AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions

Sunlight is made up of many different _______________ of light Your eyes “see” different wavelengths as different ___________ wavelengths colors

Visible light is part of electromagnetic spectrum ROYGBIV

pigments By: VanderWal Plants gather the sun’s energy with light absorbing molecules called _______________.

The main energy absorbing molecule in green plants is __________________ CHLOROPHYLL a

CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW Carotene appears orange Xanthophyll appears yellow

Pigments of photosynthesis Chlorophyll & other pigments –embedded in thylakoid membrane –arranged in a “photosystem” –structure-function relationship

Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light –chlorophyll a absorbs best in red & blue wavelengths & least in green –other pigments with different structures absorb light of different wavelengths

WHY ARE PLANTS GREEN? We “see” reflected light Light wavelengths that are reflected bounce back to your eyes... so leaves “LOOK” green. Image modified from:

WHY DON’T WE SEE THE OTHER PIGMENTS? Carotenoids are usually hidden by the presence of chlorophyll

In the fall chlorophyll production shuts down and other pigments “show”

PHOTOSYNTHESIS OVERVIEW Pearson Education Inc; Publishing as Prentice Hall

Phosphate groups Ribose Adenine LIGHT DEPENDENT REACTIONS CHARGE UP ENERGY CARRIER = _____ ATP

P i ADP Energy for cellular work (Energy- consuming) Energy from catabolism (Energy- yielding) ATP +

High energy electron carrier = _____________ NADP + NADP + + 2e - + H + → NADPH NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE

Photosynthesis Light reactions –light-dependent reactions –energy production reactions convert solar energy to chemical energy Make ATP & NADPH Calvin cycle –light-independent reactions –sugar production reactions use chemical energy (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6

Photosystems of photosynthesis 2 photosystems in thylakoid membrane –Both have a REACTION CENTER CHLOROPHYLL a molecules PRIMARY ELECTRON ACCEPTOR –Surrounded by light-gathering “ANTENNA COMPLEX” Accessory pigments (chlorophyll b, carotenoids) –Collect light energy and pass it on to chlorophyll a –Photosystem II P 680 = absorbs 680nm wavelength red light –Photosystem I P 700 = absorbs 700nm wavelength red light

ELECTRON TRANSPORT CHAIN Plastoquinone Cytochrome Plastocyanin Ferredoxin

Light Dependent reactions Electron Transport Chain –membrane-bound proteins in organelle –electron acceptors NADPH –proton (H + ) gradient across inner membrane Where’s the double membrane? –ATP synthase enzyme H+H+ H+H+ H+

LIGHT DEPENDENT REACTIONS ETC produces from light energy –ATP & NADPH go to Calvin cycle PS II absorbs light –excited electron passes from chlorophyll to “primary electron acceptor” –need to replace electron in chlorophyll –enzyme extracts electrons from H 2 O & supplies them to chlorophyll splits H 2 O O combines with another O to form O 2 O 2 released to atmosphere and we breathe easier!

MAKING ATP moves the electrons runs the pump pumps the protons forms the gradient drives the flow of protons through ATP synthase attaches P i to ADP forms the ATP H+H+ ADP + P i H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP

Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I) –PS II generates energy as ATP –PS I generates reducing power as NADPH

Cyclic photophosphorylation PS I doesn’t pass electron to NADP… it cycles back to ETC & makes more ATP, but no NADPH –coordinates light reactions to Calvin cycle –Important in maintaining proportion of ATP & NADPH for Calvin –Calvin cycle uses more ATP than NADPH X

Photophosphorylation noncyclic photophosphorylation cyclic photophosphorylation

6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Experimental evidence Where did the O 2 come from? –radioactive tracer = O 18 6CO 2 6H 2 O C 6 H 12 O 6 6O26O2 light energy  +++ Experiment 1 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Experiment 2 Proved O 2 came from H 2 O not CO 2 = plants split H 2 O

LIGHT DEPENDENT REACTION Requires ______________ Molecules embedded in ________________________ Made up of __________________ connected by ______________________ & ___________________ Uses light energy to change ADP + P → _______ NADP + + 2e - + H + → _________ Breaks apart ______ molecules and releases _____________ LIGHT ATP THYLAKOID membranes PHOTOSYSTEMS II & I ELECTRON TRANSPORT CHAIN NADPH H20H20 oxygen ATP SYNTHASE

PHOTOSYNTHESIS Light-Dependent Reaction Light-Independent Reactions CALVIN CYCLE Light & Water Oxygen ATP NADPH Carbon Dioxide (CH 2 O) n

CALVIN CYCLE

Calvin Cycle See Calvin cycle animation * * * * Molecules you need to know X 2

CALVIN CYCLE MOLECULES 5 carbon CO 2 acceptor that combines with CO 2 in the first step of the Calvin cycle ________________________________ Enzyme that catalyzes the addition of CO 2 to RuBP ________________________ 3 carbon sugar produced during the Calvin cycle that can be used to build glucose and other organic molecules ______________________________ Ribulose bisphosphate (RuBP) RuBP carboxylase (RUBISCO) Glyceraldehyde-3-phosphate (G3P)

CALVIN CYCLE (also called _________________________) ____________ require ____________ Happens in _________ between thylakoids NADPH donates _______________ ATP donates _________________ CO 2 donates ______________ to make __________________________ LIGHT LIGHT INDEPENDENT ENERGY STROMA Hydrogen ions + electrons Carbon & oxygen glyceraldehyde-3-phosphate (G3P) DOES NOT

To make one glucose molecule C 6 H 12 O 6 the Calvin cycle uses _____ molecules of CO 2 _____ molecules of ATP _____ molecules of NADPH Campbell concept check 10.3

STOMA (pl. STOMATA) GUARD CELLS

PROBLEMS ON HOT DRY DAYS If stomata are open to receive CO 2... results in water loss On hot, dry days if plant shuts stomata to conserve water... photosynthesis slows

____ plants (Ex: rice, wheat, soybeans) (1 st product of carbon fixation has 3 C’s- 3PG) On hot, dry days when plant shuts stomata plant switches to ______________________ Rubisco adds O 2 to Calvin cycle instead of CO 2 Product broken down by mitochondria/peroxisomes to release CO 2 COUNTERPRODUCTIVE: Makes NO ATP Makes NO sugar Uses ATP Decreases photosynthesis by siphoning molecules from Calvin cycle PHOTORESPIRATION C3C3

ALTERNATIVE METHODS of CARBON FIXATION ______ plants (Ex: corn & sugarcane ______ Crassulacean acid metabolism (Ex: succulents, cactus, pineapple,) WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION C4C4 CAM SEE ANIMATION

CALVIN CYCLE found in BUNDLE SHEATH CELLS in C 4 plants * ________________________ adds CO 2 to make a 4 carbon molecule before entering Calvin Cycle PEP CARBOXYLASE

Process of using H + gradient to generate ATP = ________________________ (Can refer to ATP made in mitochondria too) Process of creating ATP using a Proton gradient created by the energy gathered from sunlight. = ________________________ Process that consumes oxygen, releases CO2, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide = ___________________________________ chemiosmosis photophosphorylation photorespiration