Monday, December 12, 2011

NARAYANA EDUCATIONAL INSTITUTIONS ,ANDHRA PRADESH- NEET2014

NARAYANA EDUCATIONAL INSTITUTIONS , ANDHRA PRADESH


NARAYANA educational institution is the asia's largest educational institution and u know well it is the best college for medical entrance coaching especially for EAMCET, JIPMER and AIIMS
Now it enters in to NEET , so all the educational institutions who are giving medical entrance coaching for PMT and other exams are ready to face some sad occasions. Narayana management team now focused on NEET-2014, They are making plans to grab top ranks in NEET-2014.
they are established intensive AC CAMPUS for NEET-2013 -2014 students
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Wednesday, November 30, 2011

THE LIVING WORLD


-ADDITIONAL MATERIAL FOR EAMCET STUDENTS TO COVER NEET-2012
UNIT-1 DIVERSITY IN THE LIVING WORLD
Chapter 1 The Living World

Biology is the science of life forms and living processes.
Ernst Mayr(1904 – 2004)has been called‘The Darwin of the 20th century’,
Mayr assuming the title Alexander Agassiz Professor of Zoology Emeritus.
He almost single-handedly made the origin of species diversity the central question of
evolutionary biology that it is today.
He also pioneered the currently accepted definition of a biological species.
Mayr was awarded the three prizes widely regarded as the triple crown of biology: the Balzan Prize, the International Prize forBiology, and the Crafoord Prize
1.1 WHAT IS ‘LIVING’?
Distinctive characteristics exhibited by living organisms. Growth, reproduction, ability
to sense environment,mount a suitable metabolism, ability to self-replicate,
self-organise,interact and emergence
All living organisms grow. Increase in mass and increase in number
of individuals are twin characteristics of growth.
A multicellular organism grows by cell division. In plants, this growth by cell division occurs continuously throughout their life span. In animals, this growth is seen
only up to a certain age.
Non-living objects also grow if we take increase in body mass as a criterion for growth.
Mountains, boulders and sand mounds do grow. However, this kind of growth exhibited by non-living objects is by accumulation of material on the surface.
Growth, therefore,cannot be taken as a defining property of living organisms.
Reproduction, likewise, is a characteristic of living organisms.
Fungi multiply and spread easily due to the millions of asexual spores they produce.
In lower organisms like yeast and hydra, we observe budding.
In Planaria (flat worms), we observe true regeneration, i.e., a fragmented organism regenerates the lost part of its body and becomes, a new organism.
The fungi, the filamentous algae, the protonema of mosses, all easily multiply by fragmentation.
unicellular organisms like bacteria, unicellular algae or Amoeba,reproduction is synonymous with growth, i.e., increase in number of cells.
many organisms which do not reproduce (mules, sterile worker bees, infertile human couples, etc). Hence, reproduction also cannot be an all-inclusive defining characteristic of living organisms. Of course, no non-living object is capable of reproducing or replicating by itself.
metabolism is a defining feature of all living organisms without exception.
The sum total of all the chemical reactions occurring in our body is metabolism.
No non-living object exhibits metabolism.
            cellular organisation of the body is the defining feature of life forms.
            the most obvious and technically complicated feature of all
living organisms is this ability to sense their surroundings or environment
and respond to these environmental stimuli
All organisms, from the prokaryotes to the most complex eukaryotes can sense
 and respond to environmental cues.
Photoperiod affects reproduction in seasonal breeders, both plants and animals.
Human being is the only organism who is aware of himself, i.e., has self-consciousness.
Consciousness therefore, becomes the defining property of living organisms.
1.2 DIVERSITY IN THE LIVING WORLD
the number and types of organisms present on earth refers to biodiversity
The number of species that are known and described range between 1.7-1.8 million.
a particular organism is known by the same name all over the world. This process is called nomenclature.
nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to. This is identification.
scientific names are based on agreed principles and criteria, which are provided
in International Code for Botanical Nomenclature (ICBN), International Code
of Zoological Nomenclature (ICZN).
characterisation, identification, classification and nomenclatureare the processes that are basic to taxonomy.
knowing more about different kinds of organisms and their diversities, but also the relationships among them. This branch of study was referred to as systematics.
The word systematics is derived from the Latin word ‘systema’. Linnaeus used Systema Naturae    as the title of his publication.
Systematics takes into account evolutionary relationships between organisms.
1.3 TAXONOMIC CATEGORIES
the category is a part of overall taxonomic arrangement, it is called the
taxonomic category
all categories together constitute the taxonomic hierarchy.
Taxonomical studies of all known organisms have led to the development of common categories such as kingdom, phylum or division(for plants), class, order, family, genus and species.
1.3.1 Species
Taxonomic studies consider a group of individual organisms with
fundamental similarities as a species.
Mangifera indica, Solanum tuberosum (potato) and Panthera leo (lion). All the three names, indica, tuberosum and leo, represent the specific epithets, while the first words
Mangifera, Solanum and Panthera are genera
1.3.2 Genus
genera are aggregates of closely related species.
potato,tomato and brinjal are three different species but all belong to the genus
Solanum.
Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with
several common features, are all species of the genus Panthera. This genus
differs from another genus Felis which includes cats.
1.3.3 Family
Family, has a group of related genera with still less number of similarities as compared to genus and species.
Solanum,Petunia and Datura are placed in the family Solanaceae.
genus Panthera, comprising lion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae.
cat and a dog are separated into two different families – Felidae and Cancidae, respectively.
1.3.4 Order
Plant families like Convolvulaceae, Solanaceae are included in the order
Polymoniales mainly based on the floral characters.
The animal order, Carnivora, includes families like Felidae and Cancidae.
1.3.5 Class
order Primata comprising monkey, gorilla and gibbon is placed in class
Mammalia along with order Carnivora that includes animals like
tiger, cat and dog.
1.3.6 Phylum
fishes, amphibians, reptiles, birds along with mammals are included inphylum Chordata
due to the presence of notochord and dorsal hollow neural system,
In case of plants, classes with a few similar characters are assigned to a higher
category called Division.
1.3.7 Kingdom
All animals belonging Kingdom Animalia
The Kingdom Plantae, on the other hand, is distinct, and comprises all plants
Common        Biological      Genus      Family       Order        Class     Phylum/ Division
Name                  Name
Man          Homo sapiens     Homo      Hominidae     Primata     Mammalia      Chordata
Housefly        Musca          Musca      Muscidae       Diptera      Insecta            Arthropoda
                     domestica
Mango       Mangifera    Mangifera   Anacardiaceae   Sapindales   Dicotyledonae    Angiospermae
                     indica
Wheat    Triticum     Triticum         Poaceae        Poales       Monocotyledonae      Angiospermae
              aestivum
1.4 TAXONOMICAL AIDS
1.4.1 Herbarium
Herbariaalso serve as quick referral systems in taxonomical studies.
1.4.2 Botanical Gardens
The famous botanical gardens are at Kew (England), Indian Botanical
Garden, Howrah (India) and at National Botanical Research Institute,
Lucknow (India).
1.4.3 Museum
Museums have collections of preserved plant and animal specimens for study and reference
1.4.4 Zoological Parks
These are the places where wild animals are kept in protected environments
under human care and which enable us to learn about their food habits
and behaviour.
1.4.5 Key
The keys are based on the contrasting characters generally in a pair called couplet.
It represents the choice made between two opposite options.
This results in acceptance of only one and rejection of the other.
Each statement in the key is called a lead.

RESPIRATION MATERIAL FOR NEET-2012


Plant Respiration

Respiration
Plants, unlike animals, have no specialised organs for gaseous exchange but they have stomata and lenticels for this purpose. There are several reasons why plants can get along without respiratory organs.
First, each plant part takes care of its own gas-exchange needs. There is very little transport of gases from one plant part to another.
Second, plants do not present great demands for gas exchange. Roots, stems and leaves respire at rates far lower than animals do. Only during photosynthesis are large volumes of gases exchanged and, each leaf is well adapted to take care of its own needs during these periods. When cells photosynthesise, availability of O2 is not a problem in these cells since O2 is released within the cell.
Third, the distance that gases must diffuse even in large, bulky plants is not great. Each living cell in a plant is located quite close to the surface of the plant. Even in woody stems, the ‘living’ cells are organised in thin layers inside and beneath the bark. They also have openings called lenticels. The cells in the interior are dead and provide only mechanical support. Thus, most cells of a plant have at least a part of their surface in contact with air. This is also facilitated by the loose packing of parenchyma cells in leaves, stems and roots, which provide an interconnected network of air spaces.
The complete combustion of glucose, which produces CO2 and H2O as end products, yields energy most of which is given out as heat.
C6H12O6 + 6CO2 → 6CO2 + 6H2O + Heat
If this energy is to be useful to the cell, it should be able to utilise it to synthesise other molecules that the cell requires. The strategy that the plant cell uses is to catabolise the glucose molecule in such a way that not all the liberated energy goes out as heat. The key is to oxidise glucose not in one step but in several small steps enabling some steps to be just large enough such that the energy released can be coupled to ATP synthesis.

Glycolysis

The term glycolysis has originated from the Greek words, glycos for sugar, and lysis for splitting. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway. In anaerobic organisms, it is the only process in respiration. Glycolysis occurs in the cytoplasm of the cell and is present in all living organisms.
In this process, glucose undergoes partial oxidation to form two molecules of pyruvic acid. In plants, this glucose is derived from sucrose, which is the end product of photosynthesis, or from storage carbohydrates. Sucrose is converted into glucose and fructose by the enzyme, invertase, and these two monosaccharides readily enter the glycolytic pathway. Glucose and fructose are phosphorylated to give rise to glucose-6- phosphate by the activity of the enzyme hexokinase. This phosphorylated form of glucose then isomerises to produce fructose-6-phosphate. Subsequent steps of metabolism of glucose and fructose are same.
The various steps of glycolysis are depicted in the following figure:


In glycolysis, a chain of ten reactions, under the control of different enzymes, takes place to produce pyruvate from glucose.
Utilisation of ATP During Glycolysis:
1. During the conversion of glucose into glucose 6-phosphate
2. During the conversion of fructose 6-phosphate to fructose 1, 6-diphosphate.
There are three major ways in which different cells handle pyruvic acid produced by glycolysis. These are lactic acid fermentation, alcoholic fermentation and aerobic respiration. Fermentation takes place under anaerobic conditions in many prokaryotes and unicellular eukaryotes. For the complete oxidation of glucose to CO2 and H2O, however, organisms adopt Krebs’ cycle which is also called as aerobic respiration. This requires O2 supply.

Fermentation

Fermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor, such as oxygen, via an electron transport chain. Fermentation does not necessarily have to be carried out in an anaerobic environment. For example, even in the presence of abundant oxygen, yeast cells greatly prefer fermentation to oxidative phosphorylation, as long as sugars are readily available for consumption.
Sugars are the most common substrate of fermentation, and typical examples of fermentation products are ethanol, lactic acid, and hydrogen. However, more exotic compounds can be produced by fermentation, such as butyric acid and acetone. Yeast carries out fermentation in the production of ethanol in beers, wines and other alcoholic drinks, along with the production of large quantities of carbon dioxide. Fermentation occurs in mammalian muscle during periods of intense exercise where oxygen supply becomes limited, resulting in the creation of lactic acid.
Energy source in anaerobic conditions: Fermentation products contain chemical energy (they are not fully oxidized) but are considered waste products, since they cannot be metabolized further without the use of oxygen (or other more highly-oxidized electron acceptors). A consequence is that the production of adenosine triphosphate (ATP) by fermentation is less efficient than oxidative phosphorylation, whereby pyruvate is fully oxidized to carbon dioxide.

Aerobic Respiration

For aerobic respiration to take place within the mitochondria, the final product of glycolysis, pyruvate is transported from the cytoplasm into the mitochondria. The crucial events in aerobic respiration are:
• The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of CO2.
• The passing on of the electrons removed as part of the hydrogen atoms to molecular O2 with simultaneous synthesis of ATP.
The first process takes place in the matrix of the mitochondria while the second process is located on the inner membrane of the mitochondria.
Pyruvate, which is formed by the glycolytic catabolism of carbohydrates in the cytosol, after it enters mitochondrial matrix undergoes oxidative decarboxylation by a complex set of reactions catalysed by pyruvic dehydrogenase. The reactions catalysed by pyruvic dehydrogenase require the participation of several coenzymes, including NAD+ and Coenzyme A.
anaerobic respiration

During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced from one glucose molecule during glycolysis).
The acetyl CoA then enters a cyclic pathway, tricarboxylic acid cycle, more commonly called as Krebs’ cycle after the scientist Hans Krebs who first explained it.
Tricarboxylic Acid Cycle
The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid. The reaction is catalysed by the enzyme citrate synthase and a molecule of CoA is released. Citrate is then isomerised to isocitrate.


It is followed by two successive steps of decarboxylation, leading to the formation of α-ketoglutaric acid and then succinyl-CoA.
In the remaining steps of citric acid cycle, succinyl-CoA is oxidised to OAA allowing the cycle to continue. During the conversion of succinyl-CoA to succinic acid a molecule of GTP is synthesised. This is a substrate level phosphorylation. In a coupled reaction GTP is converted to GDP with the simultaneous synthesis of ATP from ADP. Also there are three points in the cycle where NAD+ is reduced to NADH+H+ and one point where FAD+ is reduced to FADH2.
The continued oxidation of acetic acid via the TCA cycle requires the continued replenishment of oxaloacetic acid, the first member of the cycle. In addition it also requires regeneration of NAD+ and FAD+ from NADH and FADH2 respectively.
Electron Transport System (ETS) and Oxidative Phosphorylation
The following steps in the respiratory process are to release and utilize the energy stored in NADH+H+ and FADH2. This is accomplished when they are oxidised through the electron transport system and the electrons are passed on to O2resulting in the formation of H2O. The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system (ETS) and it is present in the inner mitochondrial membrane.
Electrons from NADH produced in the mitochondrial matrix during citric acid cycle are oxidised by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone located within the inner membrane. Ubiquinone also receives reducing equivalents via FADH2 (complex II) that is generated during oxidation of succinate in the citric acid cycle.
The reduced ubiquinone (ubiquinol) is then oxidised with the transfer of electrons to cytochrome c via cytochrome bc1 complex (complex III).
Cytochrome c is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer of electrons between complex III and IV. Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, and two copper centres.
When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex V) for the production of ATP from ADP and inorganic phosphate. The number of ATP molecules synthesized depends on the nature of the electron donor.
Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of FADH2 produces 2 molecules of ATP. Although the aerobic process of respiration takes place only in the presence of oxygen, the role of oxygen is limited to the terminal stage of the process. Yet, the presence of oxygen is vital, since it drives the whole process by removing hydrogen from the system. Oxygen acts as the final hydrogen acceptor.
Unlike photophosphorylation where it is the light energy that is utilised for the production of proton gradient required for phosphorylation, in respiration it is the energy of oxidation-reduction utilised for the same process. It is for this reason that the process is called oxidative phosphorylation.
The energy released during the electron transport system is utilised in synthesising ATP with the help of ATP synthase (complex V). This complex consists of two major components, F1 and F0. The F1 headpiece is a peripheral membrane protein complex and contains the site for synthesis of ATP from ADP and inorganic phosphate. F0 is an integral membrane protein complex that forms the channel through which protons cross the inner membrane. The passage of protons through the channel is coupled to the catalytic site of the F1 component for the production of ATP. For each ATP produced, 2H+ passes through F0 from the intermembrane space to the matrix down the electrochemical proton gradient.
The Respiratory Balance Sheet
It is possible to make calculations of the net gain of ATP for every glucose molecule oxidised; but in reality this can remain only a theoretical exercise.
These calculations can be made only on certain assumptions that:
• There is a sequential, orderly pathway functioning, with one substrate forming the next and with glycolysis, TCA cycle and ETS pathway following one after another.
• The NADH synthesised in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
• None of the intermediates in the pathway are utilised to synthesise any other compound.
• Only glucose is being respired – no other alternative substrates are entering in the pathway at any of the intermediary stages.
But this kind of assumptions are not really valid in a living system; all pathways work simultaneously and do not take place one after another; substrates enter the pathways and are withdrawn from it as and when necessary; ATP is utilised as and when needed; enzymatic rates are controlled by multiple means. Yet, it is useful to do this exercise to appreciate the beauty and efficiency of the living system in extraction and storing energy. Hence, there can be a net gain of 36 ATP molecules during aerobic respiration of one molecule of glucose.
Amphibolic Pathway
Glucose is the favoured substrate for respiration. All carbohydrates are usually first converted into glucose before they are used for respiration. Other substrates can also be respired but then they do not enter the respiratory pathway at the first step.
Since respiration involves breakdown as well as synthesis of substrates, the respiratory process involves both catabolism and anabolism. That is why respiratory pathway is considered to be an amphibolic pathway rather than as a catabolic one.
Respiratory Quotient
The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.
The respiratory quotient depends upon the type of respiratory substrate used during respiration. When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1, because equal amounts of CO2 and O2 are evolved and consumed, respectively. When fats are used in respiration, the RQ is less than 1.
Respiratory Quotient
 


Plant Respiration

Question 1. Differentiate between
(a) Respiration and Combustion
(b) Glycolysis and Krebs’ cycle
(c) Aerobic respiration and Fermentation
Answer:
(a) Respiration takes place in cells of living beings, while combustion can take place anywhere. Respiration is highly controlled process while combustion cannot be controlled beyond certain level. Both of them require oxygen and are exothermic reaction. Both the processes change chemical energy to heat energy.
(b) Glycolysis is a metabolic pathway that is found in the cytoplasm of cells in all living organisms and is anaerobic, or doesn't require oxygen. The process converts one molecule of glucose into two molecules of pyruvate, and makes energy in the form of two net molecules of ATP.
Citric acid Cycle or Krebs Cycle: When oxygen is present, acetyl-CoA is produced from the pyruvate molecules created from glycolysis. Once acetyl-CoA is formed, two processes can occur, aerobic or anaerobic respiration.
When oxygen is present, the mitochondria will undergo aerobic respiration which leads to the Krebs cycle. However, if oxygen is not present, fermentation of the pyruvate molecule will occur.
In the presence of oxygen, when acetyl-CoA is produced, the molecule then enters the citric acid cycle (Krebs cycle) inside the mitochondrial matrix, and gets oxidized to CO2 while at the same time reducing NAD to NADH. NADH can be used by the electron transport chain to create further ATP as part of oxidative phosphorylation. To fully oxidize the equivalent of one glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two waste products, H2O and CO2, are created during this cycle.
The citric acid cycle is an 8-step process involving 8 different enzymes. Throughout the entire cycle, acetyl-CoA changes into citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, and finally, oxaloacetate. The net energy gain from one cycle is 3 NADH, 1 FADH, and 1 ATP. Thus, the total amount of energy yield from one whole glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH, and 2 ATP.
(c) Aerobic respiration
Aerobic respiration is the main means by which both plants and animals utilize energy in the form of organic compounds that was previously created through photosynthesis. Respiration requires oxygen in order to generate energy (ATP). It is the preferred method of pyruvate breakdown from glycolysis and requires that pyruvate enter the mitochondrion in order to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP (Adenosine Triphosphate), by substrate-level phosphorylation, NADH and FADH2.
Anaerobic Respiration or Fermentation
Without oxygen, pyruvate is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion, but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the hydrogen carriers so that they can perform glycolysis again and removing the excess pyruvate. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate phosphorylation, which is phosphorylation that does not involve oxygen.
Question 2. What are respiratory substrates? Name the most common respiratory substrate.
Answer: Compounds which are oxidized during respiration are called respiratory substrates. It is obvious that carbohydrates are the most common respiratory substrates.
Question 3. Give the schematic representation of glyolysis?
Answer:
glycolysis

Question 4. What are the main steps in aerobic respiration? Where does it take place?
Answer:


• Prior to entering the Krebs Cycle, pyruvate must be converted into acetyl CoA (pronounced: acetyl coenzyme A). This is achieved by removing a CO2molecule from pyruvate and then removing an electron to reduce an NAD+ into NADH. An enzyme called coenzyme A is combined with the remaining acetyl to make acetyl CoA which is then fed into the Krebs Cycle. The steps in the Krebs Cycle are summarized below:
• Citrate is formed when the acetyl group from acetyl CoA combines with oxaloacetate from the previous Krebs cycle..
• Citrate is converted into its isomer isocitrate..
• Isocitrate is oxidized to form the 5-carbon α-ketoglutarate. This step releases one molecule of CO2 and reduces NAD+ to NADH2+.
• The α-ketoglutarate is oxidized to succinyl CoA, yielding CO2 and NADH2+.
• Succinyl CoA releases coenzyme A and phosphorylates ADP into ATP.
• Succinate is oxidized to fumarate, converting FAD to FADH2.
• Fumarate is hydrolized to form malate.
• Malate is oxidized to oxaloacetate, reducing NAD+ to NADH2+.
Question 5. Give the schematic representation of an overall view of Krebs’ cycle.
Answer:


Question 6. Explain ETS.
Answer: The following steps in the respiratory process are to release and utilize the energy stored in NADH+H+ and FADH2. This is accomplished when they are oxidised through the electron transport system and the electrons are passed on to O2 resulting in the formation of H2O. The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system (ETS) and it is present in the inner mitochondrial membrane.
Electrons from NADH produced in the mitochondrial matrix during citric acid cycle are oxidised by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone located within the inner membrane. Ubiquinone also receives reducing equivalents via FADH2 (complex II) that is generated during oxidation of succinate in the citric acid cycle.
The reduced ubiquinone (ubiquinol) is then oxidised with the transfer of electrons to cytochrome c via cytochrome bc1 complex (complex III).
Cytochrome c is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer of electrons between complex III and IV. Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, and two copper centres.
When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex V) for the production of ATP from ADP and inorganic phosphate. The number of ATP molecules synthesized depends on the nature of the electron donor.
Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of FADH2 produces 2 molecules of ATP. Although the aerobic process of respiration takes place only in the presence of oxygen, the role of oxygen is limited to the terminal stage of the process. Yet, the presence of oxygen is vital, since it drives the whole process by removing hydrogen from the system. Oxygen acts as the final hydrogen acceptor.
Unlike photophosphorylation where it is the light energy that is utilised for the production of proton gradient required for phosphorylation, in respiration it is the energy of oxidation-reduction utilised for the same process. It is for this reason that the process is called oxidative phosphorylation.
The energy released during the electron transport system is utilised in synthesising ATP with the help of ATP synthase (complex V). This complex consists of two major components, F1 and F0. The F1 headpiece is a peripheral membrane protein complex and contains the site for synthesis of ATP from ADP and inorganic phosphate. F0 is an integral membrane protein complex that forms the channel through which protons cross the inner membrane. The passage of protons through the channel is coupled to the catalytic site of the F1component for the production of ATP. For each ATP produced, 2H+ passes through F0 from the intermembrane space to the matrix down the electrochemical proton gradient.
Question 7. What are the assumptions made during the calculation of net gain of ATP?
Answer: It is possible to make calculations of the net gain of ATP for every glucose molecule oxidised; but in reality this can remain only a theoretical exercise.
These calculations can be made only on certain assumptions that:
• There is a sequential, orderly pathway functioning, with one substrate forming the next and with glycolysis, TCA cycle and ETS pathway following one after another.
• The NADH synthesised in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
• None of the intermediates in the pathway are utilised to synthesise any other compound.
• Only glucose is being respired – no other alternative substrates are entering in the pathway at any of the intermediary stages.
But this kind of assumptions are not really valid in a living system; all pathways work simultaneously and do not take place one after another; substrates enter the pathways and are withdrawn from it as and when necessary; ATP is utilised as and when needed; enzymatic rates are controlled by multiple means. Yet, it is useful to do this exercise to appreciate the beauty and efficiency of the living system in extraction and storing energy. Hence, there can be a net gain of 36 ATP molecules during aerobic respiration of one molecule of glucose.
Question 8. Discuss “The respiratory pathway is an amphibolic pathway.”
Answer: Glucose is the favoured substrate for respiration. All carbohydrates are usually first converted into glucose before they are used for respiration. Other substrates can also be respired but then they do not enter the respiratory pathway at the first step.
Since respiration involves breakdown as well as synthesis of substrates, the respiratory process involves both catabolism and anabolism. That is why respiratory pathway is considered to be an amphibolic pathway rather than as a catabolic one.
Question 9. Define RQ. What is its value for fats?
Answer: The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.


Question 10. What is oxidative phosphorylation?
Answer: Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP). Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that supplies energy to metabolism. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentation processes such as anaerobic glycolysis.
During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen, in redox reactions. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within mitochondria, whereas, in prokaryotes, these proteins are located in the cells' inner membranes. These linked sets of enzymes are called electron transport chains. In eukaryotes, five main protein complexes are involved, whereas in prokaryotes many different enzymes are present, using a variety of electron donors and acceptors.