NUTRITIONAL TYPES

Autotroph- an organism that can manufacture its own food from inorganic substances

Photosynthetic autotroph- uses light energy

Chemosynthetic autotroph- uses energy derived from the oxidation of inorganic compounds

Heterotroph- an organism that cannot manufacture its own food

PHOTOSYNTHESIS the manufacture of food, mainly sugar, from carbon dioxide and water in the presence of chlorophyll, utilizing light energy and releasing oxygen gas.

Essential Factors in Photosynthesis:

1. Raw materials-

carbon dioxide

water

Essential Factors in Photosynthesis:

2. Source of Energy-

Sunlight with the red and blue wavelengths being the most effective

Light exhibits

wave & particle

properties

Light as a wave

Wavelength () is the distance between successive wave crests

Frequency ()

-is the number of wave crests in one second

c (speed of light; 3.0 x 108 m s-1) =

Chlorophyll

molecule

Light as a stream of particles

Photon-a discrete physical unit of radiant energy

Quantum- a packet of energy contained in a photon

E (energy of a photon)= h (Plancks constant (6.626 1034 J s) n

(frequency of light)

The amount of energy packaged in a photon is inversely related to its wavelength.

Photons with shorter wavelengths pack more energy.

Essential Factors in Photosynthesis: 3. Pigments-

chlorophyll a- participates directly in the light reactions

chlorophyll b

carotenoid pigments

carotene, xanthophyll

carotenoids

Functions:

Collecting light

Protecting chlorophyll against photodestruction in times of excess light

Pigments occur in a group-photosytem

When light meets matter, it may be:

Reflected

Transmitted

Absorbed.

For light to be used by plants it must be first be absorbed.

Pigments absorb photons of different wavelengths.

Essential Factors in Photosynthesis:

Excited electrons are unstable

Generally, they drop to their ground state

in a billionth of a second, releasing heat

energy.

Essential Factors in Photosynthesis:

Essential Factors in Photosynthesis:

Some pigments, including chlorophyll,

release a photon of light, in a process

called fluorescence, as well as heat.

Chlorophyll may participate in energy transfer, during which an excited chlorophyll transfers its energy to another molecule.

the energy of the excited state is lower nearer the reaction center than in the more peripheral portions of the antenna system.

Essential Factors in Photosynthesis:

Association of chl a with different proteins in the thylakoid membrane affects electron distribution in the chlorophyll molecule and accounts for the slight differences in light absorbing properties of P680 and P700

4. Temperature- optimum for photosynthesis C3- 20 25 0C C4- 30 - 45 0C

5. Additional essential factors- electron carriers, enzymes

6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O

or

CO2 + 2H2O (CH2O) + O2 + H2O

Photosynthesis is an oxidation reduction process

2H2O 4H+ + 4e- + O2

CO2 + 4H+ + 4e- (CH2O) + H2O

THE PROCESS OF PHOTOSYNTHESIS

1. Light reactions

a. Non-cyclic electron transport

involves cooperation of the 2 photosystems

excited electron does not return to its original position after excess energy is released

produces ATP, NADPH and O2

raw material required: H2O

Noncyclic electron transport

Cyclic electron transport

involves photosystem I

excited electron returns to its original position after excess energy is released

produces ATP above and beyond those required for CO2 fixation

THE PROCESS OF PHOTOSYNTHESIS

Cyclic electron transport

A closer look at noncyclic electron transport

large multiprotein complexes

The multiprotein complexes in the thylakoid membrane

Photosystems I and II

Contain several proteins, chlorophyll, carotenoid pigments

Antenna pigments

Reaction center

The multiprotein complexes in the thylakoid membrane

PSI and PSII

Antenna chlorophyll

Associated with specific proteins e.g. CP43 and CP47 with 20-25 chla

Do not participate directly in photochemical reactions

Reaction center chlorophyll

Association of large number of antenna pigments with a single reaction center

light harvesting complex (LHC)- expanded antenna system

LHCI associated with PSI

LHCII associated with PSII

OEC- small complex protein serve to replenish lost electrons in P680+

located on the lumen side of the thylakoid membrane

Oxygen evolving complex (OEC)

Functions:

Oxidation of H2O

Evolution of O2

Oxygen evolving complex (OEC)

Cytochrome b6f complex- links PSII with PSI

The multiprotein complexes in the thylakoid membrane

ATP synthase, CF0 -CF1 (coupling factor- synthesizes ATP

The multiprotein complexes in the thylakoid membrane

CF0 - forms H+ channel

CF1 -contains active site for ATP synthesis

Plastoquinone

Characteristic

Mobile carrier

Roles:

Transport of electrons

Translocation of H+ ions

mobile electron carriers

mobile electron carriers

Plastocyanin Small peripheral protein

Is able to diffuse freely along the luminal side of the thylakoid membrane

mobile electron carriers

Ferredoxin Iron-sulphur protein soluble in the stroma

Transfers e- to NADP+

ATP synthesis

By chemiosmosis

Synthesis of ATP is linked with electron transport

Features of the membrane:

Membrane is impermeable to H+

Electron carriers are organized asymmetrically in the membrane

some carriers also serve to translocate H+ into the lumen resulting in energy rich proton gradient

Effect is to conserve some of the free energy of e- transport as an unequal distribution of protons

ATP synthesis

Protons are pumped across the thylakoid membrane from the stroma to the lumen

Results in pH

Results in electrical potential gradient across the membrane

Protons return to the stroma through the ATP synthase (ATPase/CFo- CF1)

ATP synthesis

One ATP is formed for every 3H+ that moves through the ATP synthase

Mechanisms for accumulation of protons in the lumen during

noncyclic electron flow

Oxidation of water

- 2 protons/2e- that move from P680 to P700

PQ- cytochrome pump

- 4 protons/2e- that move from P680 to P700

noncyclic electron flow

PQ- cytochrome pump

Mechanisms for accumulation of protons in the lumen during cyclic

electron flow

PQ- cytochrome pump

- 4 protons/2e- that move during cyclic electron flow

Cyclic electron transport

Where does light

reaction

take place?