Unit 6: Energy, respiration and photosynthesis

B M Subramanya Swamy M.Sc. B.Ed.

CIE Co - ordinator & Examination OfficerKanaan Global School

Jakarta Indonesia

swamy@kanaanglobal.sch.id

Photosynthesis

Introduction

• 2 main types of nutrition

• Autotrophic nutrition

chemoautotroph

photoautotroph

Heterotrophs

4

Discovery of Photosynthesis

C. B. van Niel, 1930’s

-proposed a general formula:

CO2+H2O + light energy CH2O + H2O + 2O

where H2A is the electron donor

-van Niel identified water as the source of the O2

released from photosynthesis

-Robin Hill (in the 1950s) confirmed van Niel’s proposal that energy from the light reactions fuels carbon fixation (making glucose from CO2)

Photosynthesis

The process by which organisms use carbon di oxide and water to manufacture food.

The energy needed for synthesis is supplied by light which is absorbed by the organisms and subsequently converted by them into chemical energy in the presence of chloroplast

Structure of dicotyledonous leaf and chloroplast

Structure of chloroplast • Biconvex shape• 3 – 10 micro meter in diameter • Double membrane• Internal membrane – flattened fluid filled sacs called thylakoid • Pigments – chlorophyll – held – thylakoid membrane • Cluster – pigment with primary pigment – surrounded by accessory

pigment • Enzymes – ATP synthase – found – membrane of grana • Fluid substance surrounding grana – called stroma • Stroma – lipids and starch grains • Stroma – contains enzymes – involved – calvin cycle • Carbon di oxide – fixed and starch – made- stroma • Stroma – 70S ribosome & double stranded circular DNA • Shape of chloroplast – varies b/w different species

Adaptation of palisade mesophyll cells for Photosynthesis

• Closely packed – absorbs – more incident light • Cells – found – near- surface – leaf to maximize light interception • Cells – arranged – right angles – leaf surface to reduce the number

of light absorbing walls • Cylinder – shape – produce air spaces b/w cells • Intercellular air spaces act as reservoir – carbon di oxide • Provide large surface area for gas exchange • Cell walls – relatively thin for short diffusion pathway • Large vacuole pushes – chlorophyll in chloroplast – absorb more

light efficiently • Large number of chloroplast – maximum light is absorbed• Chloroplast – also move – within cell – towards light • Higher light intensity , chloroplast – move away from light – avoid

any damage

ELECTROMAGETIC SPECTRUM

Photosynthetic pigmentschlorophyll a – primary pigment in plants and

cyanobacteria (Porphyrin-Mg)

-absorbs violet-blue and red light

chlorophyll b – secondary pigment absorbing light wavelengths that chlorophyll a does not absorb

accessory pigments: secondary pigments absorbing light wavelengths other than those absorbed by chlorophyll a

-increase the range of light wavelengths that can be used in photosynthesis

-include: chlorophyll b, carotenoids, phycobiloproteins

-carotenoids also act as antioxidants

Photo system • Pigment molecules in chloroplast are

organized into photosystemA photosystem consists of1. an antenna complex (light harvesting

complex) of hundreds of accessory pigment molecules that gather photons and feeds energy to reaction center

2. a reaction center of one or more chlorophyll a molecules pass electrons out of photosystem (photochemical reactions)

• There are 2 types of photosystem• Photosystem I absorption peak 700nm• Photosystem II absorption peak

680nm

Absorption & Action spectrum

• Absorption spectrum of a pigment is a record of amount of light absorbed at each wavelength

• Chl a & Chl b absorbs red & blue/violet parts of the spectrum

• Xanthophylls & carotene absorb light from other parts

• This effectively increases the range of wavelength from which plants can obtain energy

Absorption & Action spectrum• Action spectrum is a record of amount of photosynthesis

occurring at each wavelength of light

• There is a close similarity b/w the absorption spectra of the major photosynthetic pigments and the action spectrum for photosynthesis

Chemistry of photosynthesis

• Photosynthesis consists of 2 stages

• Light reaction/light dependent reaction

• Dark reaction/light independent reaction

• Light reaction- grana

• Dark reaction- stroma

Light reaction

• It consists of light harvesting & electron transport

• ATP synthesized from ADP + Pi

• NADP is reduced NADPH

• Oxygen is formed from water

• ATP is synthesized by using light energy -photophosphorylation

Light reaction

• There are 2 different ways in which ATP can be synthesized by photophosphorylation

• Non cyclic photophosphorylation

• Cyclic Photophosphorylation

Non-cyclic Photophosphorylation• Non-cyclic photophosphorylation involves both photosystem I and photosystem II

• Light is absorbed by photosystem II and passed on to chlorophyll a

• The irradiated chlorophyll a molecule emits two electrons.

These energized electrons are raised to a higher energy level and are picked by an electron acceptor.

• The electron acceptor passes the electrons along the chain of electron carriers tophotosystem I.

The energy released from the electrons is used to make ATP from ADP and Pi.• Light is Absorbed by Photosystem I and Passed on to chlorophyll a.

It emits two electrons.The energized electrons rise to a high energy level and are picked up by a second electron acceptor.

Since both chlorophylls have now lost electrons they will both be positive and unstable.

• The Two electrons released from the chlorophyll a of photosystem II go to replace the two that have been lost by chlorophyll a of photosystem I.

• Chlorophyll a of photosystem II receives its replacement electrons from the splitting of water (Photolysis)

• During photolysis the water molecule dissociates into electrons, hydrogen ions and oxygen.

• Electrons go to photosystem II. The oxygen is released as a waste gas.

• The Hydrogen ions combine with electrons held by the second electron acceptor to give NADPH.

• This passes to the reaction of the light independent stage.

• So the product of the light-dependent stage are NADPH, ATP and waste oxygen gas.

Cyclic Photophosphorylation.• Cyclic Photophosphorylation involves photosystem I only.

• Light is absorbed by photosystem I and passed on to chlorophyll a.

• This causes the chlorophyll a molecule to emit an electron.

• The ‘energised electron is raised to a higher energy level and is picked up by an electron acceptor

• The electron is passed passed along a chain of electron carriers before it is returned to the chlorophyll a molecule.

• As the electron passes along the electron carrier chain, enough energy is released to make ATP from ADP and Pi. This ATP is needed for the light-independent stage.

• No NADPH is made during the cyclic photophosphorylation.

• The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane

– The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP

– In the stroma, the H+ ions combine with NADP+ to form NADPH

Chemiosmosis powers ATP synthesis in the light reactions

• The production of ATP by chemiosmosis in photosynthesis

Thylakoidcompartment(high H+)

Thylakoidmembrane

Stroma(low H+)

Light

Antennamolecules

Light

ELECTRON TRANSPORT CHAIN

PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

Distinguish between non-cyclic and cyclic photophosphorylation

Features Non-cyclic

photophosphorylation

Cyclic photophosphorylation.

Conditions under which process

occurs.

When plants require ATP and

NADPH

When plants require only ATP.

Pathway of electrons. Non-cyclic Cyclic

For electron donor (source of

electrons)

Water Photosystem I

Last electron acceptor (destination

of electrons)

NADP+ Photosystem I

Establishing proton gradient for the

synthesis of ATP

High hydrogen ion concentration in

the thylakoid space is due to

photolysis of water and active

transport of hydrogen ions from the

stroma, across the thylakoid

membrane, into the thylakoid

space.

High hydrogen ion concentration in

the thylakoid space is due to active

transport of hydrogen ions from the

stroma, across the thylakoid

membrane, into the thylakoid space.

Products ATP,NADPH and oxygen Only ATP.

The light independent stage

This cyclic pathway is sometimes called the calvin cycle.

• Carbon dioxide combines with a five carbon compound, ribulose biphosphate (RuBP)

• The reaction is catalysed by the enzyme RuBP carboxylase, the most common enzyme in the world.

• The product is an unstable six carbon compound that breaks down to form two molecules of three carbon

phospho glycerate (3C )

• ATP is used to phosphorylate the two molecules of Phosphoglycerate to form two molecules of Glycerate biphosphateof three-carbon

• The next stage involves the use of NADPH to reduce each molecule of glycerate biphosphate to

Glyceraldehyde 3-phosphate (GALP)

• For every six molecules of GALP formed, five are used in a series of reactions to regenerate ribulose biphosphate, which can then combine with more carbon dioxide.

• One of the six GALP molecules is converted to glucose and other carbohydrates, amino acids and lipids.

Role of NADP in photosynthesis

• NADP – Co Enzymes • Serves – electron acceptor in the electron transport system during

photo phosphorylation • Electrons – released – excited chlorophyll in PSI combines with

electron acceptor• From electron acceptor – pass down – a chain ETC and ends with

NADP • During photolysis, photons from splitting – water molecules –

reduces NADP – NADPH • Reduced NADP – passes along – electrons on to the calvin cycle • During cycle –GP is reduced – 3C sugar called triose phosphate by

reduced NADP • NADP then reused to light depended stage to pick up another

hydrogen ion

Regulating Stomatal Opening:-the potassium ion pump

hypothesis

Guard cells flaccid

Stoma closed

K+

K+

K+

K+

K+K+

K+

K+

K+

K+K+

K+

ATP Powered Proton pump actively transport H+ out of the guard cells

Low H+ concentration and negative charge inside the cell causes K+ channels to open

K+ diffuses into guard cell down an electro chemical gradient

Regulating Stomatal Opening:-the potassium ion pump

hypothesis

K+K+

K+

K+

K+K+

K+

K+

K+

K+K+

K+

Increased concentration of K+

in guard cells

Lowers the in the guard cells

Water moves in by osmosis, down gradient

H2O

H2O

H2O

H2O

H2O

Stoma open

Guard cells turgid

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

Increased concentration of K+

in guard cells

Lowers the in the guard cells

Water moves in by osmosis, down gradient

Entry of water increases the volume of guard cells

Thin outer wall of guard cell expands most, so the cells curve apart.

H2O

H2O

H2OH2O

H2O

H2O

FACTORS NECESSARY FOR PHOTOSYNTHESIS

• A number of factors affect the process of photosynthesis, as a result of which productivity is affected. These are

• Carbon dioxide• Water• Chlorophyll• Light• Temperature

Principle of limiting factors

• The Principle of limiting factors also states that when a biochemical process is affected by several factors, its rate is limited by that factor which is nearest its minimum value. That factor (known as limiting factor) directly affects the biochemical process if its quantity is changed.

CARBON DIOXIDE (CO2)

• Air contains 0.03% of CO2. It is released by respiration, combustion of fossil fuels and microbial decomposition.

• During early morning hours and evening hours, CO2 released in respiration is sufficient for photosynthesis. At this stage, there is no exchange of gases between the plant and the environment. This is called compensation point.

• An increase in the concentration of CO2 upto 0.1% increases the rate of photosynthesis.

• Higher concentration of CO2 decreases the rate of photosynthesis.

CARBON DIOXIDE

• The rate of photosynthesis increases with an increase in carbon dioxide concentration upto a certain level.

• Beyond that, CO2 concentration has no effect on the rate of photosynthesis. On the contrary it decreases the rate.

WATER

• Plants absorb water and mineral salts through root hair and pass it to the leaves through xylem.

• If there is less availability of H2O, then stomata closes ( to reduce the water loss by transpiration) and there is decreased CO2 absorption and sunlight absorption.

• Therefore the rate of photosynthesis decreases.

CHLOROPHYLL

• Only cells having chlorophyll are photosynthetic. There is no proportionality between the rate of photosynthesis and amount of chlorophyll.

LIGHT

• White light consists of all the seven colours. Highest rate of photosynthesis is seen in red light and minimum in green light. Chlorophyll can absorb violet, blue and red light rays.

• The rate of photosynthesis increases at the lower intensity of light and decreases in the stronger intensity of light.

TEMPERATURE

• Photosynthesis is an enzymatic process. The enzymes function within an optimum range of temperature.

• Lower temperature has an inhibitory effect on the rate of photosynthesis because the enzymes are inactivated.

• Increase in temperature increases the rate of photosynthesis but it ultimately inhibits photosynthesis.

Adaptation of leaf to photosynthesis

Upper epidermis and cuticle is transparentAllows most light to pass to photosynthetic mesophyll tissues

Adaptation of leaf to photosynthesis

Palisade mesophyll cells are closely packed and contain many chloroplastsTo carry out photosynthesis more efficiently

Adaptation of leaf to photosynthesis

Numerous stomata on lower epidermisTo allow rapid gaseous exchange with the atmosphere

Adaptation of leaf to photosynthesis

Extensive vein system• Allow sufficient

water to reach the cells in the leaf

• To carry food away from them to other parts of the plant

Summary of photosynthesis

Respiration

• Aerobic respiration

• Anaerobic respiration

• Respiratory quotient

• A respirometer

Introduction

• Respiration-Energy releasing process

• Respiration-Oxygen-aerobic respiration

• Respiration-absence of oxygen-anaerobic respiration

• Glucose-broken down-carbon dioxide, water and energy

• Energy-ATP

• 1 glucose-38 ATP molecules

Structure of ATP

• ATP-Adenosine triphosphate

• ADP-Adenosine diphosphate

• AMP-Adenosine mono phosphate

• ATP-formed from –AMP-Adding 2 phosphate groups

• Removal of terminal phosphate-ATP yields 30.6 kj/mol of free energy

• Hydrolysis of ADP to AMP yields same amount of energy but the removal of last phosphate group produce only 13.8 kj/mol

Free energy of hydrolysis of phosphate compounds

Compounds Free energy change (kj/mol)

1,3-diphosphoglycerate -49.5

ATP(to ADP and Pi) -30.6

ADP(to AMP and Pi) -30.6

AMP(to Adenosine and Pi) -13.8

Glucose 6 phosphate -13.6

Structure of Mitochondria

- Cylindrical in shape or rod shape

- Width range from 0.5 micro meter to 1.5 micro meter & length from 3 micro meter to 10 micro meter

- Bounded – double membrane

- Outer & inner membrane - separated by inter membrane space

- Inner membrane – extensively folded –from partitions called cristae

- Cristae – projected – into – semi fluid matrix

- Circular DNA molecule & 70S ribosome –present

- Endosymbiont theory

Functions of Mitochondria

- Involved – cellular respiration

- Series of bio chemical reaction – result in formation of ATP

- often known – power station – cell

- More than 1000 mitochondria –found –metabolically active cell

Cell Respiration can be divided into 4 Parts:

1) Glycolysis

2) Oxidation of Pyruvate / Transition Reaction

3) The Krebs Cycle

4) The Electron Transport Chain and

Chemiosmotic Phosphorylation

Where do the 4 parts of Cellular Respiration take place?

• Glycolysis:

– Cytosol

• Oxidation of Pyruvate:

– Matrix

• The Krebs Cycled:

– Matrix

• Electron Transport Chain and Cheimiosmotic Phosphorylation:

– Cristae

Glycolysis • Glyco-glucose,lysis-

breakdown

• Involves member of enzyme-Controlled reaction

• It takes place –cytoplasm of cell

• It does not require oxygen

• Common for both aerobic and anaerobic reaction

Glycolysis

• Glucose-phosphorylated by ATP to glucose 6 phosphate

• Phosphorylated glucose – no longer recognized – glucose transport system , therefore – trapped inside the cell

• Enzyme involved is kinase

• Glucose 6 phosphate-isomerised-fructose 6 phosphate

• Enzyme involved is isomerize

• Fructose 6 phosphate-phosphorylated by ATP to fructose 1,6phosphate

• Enzyme involved is kinase

• Fructose 1,6 phosphate splits to glycerate 3 phosphate

• Glycerate 3 phosphate converts to pyruvate

• Glycerate 3 phosphate when converted to pyruvate it forms 2 NADH2 and ATP

End product of Glycolysis

• 2 molecules of ATP( 4 molecules are produced but 2ATP are used up)

• 2 molecules of NADH2

• 2 molecule of pyruvate

Oxidation of Pyruvate /Transition Reaction

• Pyruvate- Matrix of mitochondria from cytoplasm

• Piruvate- Decarboxylated (Removal of carbon in form of carbon dioxide)

• Piruvate- Dehydrogenated (Removal of hydrogen)

• Hydrogen is transferred to hydrogen acceptor NAD+ to NADH H

• Pyruvate- Acetate

• Acetate combines with coenzyme A to form acetyl coenzyme

• Discovered by sir Hans Kerbs-1937

• Citric acid cycle / Tricarboxylic acid cycle (TCA)

• Occurs-Matrix of mitochondria

• Occurs only in aerobic reaction

• Acetyl co enzyme A (2C) + oxaloacetate(4C) –citrate• Reaction is called condensation• Enzyme involved citrate synthetase• Citrate isomerizes to isocitrate(6C)• Isocitrate undergo Oxidative decarboxylation to give α-ketogluterate(5C)• Carbon dioxide is produced• NAD+, hydrogen acceptors and NADH is formed• Enzyme involved is isocitrate dehydrogenase• X –ketogluterate(5C) undergo oxidative decarboxylation & dehydrogenation gives succinyl

CoA(4C)• CO2 is produced & NADH is formed.• Enzyme used is α- ketogluterate dehydrogenase.• Succinyl CoA(4C) gives succinate• ATP is formed from ADP+pi• Enzyme used is succinyl CoA Synthetase• Succinate undergoes dehydrogenation and gives Fumerate(4C)• FAD (Flavine adenine dinucleotide) gives hydrogen acceptor and form FADH2

• Enzyme used is succinate dehydrogenase• Fumerate undergoes hydrogenation and gives maltate(4C)• Enzyme used is fumerate• Maltate undergo dehydrogenation and gives oxaloacete (4C)• (NAD+)+(H+) gives NADH• Enzyme used is malate dehydrogenase.

The Electron Transport Chain

• Oxygen is required during the final stage of anaerobic reaction.

• Oxydative phosphorylation is a process by which ATP is formed as electron are transferred from NADH & FADH2 to oxygen via series of electron carrier.

• Location- inner membrane of the mitochondria.

• E.T.C involves Chain of electron carrier molecules.

• Electron from NADH & FADH2 are transferred to Oxygen

• Series of reaction---- Redox reaction

• Hydrogen atom splits to hydrogen ions(H+) and electrons.

• Transfer of electrons along the chain releases sufficient energy to make ATP

• Electron and hydrogen ion form hydrogen atom

• Hydrogen is passed on to oxygen to form water.

Chemiosmotic Theory• Energy from Electron transport chain is linked to

pumping hydrogen ion from matrix to space two membrane

• Result in higher Concentration of hydrogen ions in inner membrane space and Electro chemical gradient is setup

• Hydrogen ion pass into matrix through Stalk granules.

• Electrical potential energy is used to make ATP from ADP+Pi

• ATP synthetase catalyses the reaction.

• NADH & FADH2 – formed during – glycolysis & Krebs cycle are passed to ETC

• ETC – present – inner membrane space and consists of cytochromes • NADH & FADH2 – oxidized – hydrogen are released • Hydrogen now splits into electrons & protons • Electrons – pass along – electron carrier and transferred to oxygen • Protons H+ are actively pumped from – matrix to the outer

compartment i.e. intermembrane space • A proton gradient – created b/w the outer compartment and the

inner matrix • Protons cannot diffuse through cristae membrane • Protons flow only down the gradient – matrix through ATP synthase

channels this is known as chemiosmosis • Protons flow – ATP synthase channel (F1 channels) they generate

energy to phosphorylate ADP into ATP in the presence of enzyme ATP Synthase

• Later proton combines with oxygen • 2E + 2H + ½ O2 – H2O

Summary

• Glycolys- 2 ATP

• Krebs Cycle- 2 ATP (one per turn)

• Glycolysis- 2NADH

• Link reaction- 2NADH

• Krebs cycle- 6NADH (3 per turn)

• Krebs cycle- 2FADH2 (one per turn)

• 1 NADP-3 ATP

• 1FAD-2 ATP

Review ATP Production

ANAEROBIC RESPIRATION • In absence of O2 – glycolysis still occurs • Conversion – pyruvate to acetyl Co A, kerbs cycle

& oxidative phosphorylation – blocked • Oxidative phosphorylation – blocked becoz O2 –

final electron acceptor – ETC – not available • Absence – oxidative phosphorylation – no

regeneration of NAD+ & FAD+• To regenerate NAD+ cells undergo – fermentation • Two types of fermentation which is most

common - Lactate fermentation - Alcoholic fermentation

• Alcoholic fermentation – plants & yeast

• Lactate fermentation – muscles of animal during strenuous exercise & & in some bacteria such as Lactobacillus acidophilus

• Both alcoholic & Lactate fermentation don’t produce ATP Molecules but they regenerate NAD+ from NADH in order to keep glycolysis going

Chemistry of Alcoholic Fermentation • Pyruvate – first decarboxylate to ethanal• Enzyme – pyruvate decarboxylase • NADH – reduces Ethanal (2C) to Ethanol (2C) and NAD+

- Regenerated • Enzyme involved – alcohol dehydrogenase • Alcoholic fermentation – occurs – plants & Animals • Plants – respire – anaerobically only for short period of

time during waterlogged condition• Ethanol – toxic and plant – unable make use of ethanol• Yeast – ethanol produced – accumulate – medium –

around – cells – concentration rises – level that prevents further fermentation & kills – yeasts

Respiratory Quotient

• R.Q – ratio of volume of carbon di oxide formed to the volume of oxygen consumed over a given period of time

• R.Q = CO2 Formed / O2 Consumed • R.Q – used – provide information abt wht type – substrate – is

being oxidized in respiration • R.Q – value – more than 1.0 indicates – anaerobic respiration • R.Q – value for resting animals – b/w 0.8 – 0.9• R.Q – value for fats – abt 0.7, proteins is 0.9 & carbohydrates is

1.0• Bcoz – ratio of O2 to carbon – carbohydrates – greater

compared to fats and proteins • Fats and proteins – need more O2 – complete their oxidation

compared with carbohydrates

Different energy values of carbohydrates, lipids & proteins as respiratory substrate

• Respiratory substrate are lipids, proteins & Carbohydrates • Lipids has more energy value that either protein&

carbohydrate• Lipids have 39.8 Kj/g/unit mass where as protein and

carbohydrates have 17.0 and 15.8 Kj/g/unit mass • Lipids have more hydrogen atoms in molecule so it has

more energy (hydrocarbon chain)• The most of energy comes from oxidation of hydrogen to

water using reduced NAD during ETC • Lipids give more number of reduced NAD which will be

oxidized to give hydrogen • Hydrogen – splits to proton & electron • By the process of chemiosmosis the ATP are produced • Reduced NAD will give 3 molecule of ATP

Difference between photosynthesis and aerobic respiration

Features Photosynthesis Aerobic respiration

Anabolic/catabolic process An anabolic process which results in the

synthesis of carbohydrate molecules from

simple organic substances.

A catabolic process which results in

the breakdown of carbohydrate

molecules to simple inorganic

molecules

Storage of energy Energy is accumulated and stored in

carbohydrate

Energy is incorporated into ATP for

energy requiring process.

Oxygen Oxygen is released Oxygen is used.

Carbon dioxide and water Carbon dioxide and water are used Carbon dioxide and water are

produced.

Change in dry mass Process results in an increase in dry mass. Process results in a decrease in dry

mass.

Organelle involved Process occurs in the chloroplast. Majority of the reactions in the

process occurs in the mitochondrion.

Occurance Process occurs only in cells processing

chlorophyll and only in the presence of light.

Process occurs in all cells and

continuously throughout the lifetime of

cells.

Difference between photophosphorylation and oxidative

phosphorylation.Features Photophosphorylation Oxidative phosphorylation

Location Thylakoid membrane of chloroplast. Inner membrane of mitochondrion.

Involvement of light enery. Light energy is required for splitting

water.

Light energy is not required.

Source of energy for synthesis of

ATP.

Energy for synthesis of ATP comes

directly from light.

Energy for synthesis of ATP comes

from the oxidation of glucose.

Electron donors. Water is the electron donor in the

non-cyclic pathway while

photosystem I is the electron

acceptor in the cyclic pathway.

NADH and FADH2.

Electron acceptors. NADP+ is the final electron acceptor

in the non-cyclic pathway while

photosystem I is the electron

acceptor in the cyclic pathway.

Oxygen is the final electron

acceptor and is reduced to water.

Establishing proton gradient for the

synthesis of ATP.

Protons are pumped inwards, from

stroma across the Thylakoid

membrane into the Thylakoid space.

Protons are pumped outwards, from

matrix, across the inner membrane,

into the intermembrane space.

Difference between photophosphorylation and oxidative

phosphorylation.Features Photophosphorylation Oxidative phosphorylation

Location Thylakoid membrane of chloroplast. Inner membrane of mitochondrion.

Involvement of light enery. Light energy is required for splitting

water.

Light energy is not required.

Source of energy for synthesis of

ATP.

Energy for synthesis of ATP comes

directly from light.

Energy for synthesis of ATP comes

from the oxidation of glucose.

Electron donors. Water is the electron donor in the

non-cyclic pathway while

photosystem I is the electron

acceptor in the cyclic pathway.

NADH and FADH2.

Electron acceptors. NADP+ is the final electron acceptor

in the non-cyclic pathway while

photosystem I is the electron

acceptor in the cyclic pathway.

Oxygen is the final electron

acceptor and is reduced to water.

Establishing proton gradient for the

synthesis of ATP.

Protons are pumped inwards, from

stroma across the Thylakoid

membrane into the Thylakoid space.

Protons are pumped outwards, from

matrix, across the inner membrane,

into the intermembrane space.