Chapter 7 1 Biology and Society:...

© 2013 Pearson Education, Inc.Lectures by Edward J. Zalisko

PowerPoint® Lectures forCampbell Essential Biology, Fifth Edition, and

Campbell Essential Biology with Physiology,

Fourth Edition– Eric J. Simon, Jean L. Dickey, and Jane B. Reece

Chapter 7Chapter 7Photosynthesis: Using Light

to Make Food

1 Biology and Society: Biofuels

• Wood has historically been the main fuel used to

produce

– heat and

– light.

© 2013 Pearson Education, Inc.

2

Figure 7.0 3

• Industrialized societies replaced wood with fossil

fuels including

– coal,

– gas, and

– oil.

• To limit the damaging effects of fossil fuels,

researchers are investigating the use of biomass

(living material) as efficient and renewable energy

sources.

Biology and Society: Biofuels


4

• There are several types of biofuels.

– Bioethanol is a type of alcohol produced by the fermentation of glucose made from starches in crops such as grains, sugar beets, and sugar cane.

– Bioethanol may be used

– directly as a fuel source in specially designed

vehicles or

– as a gasoline additive.

Biology and Society: Biofuels


5 THE BASICS OF PHOTOSYNTHESIS

• Photosynthesis

– is used by plants, algae (protists), and some bacteria,

– transforms light energy into chemical energy, and

– uses carbon dioxide and water as starting materials.


7

• The chemical energy produced via photosynthesis

is stored in the bonds of sugar molecules.

• Organisms that use photosynthesis are

– photosynthetic autotrophs and

– the producers for most ecosystems.

THE BASICS OF PHOTOSYNTHESIS


8 Figure 7.1

Plants(mostly on land)

Photosynthetic Protists(aquatic)

PHOTOSYNTHETIC AUTOTROPHS

Photosynthetic Bacteria(aquatic)

Micrograph of cyanobacteriaKelp, a large, multicellular algaForest plants

LM

9

Chloroplasts: Sites of Photosynthesis

• Chloroplasts are

– the site of photosynthesis and

– found mostly in the interior cells of leaves.

• Inside chloroplasts are interconnected,

membranous sacs called thylakoids, which are

suspended in a thick fluid called stroma.

• Thylakoids are concentrated in stacks called grana.


10

• The green color of chloroplasts is from chlorophyll, a light-

absorbing pigment that plays a central role in converting

solar energy to chemical energy.

– The green light we see is the light that is not absorbed by

these pigments

• Stomata are tiny pores in leaves where

– carbon dioxide enters and

– oxygen exits.

– Stoma is the singular form. Do not confuse with

Stroma!!!

– Stoma is the greek root for mouth. Stomach has the same root.

Chloroplasts: Sites of Photosynthesis 11

Figure 7.2-1

Leaf cross section

Stomata

Vein

CO2O2

Photosyntheticcells

12 Figure 7.2-2

Interior cell

LM

Chloroplast

Leaf cross section

Stomata

Vein

CO2O2

Photosyntheticcells

13

Figure 7.2-3

Interior cell

LM

StromaGranum

Thylakoidspace

ChloroplastInner and outermembranes

Co

lori

zed

TE

MLeaf cross section

Stomata

Vein

CO2O2

Photosyntheticcells

14 The Simplified Equation for Photosynthesis

• In the overall equation for photosynthesis, notice

that the reactants of photosynthesis are the waste

products of cellular respiration.


15

Carbon dioxide

6 O26 CO2 6 H2O C6H12O6

Water GlucosePhoto-

synthesis Oxygen gas

Light energy

The Simplified Equation for Photosynthesis 16

C6H12O6 CO2 ATPO2 H2O

Glucose Oxygen Carbondioxide

Water Energy

6 66

The Simplified Equation for Cellular Respiration

17

Figure 6.2

Sunlight energyenters ecosystem

Photosynthesis

Cellular respiration

C6H12O6 CO2

drives cellular work

Heat energy exits ecosystem

ATP

O2 H2O

18

• In photosynthesis,

– sunlight provides the energy,

– electrons are boosted “uphill” and added to carbon dioxide, and

– sugar is produced.

The Simplified Equation for Photosynthesis


19

• During photosynthesis, water is split into

– hydrogen and

– oxygen.

• Hydrogen is transferred along with electrons and

added to carbon dioxide to produce sugar.

• Oxygen escapes through stomata into the

atmosphere.

The Simplified Equation for Photosynthesis


20 A Photosynthesis Road Map

• Photosynthesis occurs in two multistep stages:

1. the light reactions convert solar energy to chemical energy and

– This occurs in the thylakoid membrane

2. the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide.

– This occurs in the stroma


21

A Photosynthesis Road Map

• The initial incorporation of carbon from the

atmosphere into organic compounds is called

carbon fixation.

– This lowers the amount of carbon in the air.

– Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life.


22


BioFlix Animation: Photosynthesis

23

Figure 7.3-1

Light

H2O

O2

Chloroplast

Lightreactions

NADPH

ATP

– –

24 Figure 7.3-2

Calvincycle

CO2

NADP+

ADPP

Sugar

Light

H2O

O2

Chloroplast

Lightreactions

NADPH

ATP

++++

– –

25

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY

• Chloroplasts

– are chemical factories powered by the sun and

– convert sunlight into chemical energy.


26 Figure 7-UN02

Light reactions

CO2

O2

H2O

NADPH

Light

Sugar

ATP

ADP

P

NADP++++

Calvin cycle

– –

+

27

The Nature of Sunlight

• Sunlight is a type of energy called radiation, or

electromagnetic energy.

• The distance between the crests of two adjacent

waves is called a wavelength.

• The full range of radiation is called the

electromagnetic spectrum.


28 Figure 7.4

Visible light

Wavelength (nm)

Radiowaves

400 500 600 750700

Wavelength ====580 nm

Micro-waves

Gamma

raysInfraredUVX-rays

10–5 nm 1 nm 1 m

Increasing wavelength

380

10–3 nm 103 nm 106 nm 103 m

29

Figure 7.5

Light

Chloroplast

Absorbedlight

Transmittedlight (detectedby your eye)

Reflectedlight

30 Figure 7.5a

Light

Chloroplast

Absorbedlight

Transmittedlight (detectedby your eye)

Reflectedlight

31

Figure 7.5b 32 The Process of Science: What Colors of Light Drive Photosynthesis?

• Observation: In 1883, German biologist Theodor

Engelmann saw that certain bacteria tend to

cluster in areas with higher oxygen concentrations.

• Question: Could this information determine which

wavelengths of light work best for photosynthesis?

• Hypothesis: Oxygen-seeking bacteria will

congregate near regions of algae performing the

most photosynthesis.


33

• Experiment: Engelmann

– laid a string of freshwater algal cells in a drop of water on a microscope slide,

– added oxygen-sensitive bacteria to the drop, and

– used a prism to create a spectrum of light shining on the slide.

The Process of Science: What Colors of Light Drive Photosynthesis?


34

• Results: Bacteria

– mostly congregated around algae exposed to red-orange and blue-violet light and

– rarely moved to areas of green light.

• Conclusion: Chloroplasts absorb light mainly in

the blue-violet and red-orange part of the

spectrum.

The Process of Science: What Colors of Light Drive Photosynthesis?


35


Animation: Light and Pigments

Right click slide / select “Play”

36 Figure 7.6Light

Microscope slide

Prism

Bacteria

Algal cells

Bacteria

Wavelength of light (nm)

400 500 600 700

Nu

mb

er

of

bacte

ria

37

Chloroplast Pigments

• Chloroplasts contain several pigments:

1. Chlorophyll a

– absorbs mainly blue-violet and red light and

– participates directly in the light reactions.

2. Chlorophyll b

– absorbs mainly blue and orange light and

– participates indirectly in the light reactions.


38

• Carotenoids

– absorb mainly blue-green light,

– participate indirectly in the light reactions, and

– absorb and dissipate excessive light energy that might damage chlorophyll.

• The spectacular colors of fall foliage are due partly

to the yellow-orange light reflected from

carotenoids.

Chloroplast Pigments


39

Figure 7.7 40 How Photosystems Harvest Light Energy

• Light behaves as photons, a fixed quantity of light

energy.

• Chlorophyll molecules absorb photons.

– Electrons in the pigment gain energy.

– As the electrons fall back to their ground state, energy is released as heat or light.


41

Figure 7.8

Light

(b) Fluorescence of a glow stick

Photon

Heat

Light (fluorescence)

Ground stateChlorophyll

molecule

Excited state

e–

(a) Absorption of a photon

The electronfalls to itsground state.

Absorption of a photon excitesan electron.

42

• In the thylakoid membrane, chlorophyll molecules

are organized with other molecules into

photosystems.

• A photosystem is a cluster of a few hundred

pigment molecules that function as a light-

gathering antenna.

How Photosystems Harvest Light Energy


43

• The reaction center of the photosystem consists of chlorophyll a molecules that sit next to another molecule called a primary electron acceptor, which traps the light-excited electron from chlorophyll a.

• Another team of molecules built into the thylakoid membrane then uses that trapped energy to make

– ATP and

– NADPH.

How Photosystems Harvest Light Energy


44 Figure 7.9

Chloroplast

Thylakoid membrane

Cluster of pigment molecules

Pigmentmolecules

Primaryelectronacceptor

Reaction-center

chlorophyll a

Electrontransfer Reaction

center

Photosystem

Transferof energy

Photon

e–

45

How the Light Reactions Generate ATP and NADPH

• Two types of photosystems cooperate in the light

reactions:

1. the water-splitting photosystem and

2. the NADPH-producing photosystem.


46 Figure 7.10-1


Water-splittingphotosystem

Light

H2O

2 H++++

Reaction-centerchlorophyll

O2++++1

2

2e–

2e–

1

47

Figure 7.10-2



Light

H2O

2 H++++


O2++++

Energyto make ATP

1

2

2e–

2e–

1

2

48 Figure 7.10-3



Light

H2O

2 H++++ O2++++

Energyto make ATP


2e–

Light

NADPH-producingphotosystem


2e–

NADPH

NADP++++

1

2

2e–

2e–

1

2

3

– –


49

• The light reactions are located in the thylakoid

membrane.

• An electron transport chain

– connects the two photosystems and

– releases energy that the chloroplast uses to make ATP.

How the Light Reactions Generate ATP and NADPH


50 Figure 7.11

Light

H2O

Thylakoidmembrane

2e–

O2

ATP

NADP++++

Light

Stroma

Inside thylakoid

Photosystem Photosystem

Electron transport chain

NADPH

ADP ++++ P

H++++

ATPsynthase

To Calvin cycle

H++++

Electron flow

H++++

H++++

H++++

H++++

H++++

1

2

Thylakoidmembrane

– –

51

Figure 7.12


ATP

NADPH

e–


– –e–

e–

e–

e–

e–

e–

52 THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE

• The Calvin cycle

– functions like a sugar factory within a chloroplast and

– regenerates the starting material with each turn.


53


Blast Animation: Photosynthesis: Light-Independent Reactions

Select “Play”

54 Figure 7-UN03

Light reactions

CO2

O2

H2O

NADPH

Light

Sugar

ATP

ADPP

NADP++++

Calvin cycle

– –

+

55

Figure 7.13-1

P P

P

Three-carbon moleculeRuBP sugar

CO2 (from air)

Calvincycle

1

56 Figure 7.13-2

ATP

NADPH

ADP ++++ P

NADP++++

P

P P

P

G3P sugar

Three-carbon moleculeRuBP sugar

CO2 (from air)

Calvincycle – –

2

1

57

Figure 7.13-3

ATP

NADPH

ADP ++++ P

NADP++++

P

P

P

P P

P

G3P sugar

Three-carbon molecule

G3P sugar

G3P sugar

RuBP sugar

CO2 (from air)

Calvincycle

Glucose (and other

organic compounds)

– –

23

1

58 Figure 7.13-4

ATP

NADPH

ADP ++++ P

NADP++++

P

P

P

P P

P

G3P sugar

Three-carbon molecule

G3P sugar

G3P sugar

RuBP sugar

CO2 (from air)

Calvincycle

Glucose (and other

organic compounds)

– –

23

1

4

ATP

ADP ++++ P

59

Evolution Connection:Solar-Driven Evolution

• C3 plants

– use CO2 directly from the air and

– are very common and widely distributed.


60

• C4 plants

– close their stomata to save water during hot and dry weather and

– can still carry out photosynthesis.

• CAM plants

– are adapted to very dry climates and

– open their stomata only at night to conserve water.

Evolution Connection:Solar-Driven Evolution


61

Figure 7.14

Sugar

C4 Pathway(example: sugarcane)

C4 plant CAM plant

Sugar

Calvincycle

Calvincycle

Day

Celltype 1

Four-carboncompound

Night

Four-carboncompound

Celltype 2

CAM Pathway(example: pineapple)

ALTERNATIVE PHOTOSYNTHETIC PATHWAYS

CO2 CO2

CO2CO2

62 Figure 7.14a

Sugar


C4 plant

Calvincycle

Celltype 1

Four-carboncompound

Celltype 2

CAM plant

Sugar

Calvincycle

Day

Four-carboncompound

Night

CO2

CO2


CO2

CO2

63

Figure 7.14b


64


Figure 7.14c 65

Figure 7-UN04

Carbon dioxide

6 O26 CO2 6 H2O C6H12O6

Water GlucosePhotosynthesis

Oxygen gas

Light energy

66 Figure 7-UN05

Light H2O

O2

Chloroplast

Lightreactions

NADPH

ATP

Calvin

cycle

CO2

NADP++++

ADP

P

Sugar

Stack ofthylakoids Stroma

– –

Sugar used for• cellular respiration• cellulose• starch• other organic compounds

67

Figure 7-UN06

acceptor


Photon

H2O

2 H++++

Chlorophyll

2e–

O2+

ATP


Chlorophyll

NADPH

NADP++++

e–

2e–

2e–e–

acceptorADP

Photon

21

– –

2e–

68 Figure 7-UN07

NADPH

Calvincycle

ADP P

NADP++++

P

ATP

G3P

CO2

Glucose andother compounds(such as celluloseand starch)

– –

69

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