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How Cells Acquire Energy Photosynthesis. Chapter 6a. Carbon and Energy Sources. Photoautotrophs Carbon source is carbon dioxide Energy source is sunlight Heterotrophs Get carbon and energy by eating autotrophs or one another. Photoautotrophs .

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carbon and energy sources
Carbon and Energy Sources
  • Photoautotrophs
    • Carbon source is carbon dioxide
    • Energy source is sunlight
  • Heterotrophs
    • Get carbon and energy by eating autotrophs or one another
photoautotrophs
Photoautotrophs
  • Capture sunlight energy and use it to carry out photosynthesis
    • Plants
    • Some bacteria
    • Many protista
t e englemann s experiment
T.E. Englemann’s Experiment

Background

  • Certain bacterial cells will move toward places where oxygen concentration is high
  • Photosynthesis produces oxygen
t e englemann s experiment1
T.E. Englemann’s Experiment

Hypothesis

  • Movement of bacteria can be used to determine optimal light wavelengths for photosynthesis
t e englemann s experiment2
T.E. Englemann’s Experiment

Method

  • Algal strand placed on microscope slide and illuminated by light of varying wavelengths
  • Oxygen-requiring bacteria placed on same slide
t e englemann s experiment4
T.E. Englemann’s Experiment

Results

Bacteria congregated where red and violet wavelengths illuminated alga

Conclusion

Bacteria moved to where algal cells released more oxygen--areas illuminated by the most effective light for photosynthesis

linked processes
Photosynthesis

Energy-storing pathway

Releases oxygen

Requires carbon dioxide

Aerobic Respiration

Energy-releasing pathway

Requires oxygen

Releases carbon dioxide

Linked Processes
chloroplasts
Chloroplasts

Organelles of photosynthesis

photosynthesis equation
Photosynthesis Equation

LIGHT ENERGY

6O2 + C6H12O6 + 6H2O

12H2O + 6CO2

oxygen

glucose

water

carbon dioxide

water

two stages of photosynthesis
Two Stages of Photosynthesis

sunlight

water uptake

carbon dioxide uptake

ATP

ADP + Pi

LIGHT DEPENDENT-REACTIONS

LIGHT INDEPENDENT-REACTIONS

NADPH

NADP+

glucose

P

oxygen release

new water

sunlight energy
Sunlight Energy
  • Continual input of solar energy into Earth’s atmosphere
  • Almost 1/3 is reflected back into space
  • Of the energy that reaches Earth’s surface, about 1% is intercepted by photoautotrophs
electromagnetic spectrum
Electromagnetic Spectrum

Shortest Gamma rays

wavelength X-rays

UV radiation

Visible light

Infrared radiation

Microwaves

Longest Radio waves

wavelength

visible light
Visible Light
  • Wavelengths humans perceive as different colors
  • Violet (380 nm) to red (750 nm)
  • Longer wavelengths, lower energy
photons
Photons
  • Packets of light energy
  • Each type of photon has fixed amount of energy
  • Photons having most energy travel as shortest wavelength (blue-green light)
pigments
Pigments
  • Light-absorbing molecules
  • Absorb some wavelengths and transmit others
  • Color you see are the wavelengths NOT absorbed

chlorophyll a

chlorophyll b

Wavelength (nanometers)

pigment structure
Pigment Structure
  • Light-catching part of molecule often has alternating single and double bonds
  • These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light
excitation of electrons
Excitation of Electrons
  • Excitation occurs only when the quantity of energy in an incoming photon matches the amount of energy necessary to boost the electrons of that specific pigment
  • Amount of energy needed varies among pigment molecules
variety of pigments
Variety of Pigments

Chlorophylls a and b

Carotenoids

Anthocyanins

Phycobilins

chlorophylls
Chlorophylls

Main pigments in most photoautotrophs

chlorophyll a

Wavelength absorption (%)

chlorophyll b

Wavelength (nanometers)

carotenoids
Carotenoids
  • Found in all photoautotrophs
  • Absorb blue-violet and blue-green that chlorophylls miss
  • Reflect red, yellow, orange wavelengths
  • Two types
    • Carotenes - pure hydrocarbons
    • Xanthophylls - contain oxygen
anthocyanins phycobilins
Anthocyanins & Phycobilins

Red to purple pigments

  • Anthocyanins
    • Give many flowers their colors
  • Phycobilins
    • Found in red algae and cyanobacteria
pigments in photosynthesis
Pigments in Photosynthesis
  • Bacteria
    • Pigments in plasma membranes
  • Plants
    • Pigments embedded in thylakoid membrane system
    • Pigments and proteins organized into photosystems
    • Photosystems located next to electron transport systems
photosystems and electron transporters
Photosystems and Electron Transporters

water-splitting complex

thylakoid

compartment

H2O

2H + 1/2O2

P680

P700

acceptor

acceptor

PHOTOSYSTEM II

pool of electron transporters

stroma

PHOTOSYSTEM I

light dependent reactions
Light-Dependent Reactions
  • Pigments absorb light energy, give up e- which enter electron transport systems
  • Water molecules are split, ATP and NADH are formed, and oxygen is released
  • Pigments that gave up electrons get replacements from the splitting of H2O
photosystem function harvester pigments
Photosystem Function: Harvester Pigments
  • Most pigments in photosystem are harvester pigments
  • When excited by light energy, these pigments transfer energy to adjacent pigment molecules
  • Each transfer involves energy loss
photosystem function reaction center
Photosystem Function: Reaction Center
  • Energy is reduced to level that can be captured by a special molecule of chlorophyll a
  • This molecule (P700 or P680) is the reaction center of a photosystem
  • Reaction center accepts energy and donates electron to acceptor molecule
pigments in a photosystem
Pigments in a Photosystem

reaction center

(a specialized chlorophyll a molecule)

electron transport system
Electron Transport System
  • Adjacent to photosystem
  • Acceptor molecule donates electrons from reaction center to the system
  • As electrons flow through system, the energy they release is used to produce ATP and, in some cases, NADPH
cyclic electron flow
Cyclic Electron Flow
  • Electrons
    • are donated by P700 in photosystem I to acceptor molecule
    • flow through electron transport system and back to P700 via a soluble protein carrier
  • Electron flow drives ATP formation
  • No NADPH is formed
cyclic electron flow1
Cyclic Electron Flow

e–

electron acceptor

electron transport system

e–

e–

ATP

e–

noncyclic electron flow
Noncyclic Electron Flow
  • Two-step pathway for light absorption and electron excitation
  • Uses two photosystems: type I and type II
  • Produces ATP and NADPH
  • Involves photolysis - splitting of water
pigments in a photosystem1
Pigments in a Photosystem

reaction center

(a specialized chlorophyll a molecule)

machinery of noncyclic electron flow
Machinery of Noncyclic Electron Flow

H2O

photolysis

PCH2

PC

e–

Ferredoxin

PQ

PQH2

ATP SYNTHASE

Cytochrome b/ f complex

e–

NADP+

NADPH

ATP

PHOTOSYSTEM II

PHOTOSYSTEM I

ADP + Pi

energy changes
Energy Changes

second

transport

system

e–

NADPH

e–

first

transport

system

e–

Potential to transfer energy (voids)

e–

(PHOTOSYSTEM I)

(PHOTOSYSTEM II)

1/2 O2 + 2H+

H2O

chemiosmotic model of atp formation
Chemiosmotic Model of ATP Formation
  • When water is split during photolysis, hydrogen ions are released into thylakoid compartment
  • More hydrogen ions are pumped into the thylakoid compartment when the electron transport system operates
chemiosmotic model of atp formation1
Chemiosmotic Model of ATP Formation
  • Electrical and H+concentration gradients exist between thylakoid compartment and stroma
  • H+ flows down gradients into stroma through a channel in an integral thylakoid membrane protein, ATP synthetase
  • Flow of ions drives formation of ATP
light independent reactions
Light-Independent Reactions
  • Synthesis part of photosynthesis
  • Can proceed in the dark
  • Take place in the stroma
  • Calvin-Benson cycle
calvin benson cycle
Overall reactants

Carbon dioxide

ATP

NADPH

Overall products

Glucose

ADP

NADP+

Calvin-Benson Cycle

Reaction pathway is cyclic and RuBP

(ribulose bisphosphate) is regenerated

calvin benson cycle1

6

CO2 (from the air)

Calvin- Benson Cycle

CARBON FIXATION

6

6

RuBP

unstable intermediate

12

PGA

6 ADP

12

ATP

6

ATP

12

NADPH

4 Pi

12 ADP

12 Pi

12NADP+

10

PGAL

12

PGAL

2

PGAL

Pi

P

glucose

building glucose
Building Glucose
  • PGA accepts
    • phosphate from ATP
    • hydrogen and electrons from NADPH
  • PGAL (phosphoglyceraldehyde) forms
  • When 12 PGAL have formed
    • 10 are used to regenerate RuBP
    • 2 combine to form phosphorylated glucose
using the products of photosynthesis
Using the Products of Photosynthesis
  • Phosphorylated glucose is the building block for:
    • sucrose
      • The most easily transported plant carbohydrate
    • starch
      • The most common storage form
the c3 pathway
The C3 Pathway
  • In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA
  • Because the first intermediate has three carbons, the pathway is called the C3 pathway
photorespiration in c3 plants
Photorespiration in C3 Plants
  • On hot, dry days stomata close
  • Inside leaf
    • Oxygen levels rise
    • Carbon dioxide levels drop
  • Rubisco attaches RuBP to oxygen instead of carbon dioxide
  • Only one PGAL forms instead of two plus one glycolate ( OH-CH2-COOH)
c4 plants
C4 Plants
  • Carbon dioxide is fixed twice
    • In mesophyll cells, carbon dioxide is fixed by PEP to form four-carbon oxaloacetate
    • Oxaloacetate is reduced to malate, which is then transferred to bundle-sheath cells
    • Carbon dioxide is released from malate and fixed again in Calvin-Benson cycle
cam plants
CAM Plants
  • Carbon is fixed twice (in same cells)
  • Night
    • Carbon dioxide is fixed as C4 organic acids
  • Day
    • Fixed Carbon dioxide released from C4 acids is fixed again by ribulose biphosphate in Calvin-Benson cycle
slide48

CO2or O2

CO2+ H2O

Inmesophyll cell, Rubisco affixes O2 to RibuloseBP.

CO2

One glycolate

and only one

PGA (not two)

lower CO2 uptake, fewer sugars can form

CALVIN-

BENSON

CYCLE

ATP+ Pyruvate

+ PEP (phosphoenolpyruvate)

Oxaloacetate

in mesophyll cell,

cell carbon fixation

Malate

C3 PLANTS. With low CO2 / high O2, photorespiration predominates.

-

Malate  Pyruvate + CO2 .

CO2

in bundle-sheath cell, carbon is fixed again

more CO2 in leaf; no photorespiration

(See next slide.)

At night CO2 is high & O2 low . In mesophyll cells, stomata open at night; CO2 uptake but no water loss

CALVIN-

BENSON

CYCLE

CO2 CO2

PEP + CO2 C4

C4 PLANTS. With low CO2 / high O2, Calvin-Benson cycle predominates during the hot day (stomata are closed to preserve water).

CO2 + C3

Stomata close during day;CO2 is low. Fixed CO2 that accumulated overnight as C4 in leaf is used during day by

Calvin Benson cycle.

CALVIN-

BENSON

CYCLE

Fig. 6.15, p. 102

CAM PLANTS. With low CO2 / high O2, Calvin-Benson cycle predominates.

hydrothermal vents
Hydrothermal Vents
  • Fissures in sea-floor where seawater mixes with molten rock
  • Complex ecosystem is based on energy from these vents
  • Bacteria are producers in this system
light and life at the vents
Light and Life at the Vents
  • Vents release faint radiation at low end of visible spectrum
  • These photons could be used to carry out photosynthesis
  • Nisbet and Van Dover hypothesize that the first cells may have arisen at hydrothermal vent systems
supporting evidence
Supporting Evidence
  • Absorption spectra for ancient photosynthetic bacteria correspond to wavelengths measured at the vents
  • Photosynthetic machinery contains iron, sulfur, manganese, and other minerals that are abundant at the vents
summary of photosynthesis
Summary of Photosynthesis

light

LIGHT-DEPENDENT REACTIONS

6O2

12H2O

ATP

NADP+

NADPH

ADP + Pi

PGA

CALVIN-BENSON CYCLE

PGAL

6CO2

RuBP

P

C6H12O6

(phosphorylated glucose)

end product (e.g. sucrose, starch, cellulose)