photosynthesis details - wordpress.com · 2017. 12. 5. · ap biology photosynthesis §light...

AP Biology

Photosynthesis Details

AP Biology

§ Chloroplastsu double membraneu stroma

§ fluid-filled interioru thylakoid sacsu grana stacks

§ Thylakoid membrane containsu chlorophyll moleculesu electron transport chainu ATP synthase

§ H+ gradient built up within thylakoid sac

Plant structure H+H+

H+H+

H+H+

H+H+H+H+

H+

outer membrane inner membrane

thylakoidgranum

stroma

thylakoid

chloroplast

ATP

AP Biology

Photosynthesis

§ Light reactionsu light-dependent reactionsu energy conversion reactions

§ convert solar energy to chemical energy§ ATP & NADPH

§ Calvin cycleu light-independent reactionsu sugar building reactions

§ uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

It’s not theDark Reactions!

AP Biology

§ Electron Transport Chain§ like in cellular respiration

u proteins in organelle membrane u electron acceptors

§ NADPHu proton (H+)

gradient across inner membrane§ find the double membrane!

u ATP synthase enzyme

Light reactionsH+H+

H+H+

H+H+H+H+

H+H+H+

H+H+H+H+

H+H+H+H+

H+H+H+ATP

thylakoidchloroplast

AP Biology

Mitochondria transfer chemical energy from food molecules into chemical energy of ATP

u use electron carrier NADH

ETC of Respiration

generates H2O

AP Biology

ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP

u use electron carrier NADPH

generates O2

AP Biology

ATP Synthase

§ moves the electrons § runs the pump§ pumps the protons§ builds the gradient§ drives the flow of protons

through ATP synthase§ bonds Pi to ADP§ generates the ATP

sunlight breakdown of C6H12O6

respirationphotosynthesis

H+

ADP + Pi

H+ H+

H+

H+ H+

H+H+H+

ATP

AP Biology

Pigments of photosynthesis

§ Chlorophylls & other pigmentsu embedded in thylakoid membraneu arranged in a “photosystem”

§ collection of moleculesu structure-function relationship

How does thismolecular structurefit its function?

AP Biology

Photosystems of photosynthesis § 2 photosystems in thylakoid membrane

u collections of chlorophyll molecules u act as light-gathering moleculesu Photosystem II

§ chlorophyll a§ P680 = absorbs 680nm

wavelength red light u Photosystem I

§ chlorophyll b§ P700 = absorbs 700nm

wavelength red light

reactioncenter

antennapigments

AP Biology

ETC of PhotosynthesisPhotosystem II

Photosystem I

chlorophyll a

chlorophyll b

AP Biology

1

ETC of Photosynthesis

ee

sun

Photosystem IIP680

chlorophyll a

AP Biology

12


Photosystem IIP680

chlorophyll a

OH H

H

H

Inhale, baby!

e e

ee

e-e-

H+H+H+H+

H+H+H+H+

H+H+H+

H+H+H+H+

H+H+H+H+

H+H+H+ATP


H+ +H

OO

AP Biology

12 H+

H+

3

4

H+

ADP + Pi

H+ H+

H+

H+ H+

H+H+H+

ee

ATP

to Calvin Cycle

energy to buildcarbohydrates

H+H+H+H+

H+H+H+H+

H+H+H+

H+H+H+H+

H+H+H+H+

H+H+H+ATP


Photosystem IIP680

chlorophyll a


ATP

AP Biology

ee sun

5

Photosystem IIP680

chlorophyll a

Photosystem IP700

chlorophyll b

e e


AP Biology

6

electron carrier

ee

5sun

Photosystem IIP680

chlorophyll a

Photosystem IP700

chlorophyll b


AP Biology

split H2O


O

ATP

to Calvin CycleH+

H+H+

H+

H+H+

H+

H+

H+H+

H+

sun sun

AP Biology

ETC of Photosynthesis§ ETC uses light energy to produce

u ATP & NADPH§ go to Calvin cycle

§ PS II absorbs lightu excited electron passes from chlorophyll to

“primary electron acceptor”u need to replace electron in chlorophyllu enzyme extracts electrons from H2O &

supplies them to chlorophyll§ splits H2O§ O combines with another O to form O2§ O2 released to atmosphere§ and we breathe easier!

AP Biology

6CO2 6H2O C6H12O6 6O2light

energy ®+ ++

Experimental evidence§ Where did the O2 come from?

u radioactive tracer = O18


energy ®+ ++

Experiment 1


energy ®+ ++

Experiment 2

Proved O2 came from H2O not CO2 = plants split H2O!

AP Biology

Noncyclic Photophosphorylation§ Light reactions elevate

electrons in 2 steps (PS II & PS I)u PS II generates

energy as ATPu PS I generates

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 NADPHu coordinates light

reactions to Calvin cycleu Calvin cycle uses more

ATP than NADPH

7

18 ATP +12 NADPH 1 C6H12O6®

ATP

AP Biology

Photophosphorylation

NONcyclicphotophosphorylation

cyclicphotophosphorylation

ATP

NADP

AP Biology

Lets Review!

Photosystems Animation

AP Biology

Photosynthesis summary Where did the energy come from?Where did the electrons come from? Where did the H2O come from?Where did the O2 come from?Where did the O2 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?

…stay tuned for the Calvin cycle

AP Biology

Calvin Cycle

Light Independent Reactions

AP Biology

Light reactions§ Convert solar energy to chemical

energyuATPuNADPH

§ What can we do now?

® energy® energy carrier

®® build stuff !!photosynthesis

ATP

AP Biology

How is that helpful?§ Want to make C6H12O6

u synthesisu How? From what?

What raw materials are available?

CO2

C6H12O6

NADPH

NADPcarbon fixation

NADP

AP Biology

From CO2 ® C6H12O6§ CO2 has very little chemical energy§ C6H12O6 contains a lot of chemical energy§ Synthesis = endergonic process

u put in a lot of energy § CO2® C6H12O6 proceeds in many small

uphill stepsu each catalyzed by a specific enzymeu using energy stored in ATP & NADPH

AP Biology

From Light reactions to Calvin cycle§ Calvin cycle

u chloroplast stroma§ Need products of light reactions to

drive synthesis reactionsu ATPu NADPH

stroma

thylakoid

ATP

AP Biology

To G3P and Beyond!§ Glyceraldehyde-3-P

u end product of Calvin cycleu energy rich 3 carbon sugaru “C3 photosynthesis”

§ G3P is an important intermediate§ G3P ®®glucose ®® carbohydrates

®® lipids ®® phospholipids, fats, waxes®® amino acids ®® proteins®® nucleic acids ®® DNA, RNA

To G3Pand beyond!

AP Biology

Calvin Cycle§ Main part of light-independent reaction

u Doesn't need light, but only occurs in lightu Uses products from light reaction (ATP and NADPH)

§ Cyclic process: produces 3-carbon sugar PGAL or G3P

§ Carbon Fixation: Carbon enters leaf as CO2, becomes fixed as PGAL

§ Net synthesis of one G3P moleculeu Nine ATP and 6 NADPH molecules were used.u G3P is the starting material for metabolic pathways that

synthesize other organic compounds, including glucose.§ ADP & NADP are passed to the light reactions and

used to regenerate ATP and NADPH.

AP Biology

AP Biology

Photosynthesis summary§ Light reactions

u produced ATPu produced NADPHu consumed H2Ou produced O2 as byproduct

§ Calvin cycleu consumed CO2u produced G3P (sugar)u regenerated ADPu regenerated NADP NADPADP

AP Biology

Light Reactions

O2

H2O

Energy BuildingReactions

ATP

§ produces ATP§ produces NADPH§ releases O2 as a

waste product

sunlight

H2O ATP O2light

energy ® ++ + NADPH

NADPH

AP Biology

Calvin Cycle

sugars

CO2

SugarBuilding

Reactions

ADP

§ builds sugars§ uses ATP &

NADPH§ recycles ADP

& NADP § back to make

more ATP & NADPHATP

NADPH

NADP

CO2 C6H12O6® ++ + NADPATP + NADPH ADP

AP Biology

Putting it all togetherCO2 H2O C6H12O6 O2

lightenergy ®+ ++

SugarBuilding

Reactions

Energy Building

Reactions

Plants make both:§energy§ATP & NADPH

§sugars

sunlight

O2

H2O

sugars

CO2

ADP

ATP

NADPH

NADP

AP Biology

H2O

Energy cycle

Photosynthesis

Cellular Respiration

sun

glucose O2CO2

plants

animals, plants

ATPThe Great Circleof Life,Mufasa!

CO2 H2O C6H12O6 O2light

energy ®+ ++

CO2 H2OC6H12O6 O2ATP

energy®+ ++

AP Biology

Summary of photosynthesis

§ Where did the CO2 come from?§ Where did the CO2 go?§ Where did the H2O come from?§ Where did the H2O go?§ Where did the energy come from?§ What’s the energy used for?§ What will the C6H12O6 be used for?§ Where did the O2 come from?§ Where will the O2 go?§ What else is involved…not listed in this equation?


energy ®+ ++

AP Biology

Supporting a biosphere§ On global scale,

photosynthesis is the most important process for the continuation of life on Earthu each year photosynthesis…

§ captures 121 billion tons of CO2

§ synthesizes 160 billion tons of carbohydrate u heterotrophs are dependent on plants as

food source for fuel & raw materials

AP Biology

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

Then all the plants, cats, dogs, elephants & people …

are really particles of air woven together by strands of sunlight!

sunair

AP Biology

Factors affecting photosynthesis�Factor - any of certain substances

necessary to a biochemical or physiological process

�Limiting Factor - any factor that causes the rate of a reaction to plateau or decrease, i.e. limiting the reaction

�Optimum - the best or most favorable point, degree, amount, etc., as of temperature, light, and moisture for the growth or reproduction of an organism

AP Biology

Factors Affecting Photosynthesis§ Water Availability§ Light Intensity§ CO2 Availability§ Nutrient Availability

u Magnesiumu Nitrogen

AP Biology 2007-2008

Photosynthesis:Variations on the Theme

AP Biology

Alternative mechanisms for Carbon Fixation

§ Plant adaptations that prevent dehydration may also reduce availability of CO2

§ On hot, dry days, most plants (C3 plants) close their stomata to conserve water.

§ When stomata close, CO2 levels drop as CO2 is consumed in the Calvin Cycle

§ At the same time, O2 levels rise as the light reaction converts light to chemical energy

AP Biology

C4 Plants§ C4 plants fix CO2 into a four-carbon

compound§ Several thousand plants use this including

sugar cane and corn§ Modification for dry environments

u Minimize water loss and maximize sugar production

AP Biology

CAM plants§ These plants open stomata during the

night and close them during the day.§ Temperatures are typically lower at night &

humidity is high§ Includes cacti, pineapples

§ At night, CAM plants fix CO2 into a variety of organic acids in mesophyll cells.

§ During the day, the light reactions supply ATP and NADPH to Calvin cycle and CO2 is released from organic acids.

photosynthesis details - wordpress.com · 2017. 12. 5. · ap biology photosynthesis §light...

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