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Unit Five

 Respiration: - is the process by which chemical energy in
organic molecule is released by oxidation.
ATP: - is the energy currency of a cell.
• Is a nucleotide that has energy rich bonds joining the two
terminal phosphate groups to the nucleotide
•It is described as a phosphorylated nucleotide
•ATP molecule consist of :- A nitrogenous base (Adenine), A
pentose sugar (deoxyribose) & A phosphate group.
Some process that require ATP energy
• Active transport
• Muscle contraction
•Conduction of nerve impulse
• Synthesis of macro molecules
•Intial stage of cellular respiration
 How ATP is produced in a cell
The formation of ATP by ADP and Pi involves an enzyme
called ATP synthase.
There are two main path ways in which respiration can
produce ATP. These are
 Aerobic Pathway:- occurs in the presence of oxygen
 Anaerobic Pathway:- occurs in the absence of oxygen
How ATP is produced in aerobic respiration
There are two main ways of ATP production in
aerobic path way these are
Substrate level Phosphorylation: - When another
molecule (substrate) is able to transfer phosphate
group directly to ADP.
ATP Synthase is not involved.
 10%of ATP is produced
 It occurs during glycolysis and kreb cycle
 Oxidative Phosphorylation:-oxygen dependent
production of ATP
Uses ATP Synthase enzyme
 90%of ATP is produced
It involves oxidation of organic molecules
Stages of aerobic respiration of glucose:
There are four main stages of aerobic respiration
of glucose these are : Glycolysis
 Link reaction
 Kreb cycle
Electron transport chain and chemiosmosis
 Glycolysis: - it means that glucose splitting
• It involves oxidation of glucose to pyruvate
• It takes place in the cytosol of cytoplasm
• It is the first stage of cellular respiration
• It occurs in the absence of oxygen
Link reaction: -it is involved in the presence of oxygen
 It is the transition between glycolysis and kreb cycle
 A molecule of pyruvate react with a molecule of co enzyme
A (COA) to form a molecule of acetyl co enzyme A .
 It involves three main steps these are
 A carboxyl group is removed as CO2 by pyruvate
A redox reaction occur where 2NAD + is reduced to
2NADH and pyruvate is oxidized to acetate
 A sulfur containing COA binds to acetate group to form
acetyl –COA.
Kreb cycle: - It is called Tricarboxylic acid cycle
The path way begins when the acetyl co enzyme A
reacts with a four carbon containing compound called
oxaloacetate to form a six carbon containing
compound called citrate.
 In kreb cycle one cycle produces two carbon dioxide
, three reduced NAD, one reduced FAD and one ATP
 Two pyruvate enter the kreb cycle from one glucose
Two citric acid cycle occur for one glucose molecule
Involves the following main steps
Formation of Citrate
The condensation of acetyl-CoA with oxaloacetate produces citrate. This
reaction is catalyzed by citrate synthase.Once oxaloacetate is joined with
acetyl-CoA, a water molecule attacks the acetyl leading to the release of
coenzyme A from the complex.
Acetyl CoA(2C) + Oxaloacetate(4C) →→→→→Citrate (6C)
Oxidative decarboxylation of citrate
Catalyzed by dehydrogenase enzyme and releases/ removes a molecule of
CO2 Produces a 5-carbon compound called α-Ketoglutarate.
Oxidative decarboxylation of α-Ketoglutarate
A molecule of CO2 is released and a 4-carbon compound (Succinyl CoA) is
formed.Catalyzed by alpha-ketoglutarate dehydrogenase.A molecule of NAD
is reduced while α-Ketoglutarateis oxidized.
 Regeneration of oxaloacetate
• Succinic CoA undergoes several molecular transformations
to produce oxaloacetate. At this step the following two
vital processes (events) take place.
 Reduction of NAD and FAD
 During the course of the cycle, the cell harvests:
 One ATP
 Three reduced NAD/NADH/ molecules
 One FADH2
❖ For every glucose that enters cellular respiration, the
Krebs cycle runs twice becauseglucose gets broken down to
two pyruvates, which become two Acetyl Synthesis of ATP
by substrate level phosphorylation
Electron transport chain
•The final stage of aerobic respiration that generates much amount of ATP.
•Takes place on the inner mitochondrial membrane.
•The inner membrane is arranged into folds (cristae), which increases the
surface area available for the transport chain.
•Releases the energy stored within the reduced hydrogen carriers in order to
synthesize ATP.
•Involves chemiosmosis and oxidative phosphorylation.
Consists of the following vital steps/processes.
1.Dehydrogenation of NADH and FADH2
•The hydrogen carriers (NADH and FADH2) are oxidized and release high
energy electrons and protons.
•NADH dehydrogenase oxidizes NADH and Ubiquinone oxidizes FADH2
.The electrons are transferred to the electron transport chain, which consists
of several Transmembrane carrier proteins.
•As electrons pass through the chain, they lose energy – which is used by the
chain to pump protons (H+ ions) from the matrix.
•The accumulation of H+ ions(protons) within the intermembrane space
creates an electrochemical gradient (or a proton motive force).
2. Chemiosmosis and ATP synthesis
•The proton motive force will cause protons(H+ ions) to move down
their electrochemical gradient and diffuse back into matrix.
•ATP synthase uses the subsequent diffusion of protons
(chemiosmosis) to synthesize ATP.
•As the protons(H+ ions) move through ATP synthase they trigger
the molecular rotation of the enzyme, synthesizing ATP.
•Aerobic respiration involves four stages: glycolysis, a transition
reaction that forms acetyl coenzyme A, the citric acid (Krebs) cycle,
and an electron transport chain and chemiosmosis.
•During various steps in glycolysis and the citric acid cycle, the
oxidation of certain intermediate precursor molecules causes the
reduction of NAD to NADH + H and FAD to FADH. NADH and
FADH then transfer protons and electrons to the electron transport
chain to produce additional ATPs by oxidative phosphorylation.
•The electron transport chain consists of a series of electron
carriers that eventually transfer electrons from NADH and
FADH to oxygen. These include:
•NADH dehydrogenase
•Ubiqinone, and
•Cytochrome complex
•During aerobic respiration, the last electron carrier in the
membrane transfers 2 electrons to half an oxygen molecule (an
oxygen atom) that simultaneously combines with 2 protons from
the surrounding medium to produce water as an end product.
•The summary equation for aerobic respiration is:
C6H12O6 + 6O2 ➞ 6H2O + 6CO2 + 36ATP
A device used to measure the rate of respiration of a living organism by measuring its rate
of exchange of oxygen and/or carbon dioxide.
Allows investigation into how factors such as age, or chemicals affect the rate of
Designed to measure respiration either on the level of a whole animal or plant or on the
cellular level.
The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a
sealed container.
Carbon dioxide production can be measured with a data logger or by PH changes if the
specimen is immersed in water.
When an alkali is included to absorb CO2, oxygen consumption can be measured as a
change in pressure within the system
The pressure change can be detected with a data logger or via use of a U-tube manometer.
Factors which may affect respiration rates include temperature, hydration, light (plants), age
and activity levels
An increase in carbon dioxide levels will indicate an increase in respiration (CO2 is a
product of aerobic respiration).
A decrease in oxygen levels will indicate an increase in respiration (O2 is a requirement for
aerobic respiration).
Anaerobic Respiration
Type of respiration through which cells can break down sugars to
generate energy in the absence of oxygen.
Is in contrast to the highly efficient process of aerobic respiration, which
relies on oxygen to produce energy.
Molecular oxygen is the most efficient electron acceptor for respiration,
due to its high affinity for electrons. However, some organisms have
evolved to use other final electron acceptors, and as such, can perform
respiration without oxygen.
Takes place in the cytoplasm of both prokaryotic and eukaryotic cells. Is
a less efficient method of generating cellular energy.
Produces less ATP for each sugar molecule digested than aerobic
Can be described as fermentation.
The types of anaerobic respiration are as varied as its electron acceptors.
 Important types of anaerobic respiration include:
Lactic acid fermentation
Glucose is split into two molecules of lactic acid to produce two ATP.
Occurs in certain types of bacteria and some animal tissues, such as
muscle cells.
( C6 H12 O6 (glucose) + 2 ADP + 2 Pi 2 C3 H6 O3 + 2ATP)
Alcoholic fermentation
Glucose is split into ethanol or ethyl alcohol.
Also produces two ATP per sugar molecule.
Releases CO2 as a byproduct.
Occurs in yeast and even in some types of fish, such as goldfish.
C6 H12 O6 (glucose) + 2 ADP + 2 Pi→ 2 C2 H5 OH (ethanol) + 2 CO2
+ 2 ATP
Cori cycle
1..How many moles of ATP will be generated as a result of FADH2 in actively respiring
2. In a bacterium what is the net production of ATP molecules from a four glucose molecule in
the absence of oxygen.
3.How many ATP molecules are synthesized directly in the Krebs citric acid cycle if you supply
an aerobic cell with 20 pyruvic acid molecules?
4. What will be the net amount of ATP that is produced when a molecule of pyruvate oxidized
into acetyl COA?
5. What net amount of ATP will be produced through oxidative phosphorylation from 3
molecules of glucose in actively respiring mitochondria?
6. How much ATP can be produced if 5 FADH2 and 12NADH give their electrons to the
electron transport system in the presence of oxygen?
7.How many Krebs cycles and FADH2 can be produced when 4 glucose molecules undergo full
respiratory process?
8.Work out the grand total ATP molecule produced from 20 mole of glucose during
chemiosmotic phosphorylation in a certain liver cell.
9.What effect would be resulted whether NADH or FADH is used as an initial hydrogen donor
in the carrier chain during aerobic respiration?
10.How many molecule of ATP is gained by a cell during the process of glycolysis from 12
molecules of glucose?
• is the process by which light energy is converted into chemical energy of organic
• It involves transduction of light energy into chemical energy.
• Light energy is absorbed by a pigment molecule known as chlorophyll.
• It takes place inside the chloroplast
• it is carried out by a groups of organisms called photo autotrophs such as plants,
algae and photosynthetic bacterias.
• Transduced means conversion of energy from one form to another
Structures and functions of chloroplast
Chloroplast is an organelle which enclosed by a double membrane.
it consist of major parts
 Grana:- is the sack of thylakoids where the light dependent reaction of
photosynthesis takes place.
 stroma :- is a part wher the light independent reaction (calvin cycle)of
photosynthesis takes place.
 thylakoids flattened sacs inside a chloroplast on which light-dependent reactions
of photosynthesis take place
 Photosystems biochemical mechanism by which chlorophyll absorbs light
energy. photosystem I photosystem in photosynthetic light reactions discovered
before photosystem II.
It involves two major stages these are
Light dependent stage (Light reaction):- is the stage on which light energy is
directly required.
12H2O + 12NADP+ +18ADP + 18Pi → 6O2 + 12NADPH + 12H+ + 18ATP
Light independent (Dark reaction):- light energy is not required.
12NADPH + 12H+ + 18ATP + 6CO2 → C6H12O6 + 12NADP+ + 18ADP +
18Pi +6H2O
Both stages of Photosynthesis occur at the day time when there is light.The
light-dependent reactions use light energy to ‘drive’ the synthesis of two
molecules that will, in turn, drive the light independent reactions. These two
molecules are:
•ATP – this provides the energy for the reactions, and
•reduced NADP – this provides the hydrogen ions for a key reduction reaction.
NADP is very similar to NAD that is used in respiration and it has the same
function – transporting hydrogen ions.
Is the process by which electron energized by photons (light particles) contribute
their energy to the phosphorylation o ADP in synthesizing ATP. There are two
forms of phosphorylation that are used in the light dependent reaction. these are:Is the simplest route of light dependent reaction in which only photosystem I is
The pathway is cyclic because excited electrons originate from P700 at the
reaction center and return to P 700.
No oxygen and no reduced NADP are formed
The whole Photosynthetic units are not involved.
it is known as back to back phosphorylation from PSI to PSI for the production of
No NADPH is produced.
it is not the basis for photosynthesis because NADPH is necessary for CO2 tobe
reduced to carbohydrate .
Is the most common type of photophosphorylation
Both photosytems are involved
There is one way flow of electrons from water to NADP+
It yeilds 2 ATP and 1 NADPH
photosynthetic unit an arrangement of molecules capable of carrying out all the
reactions in the light-dependent stage of photosynthesis.
In cyclic and non-cyclic photophosphorylation, ATP is produced because:
• there is an accumulation of protons (hydrogen ions) in the interior of a thylakoid
• this creates a concentration gradient between the thylakoid interior and the
stroma of the chloroplast
• protons move down this concentration gradient, through ATP synthase, causing
the rotor to spin, just as in mitochondria during respiration.
The light-independent reactions of photosynthesis occur in the stroma of the
photolysis means light-dependent splitting of water
Non cyclic photo
cyclic photo
path way of electrons
Non cyclic
first electron donor
PSI (P700)
last electron acceptor
ATP only
photosystem involved
Reaction centre molecule are molecules where light-dependent reactions begin.
NADP reductase are enzymes that makes the NADP to react with Hydrogen ions
inorder to form a reduced NADP (NADPH).
Photosystem II is active upto a maximum of 680nm wavelength of light.
Photosystem I is active with in a maximum of 700nm wavelength of light.
The efficiency of Photosynthesis increases as the intensity of light increases upto a
limiting value.
Light dependent
Light independent
Takes place
In the Thylakoid
in the stroma of
Light requirement
Requires light
Do not require light
reaction process
• Photolysis of water
• Cyclic and non cyclic
photo phosphorylation
• CO2 fixation
• Reduction of ATP and
• REgeneration of RUBP
Raw materials
Light energy, Water, ADP
and NADP
CO2, RUBP, ATP and
End product
18ATP, 12NADPH,6O2
18ADP+18Pi, 12NADP,
C6H12O6,and RUBP
overall chemical equation
12H2O -----→24H++ 6O2
Pi ---→ C6H12O6+ 6H2O
• carbon dioxide reacts with ribulose bisphosphate (RuBP) – a five-carbon compound in the
stroma; the reaction is catalysed by the enzyme Rubisco.
• two molecules of the three-carbon compound GP are formed from this reaction.
• each molecule of GP is converted to TP (triose phosphate – another three-carbon compound);
this is a reduction reaction using hydrogen ions from reduced NADP and energy from ATP
• some of the TP formed is used to regenerate the RuBP (ATP is again required) whilst some is
used to form glucose and other useful organic compounds.
The amount of light in an environment.
Cold bright day (arctic area):- High light intensity but low temprature which affect the
enzymatic activity.
On warm cloudy day:- Low light intensity but high temprature. Low light intensity affects the
number of electrons excited in the light dependent reaction.
On warm sunny day:- High light intensity and high temprature. The rate of photosynthesis is
affected since the stomatal pores close and sufficient amount of CO2 donot enter the
At low concentration of CO2 the rate of
photosynthesis declines.
The change in temprature affects enzymatic activity that
regulate the rate of photosynthesis.
Photosynthesis takes place efficiently in red and blue
wave length than others.
Low chlorophyll concentration
can result in deacrease the rate of photosynthesis.
The lack of watr affect the rate of photosynthesis even it result wilting
and drying of the plant.
C3 photosynthesis and photorespiration:- It is also known as Calvin cycle.
It takes place in the stroma of chloroplast.
Crop plants that are grown in temperate areas (such as peas and carrots) are C3
photorespiration is the process involving the oxidation of carbon it occurs in
organelles of chloroplast, peroxisomes and mitochondria.
Ribulose bisphosphate + Oxygen --Rubisco--→ GP + Phosphoglycolate
They have broad leaves.
Their palaside cells are nearest to the upper surface of the upper
surface of the leaf to bsorb more light.
Their stomata are open to allow the entry of CO2, but closed if water
loss is too high on a hot day.
Spongy mesophyll has air spaces that allow easy diffusion of CO2 and
Photorespiration reduces the efficiency of photosynthesis for several
reasons, including:
• the carbon is oxidised, which is the reverse of photosynthesis – the
reduction of carbon to carbohydrate
• the ribulose bisphosphate must be resynthesised and the
phosphoglycolate removed
• ATP is used in the resynthesis of RuBP.
Unlike C3 plant the first compound formed in the light independent reaction is C4 compound.
The light independent reaction takes place in mesophyll cells.
C4 photosynthesis include plants that grow in tropical areas like Ethiopia (such as maize,
crabgrass, wheat, sorghum and sugar cane).
C4 photosynthesis is most efficient in conditions of:
• low carbon dioxide concentration
• high light intensity
• high temperature
CAM uses PEP carboxylase to fix CO2 at night time.
They are mostly grow in desert and arid regions of the world.
It includes plants like pineapple, cactus.
Leaf structure
Bundle sheath cell Bundle sheath cell Large vacuole in
lacking chloroplast having chloroplast mesophyll cell
and no thylakoid
Enzyme used to
fix CO2
Optimum CO2
Mesophyll cells
Mesophyll cells
Mesophyll cells
Mesophyll cells
Bundle sheath
Bundle sheath
Fixation of CO2
Calvin cycle
 CAM photosynthesis is effective in desert plants because it : separates the light-dependent and light-independent stages in time;
 the leaves only open their stomata to allow the light-independent reactions
to take place during the night, saving precious water.
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