stomate transpiration AP Biology gas exchange AP Biology

stomate ütranspiration AP ü Biology gas exchange

AP Biology 2007 -2008

Photosynthesis: Life from Light and Air AP Biology

Energy needs of life § All life needs a constant input of energy u Heterotrophs (Animals) § get their energy from “eating others” consumers w eat food = other organisms = organic molecules § make energy through respiration u Autotrophs (Plants) § produce their own energy (from “self”) § convert energy of sunlight producers § build organic molecules (CHO) from CO 2 § make energy & synthesize sugars through photosynthesis AP Biology

How are they connected? Heterotrophs making energy & organic molecules from ingesting organic molecules glucose + oxygen carbon + water + energy dioxide C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP oxidation = exergonic Autotrophs making energy & organic molecules from light energy Where’s the ATP? carbon + water + energy glucose + oxygen dioxide 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy AP Biology reduction = endergonic

What does it mean to be a plant § Need to… u collect light energy ATP § transform it into chemical energy u glucose u store light energy § in a stable form to be moved around the plant or stored need to get building block atoms CO 2 from the environment § C, H, O, N, P, K, S, Mg u produce all organic molecules needed for growth H 2 O N K P … § carbohydrates, proteins, lipids, nucleic acids AP Biology

Plant structure § Obtaining raw materials u sunlight § leaves = solar collectors u CO 2 § stomates = gas exchange u H 2 O § uptake from roots u nutrients § N, P, K, S, Mg, Fe… § uptake from roots AP Biology

Stomates AP Biology

Chloroplasts leaves cross section of leaf absorb sunlight & CO 2 chloroplasts in plant cell chloroplast AP Biology chloroplasts contain chlorophyll make energy & sugar

chloroplast Plant structure H+ ATP + + H+ H H+ + H H + H+ H+ H+ + H H thylakoid § Chloroplasts u u double membrane stroma outer membrane inner membrane § fluid-filled interior u u thylakoid sacs grana stacks stroma § Thylakoid membrane contains u u u chlorophyll molecules electron transport chain ATP synthase § H+ gradient built up within AP Biology thylakoid sac thylakoid granum

Photosynthesis § Light reactions light-dependent reactions u energy conversion reactions u § convert solar energy to chemical energy § ATP & NADPH § Calvin cycle It’s not the Dark Reactions! light-independent reactions u sugar building reactions u § uses chemical energy (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6 AP Biology

thylakoid chloroplast Light reactions § Electron Transport Chain § like in cellular respiration proteins in organelle membrane u electron acceptors u § NADPH u proton (H+) gradient across inner membrane § find the double membrane! u ATP synthase enzyme AP Biology + +H+ H H+ + H+ H+H +H+ H H ATP + +H+ H H+ + H+ H+H H H H

ETC of Respiration Mitochondria transfer chemical energy from food molecules into chemical energy of ATP u use electron carrier NADH generates H 2 O AP Biology

ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP u generates O 2 AP Biology use electron carrier NADPH

The ATP that “Jack” built photosynthesis sunlight respiration breakdown of C 6 H 12 O 6 H+ H+ moves the electrons runs the pumps the protons builds the gradient drives the flow of protons ADP + Pi through ATP synthase § bonds Pi to ADP ATP § generates the ATP AP Biology … that evolution built § § § H+ H+

Pigments of photosynthesis How does this molecular structure fit its function? § Chlorophylls & other pigments u u embedded in thylakoid membrane arranged in a “photosystem” § collection of molecules AP Biology u structure-function relationship

A Look at Light § The spectrum of color V AP Biology I B G Y O R

Light: absorption spectra § Photosynthesis gets energy by absorbing wavelengths of light u chlorophyll a § absorbs best in red & blue wavelengths & least in green u accessory pigments with different structures absorb light of different wavelengths § chlorophyll b, carotenoids, xanthophylls Why are plants green? AP Biology

Photosystems of photosynthesis § 2 photosystems in thylakoid membrane collections of chlorophyll molecules u act as light-gathering molecules u Photosystem II reaction u § chlorophyll a center § P 680 = absorbs 680 nm wavelength red light u Photosystem I § chlorophyll b § P 700 = absorbs 700 nm wavelength red light AP Biology antenna pigments

chlorophyll a ETC of Photosynthesis Photosystem II chlorophyll b Photosystem I AP Biology

ETC of Photosynthesis sun 1 e e AP Biology Photosystem II P 680 chlorophyll a

Inhale, baby! ETC of Photosynthesis thylakoid chloroplast + +H+ H H+ + H+ H+H +H+ H H H+ ATP + +H+ H H+ + H H+ H+ HH Plants SPLIT water! H H 1 e- e e fill the e– vacancy AP Biology Photosystem II P 680 chlorophyll a e- H+ +H OO H H e e O 2

ETC of Photosynthesis thylakoid chloroplast H+ + +H+ H H+ + H H+ H+ HH + +H+ H H+ + H+ H+H H H H e e ATP 3 2 1 e e H+ 4 ATP H+ H+ H+ AP Biology Photosystem II P 680 chlorophyll a H+ to Calvin Cycle H+ H+ H ADP + Pi ATP H+ H+ energy to build carbohydrates

e e ETC of Photosynthesis e e y c an e e – 5 fil he t l e e AP Biology Photosystem II P 680 chlorophyll a Photosystem I P 700 chlorophyll b e c a v sun

ETC of Photosynthesis e e electron carrier 6 e e 5 AP Biology Photosystem II P 680 chlorophyll a Photosystem I P 700 chlorophyll b $$ in the bank… reducing power! N Cal ADPH vin Cyc to sun le

ETC of Photosynthesis e e sun O split H 2 O H+ + H+ H + H+ +H H+ H+ H to Calvin Cycle ATP AP Biology

ETC of Photosynthesis § ETC uses light energy to produce u ATP & NADPH § go to Calvin cycle § PS II absorbs light u u u AP Biology 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!

Experimental evidence § Where did the O 2 come from? u radioactive tracer = O 18 Experiment 1 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy Experiment 2 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy Proved O 2 came from H 2 O not CO 2 = plants split H 2 O! AP Biology

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

Cyclic photophosphorylation § If PS I can’t pass electron to NADP…it cycles back to PS II & makes more ATP, but no NADPH coordinates light reactions to Calvin cycle uses more ATP than NADPH u 18 ATP + NADPH AP 12 Biology 1 C 6 H 12 O 6 ATP

Photophosphorylation cyclic photophosphorylation NADP NONcyclic photophosphorylation ATP AP Biology

Photosynthesis summary Where did the energy come from? Where did the electrons come from? Where did the H 2 O come from? Where did the O 2 go? Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for? AP Biology …stay tuned for the Calvin cycle

You can grow if you Ask Questions! AP Biology

Photosynthesis: The Calvin Cycle Life from Air AP Biology 2007 -2008

Whoops! Wrong Calvin… The Calvin Cycle AP Biology 1950 s | 1961

Remember what it means to be a plant… § Need to produce all organic molecules necessary for growth u carbohydrates, lipids, proteins, nucleic acids § Need to store chemical energy (ATP) produced from light reactions in a more stable form u that can be moved around plant u saved a rainy day glucose + oxygen carbon + for water + energy u dioxide 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy AP Biology

Light reactions § Convert solar energy to chemical energy ATP u ATP energy u NADPH reducing power § What can we do now? build stuff !! AP Biology photosynthesis

How is that helpful? § Want to make C 6 H 12 O 6 synthesis u How? From what? What raw materials are available? u CO 2 NADPH carbon fixation NADP C 6 H 12 O 6 AP Biology reduces CO 2 NADP

From CO 2 C 6 H 12 O 6 § CO 2 has very little chemical energy u fully oxidized § C 6 H 12 O 6 contains a lot of chemical energy u highly reduced § Synthesis = endergonic process u put in a lot of energy § Reduction of CO 2 C 6 H 12 O 6 proceeds in many small uphill steps each catalyzed by a specific enzyme u using energy stored in ATP & NADPH u AP Biology

From Light reactions to Calvin cycle § Calvin cycle u chloroplast stroma § Need products of light reactions to drive synthesis reactions ATP u NADPH u ATP thylakoid AP Biology stroma

C Calvin cycle 1 C C C 3. Regeneration C C C of Ru. BP starch, sucrose, cellulose & more ribulose bisphosphate 3 ATP H H H | | | C–C–C AP Biology C C C C CO 2 5 C Ru. Bis. Co glyceraldehyde-3 -P G 3 P 3 C C 6 NADP 6 C PGA phosphoglycerate C C C 3 C C C C C 6 ATP 2. Reduction 6 NADPH 1. Carbon fixation C C C ribulose bisphosphate carboxylase 3 ADP used to make glucose C=C=C 5 C C C 3 C 6 ADP H | H |

Remember G 3 P? glycolysis glucose C-C-C-C 2 ATP 2 ADP fructose-1, 6 b. P P-C-C-C-P DHAP P-C-C-C G 3 P glyceraldehyde 3 -phosphate C-C-C-P 2 NAD+ 2 4 ADP AP Biology Photosynthesis pyruvate C-C-C 4 ATP

To G 3 P and Beyond! § Glyceraldehyde-3 -P To G 3 P and beyond! end product of Calvin cycle u energy rich 3 carbon sugar u “C 3 photosynthesis” u § G 3 P is an important intermediate § G 3 P glucose carbohydrates lipids phospholipids, fats, waxes amino acids proteins nucleic acids DNA, RNA AP Biology

Ru. Bis. Co § Enzyme which fixes carbon from air ribulose bisphosphate carboxylase u the most important enzyme in the world! u § it makes life out of air! definitely the most abundant enzyme It’s not easy u I’m green with envy! AP Biology being green!

Accounting § The accounting is complicated u 3 turns of Calvin cycle = 1 G 3 P u 3 CO 2 1 G 3 P (3 C) u 6 turns of Calvin cycle = 1 C 6 H 12 O 6 (6 C) u 6 CO 2 1 C 6 H 12 O 6 (6 C) u 18 ATP + 12 NADPH 1 C 6 H 12 O 6 u AP Biology any ATP left over from light reactions will be used elsewhere by the cell

Photosynthesis summary § Light reactions produced ATP u produced NADPH u consumed H 2 O u produced O 2 as byproduct u § Calvin cycle consumed CO 2 u produced G 3 P (sugar) u regenerated ADP u regenerated NADP u AP Biology ADP NADP

Light Reactions light ATP + NADPH + O 2 energy H 2 O + H 2 O sunlight Energy Building Reactions NADPH ATP AP Biology O 2 § produces ATP § produces NADPH § releases O 2 as a waste product

Calvin Cycle CO 2 + ATP + NADPH C 6 H 12 O 6 + ADP + NADP CO 2 ADP NADP Sugar Building Reactions NADPH ATP AP Biology sugars § builds sugars § uses ATP & NADPH § recycles ADP & NADP § back to make more ATP & NADPH

Putting it all together light CO 2 + H 2 O + energy C 6 H 12 O 6 + O 2 H 2 O CO 2 sunlight ADP Energy NADP Building Reactions Sugar Building Reactions NADPH ATP AP Biology O 2 sugars Plants make both: § energy § ATP & NADPH § sugars

even though this equation is a bit of a lie… it makes a better story Energy cycle sun Photosynthesis light CO 2 + H 2 O + energy C 6 H 12 O 6 + O 2 plants CO 2 H 2 O glucose animals, plants ATP C 6 H 12 O 6 + O 2 energy + CO 2 + H 2 O Cellular Respiration AP Biology The Great Circle of Life, Mufasa! ATP O 2

Summary of photosynthesis 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy § § § § § Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the H 2 O go? Where did the energy come from? What’s the energy used for? What will the C 6 H 12 O 6 be used for? Where did the O 2 come from? Where will the O 2 go? What else is involved…not listed in this equation? AP Biology

Supporting a biosphere § On global scale, photosynthesis is the most important process for the continuation of life on Earth u each year photosynthesis… § captures 121 billion tons of CO 2 § synthesizes 160 billion tons of carbohydrate u AP Biology heterotrophs are dependent on plants as food source for fuel & raw materials

The poetic perspective… § All the solid material of every plant § was built by sunlight out of thin air All the solid material of every animal was built from plant material air AP Biology sun Then all the plants, cats, dogs, elephants & people … are really particles of air woven together by strands of sunlight!

If plants can do it… You can learn it! Ask Questions!! AP Biology 2007 -2008

Photosynthesis: Variations on the Theme AP Biology 2007 -2008

Remember what plants need… § Photosynthesis u light reactions § light sun § H 2 O ground u Calvin cycle § CO 2 air What structures have plants evolved to APsupply Biology these needs? O C O

vascular bundle xylem (water) Leaf Structure phloem (sugar) cuticle epidermis palisades layer spongy layer O 2 H O 2 CO 2 stomate Transpiration Gas exchange AP Biology O 2 H 2 O CO 2 guard cell

A second look inside a leaf… § Gas exchange & water flow CO 2 in for Calvin cycle waste from light reactions u O 2 out u H 2 O out for light reactions u photosynthesis xylem (water) O 2 CO 2 gas exchange water loss AP Biology phloem (sugars) H 2 O O 2 CO 2

Controlling water loss from leaves § Hot or dry days stomates close to conserve water u guard cells u § gain H 2 O = stomates open § lose H 2 O = stomates close u adaptation to living on land, but… creates PROBLEMS! AP Biology

When stomates close… § Closed stomates lead to… O 2 build up from light reactions u CO 2 is depleted in Calvin cycle u § causes problems in Calvin Cycle O 2 xylem (water) CO 2 AP Biology O 2 CO 2 phloem (sugars) H 2 O The best laid schemes of mice and men… and plants!

Inefficiency of Ru. Bis. Co: CO 2 vs O 2 § Ru. Bis. Co in Calvin cycle u carbon fixation enzyme § § u when O 2 concentration is high § § AP Biology normally bonds C to Ru. BP CO 2 is the optimal substrate reduction of Ru. BP photosynthesis building sugars Ru. Bis. Co bonds O to Ru. BP O 2 is a competitive substrate oxidation of Ru. BP photorespiration breakdown sugars

Calvin cycle when CO 2 is abundant 1 C ATP Ru. BP ADP G 3 P to make glucose 5 C Ru. Bis. Co 6 C unstable intermediate 5 C G 3 P 3 C AP Biology CO 2 C 3 plants 3 C PGA NADPH ATP NADP 3 C

Calvin cycle when O 2 is high O 2 Ru. BP Hey Dude, are you high on oxygen! It’s so sad to see a good enzyme, go BAD! AP Biology 5 C Ru. Bis. Co to mitochondria ––––––– lost as CO 2 without making ATP 2 C 3 C photorespiration

Impact of Photorespiration § Oxidation of Ru. BP short circuit of Calvin cycle u loss of carbons to CO 2 u § can lose 50% of carbons fixed by Calvin cycle u reduces production of photosynthesis § no ATP (energy) produced § no C 6 H 12 O 6 (food) produced u AP Biology if photorespiration could be reduced, plant would become 50% more efficient § strong selection pressure to evolve alternative carbon fixation systems

Reducing photorespiration § Separate carbon fixation from Calvin cycle u C 4 plants § PHYSICALLY separate carbon fixation from Calvin cycle w different cells to fix carbon vs. where Calvin cycle occurs w store carbon in 4 C compounds § different enzyme to capture CO 2 (fix carbon) w PEP carboxylase § different leaf structure u CAM plants § separate carbon fixation from Calvin cycle by TIME OF DAY § fix carbon during night w store carbon in 4 C compounds § perform Calvin cycle during day AP Biology

C 4 plants § A better way to capture CO 2 u 1 st step before Calvin cycle, fix carbon with enzyme PEP carboxylase corn § store as 4 C compound u adaptation to hot, dry climates § have to close stomates a lot § different leaf anatomy u sugar cane, corn, other grasses… AP Biology sugar cane

PEP (3 C) + CO 2 oxaloacetate (4 C) C 4 leaf anatomy O 2 light reactions CO 2 PEP carboxylase C 3 anatomy stomate § PEP carboxylase enzyme u bundle sheath cell CO 2 Ru. Bis. Co higher attraction for CO 2 than O 2 § better than Ru. Bis. Co u u fixes CO 2 in 4 C compounds regenerates CO 2 in inner cells for Ru. Bis. Co AP Biology § keeping O 2 away from Ru. Bis. Co C 4 anatomy

C 4 photosynthesis PHYSICALLY separated C fixation from Calvin cycle § Outer cells light reaction & carbon fixation u pumps CO 2 to inner cells u keeps O 2 away from inner cells u § away from Ru. Bis. Co § Inner cells CO 2 AP Biology O 2 Calvin cycle u glucose to veins u

Comparative anatomy C 3 Location, location! C 4 PHYSICALLY separate C fixation from Calvin cycle AP Biology

CAM (Crassulacean Acid Metabolism) plants § Adaptation to hot, dry climates u separate carbon fixation from Calvin cycle by TIME § close stomates during day § open stomates during night at night: open stomates & fix carbon in 4 C “storage” compounds u in day: release CO 2 from 4 C acids to Calvin cycle u § increases concentration of CO 2 in cells u AP Biology succulents, some cacti, pineapple It’s all in the timing!

CAM plants cacti succulents AP Biology pineapple

C 4 vs CAM Summary solves CO 2 / O 2 gas exchange vs. H 2 O loss challenge C 4 plants CAM plants separate 2 steps of C fixation anatomically in 2 different cells separate 2 steps of C fixation temporally = 2 different times night vs. day AP Biology

Why the C 3 problem? We’ve all got baggage! § Possibly evolutionary baggage u Rubisco evolved in high CO 2 atmosphere § there wasn’t strong selection against active site of Rubisco accepting both CO 2 & O 2 § Today it makes a difference u u u AP Biology 21% O 2 vs. 0. 03% CO 2 photorespiration can drain away 50% of carbon fixed by Calvin cycle on a hot, dry day strong selection pressure to evolve better way to fix carbon & minimize photorespiration

It’s not so easy as it looks… Any Questions? ? AP Biology 2007 -2008