light differently

Introduction Photosynthesis – the conversion of sunlight energy to chemical energy (glucose) CO2 + H2O + light energy C6H12O6 + O2 Carbon Dioxide Water Glucose Oxygen

Why is it important? The products are glucose and oxygen: Many organisms (including humans) use glucose as an energy source All aerobic organisms use oxygen

Plant Photosynthesis CO2 is obtained through adjustable pores called stomata Water and minerals provided by a system of veins in the plant Mostly absorbed through the roots Veins also carry sugars to other parts of the plant

Plant Photosynthesis Photosynthesis takes place in the chloroplasts Thylakoid= membranous sac Granum= Stack of thylakoids Stroma= Fluid inside chloroplast MAKE A DIAGRAM OF A CHLOROPLAST: Label: Thylakoid, Granum (p.= grana), Stroma

Anatomy of a Chloroplast Why have stacks? More surface area (more room to do photosynthesis)

Plant Photosynthesis Photosynthesis can be divided into two types of reactions: Light-dependent reaction Light-independent reaction (Dark reactions)

AN OVERVIEW OF PHOTOSYNTHESIS The light reactions convert solar energy to chemical energy Produce ATP & NADPH Light Chloroplast NADP ADP + P The Calvin cycle makes sugar from carbon dioxide ATP generated by the light reactions provides the energy to make sugar The NADPH produced by the light reactions provides the electrons to make glucose from carbon dioxide Calvin cycle Light reactions

Homework Write out question and answer in complete sentences! What makes the parts of the electromagnetic spectrum different from each other? What color of light is not absorbed by plants? What happens to this color? What are the reactants and products to photosynthesis?

ELECTRON TRANSPORT CHAIN Thylakoid space (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

Plant Photosynthesis Steps to Light-Dependent Reactions: Photosystem II: Has chlorophyll inside (captures sunlight) Splits water: Things made from splitting water: H+ (protons) O Electrons (e-) Electrons from splitting of water get excited by sunlight energy in the reaction center Electrons and H+ drive ATP synthesis O2 gas is a by-product

Primary electron acceptor Molecular Game of “Hot Potato” Primary electron acceptor Photon Reaction center PHOTOSYSTEM Pigment molecules of antenna

ELECTRON TRANSPORT CHAIN Thylakoid compartment (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

Electron Transport Chain Photosystem I: Has chlorophyll inside Light excites electrons again, electrons used to produce NADPH (electron carrier)

Two types of photosystems cooperate in the light reactions Photon ATP mill Gold hammers= photon Photon Water-splitting photosystem NADPH-producing photosystem

Plants produce O2 gas by splitting H2O The O2 made by photosynthesis is from the oxygen in water

Light-dependent rxn Light-dependent reactions continue as long as water and sunlight are available

ETC Continued The Electron transport chain is made up of proteins that accept and transfer the electrons. The electrons are passed from protein to protein and energy is given off along the way. Demonstration: 3 Students in a line passing an electron (any object): students should yelp (give off energy) as they pass the electron quickly (Could have two desks represent photosystems)

Electron Transport Chain The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane into the thylakoid Creates a high concentration of H+ inside and low concentration of H+ outside membrane The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP

ELECTRON TRANSPORT CHAIN Thylakoid compartment (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

ATP Synthase and Chemiosmosis The protons (H+) diffuse out of the thylakoid through an enzyme complex called ATP Synthase Uses ETC (to pump H+ in) Protons (H+) move down their concentration gradient through channels of ATP synthase forming ATP from ADP

Chemiosmosis ADP + Pi  ATP

Formation of NADPH Electrons at the end of the “chain” are used to make NADPH from NADP+. NADP+ + 2e- + H+  NADPH NADPH is an energy carrier molecule that takes electrons to the stroma for the Calvin Cycle.

ELECTRON TRANSPORT CHAIN The production of ATP by chemiosmosis in photosynthesis Thylakoid compartment (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

Light Rxn Qs Write out question and answer in complete sentences! What happens in: photosystem I? photosystem II? Describe what happens on the electron transport chain. Chemiosmosis: Where does it happen? What does it make?

Photosynthesis Part II The Calvin Cycle Photosynthesis Part II

Sun light + CO2 + H2O  C6H12O6 + O2 Equation Sun light + CO2 + H2O  C6H12O6 + O2

The Calvin Cycle Overview The Calvin Cycle (sometimes called the dark reaction) uses the potential energy (ATP and NADPH) produced in the light reactions to make sugars that organisms can use for growth.

Calvin Cycle The Calvin Cycle occurs in the stroma of chloroplasts. Carbon dioxide is captured by the chemical ribulose biphosphate (RuBP). Six molecules of carbon dioxide enter the Calvin Cycle, eventually producing one molecule of glucose.

Carbon dioxide comes in through the stomata and is fixed (attached) Steps to Calvin Cycle: Carbon dioxide comes in through the stomata and is fixed (attached) to a molecule called RuBP to make PGA The energy from ATP and electrons from NADPH (both from the light rxn) are used to convert PGA to PGAL PGAL =3 carbon molecule. One PGAL is released from the cycle to be made into glucose later Rest of PGAL is used to regenerate RuBP ** Must go through the cycle twice Glucose is a 6-carbon sugar (3 + 3 = 6)

Energy Cycles The glucose produced and the O2 released by plants are used by other organisms to produce energy (and the other organisms release CO2) This CO2 is then used by plants to produce more glucose via photosynthesis

Alternative Pathways Typical plants are called C3 plants because they use a three-carbon compound . One of the alternative pathways is the C4 pathway (C4 plants) Uses a four-carbon compound to store CO2 Corn, sugar cane, and crabgrass Store CO2 and do Calvin Cycle different cells (allows plant to be more efficient) -The fourth carbon is storage for carbon dioxide (so the Calvin Cycle can run during times of low CO2 levels) -Fixes a CO2 molecule withl a 3-c molecule -Separates these reactions into different cells

CAM Pathway Cacti, pineapples, and others have an adaptation to hot, dry climates. These plants use a four-carbon compound in a pathway called CAM. CAM plants open their stomata at night and close them during the day (the opposite of C3 plants). Prevents water loss to evaporation Most CO2 available at night Most desert animals are nocturnal At night, CAM plants fix (store) CO2 so that during the day these compounds enter the Calvin cycle (Opposite of C4 plants). Typical C4 plants take in and store CO2 during the day for use at night Stomata close during the day to prevent water loss Four-c molecule stores CO2 for when CO2 levels are low during day (most desert animals are nocturnal- most CO2 available at night) Stranded in desert? Eat the plants during the day (CAM plants are sour in morning (due to acid build-up) and become bland during the day due to running Calvin Cycle, and bitter at night bc c-fixing molecule presence) WARNING- most desert plants are poisonous

Dark Rxn Qs Write out question and answer in complete sentences! What does the dark RXN use from the light RXN? How many carbons does PGAL have? Why does it go through the cycle twice to make glucose? How are CAM plants able to store water better than others?