Chapter 7 ppt

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Biology

Sylvia S. Mader Michael Windelspecht

Chapter 7 Photosynthesis

Lecture Outline

See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into

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Outline

• 7.1 Photosynthetic Organisms

• 7.2 The Process of Photosynthesis

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7.1 Photosynthetic Organisms

• All life on Earth depends on solar energy

• Photosynthetic organisms (algae, plants, and

cyanobacteria

)

transform solar energy into the chemical

energy of carbohydrates



Called

autotrophs

because they produce their own

food.

• Photosynthesis

:

 A process that captures solar energy

 Transforms solar energy into chemical energy

 Energy ends up stored in a carbohydrate

• Photosynthesizers produce food energy

(4)

Photosynthetic Organisms

mosses

garden plants trees

cyanobacteria

Euglena diatoms

kelp

(5)

Photosynthetic Organisms

• Photosynthesis

takes place in the green portions of

plants

 Leaf of flowering plant contains mesophyll tissue

 Cells containing chloroplasts are specialized to carry out photosynthesis

• The raw materials for photosynthesis are carbon dioxide

and water

 Roots absorb water that moves up vascular tissue

 Carbon dioxide enters a leaf through small openings called stomata and diffuses into chloroplasts in mesophyll cells

 In stroma, CO₂ is combined with H₂O to form C₆H₁₂O₆ (sugar)

 Energy supplied by light

• Chlorophyll and other pigments absorb solar energy and energize

(6)

Leaves and Photosynthesis

Grana Chloroplast Leaf cross section

granum

independent thylakoid in a granum

mesophyll

lower epidermis upper epidermis cuticle

leaf vein outer membrane

inner membrane

thylakoid space thylakoid membrane

overlapping thylakoid in a granum

CO2

O2

stoma

stroma stroma

37,000

(7)

7.2 The Process of Photosynthesis

• Light Reactions

– take place only in the

presence of light



Energy-capturing reactions



Chlorophyll absorbs solar energy



This energizes electrons



Electrons move down an electron transport chain

• Pumps H+_{into thylakoids}

• Used to make ATP out of ADP and NADPH out of NADP

• Calvin Cycle Reactions

– take place in the

stroma



CO

₂

is reduced to a carbohydrate

(8)

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Overview of Photosynthesis

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Overview of Photosynthesis

solar energy

(11)

Overview of Photosynthesis

thylakoid membrane

Light reactions

ADP +

NADP+

H₂O

(12)

Overview of Photosynthesis

O₂ solar

energy

ADP +

NADP+

NADPH

ATP H₂O

(13)

Overview of Photosynthesis

CO₂

CH2O

stroma Calvin

cycle reactions

O₂ solar

energy

ADP + P

NADP+

NADPH

ATP H₂O

(14)

7.3 Plants as Solar Energy

Converters

• Pigments:



Chemicals that absorb certain wavelengths of light



Wavelengths that are not absorbed are

reflected/transmitted

• Absorption Spectrum



Pigments found in chlorophyll absorb various portions

of visible light



Graph showing relative absorption of the various

colors of the rainbow



Chlorophyll is green because it absorbs much of the

(15)

Photosynthetic Pigments

and Photosynthesis

Wavelengths (nm) Increasing wavelength

a. The electromagnetic spectrum includes visible light. b. Absorption spectrum of photosynthetic pigments. Increasing energy

Gamma

rays X rays UV Infrared

Micro- waves

Radio waves

visible light

500 600 750

Wavelengths (nm)

380 500 600 750 chlorophyll a

chlorophyll b carotenoids

Rel

a

tiv

e

A

bs

orpti

on

(16)

Plants as Solar Energy

Converters

• The light reactions consist of two alternate

electron pathways:



Noncyclic pathway



Cyclic pathway

• Capture light energy with photosystems



Pigment complex helps collect solar energy like an

antenna



Occur in the thylakoid membranes

• Both pathways produce ATP

(17)

Plants as Solar Energy

Converters

• Noncyclic pathway

 Takes place in the thylakoid membrane

 Uses two photosystems, PS I and PS II

 PS II captures light energy

 Causes an electron to be ejected from the reaction center (chlorophyll a)

• Electron travels down electron transport chain to PS I • Replaced with an electron from water, which is split to form

O₂ and H+

• This causes H+_{to accumulate in thylakoid chambers}

• The H+_{gradient is used to produce ATP}

 PS I captures light energy and ejects an electron

• The electron is transferred permanently to a molecule of NADP+

(18)

Noncyclic Electron Pathway

P

CO₂ H₂O

Calvin cycle

ADP+

NADP+

(19)

Noncyclic Electron Pathway

e– O ener g y le v el P CO2

H2O

sun

electron acceptor

H2O

pigment complex reaction center Photosystem II Calvin cycle e– thylakoid membrane e– ADP+ Light reactions NADP+

CH2O

NADPH

(20)

Noncyclic Electron Pathway

e– O e ne rgy le v e l P CO2

H2O

sun

electron acceptor

CH2O

CO2 H2O

pigment complex reaction center Photosystem II Calvin cycle thylakoid membrane e– ADP+ Light reactions NADP+ ATP

CH2O

NADPH

ATP

(21)

Noncyclic Electron Pathway

H +

NADP+

NADPH

reaction center

pigment complex

CH₂O CO₂ Photosystem I e– e– e– ATP e– O P CO2

H2O

solar energy Calvin cycle thylakoid membrane ADP+ Light reactions NADP+

CH2O

(22)

Plants as Solar Energy

Converters

• PS II:

 Consists of a pigment complex and electron acceptors

 Receives electrons from the splitting of water

 Oxygen is released as a gas

• Electron transport chain:

 Consists of cytochrome complexes and plastoquinone

 Carries electrons between PS II and PS I

 Also pumps H+_{from the stroma into the thylakoid space}

• PS I:

 Has a pigment complex and electron acceptors

 Adjacent to the enzyme that reduces NADP+_{to NADPH}

• ATP synthase

complex:

 Has a channel for H+_flow

 H+_{flow through the channel drives ATP synthase to join ADP}

(23)

Organization of a Thylakoid

H+ H+ e- O2 2 + 2 1 P

H2O CO2

solar energy thylakoid thylakoid membrane thylakoid space NADPH ATP ATP synthase

e- _NADP+

granum photosystem II stroma H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

H2O

electron transport chain e- thylakoid membrane Calvin cycle reactions ADP + NADP + Light

reactions _NADPH

ATP

CH2O

(24)

Plants as Solar Energy

Converters

• The thylakoid space acts as a reservoir for hydrogen ions

(H

+

₎

• Each time water is oxidized, two H

+

_{remain in the thylakoid}

space

• Transfer of electrons in the electron transport chain yields

energy

 Used to pump H+_{across the thylakoid membrane}

 Protons move from stroma into the thylakoid space

• Flow of H

+

_{back across the thylakoid membrane}

 Energizes ATP synthase, which

 Enzymatically produces ATP from ADP + P_i

(25)

Tropical Rain Forest Destruction

and Climate Change

• Tropical rain forests can exist where

 Temperatures are above 26º C

 Rainfall is heavy (100-200 cm) and regular

• Most plants are woody; many vines and epiphytes; little

or no undergrowth

• Contribute greatly to CO

₂

uptake, slowing global

warming

 Development has reduced them from 14% to 6% of Earth’s surface

(26)

Tropical Rain Forest Destruction

and Climate Change

Me a n Glo b a l T e mp e ra tur e Ch a n g e ( 0 c)

maximum likely increase

most probable temperature increase for 2 × CO₂

Minimum likely increase 5.5 4.5 3.5 2.5 1.5 0.5 –0.5

(27)

7.4 Plants as Carbon Dioxide

Fixers

• A cyclical series of reactions

• Utilizes atmospheric carbon dioxide to

produce carbohydrates

• Known as C

₃

photosynthesis

• Involves three stages:

• Carbon dioxide fixation

(28)

Plants as Carbon Dioxide

Fixers

• CO

₂

is attached to 5-carbon

RuBP carboxylase



Results in a 6-carbon molecule



This splits into two 3-carbon molecules (3PG)



Reaction is accelerated by RuBP carboxylase

(Rubisco)

(29)

The Calvin Cycle Reactions

P

H2O CO2

Calvin cycle ADP +

NADP +

Light

reactions NADPH

ATP

CH2O

O2

stroma

3 RuBP C₅

G3P glyceraldehyde-3-phosphate BPG 1,3-bisphosphoglycerate 3PG 3-phosphoglycerate RuBP ribulose-1,5-bisphosphate

(30)

The Calvin Cycle Reactions

P

H2O CO2

NADP +

Light

ATP

CH2O

O2

stroma

3 RuBP C5

Metabolites of the Calvin Cycle

3CO2

(31)

The Calvin Cycle Reactions

P

H2O CO2

NADP +

Light

ATP

CH2O

O2

stroma

intermediate

3 RuBP C5

3CO2

3 C₆

(32)

The Calvin Cycle Reactions

P

H2O CO2

NADP +

Light

ATP

CH2O

O2

stroma

6 3PG C3

intermediate

3 RuBP C5

3CO2

3 C₆

(33)

The Calvin Cycle Reactions

P

H2O CO2

solar energy Calvin cycle ADP + NADP + Light

ATP

CH2O

O2 stroma 6 3PG C₃ intermediate 3 RuBP C5 6 BPG C

3CO₂

3 C6

6 ATP

(34)

The Calvin Cycle Reactions

P

H2O CO2

solar energy Calvin cycle ADP + NADP + Light

ATP

CH2O

O2 stroma 6 3PG C3 intermediate 3 RuBP C5 6 BPG C3

6 G3P

6 NADPH

3CO2

3 C6

These ATP and NADPH molecules were produced by the light reactions. 6

ATP

(35)

The Calvin Cycle Reactions

P

H2O CO2

solar energy Calvin cycle ADP + NADP + Light reactions NADPH

ATP

CH2O

O2 stroma 6 3PG C3 intermediate 3 RuBP C5 6 BPG C3

6 NADP+

6 G3P C3

6 NADPH 3CO2

3 C6

ATP

(36)

The Calvin Cycle Reactions

P

H2O CO2

ATP

CH2O

O2 stroma 6 3PG C3 intermediate 3 RuBP C5 5 G3P C3 6 BPG C3

6 NADP+

6 G3P C3

6 NADPH 3CO2

3 C6

ATP

(37)

The Calvin Cycle Reactions

P

H2O CO2

ATP

CH2O

O2

stroma

These ATP molecules were produced by the light reactions. 6 3PG C3 intermediate 3 RuBP C5 5 G3P C3 6 BPG C3

3 ADP + 3

3 ATP

6 NADP+

6 G3P C3

regeneration of RuBP

Calvin cycle CO2

reduction CO2

fixation

6 NADPH 3CO2

3 C6

ATP

(38)

Plants as Carbon Dioxide

Fixers

• 3PG is reduced to BPG

• BPG is then reduced to G3P

(39)

Reduction of Carbon Dioxide

NADPH NADP+

ATP

3PG BPG _G3P

ADP + P

As 3PG becomes G3P, ATP becomes

ADP + _P and NADPH becomes NADP+

(40)

Plants as Carbon Dioxide

Fixers

• Regeneration of RuBP



RuBP used in CO

₂

fixation must be replaced



Every three turns of Calvin Cycle:

• Five G3P (a 3-carbon molecule) are used

• To remake three RuBP (a 5-carbon molecule)

(41)

Regeneration of RuBP

As five molecules of G3P become three molecules of RuBP, three molecules of ATP become three molecules of ADP + .

3 ATP

5 G3P 3 RuBP

3 ADP + P

P

(42)

Plants as Carbon Dioxide

Fixers

• Importance of the Calvin Cycle:



G3P (glyceraldehyde-3-phosphate) can be converted

to many other molecules



The hydrocarbon skeleton of G3P can form

• Fatty acids and glycerol to make plant oils

• Glucose phosphate (simple sugar)

• Fructose (which with glucose = sucrose)

• Starch and cellulose

(43)

Fate of G3P

(44)

Fate of G3P

(45)

Fate of G3P

G3P

amino acid synthesis fatty acid

synthesis glucose

(46)

Fate of G3P

G3P

amino acid synthesis glucose

phosphate

fatty acid synthesis

+ fructose phosphate

Cellulose (in trunks, roots, and branches) Starch (in roots

(47)

Fate of G3P

Sucrose (in leaves, fruits, and seeds)

G3P

amino acid synthesis glucose

phosphate

fatty acid synthesis

+ fructose phosphate

Cellulose (in trunks, roots, and branches) Starch (in roots

(48)

7.5 Other Types of

Photosynthesis

• In hot, dry climates

 Stomata must close to avoid wilting

 CO₂ decreases and O₂ increases

 O₂ starts combining with RuBP, leading to the production of CO₂

 This is called photorespiration

• C

₄

plants solve the problem of photorespiration

 Fix CO₂ to PEP (a C₃ molecule)

 The result is oxaloacetate, a C₄ molecule

 In hot & dry climates

• C₄ plants avoid photorespiration

• Net productivity is about 2-3 times greater than C₃ plants

(49)

Chloroplast Distribution in C

₄

vs. C

₃

Plants

C₃ Plant C₄ Plant

bundle sheath bundle sheath

cell

mesophyll cells

vein vein

stoma stoma

(50)

CO

₂

Fixation in C

₃

and C

₄

Plants

C4

CO2

RuBP

Calvin cycle

3PG

mesophyll cell G3P

a. CO2 fixation in a C3 plant, wildflowers

CO2

mesophyll cell

CO2

Calvin cycle bundle sheath cell

(51)

Other Types of

Photosynthesis

• CAM

Photosynthesis



Crassulacean-Acid Metabolism



CAM plants partition carbon fixation by time

• During the night

– CAM plants fix CO₂

– Form C₄ molecules, which are – Stored in large vacuoles

• During daylight

– NADPH and ATP are available

(52)

CO

₂

Fixation in a CAM Plant

Calvin

cycle

CO

2

CO 2

C₄

G3P

CO₂ fixation in a CAM plant, pineapple, Ananas comosus

night

day

(53)

Other Types of Photosynthesis

• Each method of photosynthesis has advantages and

disadvantages

 Depends on the climate

• C

₄

plants most adapted to:

 High light intensities

 High temperatures

 Limited rainfall

• C

₃

plants better adapted to

 Cold (below 25°C)

 High moisture

• CAM plants are better adapted to extreme aridity

 CAM occurs in 23 families of flowering plants