Photosynthesis Life Is Solar Powered!

What Would Plants Look Like On Alien Planets?

Why Would They Look Different? Different Stars Give off Different types of light or Electromagnetic Waves The color of plants depends on the spectrum of the star’s light, which astronomers can easily observe. (Our Sun is a type “G” star.)

Anatomy of a Wave Wavelength Is the distance between the crests of waves Determines the type of electromagnetic energy

Electromagnetic Spectrum Is the entire range of electromagnetic energy, or radiation The longer the wavelength the lower the energy associated with the wave.

Visible Light Light is a form of electromagnetic energy, which travels in waves When white light passes through a prism the individual wavelengths are separated out.

Visible Light Spectrum Light travels in waves Light is a form of radiant energy Radiant energy is made of tiny packets of energy called photons The red end of the spectrum has the lowest energy (longer wavelength) while the blue end is the highest energy (shorter wavelength). The order of visible light is ROY-G-BIV This is the same order you will see in a rainbow b/c water droplets in the air act as tiny prisms

Light Options When It Strikes A Leaf Reflect – a small amount of light is reflected off of the leaf. Most leaves reflect the color green, which means that it absorbs all of the other colors or wavelengths. Absorbed – most of the light is absorbed by plants providing the energy needed for the production of Glucose (photosynthesis) Transmitted – some light passes through the leaf Light Reflected Chloroplast Absorbed light Granum Transmitted Figure 10.7

Photosynthesis Overview Concept Map Photosynthesis includes Light dependent reactions Light independent reactions occurs in uses uses occur in Light Energy Thylakoid membranes Stroma ATP NADPH to produce of to produce ATP NADPH O2 Chloroplasts Glucose

Anatomy of a Leaf Figure 10.3 Leaf cross section Vein Mesophyll CO2 O2 Stomata

Chloroplast

Chloroplast Are located within the palisade layer of the leaf Stacks of membrane sacs called Thylakoids Contain pigments on the surface Pigments absorb certain wavelenghts of light A Stack of Thylakoids is called a Granum Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner Thylakoid Granum Stroma 1 µm

Pigments Are molecules that absorb light Chlorophyll, a green pigment, is the primary absorber for photosynthesis There are two types of cholorophyll Chlorophyll a Chlorophyll b Carotenoids, yellow & orange pigments, are those that produce fall colors. Lots of Vitamin A for your eyes! Chlorophyll is so abundant that the other pigments are not visible so the plant is green…Then why do leaves change color in the fall?

Color Change In the fall when the temperature drops plants stop making Chrlorophyll and the Carotenoids and other pigments are left over (that’s why leaves change color in the fall).

Wavelength of light (nm) The absorption spectra of three types of pigments in chloroplasts Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. EXPERIMENT RESULTS Absorption of light by chloroplast pigments Chlorophyll a (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Wavelength of light (nm) Chlorophyll b Carotenoids Figure 10.9

The action spectrum of a pigment Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis (measured by O2 release) Rate of photosynthesis Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids. (b)

The action spectrum for photosynthesis Was first demonstrated by Theodor W. Engelmann 400 500 600 700 Aerobic bacteria Filament of alga Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b. (c) Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis. CONCLUSION

Chlorophyll Chlorophyll a Chlorophyll b Is the main photosynthetic pigment Chlorophyll b Is an accessory pigment C CH CH2 N H3C Mg H CH3 O CHO in chlorophyll a in chlorophyll b Porphyrin ring: Light-absorbing “head” of molecule note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Figure 10.10

PHOTOSYNTHESIS Comes from Greek Word “photo” meaning “Light” and “syntithenai” meaning “to put together” Photosynthesis puts together sugar molecules using water, carbon dioxide, & energy from light.

Happens in two phases Light-Dependent Reaction Converts light energy into chemical energy Light-Independent Reaction Produces simple sugars (glucose) General Equation 6 CO2 + 6 H2O  C6H12O6 + 6 O2

First Phase Requires Light = Light Dependent Reaction Sun’s energy energizes an electron in chlorophyll molecule Electron is passed to nearby protein molecules in the thylakoid membrane of the chloroplast

Excitation of Chlorophyll by Light When a pigment absorbs light It goes from a ground state to an excited state, which is unstable Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground e– Figure 10.11 A

If an isolated solution of chlorophyll is illuminated It will fluoresce, giving off light and heat Figure 10.11 B

ETC Electron from Chlorophyll is passed from protein to protein along an electron transport chain Electrons lose energy (energy changes form) Finally bonded with electron carrier called NADP+ to form NADPH or ATP Energy is stored for later use

Two Photosystems Photosystem II: Clusters of pigments boost e- by absorbing light w/ wavelength of ~680 nm Photosystem I: Clusters boost e- by absorbing light w/ wavelength of ~760 nm. Reaction Center: Both PS have it. Energy is passed to a special Chlorophyll a molecule which boosts an e-

A mechanical analogy for the light reactions Mill makes ATP e– Photon Photosystem II Photosystem I NADPH Figure 10.14 

(INTERIOR OF THYLAKOID) Photosystem A photosystem Is composed of a reaction center surrounded by a number of light-harvesting complexes Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment THYLAKOID SPACE (INTERIOR OF THYLAKOID) Figure 10.12 e–

Where those electrons come from Water Electrons from the splitting of water (photolysis) supply the chlorophyll molecules with the electrons they need The left over oxygen is given off as gas

The Splitting of Water Chloroplasts split water into Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules 6 CO2 12 H2O Reactants: Products: C6H12O6 6 H2O 6 O2 Figure 10.4

High Quality H2O Photolysis – Splitting of water with light energy Hydrogen ions (H+) from water are used to power ATP formation with the electrons Hydrogen ions (charged particle) actually move from one side of the thylakoid membrane to the other Chemiosmosis – Coupling the movement of Hydrogen Ions to ATP production

Animation – takes a min. to load…be patient Animation II – Does not take as long to load but it is not as good

The light reactions and chemiosmosis: the organization of the thylakoid membrane REACTOR NADP+ ADP ATP NADPH CALVIN CYCLE [CH2O] (sugar) STROMA (Low H+ concentration) Photosystem II H2O CO2 Cytochrome complex O2 1 1⁄2 2 Photosystem I Light THYLAKOID SPACE (High H+ concentration) Thylakoid membrane synthase Pq Pc Fd reductase + H+ NADP+ + 2H+ To Calvin cycle P 3 H+ 2 H+ +2 H+ Figure 10.17

Vocabulary Review Light-Dependent Pigment Chlorophyll Electron Transport Chain ATP NADPH Photolysis Chemiosmosis

Light-Dependent Converts light into chemical energy (ATP & NADPH are the chemical products). Oxygen is a by-product Mill makes ATP e– Photon Photosystem II Photosystem I NADPH Figure 10.14 

Pigment Molecules that absorb specific wavelengths of light Chlorophyll absorbs reds & blues and reflects green Xanthophyll absorbs red, blues, greens & reflects yellow Carotenoids reflect orange

Chlorophyll Green pigment in plants Traps sun’s energy Sunlight energizes electron in chlorophyll

Electron Transport Chain Series of Proteins embedded in a membrane that transports electrons to an electron carrier

ATP Adenosine Triphosphate Stores energy in high energy bonds between phosphates

NADPH Made from NADP+; electrons and hydrogen ions Made during light reaction Stores high energy electrons for use during light-Independent reaction (Calvin Cycle)

Chemiosmosis The combination of moving hydrogen ions across a membrane to make ATP

Figure 10.5 H2O CO2 [CH2O] O2 (sugar) Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH2O] (sugar) NADPH NADP  ADP + P O2 Figure 10.5 ATP

PART II LIGHT INDEPENDENT REACTION Also called the Calvin Cycle No Light Required Takes place in the stroma of the chloroplast Takes carbon dioxide & converts into sugar It is a cycle because it ends with a chemical used in the first step

Begins & Ends The Calvin Cycle begins and ends with RuBP CO2 is added to RuBP; “fixing” the CO2 in a compound One compound made along the way is PGAL PGAL can be made into sugars or RuBP Calvin Cycle uses ATP & NADPH

The Calvin cycle Figure 10.18 Input Light 3 CO2 CALVIN CYCLE (G3P) Input (Entering one at a time) CO2 3 Rubisco Short-lived intermediate 3 P P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 P 6 1,3-Bisphoglycerate 6 NADPH 6 NADPH+ Glyceraldehyde-3-phosphate 6 ATP 3 ATP 3 ADP CALVIN CYCLE 5 1 G3P (a sugar) Output Light H2O LIGHT REACTION ATP NADPH NADP+ ADP [CH2O] (sugar) CALVIN CYCLE Figure 10.18 O2 6 ADP Glucose and other organic compounds Phase 1: Carbon fixation Phase 3: Regeneration of the CO2 acceptor (RuBP) Phase 2: Reduction

Chloroplast – Where the Magic Happens! + H2O CO2 Energy ATP and NADPH2 Which splits water Light is Adsorbed By Chlorophyll Calvin Cycle ADP NADP Chloroplast Used Energy and is recycled. O2 + C6H12O6 Light Reaction Dark Reaction 6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O