photosynthesis ppt

(1)

Figure 7.0-2

Chapter 7: Big Ideas

An Introduction to Photosynthesis

The Light Reactions: Converting Solar Energy

to Chemical Energy

(2)

(3)

7.1 Photosynthesis fuels the biosphere

• Plants are autotrophs, which

• sustain themselves,

• do not usually consume organic molecules derived from other organisms, and

• make their own food through the process of

(4)

7.1 Photosynthesis fuels the biosphere

• Photoautotrophs use the energy of light to

produce organic molecules.

• Chemoautotrophs are prokaryotes that use

inorganic chemicals as their energy source.

• Heterotrophs are consumers that feed on plants

(5)

7.1 Photosynthesis fuels the biosphere

• Photoautotrophs

• feed us,

• clothe us (think cotton),

• house us (think wood), and

(6)

7.1 Photosynthesis fuels the biosphere

• Photosynthesis in plants takes place in chloroplasts.

• Photosynthetic bacteria have infolded regions of

(7)

7.2 Photosynthesis occurs in chloroplasts in

plant cells

• Chlorophyll

• is an important light-absorbing pigment in chloroplasts,

• is responsible for the green color of plants, and

(8)

7.2 Photosynthesis occurs in chloroplasts in

plant cells

• Chloroplasts are concentrated in the cells of the

mesophyll, the green tissue in the interior of the

leaf.

• _Stomata_{are tiny pores in the leaf that allow}

• carbon dioxide to enter and

• oxygen to exit.

(9)

Figure 7.2-0

Leaf Cross Section Mesophyll

Leaf Vein

Mesophyll Cell

CO2

O2

Stoma

Chloroplast

Granum

Inner and outer membranes

(10)

7.2 Photosynthesis occurs in chloroplasts in

plant cells

• Chloroplasts consist of an envelope of two

membranes, which encloses an inner compartment filled with a thick fluid called stroma that contains a system of interconnected membranous sacs

(11)

7.2 Photosynthesis occurs in chloroplasts in

plant cells

• Thylakoids

• are often concentrated in stacks called grana and

• have an internal compartment called the thylakoid space, which has functions analogous to the

(12)

7.2 Photosynthesis occurs in chloroplasts in

plant cells

• Thylakoid membranes also house much of the

machinery that converts light energy to chemical energy.

• _{Chlorophyll molecules}

• are built into the thylakoid membrane and

(13)

Figure 7.2-2

Mesophyll Cell

Chloroplast

Granum

Inner and outer membranes

(14)

7.4 Photosynthesis is a redox process, as is

cellular respiration

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

• CO₂ becomes reduced to sugar as electrons, along with hydrogen ions (H+) from water, are added to it.

(15)

Figure 7.4a

Becomes reduced

Becomes oxidized

(16)

7.4 Photosynthesis is a redox process, as is

• Cellular respiration uses redox reactions to harvest the chemical energy stored in a glucose molecule.

• This is accomplished by oxidizing the sugar and reducing O₂ to H₂O.

• The electrons lose potential as they travel down the electron transport chain to O₂.

(17)

7.4 Photosynthesis is a redox process, as is

• In photosynthesis,

• light energy is captured by chlorophyll molecules to boost the energy of electrons,

• light energy is converted to chemical energy, and

(18)

Figure 7.4b

C₆H₁₂O₆ + 6 O₂ 6 CO₂ + 6 H₂O

(19)

7.5 The two stages of photosynthesis are

linked by ATP and NADPH

• Photosynthesis occurs in two stages.

1. The light reactions occur in the thylakoid membranes. In these reactions

• water is split, providing a source of electrons and giving off oxygen as a by-product,

• ATP is generated from ADP and a phosphate group, and

• light energy is absorbed by the chlorophyll molecules to drive the transfer of electrons and H+ from water to the

electron acceptor NADP+_{, reducing it to NADPH.}

(20)

7.5 The two stages of photosynthesis are

linked by ATP and NADPH

2. The second stage is the Calvin cycle, which occurs

in the stroma of the chloroplast.

• The Calvin cycle is a cyclic series of reactions that

assembles sugar molecules using CO₂ and the energy-rich products of the light reactions.

• During the Calvin cycle, CO₂ is incorporated into organic compounds in a process called carbon fixation.

• After carbon fixation, the carbon compounds are reduced to sugars.

(21)

Figure 7.5-3

Light

Chloroplast

Light Reactions (in thylakoids)

NADP+

ADP

H₂O

P

+

ATP

NADPH

O

CO₂

Calvin Cycle (in stroma)

(22)

THE LIGHT REACTIONS:

(23)

7.6 Visible radiation absorbed by pigments

drives the light reactions

• Sunlight contains energy called electromagnetic

energy or radiation.

• Visible light is only a small part of the

electromagnetic spectrum, the full range of electromagnetic wavelengths.

• Electromagnetic energy travels in waves.

(24)

7.6 Visible radiation absorbed by pigments

• Light behaves as discrete packets of energy called

photons.

• A photon is a fixed quantity of light energy.

(25)

Figure 7.6a

Shorter wavelength Longer wavelength

Lower energy Higher energy

Visible light

Wavelength (nm)

380 400 500 600 700 750

Gamma

rays X-rays UV Infrared

Micro-waves

Radio waves

(26)

7.6 Visible radiation absorbed by pigments

• Plant pigments

• are built into the thylakoid membrane,

• absorb some wavelengths of light, and

• reflect or transmit other wavelengths.

• _{We see the color of the wavelengths that are}

(27)

(28)

Figure 7.6b-0

Light

Reflected light

Transmitted light

Absorbed light

(29)

7.6 Visible radiation absorbed by pigments

• Chloroplasts contain several different pigments, which absorb light of different wavelengths.

• Chlorophyll a absorbs mainly blue-violet and red light and reflects mainly green light.

• Chlorophyll b absorbs mainly blue and orange and

reflects (appears) olive-green.

• Carotenoids

• broaden the spectrum of colors that can drive photosynthesis and

(30)

7.7 Photosystems capture solar energy

• Pigments in chloroplasts absorb photons

(capturing solar power), which

• increases the potential energy of the pigments’ electrons and

• sends the electrons into an unstable state.

• Generally, when isolated pigment molecules

absorb light, their excited electrons drop back

(31)

Figure 7.7a-0

Excited state

Heat Photon

of light

Chlorophyll molecule

(32)

7.7 Photosystems capture solar energy

• Within a thylakoid membrane, chlorophyll and

other pigment molecules

• absorb photons and

• _{transfer the energy to other pigment molecules.}

• _{In the thylakoid membrane, chlorophyll molecules}

(33)

7.7 Photosystems capture solar energy

• A photosystem consists of a number of

light-harvesting complexes surrounding a reaction-center complex.

• _{A light-harvesting complex contains various}

pigment molecules bound to proteins.

(34)

Figure 7.7b Light STROMA Light-harvesting complexes Photosystem Reaction-center complex Primary electron acceptor THYLAKOID SPACE _Transfer of energy Pair of

chlorophyll a

(35)

7.7 Photosystems capture solar energy

• The light energy is passed from molecule to

molecule within the photosystem.

• Finally it reaches the reaction center, where a

primary electron acceptor accepts these electrons and consequently becomes reduced.

• The solar-powered transfer of an electron from the reaction-center chlorophyll a pair to the primary

electron acceptor is the first step in the

(36)

7.7 Photosystems capture solar energy

• Two types of photosystems (photosystem I and

photosystem II) cooperate in the light reactions.

• Each photosystem has a characteristic

reaction-center complex, with a special pair of chlorophyll a

(37)

7.8 Two photosystems connected by an

electron transport chain generate ATP and

NADPH

• In the light reactions, light energy is transformed into the chemical energy of ATP and NADPH.

• To accomplish this, electrons are

• removed from water,

• passed from photosystem II to photosystem I, and

• accepted by NADP+, reducing it to NADPH.

• Between the two photosystems, the electrons

• move down an electron transport chain and

(38)

7.8 Two photosystems connected by an

electron transport chain generate ATP and

NADPH

• A simple mechanical analogy helps unpack this

rather complicated system.

• This construction analogy shows how the coupling

(39)

Figure 7.8

ATP

NADPH

Electron transport

chain ramp hP

o to n

Ph oto

n

(40)

7.9 VISUALIZING THE CONCEPT: The light

reactions take place within the thylakoid

membranes

• A thylakoid membrane includes numerous copies

of

• the two photosystems and

(41)

7.9 VISUALIZING THE CONCEPT: The light

reactions take place within the thylakoid

membranes

• Light energy absorbed by the two photosystems

drives the flow of electrons from water to NADPH.

• The electron transport chain helps to produce the

concentration gradient of H+ across the thylakoid

membrane, which drives H+ through ATP synthase,

producing ATP.

• _{Because the initial energy input is light (“}_photo_”),

this chemiosmotic production of ATP is called

(42)

Figure 7.9-0 Thylakoid sac Light Photosystem II H+ H+ H+ H+ H+ H+ H+ Electron transport chain Light Photosystem I H+

H₂O

H+

H+ H + H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ THYLAKOID SPACE

O₂ + 2

1 2

NADP+_{+ H}+

NADPH To Calvin Cycle Chloroplast STROMA H+ H+

(43)

Figure 7.9-1

Light

Photosystem

II

Primary electron acceptor Pigment molecules

Reaction center pair of

chlorophyll a molecules

H2O

O2 + 2 H+

(44)

Figure 7.9-5

Light

Photosystem

II

H2O

O2 + 2 H+

1 2 1 Electron transport chain H+ H+ H+ H+ H+ H+ H+ H+ Light Photosystem I H+ H+ H+ H+ H+ NADP+ NADPH To Calvin Cycle H+ H+ THYLAKOID SPACE STROMA Thylakoid membrane H+ ATP synthase H+ H+ H+ H+ H+

H+ H

+ H

+

H+ H+

P _ATP

(45)

THE CALVIN CYCLE:

(46)

7.10 ATP and NADPH power sugar synthesis

in the Calvin cycle

• The Calvin cycle makes sugar within a chloroplast.

• _{To produce sugar, the necessary ingredients are}

• atmospheric CO₂ and

(47)

7.10 ATP and NADPH power sugar synthesis

in the Calvin cycle

• The Calvin cycle uses these three ingredients to

produce an energy-rich, three-carbon sugar called glyceraldehyde 3-phosphate (G3P).

• _{A plant cell uses G3P to make}

• glucose,

• the disaccharide sucrose, and

(48)

7.10 ATP and NADPH power sugar synthesis

in the Calvin cycle

• The steps of the Calvin cycle include

• carbon fixation,

• reduction,

• release of one molecule of G3P, and

• regeneration of the starting molecule, ribulose bisphosphate (RuBP).

• _{Photosynthesis is an emergent property of the}

(49)

Figure 7.10-1

Chloroplast

O₂ _Sugar

Light

Reactions Calvin_Cycle CO₂ H₂O

NADP+

ADP P +

(50)

Figure 7.10-2 Step 4 Regeneration of RuBP 3 P P RuBP 3 ATP 3 ADP Rubisco 5 G3P 1 Step 3

Release of one molecule of G3P

Glucose and other Step 2 Reduction G3P 6 P P P P CALVIN CYCLE 6 6 ATP

6 ADP + P

(51)

Figure 7.10-3-1

3 P

RuBP

Rubisco

P 6 3-PGA P

3 CO₂

Input

Step 1

Carbon fixation

(52)

Figure 7.10-3-2

3 P

RuBP

Rubisco

P 6 3-PGA P

3 CO2 Input Step 1 Carbon fixation CALVIN CYCLE Step 2 Reduction G3P 6 P 6 ATP

6 ADP + P

6

NADPH

(53)

Figure 7.10-3-3

3 P

RuBP

Rubisco

P 6 3-PGA P

3 CO2 Input Step 1 Carbon fixation CALVIN CYCLE Step 2 Reduction G3P 6 P 6 ATP

6 ADP + P

6 6 NADPH NADP+ P 5 G3P 1 G3P Step 3

Glucose and other

(54)

Figure 7.10-3-4

3 P

RuBP

Rubisco

P 6 3-PGA P

3 CO2 Input Step 1 Carbon fixation CALVIN CYCLE Step 2 Reduction G3P 6 P 6 ATP

6 ADP + P

6 6 NADPH NADP+ P 5 G3P 1 Step 3

Glucose and other

(55)

7.11 EVOLUTION CONNECTION: Other

methods of carbon fixation have evolved in

hot, dry climates

• Most plants use CO₂ directly from the air, and

carbon fixation occurs when the enzyme rubisco

adds CO₂ to RuBP.

• Such plants are called C₃ plants because the first product of carbon fixation is a three-carbon

(56)

7.11 EVOLUTION CONNECTION: Other

hot, dry climates

• In hot and dry weather, C₃ plants close their

stomata to reduce water loss, but this prevents CO₂ from entering the leaf and O₂ from leaving.

• As O₂ builds up in a leaf, rubisco adds O₂ instead of CO₂ to RuBP, and a two-carbon product of this

reaction is then broken down in the cell.

• This process is called photorespiration because it occurs in the light, consumes O₂, and releases CO₂.

(57)

7.11 EVOLUTION CONNECTION: Other

hot, dry climates

• An alternate mode of carbon fixation has evolved

that

• minimizes photorespiration and

• _{optimizes the Calvin cycle.}

• C₄ plants are so named because they first fix CO₂

into a four-carbon compound.

• When the weather is hot and dry, C₄ plants keep their stomata mostly closed, thus conserving

(58)

7.11 EVOLUTION CONNECTION: Other

hot, dry climates

• Another adaptation to hot and dry environments

has evolved in the CAM plants, such as pineapples, cacti, aloe, and jade.

• CAM plants conserve water by opening their

stomata and admitting CO₂ only at night.

• _CO₂_{is fixed into a four-carbon compound, which}

(59)

Figure 7.11-0

Mesophyll cell

Bundle-sheath cell

Sugarcane Pineapple

Day CAM plant Sugar Sugar

C₄ plant Calvin

Cycle

Calvin Cycle

CO₂ _Night CO₂

4-C compound

(60)

(61)

7.12 Photosynthesis makes sugar from CO

₂

and H

₂

O, providing food and O

₂

for almost all

living organisms

• Two photosystems in the thylakoid membranes

capture solar energy, energizing electrons in chlorophyll molecules.

• _{Simultaneously,}

• water is split,

• O₂ is released, and

(62)

7.12 Photosynthesis makes sugar from CO

₂

and H

₂

O, providing food and O

₂

for almost all

living organisms

• The photoexcited electrons are transferred through

an electron transport chain, where energy is harvested to make ATP by the process of

chemiosmosis, and finally to NADP+, reducing it to

(63)

Figure 7.12

Chloroplast

O₂ _Sugars

Light Light Reactions Calvin Cycle (in stroma) CO₂

H₂O

NADP+ ADP P + NADPH ATP RuBP G3P Stroma

Photosystem II

Electron transport chain

Thylakoids _Photosystem_I

(64)

7.12 Photosynthesis makes sugar from CO

₂

and H

₂

for almost all

living organisms

• About 50% of the carbohydrates made by

photosynthesis is consumed as fuel for cellular respiration in the mitochondria of plant cells.

• _{Sugars also serve as the starting material for}

making other organic molecules, such as proteins, lipids, and cellulose.

• _{Many glucose molecules are linked together to}

(65)

7.12 Photosynthesis makes sugar from CO

₂

and H

₂

for almost all

living organisms

• Most plants make much more food each day than

they need. They store the excess in

• roots,

• _tubers,

• seeds, and

• fruits.

• Plants (and other photosynthesizers) are the

(66)

7.13 SCIENTIFIC THINKING: Rising

atmospheric levels of carbon dioxide and

global climate change will affect plants in

various ways

• The greenhouse effect operates on a global scale.

• Solar radiation passes through the atmosphere and warms Earth’s surface.

• Heat radiating from the warmed planet is absorbed by greenhouse gases, such as CO₂, water vapor, and methane, which then reflect some of the heat back to Earth.

(67)

7.13 SCIENTIFIC THINKING: Rising

various ways

• Increasing concentrations of greenhouse gases

have been linked to global climate change, of

(68)

7.13 SCIENTIFIC THINKING: Rising

global climate change will affect plants in

various ways

• The predicted consequences of global climate

change include

• _{melting of polar ice,} • rising sea levels,

• extreme weather patterns,

• droughts,

• _{increased extinction rates, and} • the spread of tropical diseases.

(69)

global climate change will affect plants in

various ways

• How may global climate change affect plants?

• Increasing CO₂ levels can increase plant productivity.

• Research has documented such an increase,

(70)

various ways

• How do scientists study the effects of increasing CO₂ on plants?

• Many experiments are done in small growth chambers in which variables can be carefully controlled.

• Other scientists are turning to long-term field

(71)

global climate change will affect plants in

various ways

• In the Free-Air CO₂ Enrichment (FACE) experiment

set up in Duke University’s experimental forest, scientists monitored the effects of elevated CO₂

levels on an intact forest ecosystem over a period of 15 years, using six study sites, each 30 m in

(72)

atmospheric levels of carbon dioxide and

various ways

• Another study compared the growth of poison ivy

in experimental and control plots. The results

showed that poison ivy in the elevated CO₂ plots

• showed an average annual growth increase of 149% compared to control plots and

• _{produced a more potent form of poison ivy’s}

(73)

Figure 7.13b

Control plots Key

Elevated CO₂ plots

Year

Source: Adaptation of Figure 1A from “Biomass and Toxicity Responses of Poison Ivy (Toxicodendron Radicans) to Elevated Atmospheric CO₂” by Jacqueline E. Mohan, et al., from PNAS, June 2006, Volume 103(24). Copyright © 2006 by National Academy of

(74)

7.14 Scientific research and international

treaties have helped slow the depletion of

Earth’s ozone layer

• Solar radiation converts O₂ high in the atmosphere to ozone (O₃), which shields organisms from

damaging UV radiation.

• _{A gigantic hole in the ozone layer has appeared}

(75)

Figure 7.14a

September 2012 Southern

tip of South America

(76)

7.14 Scientific research and international

• Industrial chemicals called CFCs have caused

dangerous thinning of the ozone layer.

• This destruction of the ozone layer was

documented by scientists from the British Antarctic Survey, NASA, and National Oceanic and

(77)

7.14 Scientific research and international

• In response to these scientific findings, the first treaty to address Earth’s environment was signed in 1987.

• _{As research continued to establish the extent and}

(78)

7.14 Scientific research and international

treaties have helped slow the depletion of

• In 1995, Molina and Rowland shared a Nobel Prize

for their work in determining how CFCs were damaging the atmosphere.

• _{Global emissions of CFCs are near zero now, but}

because these compounds are so stable, recovery of the ozone layer is not expected until around

2060.

• Meanwhile, unblocked UV radiation is predicted to

(79)

Figure 7.UN03 (a) (b) (c) (d) (e) (f) (g) (h) converts includes both in which Photosynthesis chemical energy

H2O is split light-excitedelectrons of chlorophyll

CO₂ is fixed to RuBP 3-PGA is reduced are passed down in which to and producing to produce by chemiosmosis Reduce

NADP+_to

using

(80)

Figure 7.UN04

Mitochondrion

Intermembrane space

Membrane

Matrix

a. b.

Chloroplast

H+ _c.

d.