biol1003 -9_photosynthesis - fall2014

7/24/2019 BIOL1003 -9_Photosynthesis - Fall2014

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BIOL 1003

INTRODUCTORY

BIOLOGY I9. Greenhouses, global warming and photosynthesis - FALL2014

Iain McKinnellDept. Biology


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Sunlight

Atmosphere

Some heat

energy escapes

into space

Radiant heat

trapped by CO2

and other gases

The gases in the atmosphere that absorb heat radiation arecalled greenhouse gases. These include

water vapor

carbon dioxide

methane

ozone

The Greenhouse effect


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Antarctica

Southern tip of

South America

Solar radiation converts O2high inthe atmosphere to ozone (O3),

which shields organisms from

damaging UV radiation.

Industrial chemicals called CFCs

have caused dangerous thinning of

the ozone layer, but international

restrictions on CFC use are

allowing a slow recovery.

Study of Earths atmospheric composition has global significance


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Greenhouse effect and global climate change

Increasing concentrations of greenhouse gaseshave been linked to global climate change(also

called global warming), a slow but steady rise in

Earths surface temperature.

Since 1850, the atmospheric concentration of CO2

has increased by about 40%, mostly due to the

combustion of fossil fuels including

coal oil

gasoline.


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The carbon cycle

http://earthobservatory.nasa.gov/Features/CarbonCycle/
http://earthobservatory.nasa.gov/Features/CarbonCycle/http://earthobservatory.nasa.gov/Features/CarbonCycle/


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Photosynthesis & CO2- Introduction

Autotrophs make their own food through the process of

photosynthesis,

sustain themselves, and

do not usually consume organic molecules derivedfrom other organisms.

Photosynthesis in plants

converts carbon dioxide and water into organic

molecules,

releases oxygen,

takes place in chloroplasts.


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Leaf Cross

Section

Mesophyll

CO2

O2

Vein

Leaf

Stoma

Mesophyll Cell

Chloroplast

Photosynthesis occurs in chloroplasts in plant cells


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Chloroplast

Thylakoid

Thylakoid space

Stroma

Granum

Inner and outer

membranes

Photosynthesis occurs in chloroplasts in plant cells


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Becomes reduced

Becomes oxidized

Photosynthesis, like respiration, is a redox (oxidation-reduction) process.

CO2becomes reduced to sugar as electrons along with

hydrogen ions from water are added to it.

Water molecules are oxidized when they lose electronsalong with hydrogen ions.

Photosynthesis is a redox process, as is cellularrespiration


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LightReactions

(in thylakoids)

Calvin

Cycle(in stroma)

SugarO2

NADPH

ATP

NADP+

ADP

P

H2O CO2

Light

Chloroplast


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Increasing energy

105nm 103nm 1 nm 103nm 106nm 1 m 103m

650nm

380 400 500 600 700 750

Wavelength (nm)

Visible light

Gamma

rays

Micro-

waves

Radio

wavesX-rays UV Infrared

Visible radiation absorbed by pigments drives the light reactions


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Excited

state

Heat

Ground state

Photon

of light

Photon

(fluorescence)

Chlorophyll

molecule

Pigments in chloroplastsabsorb photons (capturing

solar power), which

increases the potential

energy of the pigmentselectrons and

sends the electrons into an

unstable state.

These unstable electrons drop back down to their

ground state, and as they do,

release their excess energy as

heat.

Visible radiation absorbed by pigments drivesthe light reactions


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Photosystem

Light Light-harvestingcomplexes

Reaction-centercomplex

Primary electron

acceptor

Pigment

moleculesPair ofchlorophyll amoleculesTransferof energy

Thyla

koidmembrane

Photosystems capture solar energy


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Two types of photosystems (photosystem I and

photosystem II) cooperate in the light reactions.

Each type of photosystem has a characteristic

reaction center. Photosystem II, which functions first, is called P680

because its pigment absorbs light with a

wavelength of 680 nm.

Photosystem I, which functions second, is calledP700 because it absorbs light with a wavelength of

700 nm.

Photosystems capture solar energy


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Light

StromaPhotosystem II

Thylakoid

space

Thylakoidmembrane Primary

acceptor

Primary

acceptor

P680 P700

Photosystem I

Light NADP NADPHElectron transport chain

Provides energy for

synthesis of ATP

by chemiosmosis

21

H2O

3

1

2

45

6

H

O2 H2

Two photosystems connected by an electron transport

chain generate ATP and NADPH


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Photosystem IPhotosystem II

NADPH

ATP

Mill

makes

ATP

The products of the lightreactions are

NADPH,

ATP, and

oxygen.


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H+

ATP synthasePhotosystem IPhotosystem IIElectron

transport chain

ATPPADP

NADPHNADP+

Light Light

Chloroplast

To Calvin

Cycle

Stroma(low H+

concentration)

Thylakoid

membrane

Thylakoid space

(high H+

concentration)

H2O

O2 + 212

H+ H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Chemiosmosis powers ATP synthesis in the light reactions


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Input

Output: G3P

Calvin

Cycle

CO2

ATP

NADPH

ATP and NADPH power sugar synthesis in theCalvin cycle

The Calvin cycle makes sugar within achloroplast.

To produce sugar, the necessaryingredients are

atmospheric CO2and ATP and NADPH generated by the

light reactions.

The Calvin cycle uses these threeingredients to produce an energy-rich,three-carbon sugar calledglyceraldehyde-3-phosphate (G3P).

A plant cell may then use G3P to makeglucose and other organic molecules.


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The steps of the Calvin cycle include

carbon fixation,

reduction, release of G3P, and

regeneration of the starting molecule

ribulose bisphosphate (RuBP).

ATP and NADPH power sugar synthesis in theCalvin cycle


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2

2

1

1

3

4

4

3

Glucose

and other

compounds

P

P

P

P

P

PP

ATP

ATP

ADP

3

ADP3

3

3

5

1

6

6

6

6

6

6

NADPH

NADP

G3P

G3P

G3P

3-PGARuBP

CO2

Rubisco

Input:

Output:Step Regeneration of RuBP

Step Release of one

molecule of G3P

Step Reduction

Step Carbon fixation

CalvinCycle


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Other methods of carbon fixation have evolved in

hot, dry climates

Most plants use CO2directly from the air,

and carbon fixation occurs when the

enzyme rubisco adds CO2to RuBP.

Such plants are called C3plants because

the first product of carbon fixation is a

three-carbon compound, 3-PGA.

Oth th d f b fi ti h l d i h t


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Calvin

Cycle

Mesophyllcell

Bundle-sheathcell

CO2

4-C compound

CO2

3-C sugar

C4plant

C4plants have evolved a means

of carbon fixation that saves water

during photosynthesis while

optimizing the Calvin cycle.

C4plants are so named becausethey first fix CO2into a four-carboncompound.

When the weather is hot and dry,C4plants keep their stomatamostly closed, thus conserving

water.

Other methods of carbon fixation have evolved in hot,dry climates

Oth th d f b fi ti h l d i h t


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Calvin

Cycle

CO2

3-C sugar

CAM plantDay

CO2

4-C compound

Night Another adaptation to hot and dry

environments has evolved in theCAM plants, such as pineapples andcacti.

CAM plants conserve water byopening their stomata and admittingCO2only at night.

CO2is fixed into a four-carboncompound,

which banks CO2at night and

releases it to the Calvin cycle during

the day.

Other methods of carbon fixation have evolved in hot,dry climates


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Light

Thylakoids

H2O CO2

O2

NADP

ADP

P

ATP

NADPHG3P

3-PGA

RuBP

Chloroplast

Sugars

Photosystem II

PhotosystemI

LightReactions

Electron

transport chain

Calvin

Cycle

(in stroma)

Stroma

Cellular

respiration

Other organiccompounds

Cellulose

Starch

Review: The chloroplast integrates the two stages of photosynthesis

Photosynthesis possible moderator of global climate


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Photosynthesispossible moderator of global climate

change

Root cause of climate change is build up of CO2 Photosynthesizing organisms are carbon sinks

Widespread deforestation has aggravated the global

warming problem by reducing an effective CO2sink.

Global warming caused by increasing CO2levels may be

reduced by

limiting deforestation,

reducing fossil fuel consumption,

growing biofuel crops that remove

CO2from the atmosphere.


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Summary

Understand significance of photosynthesis to all organisms.

Ultimately, how is light energy turned into carbohydrate?

Understand the structure & function of the chloroplasts

Why are the photosystems so important? What are the key steps in the light & light-independent

processes?

What is the significance of ATP, NADPH, Rubisco to the

entire process? What are alternative methods of carbon fixation?

Next upChapter 8.1-8.5 & Chapter 10.1-10.3

biol1003 -9_photosynthesis - fall2014

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