CHAPTER 8 PHOTOSYNTHES

ISBiology1-2

Mrs. Hennings

http://www.youtube.com/watch?v=C1_uez5WX1o&feature=related

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THE ULTIMATE SOURCE OF “E” The Sun is the ultimate source of

energy. Photosynthesis is the process in which

plants capture light energy and change it into chemical energy.

Organisms are classified to how the obtain energy.

TWO MAIN CATEGORIES….Autotrophic organisms- “self feeders” make

their own food. Producers of ecosystems Photoautotroph Chemoautotroph

Heterotrophic organisms- can’t make their own food. They live on compounds made by other living organisms. Consumers of ecosystems. That is

really important

!

That is really

important !

THE ENERGY NEEDS OF LIFE Organisms are endergonic systems

What do we need energy for? synthesis

building biomolecules reproduction movement active transport temperature regulation

WHERE DO WE GET THE ENERGY FROM?

Work of life is done by energy coupling use exergonic (catabolic) reactions to fuel endergonic

(anabolic) reactions

+ + energy

+ energy+

digestion

synthesis

ATP

LIVING ECONOMY Fueling the body’s economy

eat high energy organic molecules food = carbohydrates, lipids, proteins, nucleic acids

break them down digest = catabolism

capture released energy in a form the cell can use Need an energy currency

a way to pass energy aroundneed a short term energy

storage molecule

Whoa! Hot stuff!

ATP

high energy bondsHow efficient!Build once,use many ways

Adenosine TriPhosphate modified nucleotide

nucleotide = adenine + ribose + Pi AMP

AMP + Pi ADP ADP + Pi ATP

adding phosphates is endergonic

HOW DOES ATP STORE ENERGY?

PO–

O–

O

–O PO–

O–

O

–O PO–

O–

O

–OPO–

O–

O

–O PO–

O–

O

–OPO–

O–

O

–O PO–

O–

O

–O PO–

O–

O

–O

Each negative PO4 more difficult to adda lot of stored energy in each bond

most energy stored in 3rd Pi

3rd Pi is hardest group to keep bonded to molecule

Bonding of negative Pi groups is unstablespring-loadedPi groups “pop” off easily & release energy

Instability of its P bonds makes ATP an excellent energy donor

I thinkhe’s a bitunstable…don’t you?

AMPAMPADPATP

HOW DOES ATP TRANSFER ENERGY?

PO–

O–

O

–O PO–

O–

O

–O PO–

O–

O

–O7.3energy+P

O–

O–

O

–O

ATP ADP releases energy

∆G = -7.3 kcal/mole Fuel other reactions Phosphorylation

released Pi can transfer to other molecules destabilizing the other molecules

enzyme that phosphorylates = “kinase”

ADPATP

It’snever thatsimple!

AN EXAMPLE OF PHOSPHORYLATION… Building polymers from monomers

need to destabilize the monomersphosphorylate!

C

H

OH

H

HOC C

H

O

H

C+ H2O++4.2 kcal/mol

C

H

OHC

H

P+ ATP + ADP

H

HOC+ C

H

O

H

CC

H

P+ Pi

“kinase” enzyme

-7.3 kcal/mol

-3.1 kcal/mol

enzyme

H

OHC

H

HOC

synthesis

Can’t store ATP good energy donor,

not good energy storagetoo reactivetransfers Pi too easilyonly short term energy

storage carbohydrates & fats are long term energy storage

ATP / ADP CYCLE

A working muscle recycles over 10 million ATPs per second

Whoa!Pass methe glucose(and O2)!

ATP

ADP Pi+

7.3 kcal/mole

cellularrespiration

THE CROSS SECTION OF A LEAF

CHLOROPLAST ANATOMY

Think about how the structure of this organelle determines its

function!

CHLOROPLASTS Organelles in plants. All green parts of plants have

chloroplasts Leaves is the major place where

photosynthesis happens. Contains chlorophyll- a green pigment

that is used to absorb light energy and drive photosynthesis.

Mainly in spongy mesophyll cells- also in palisade mesophyll cells.

1.5 million chloroplasts per 1 sq meter of leaf surface.

CHLOROPHYLL

Chloroplasts in Elodea leaves!

THYLAKOID ANATOMYIt has a

phospholipid bilayer

membrane around the thylakoid!

PHOTOSYNTHESIS EQUATION

•Where does it come from?

• How does it get into plants?

• What is it used for?

•Where does it come from?

• How does it get into plants?

• What is it used for?

•What provided the building blocks to make it?

• How is it made?

• What is it used for? •Where does it go?

•Where does it come from?

• How does it get out of plants?

• What is it used for?

TWO STEPS OF PHOTOSYNTHESIS Light Dependent: Light Reactions:

Change solar energy into chemical energy. Happens in the thylakoid membrane.

Light Independent: Calvin Cycle: Takes carbon dioxide from air and “fixes” into Calvin cycle. Changes carbon dioxide into sugar. Happens in the stroma.

LIGHT

A LOOK AT LIGHT The spectrum of color

ROYGBIV

LIGHT When light comes into contact with

matter it can be:ReflectedTransmittedAbsorbed- substances that absorb light are

called pigments. Different pigments absorb different wavelengths of light.

LIGHT: ABSORPTION SPECTRA

Photosynthesis gets energy by absorbing wavelengths of lightchlorophyll a

absorbs best in red & blue wavelengths & least in green

other pigments with different structures absorb light of different wavelengths

Why areplants green?

THE LIGHT REACTIONS IN DETAIL

LIGHT REACTIONS

O2

H2O

Energy BuildingReactions

ATP

produces ATP produces

NADPH releases O2 as

a waste product

sunlight

H2O ATP O2lightenergy ++ + NADPH

NADPH

ETC of Photosynthesis Chloroplasts transform

light energy into chemical energy of ATP

use electron carrier NADP+

ETC OF PHOTOSYNTHESIS ETC produces from light energy

ATP & NADPH go to Calvin cycle

PS II absorbs lightexcited electron passes from chlorophyll to

“primary electron acceptor”need to replace electron in chlorophyllenzyme 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!

THE SIMPLE EXPLANATION OF THE LIGHT REACTIONS!

PS II

H2

0

e e e e e PS I

NADP +

O O

H+

H+

H+

H+

PADP

ATP

H+

H+

H+

H+H

+ H+ NADPH

FROM CO2 C6H12O6 CO2 has very little chemical energy

fully oxidized C6H12O6 contains a lot of chemical energy

reducedendergonic

Reduction of CO2 C6H12O6 proceeds in many small uphill steps

each catalyzed by specific enzymeusing energy stored in ATP & NADPH

FROM LIGHT REACTIONS TO CALVIN CYCLE

Calvin cycle chloroplast stroma

Need products of light reactions to drive synthesis reactionsATPNADPH

CALVIN CYCLE

sugarsC6H12O6

CO2

SugarBuildingReactions

ADP

builds sugars

uses ATP & NADPH

recycles ADP & NADP back to make more ATP & NADPH

ATP

NADPH

NADP

CO2C6H12O6 ++ + NADPATP + NADPH ADP

TO G-3-P AND BEYOND! Glyceraldehyde-3-P

end product of Calvin cycleenergy rich 3 carbon sugar“C3 photosynthesis”

G-3-P = important intermediate G-3-P glucose carbohydrates

lipids amino acids nucleic acids

PHOTOSYNTHESIS SUMMARY

Light reactionsproduced ATPproduced NADPHconsumed H2Oproduced O2 as byproduct

Calvin cycleconsumed CO2

produced G3P (sugar) regenerated ADP regenerated NADP

NADPADP

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?

6CO2 6H2O C6H12O6 6O2lightenergy + ++

RATE OF PHOTOSYNTHESIS Rate: activity per unit of time. Photosynthesis can be measured by:

How much carbon dioxide is consumed.How much oxygen is produced.How much glucose is produced.

There are 3 main factors that affect the rate: Light intensity Temperature Concentrations of Carbon Dioxide and/or Oxygen

LIGHT INTENSITY

TEMPERATURE

INEFFICIENCY OF RUBISCO: CO2 VS O2

Rubisco in Calvin cyclecarbon fixation enzyme

normally bonds C to RuBP reduction of RuBP building sugars

when O2 concentration is high Rubisco bonds O to RuBP O2 is alternative substrate oxidation of RuBP breakdown sugars

photosynthesis

photorespiration

IMPACT OF PHOTORESPIRATION

Oxidation of RuBPshort circuit of Calvin cycle loss of carbons to CO2

can lose 50% of carbons fixed by Calvin cycle reduces production of photosynthesis

no ATP (energy) produced no C6H12O6 (food) produced

if photorespiration could be reduced, plant would become 50% more efficient

strong selection pressure to evolve alternative systems

REDUCING PHOTORESPIRATION

Separate carbon fixation from Calvin cycleC4 plants

physically separate carbon fixation from actual Calvin cycle

different enzyme to capture CO2

PEP carboxylase stores carbon in 4C compounds different leaf structure

CAM plants separate carbon fixation from actual Calvin cycle by time

of day fix carbon (capture CO2) during night

store carbon in organic acids perform Calvin cycle during day

C4 PLANTS A better way to capture CO2

1st step before Calvin cycle, fix carbon with enzymePEP carboxylase store as 4C compound

adaptation to hot, dry climates have to close stomates a lot different leaf anatomy

sugar cane, corn, other grasses…

COMPARATIVE ANATOMY

Separate reactions in different cells light reactions carbon fixation Calvin cycle

C3 C4

C4 PHOTOSYNTHESIS

CO2O2

CO2

O2

Outer cells light reaction &

carbon fixation pumps CO2 to

inner cells keeps O2 away

from inner cells away from

Rubisco

Inner cells Calvin cycle glucose to veins

Physically separated C fixation from Calvin cycle

CAM (CRASSULACEAN ACID METABOLISM) PLANTS Different adaptation to hot, dry

climates separate carbon fixation from Calvin cycle by time

close stomates during day open stomates during night

at night, open stomates & fix carbon in “storage” compounds organic acids: malic acid, isocitric acid

in day, close stomates & release CO2 from “storage” compounds to Calvin cycle increases concentration of CO2 in cells

succulents, some cacti, pineapple

CAM PLANTS

C4 VS CAM SUMMARY

C4 plants separate 2 steps of C fixation anatomically in 2 different cells

CAM plants separate 2 steps of C fixation temporally at2 different times

solves CO2 / O2 gas exchange vs. H2O loss challenge

SUPPORTING A BIOSPHERE

On global scale, photosynthesis is the most important process for the continuation of life on Eartheach year photosynthesis synthesizes 160

billion tons of carbohydrate heterotrophs are dependent on plants as food

source for fuel & raw materials

REVIEW

PUTTING IT ALL TOGETHER

CO2 H2O C6H12O6 O2lightenergy + ++

SugarBuildingReactions

Energy BuildingReactions

Plants make both:energy

ATP & NADPH

sugars

sunlight

O2

H2O

sugarsC6H12O6

CO2

ADP

ATP

NADPH

NADP

HOW ARE THEY CONNECTED?

glucose + oxygen carbon + water + energydioxide

C6H12O6 6O2 6CO2 6H2O ATP+ + +

Heterotrophs

+ water + energy glucose + oxygencarbondioxide

6CO2 6H2O C6H12O6 6O2lightenergy + ++

Autotrophsmaking energy & organic molecules from light energy

making energy & organic molecules from ingesting organic molecules

exergonic

endergonic

H2O

ENERGY CYCLE

Photosynthesis

Cellular Respiration

sun

glucose O2CO2

plants

animals, plants

ATP

THE END!