LEARNING OBJECTIVES By the end of this lecture you will be able to: 1. Understand that ENERGY can be transformed from one form to another. 2. Know that energy exist in two forms; free energy - available for doing work or as heat - a form unavailable for doing work. 3. Appreciate that the Sun provides most of the energy needed for life on Earth. 4. Explain why photosynthesis is so important to energy and material flow for life on earth. 5. Know why plants tend to be green in appearance. 6. Equate the organelle of photosynthesis in eukaryotes with the chloroplast. 7. Describe the organization of the chloroplast. 8. Understand that photosynthesis is a two fold process composed of the light-dependent reactions (i.e., light reactions) and the light independent reactions (i.e. Calvin Cycle or Dark Reactions). 9. Tell where the light reactions and the CO2 fixation reactions occur in the chloroplast.

10. Define chlorophylls giving their basic composition and structure. 11. Draw the absorption spectrum of chlorophyll and compare it to the action spectrum of photosynthesis. 12. Define the Reaction Centers and Antennae and describe how it operates. 13. Describe cyclic photophosphorylation of photosynthesis. 14. Describe noncyclic photophosphorylation of photosynthesis. Energy can be transformed from one form to another FREE ENERGY (available for work) vs. HEAT (not available for work) THE SUN: MAIN SOURCE OF

ENERGY FOR LIFE ON EARTH THE BASICS OF PHOTOSYNTHESIS Almost all plants are photosynthetic autotrophs, as are some bacteria and protists Autotrophs generate their own organic matter through photosynthesis Sunlight energy is transformed to energy stored in the form of chemical bonds (c) Euglena (b) Kelp (a) Mosses, ferns, and flowering plants (d) Cyanobacteria

Light Energy Harvested by Plants & Other Photosynthetic Autotrophs 6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2 Food Chain THE FOOD WEB WHY ARE PLANTS GREEN? It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that Kermit the Frog

Electromagnetic Spectrum and Visible Light Gamma rays X-rays UV Infrared & Microwaves Visible light Wavelength (nm) Radio waves

WHY ARE PLANTS GREEN? Different wavelengths of visible light are seen by the human eye as different colors. Gamma rays X-rays UV Infrared Visible light Wavelength (nm)

Microwaves Radio waves The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. lig h d e ect l

f e R t Sunlight minus absorbed wavelengths or colors equals the apparent color of an object. Why are plants green? ted c fl e e R

h lig t Transmitted light WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts The thylakoid membrane of the chloroplast is impregnated with

photosynthetic pigments (i.e., chlorophylls, carotenoids). THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light

Absorbed light Transmitted light Chloroplast AN OVERVIEW OF PHOTOSYNTHESIS Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water Carbon dioxide

Water Glucose PHOTOSYNTHESIS Oxygen gas AN OVERVIEW OF PHOTOSYNTHESIS The light reactions convert solar energy to chemical energy Light Chloroplast NADP

ADP +P Produce ATP & NADPH The Calvin cycle makes sugar from carbon dioxide ATP generated by the light reactions provides the energy for sugar synthesis The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Light

reactions Calvin cycle Chloroplasts: Sites of Photosynthesis Photosynthesis Occurs in chloroplasts, organelles in certain plants All green plant parts have chloroplasts and carry out photosynthesis The leaves have the most chloroplasts The green color comes from chlorophyll in the chloroplasts The pigments absorb light energy Photosynthesis occurs in chloroplasts

In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts A chloroplast contains: stroma, a fluid grana, stacks of thylakoids The thylakoids contain chlorophyll Chlorophyll is the green pigment that captures light for photosynthesis The location and structure of chloroplasts Chloroplast LEAF CROSS SECTION MESOPHYLL CELL LEAF

Mesophyll CHLOROPLAST Intermembrane space Outer membrane Granum Grana Stroma Inner membrane Stroma

Thylakoid Thylakoid compartment Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a Chlorophyll b Carotenoids Figure 7.7 Chlorophyll a & b Chl a has a methyl group Chl b has a carbonyl

group Porphyrin ring delocalized e- Phytol tail Different pigments absorb light differently Excitation of chlorophyll in a chloroplast Loss of energy due to heat causes the photons of light to be less energetic. Less energy translates into longer wavelength.

e 2 Excited state Heat Energy = (Plancks constant) x (velocity of light)/(wavelength of light) Transition toward the red end of the visible spectrum. Light Light

(fluorescence) Photon Ground state Chlorophyll molecule (a) Absorption of a photon (b) fluorescence of isolated chlorophyll in solution Molecular Game of Hot Potato Primary electron acceptor Photon

PHOTOSYSTEM Reaction center Pigment molecules of antenna Cyclic Photophosphorylation Process for ATP generation associated with some Photosynthetic Bacteria Reaction Center => 700 nm Two types of photosystems cooperate in the light reactions

Photon Photon ATP mill Water-splitting photosystem NADPH-producing photosystem Noncyclic Photophosphorylation Photosystem II regains electrons by splitting water, leaving O2 gas as a by-productE

Primary electron acceptor Primary electron acceptor El ec tro n tra ns po rt

l ec tro n tra ns po rt ch ai n Photons Energy for synthesis of

PHOTOSYSTEM I PHOTOSYSTEM II by chemiosmosis Plants produce O2 gas by splitting H2O The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-) How the Light Reactions Generate ATP and NADPH Primary electron acceptor Energy to make Primary

electron acceptor NADP 3 2 Light Ele c Light tr o nt r an

sp o rt ch ai n Primary electron acceptor 1 Reactioncenter chlorophyll

Water-splitting photosystem 2 H + 1/2 NADPH-producing photosystem In the light reactions, electron transport chains generate ATP, NADPH, & O2 Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from the primary electron acceptor to electron transport chains Their energy ends up in ATP and NADPH

Chemiosmosis powers ATP synthesis in the light reactions The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP In the stroma, the H+ ions combine with NADP+ to form NADPH 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 A Photosynthesis Road Map Chloroplast Light Stroma NADP Stack of thylakoids ADP +P

Light reactions Calvin cycle Sugar used for Cellular respiration Cellulose Starch Other organic compounds Review: Photosynthesis uses light energy to make food molecules A summary of the chemical processes of

photosynthesis Chloroplast Light Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma

Elec tron s Cellular respiration Cellulose Starch LIGHT REACTIONS CALVIN CYCLE Other organic compounds It's not that

easy bein' green but it is essential for life on earth!

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