Samacheer Class 11 Bio Botany - Respiration

In some succulent plants like Opuntia, Bryophyllum carbohydrates are partially oxidised to organic acid, particularly malic acid without the corresponding release of CO 2 but O 2 is consumed hence the RQ value will be zero.

Electron and hydrogen (proton) transport takes place across four multiprotein complexes (I-IV). They are.
1. Complex-I (NADH dehydrogenase).
It contains a flavoprotein (FMN) and associated with non-heme iron Sulphur protein (Fe-S). This complex is responsible for passing electrons and protons from mitochondrial NADFI (Internal) to Ubiquinone (UQ)
NADH+H + UQ ⇌ NAD – +UQH 2
2. In plants, an additional NADH dehydrogenase (External) complex is present on the outer surface of inner membrane of mitochondria which can oxidise cytosolic NADH + H +.
Ubiquinone (UQ) or Coenzyme Quinone (CoQ) is a small, lipid-soluble electron, proton carrier located within the inner membrane of mitochondria).
3. Complex-II (succinic dehydrogenase) It contains FAD flavoprotein is associated with non-heme iron Sulphur (Fe-S) protein. This complex receives electrons and protons from succinate in Kerbs cycle and is converted into fumarate and passes to ubiquinone.
Succinate + UQ Fumaraic LQH 2
4. Complex-III (Cytochrome bcj complex) This complex oxidises reduced ubiquinone (ubiquinol) and transfers the electrons through Cytochrome bc 1 Complex (Iron Sulphur centci bcl complex) to cytochrome c.
5. Complex IV (Cytochrome c oxidase) Complex IV is the terminal oxidase and brings about the reduction of 1/2 O 2 to H 2 O. TWO protons are needed to form a molecule of H 2 O (terminal oxidation).

* Pentose phosphate pathway is the alternate pathway for breakdown of glucose.
* Pentose phosphate pathway was described by Warburg, Dickens and Lipmami (1938).
* It is also known as Hexose monophosphate shunt (HMP shunt) or Direct oxidative phase and non – oxidative phase.
* The oxidative phase convert six molecules of six carbon Glucose 6 phosphate to 6 molecules of five-carbon sugar Ribulose – 5 Phosphate with loss of 6CO 2 and generation of 12 NADPH + H +
Non oxidative pathway convert Ribulose – 5 – phosphate molecules to various intermediates such as
Ribose – 5 – phosphate (5C)
Xylulose – 5 – phosphate (5C)
Glyceraldehyde – 3 – phosphate (3C)
Sedoheptulose – 7 – phosphate (7C) and
Erythrose – 4 – phosphate (4C)
Finally five molecules of glucose 6 – phosphate is regenerated
6 x Glucose – 6 – phosphate + 12NADP + + 6H 2 O
↓
5 x glucose – 6 – phosphate + 6CO 2 + Pi + 12 NADPH + 2H +
The net result of complete oxidation of one glucose – 6 – phosphate yield 6CO 2 and 12 NADPH + H +. The oxidative pentose phosphate pathway is controlled by glucose – 6 – phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to NADP +.

When the cost of transport of ATPs from the matrix into the cytosol is considered, the number will be 2.5 ATPs for each NADH + H + and 1.5 ATPs for each FADH 2 oxidized during the electron transport system. Therefore, in plant cells net yield of 30 ATP molecules for complete aerobic oxidation of one molecule of glucose. But in those animal cells (showing malate shuttle mechanism) net yield will be 32 ATP molecules. Since the sucrose molecule gives, two molecules of glucose and net ATP in plant cell will be 30 × 2 = 60.
In an animal cell, it will be 32 × 2 = 64.
Part-II.
11th Bio Botany Guide Respiration Additional Important Questions and Answers
I. Choose The Correct Answer

Respiration is a biological process in which oxidation of various food substances like carbohydrates, proteins, and fats take place and as a result of this, energy is produced where O 2 is taken in and CO 2 is liberated.

The point at which CO 2 released in respiration is exactly compensated by CO 2 fixed in photosynthesis that means no net gaseous exchange takes place, it is called the compensation point.

In aerobic respiration, Conversion of Pyruvic acid into acetyl coenzyme – A in the mitochondrial matrix with two molecules of NADH + H + and 2 CO 2. This is called Link reaction (or) transition reaction.

Sir Hans Adolf Krebs was born in Germany on 25th August 1900. He was awarded Nobel Prize for his discovery of Citric acid cycle in Physiology in 1953.

• TCA cycle starts with condensation of acetyl COA with oxaloacetate in the presence of water to yield Citri acid (or) Citrate.
• So it is also known as citric acid cycle (or) Tricarboxylic acid cycle.

NADH dehydrogenase contains a flavoprotein (FMN) and associated with non – heme iron Sulphur protein (Fe – S). This complex is responsible for passing electrons and protons from mitochondrial NADH (Internal) to Ubiquinone (UQ).

Two electron transport chain inhibitors:
* 2, 4 DNP (Dinitrophenol) – It prevents synthesis of ATP from ADP, as it directs electrons from Co Q to O 2.
* Cyanide – It prevents flow of electrons from Cytochrome a 3 to O 2.

The significances of Respiratory Quotient:
* RQ value indicates which type of respiration occurs in living cells, either aerobic or anaerobic.
* It also helps to know which type of respiratory substrate is involved.

Two internal factors, that affect the rate of respiration in plants:
* The amount of protoplasm and its state of activity influence the rate of respiration.
* The concentration of respiratory substrate is proportional to the rate of respiration.

Two significance of pentose phosphate pathway:
* HMP shunt is associated with the generation of two important products.
* Coenzyme NADPH generated is used for reductive biosynthesis and counter damaging the effects of oxygen-free radicals.

In plants, oxygen enters through the stomata and it is transported to cells, where oxygen is utilized for energy production. Plants require carbon dioxide to survive, to produce carbohydrates, and to release oxygen through photosynthesis, these oxygen molecules are inhaled by humans through the nose, which reaches the lungs where oxygen is transported through the blood and it reaches cells. Cellular respiration takes place inside or the cell for obtaining energy.

• Breaking of C-C bonds of complex organic compounds through oxidation within the cells.
• The energy released during respiration is stored in the form of ATP and heat is liberated.
• It occurs in all the living cells of organisms.

The two common factors associated with compensation points are CO 2 and light. Based on this there are two types of compensation points. They are the CO 2 compensation point and light compensation point. C 3 plants have compensation points ranging from 40 – 60 ppm (parts per million) CO 2 while those of C 4 plants range from 1 – 5 ppm CO 2.

Floating respiration
Protoplasmic respiration
Carbohydrate (or) fat (or) organic acid serves as a respiratory substrate
Whereas protein is a respiratory substrate.
It is a common mode of respiration and does not produce any toxic product.
It is rare and liberates toxic ammonia.

NAD + + 2e – + 2H + → NADH + H +
FAD + 2e – + 2H + → FADH 2
When NAD + (Nicotinamide Adenine Dinucleotide – oxidized form) and FAD (Flavin Adenine Dinucleotide) pick up electrons and one or two hydrogen ions (protons), they get reduced to NADH + H + and FADH 2 respectively. When they drop electrons and hydrogen off they go back to their original form. The reaction in which NAD + and FAD gain (reduction) or lose (oxidation) electrons are called redox reactions (Oxidation-reduction reactions). These reactions are important in cellular respiration.

• Electron transport chain and oxidative phosphorylation remove hydrogen atoms from the products of glycolysis, link reaction, and Kreb cycle.
• It releases water molecule with energy in the form of ATP molecules in the mitochondrial inner membrane.

The significance of Kreb’s cycle:
* TCA cycle is to provide energy in the form of ATP for metabolism in plants.
* It provides carbon skeleton or raw material for various anabolic processes.
* Many intermediates of the TCA cycle are further metabolised to produce amino acids, proteins, and nucleic acids.
* Succinyl CoA is the raw material for the formation of chlorophylls, cytochrome, phytochrome, and other pyrrole substances.
* α – ketoglutarate and oxaloacetate undergo reductive amination and produce amino acids.
* It acts as a metabolic sink which plays a central role in intermediary metabolism.

Ubiquinone
Cytochrome C
It is a small, lipid-soluble electron, proton carrier located within the inner membrane of mitochondria.
It is a small protein attached to the outer surface of inner membrane of mitochondria
It is associated with ETS – complex I
It is associated with ETS – complex IIII

The characteristic of Anaerobic respiration:
* Anaerobic respiration is less efficient than aerobic respiration.
* A limited number of ATP molecules is generated per glucose molecule.
* It is characterized by the production of CO 2 and is used for Carbon fixation in photosynthesis.

• Red colour parts present in plants is due to the presence of anthocyanin
• Synthesis of anthocyanin require more O 2 than CO 2 evolved.
• So RQ will be less than one.

Three external factors, that affect respiration in plants:
* The optimum temperature for respiration is 30°C. At low temperatures and very high temperatures rate of respiration decreases.
* When a sufficient amount of O 2 is available the rate of aerobic respiration will be optimum and anaerobic respiration is completely stopped. This is called the Extinction point.
* The high concentration of CO 2 reduces the rate of respiration.

• It is an alternate pathway for break down of glucose.
• It takes place in the cytoplasm of mature plant cells.
• In this pathway glucose 6 phosphate molecule is converted to Ribulose 5 phosphate with CO 2 and NADPH – + H +.

* The conversion of pyruvate to ethanol takes place in malted barley and grapes through fermentation.
* Yeast Carryout this process under anaerobic conditions and this conversion increases ethanol concentration.
* If the concentration increases It’s toxic effect kills yeast cells and the left out is called beer and wine respectively.
IV. 5 Mark Questions

Aerobic respiration
Anaerobic respiration
1. It occurs in all living cells of higher organisms.
It occurs yeast and some bacteria.
2. It requires oxygen for breaking the respiratory substrate
Oxygen is not required for breaking the respiratory substrate.
3. The end products are CO 2 and H 2 O
The end products are alcohol and CO 2 (or) lactic acid
4. Oxidation of one molecule of glucose produces 36 ATP molecules
Only 2 ATP molecules are produced.
5. It consists of four stages – glycolysis, link reaction, TCA cycle and electron transport chain.
It consists of two stages – glycolysis and fermentation.
6. It occurs in cytoplasm and mitochondria
It occurs only in cytoplasm

* Two molecules of glyceraldehyde 3 – phosphate oxidatively phosphorylated into two molecules of 1-3
bisphospho glycerate.
* During this reaction 2 NAD + is reduced to 2NADH+ H + by glyceraldehyde 3-phosphate dehydrogenase.
* Further reactions are carried out by different enzymes at the end two molecules of pyruvate are produced.
* In this phase 4 ATPS are produced (at step 7 and step 10)
* Through Direct transfer of phosphate from substrate molecule to ADP and is converted into ATP is called substrate Phosphotylation. (or) Direct Phosphorylation (or) transphosphorylation.
* During the reaction (at step 9)2 phospo glycerate dehydrated into phosphoenol pyurvate, a water molecule is removed by the enzyme enolase.
* As a result enol group is formed within the molecule. This process is called Enolation.
Energy Budge of pay off phase:
* In the payoff phase totally 4 ATP and 2NADH + H + molecules are produced.
* Since 2 ATP molecules are already consumed in the preparatory phase the net products in glycolysis are 2ATP and 2NADH + H +

Glycolysis is a linear series of reactions in which 6- carbon glucose split into two molecules of 3 carbon pyruvic acid.
Preparatory phase:
* Glucose enters glycolysis which is the end product of photosynthesis.
* Glucose is phosphorylated into glucose 6 phosphate by the enzyme hexokinase and subsequent reactions are carried out by different enzymes.
* At the end of this phase fructose 1,6 – bisphote is cleaved into glyceraldehyde 3- phosphate and dihydroxyacetone phosphate by the enzyme aldolase.
* These two are Isomers.
* Dihydroxyacetone phosphate is isomerised into glyceraldehyde 3- phosphate by the enzyme triose phosphate isomerase.
* Now two molecules of glyceraldehyde 3 phosphate enter into pay off phase.
During the preparatory phase, two ATP molecules are àonsumed.

* Two molecules of pyruvate formed by glycolysis in the cytosol enter into mitochondnalrnatrxi.
* In aerobic respiration this pyruvate with coenzyme A is oxidatively decarboxylated into acetyl CoA by pyruvate dehydrogenase complex..
* It produces two molecules of NADH + H + and 2CO 2
It is also called transition reaction (or) Link reaction.
The pyruvate dehydrogenase complex consists of three distinct enzymes.
* Pyruvate dehydrogenase
* Dihydroiipoyil transacetylase
* Dihydrolipoyil dehydrogenase and 5 coenzymes TPP (thymine pyrophosphate)
* NAD +
* FAD
* COA and lipoate.

• Two molecules of acetyl CoA formed from link reaction now enter into Kreb Cycle.
• It is named after its discoverer German Biochemist Sir Hans Adolf Kreb (1937).
• It is takes place in the mitochondrial matrix and inner membrane of mitochondria.
• The enzymes needed for TCA cycle are found in the mitochondrial matrix except for succinate dehydrogenase which is found in the mitochondrial inner membrane.
• First step starts with condensation of acetyl CoA with oxaloacetate in the presence of water to yield citric acid (or) citrate.
• It is followed by the action of different enzymes in cyclic manner.
• During the conversion of succinyl CoA to succinate by the enzyme succinyl CoA synthetase a molecule of ATP Synthesis from Substrate without entering the electron transport chain is called substrate-level phosphorylation.
• Kreb Cycle is repeated twice for every glucose molecule.
• Where two molecules of pyruvic acid produces six molecules of CO 2, eight molecules of NADH+H + two molecules of FADH 2 and two molecules of ATP.

* TCA cycle is to provide energy in the form of ATP for metabolism in plants.
* It provides carbon skeleton or raw material for various anabolic process.
* many intermediates of TCA cycle are further metabolised to produce amino acids, proteins and nucleic acids.
* Succinyl CoA is raw material for formation of chlorophyll, cytochrome, phytochrome and other pyrroles
substances.
* α – ketoglutarate and oxaloacetate undergo reductive amination and produce amino acids.
* it acts as metabolic sink which plays a central role in intermediary metabolism.

• 2,4 DNP (Dinitrophenol) – It prevents the synthesis of ATP from ADP, as it directs electrons from CoQ to O 2
• Cyanide – It prevents the flow of electrons from Cytochrome a 3 to O 2
• Rotenone – It prevents flow of electrons from NADH + H + / FADH 2 to Co Q
• Oligomycin – It inhibits oxidative phosphorylation

* Take small quantity of any seed (groundnut or bean seeds) and allow them to germinate by imbibing them.
* While they are germinating place them in a conical flask.
* A small glass tube containing 4 ml of freshly prepared Potassium hydroxide (KOH) solution is hing into the conical flask with the help of a thread and tightly close the one holed cork.
* Take a bent glass tube, the shorted end of which is inserted into the conical flask through the hole in the cork.
* The longer end is dipped in a beaker containing water.
* Observe the position of initial water level in bent glass tube.
* This experimental setup is kept for two hours.
* After two hours, the level of water rises in the glass tube. It is because the CO 2 evolved during aerobic
respiration by germinating seeds will be absorbed by KOH solution and the level of water will rise in the glass tube.
* CO 2 + 2KOH → K 2 CO 3 + H 2 O

Alcoholic fermentation
Lactic acid fermentation
1. it produces alcohol and releases CO 2 from pyruvic acid
It produces lactic acid and does not release CO 2 from pyruvic acid
2. It takes place in two steps.
It takes place in single steps.
3. It involves two enzymes, pyruvate decarboxylase with Mg ++ and alcohol dehydrogenase
It uses one enzyme, lactate dehydrogenase with Zn + +
4. It forms acetaldehyde as an intermediate compound
Does not form an intermediate compound.
5. It commonly occurs in yeast.
Occurs in bacteria, some fungi, and vertebrate muscles.

• In bakeries, it is used for preparing bread, cakes, biscuits.
• In beverage industries for preparing wine and alcoholic drinks.
• In producing vinegar and in tanning, curing of leather.
• Ethanol is used to make gasohol (a fuel that is used for cars in Brazil).

Glycolysis
Fermentation
1. Glucose is converted into pyruvic acid
Stars from pyruvic acid and is converted into alcohol or lactic acid.
2. It takes place in the presence or absence of oxygen.
it takes place in the absence of oxygen.
3. Net gain is 2ATP.
No net gain of ATP molecules.
4. 2NADH + H + molecules are produced.
2NADH+ H + molecules are utilised
5. It commonly occurs in yeast.
Occurs in bacteria, some fungi and vertebrate muscles.

* Take a Kuhne’s fermentation tube which consists of an upright glass tube with a side bulb
* Pour 10% sugar solution mixed with baker’s yeast into the fermentation tube the side tube is filled plug the mouth with lid.
After some time, the glucose solution will be fermented. The solution will give out an alcoholic smell.
* The level of the solution in the glass column will fall due to the accumulation of CO 2 gas.
* It is due to the presence of zymase enzyme yeast which converts the glucose solution into alcohol and CO 2
* Now introduce a pellet of KOH into the tube, the KOH will absorb CO 2 and the level of solution will rise in the upright tube.
* This experiment proves during fermentation CO 2 gas is evolved.

External Factors:
* The optimum temperature for respiration is 30°C. At low temperatures and very high temperatures rate, respiration decreases.
* When sufficient amount of O 2 is available the rate of aerobic respiration will be optimum and anaerobic respiration is completely stopped. This is called Extinction point.
* The high concentration of CO 2 reduces the rate of respiration.
* A plant or tissue transferred from water to salt solution wi li increase the rate of respiration. It is called silt respiration.
* Light is an indirect factor affecting the rate of respiration.
* Wounding of plant organs stimulates the rate of respiration in that region.
Internal Factors:
* The concentration of respiratory substrate is proportional to the rate of respiration
* The amount of protoplasm and its state of activity influence the rate of respiration.

* The pentose phosphate pathway was described by Warburg, Dickens, and Lipmann (1938). Hence, it is also called Warburg – Dickens Lipmann pathway.
* It takes place in the cytoplasm of mature plant cells. It is an alternate way for break4own of glucose.
* It consists of two phases, oxidative phase, and non-oxidative phase.
* The oxidative events concert six molecules of six carbon Glucose 6 phosphate to 6 molecules of five-carbon sugar Ribulose -5 phosphate with loss of 12 NADPH + H + (not NADH).
* The remaining reactions known as non oxidative pathway, covert Rihulose 5phosphate molecules to various intermediates such as Ribose – 5 – phosphate (5C), Xylulose – 5 – phosphate (5C), Glyceraldehyde – 7 – Phosphate (7C), and Eiythrose -4- phosphate (4C).
* Finally, five molecules of glucose -6- phosphate is regenerated. The overall reaction is:
6 x Glucose – 6 – Phosphate + 12NADP + + 6H 2 O
↓
5 x Glucose-6- Phosphate + 6CO 2 + Pi + 12NADPH + 12H +
* The net result of complete oxidation of one glucose-6-phosphate yield 6CO 2 and12NADPH+H +

* HMP shunt is associated with the generation of two important products. NADPH and pentsoe sugars, which play a vital role in anaholic reactions.
* Coenzyme NADPH generated is used by reductive bisynthesìs and counter damaging the effects of oxygen-free radicals.
* Ribose – 5 – phosphate and its derivatives are used in the synthesis of DNA, RNA, ATP, NAD, FAD and
Coenzynie A..
* Erythrose is used for the synthesis of anthocyanin Jignin and other aromatic compounds.