Past Entrance Papers

Hint

(b) Oxidation of one molecule of NADH gives rise to 3 molecules of ATP and one molecule of \(\mathrm{FADH}_{2}\) produces 2 molecules of ATP.
NADH and \(\mathrm{FADH}_{2}\) are two different types of electron donors. They differ in the ways they feed electrons during the electron transport chain. NADH feeds its electrons into the electron transport chain at the beginning (Complexl). \(\mathrm{FADH}_{2}\) feeds into the electron transport chain at Complex II (at a lower energy level down the chain). The high-energy electrons from NADH have sufficient energy to result in 3 ATP whereas the lower-energy electrons in \(\mathrm{FADH}_{2}\) have energy for 2 ATP production.

Hint

(d) Pyruvate dehydrogenase enzyme is involved in the conversion of pyruvate to acetyl Co-A, after the completion of glycolysis and before the start of Krebs’ cycle. This enzyme is made up of decarboxylase, lipoic acid, transacetylase, and \(\mathrm{Mg}^{2+}\) ion. The reaction occurs in the following way
Pyruvate \(+\mathrm{NAD}^{+}+\mathrm{CO}-\mathrm{A} \underset{\text { dehydrogenase, } \mathrm{Mg}^{2+}}{\stackrel{\text { Pynvate }}{\longrightarrow}}\)
Acetyl Co- A + NADH \(+\mathrm{H}^{+}+\mathrm{CO}_{2}\)
In this reaction \(\mathrm{Mg}^{2+}\) acts as a cofactor.

Hint

(a) The number of substrate-level phosphorylation in one turn of citric acid cycle is 1 . During Krebs’ or citric acid cycle, succinyl-Co-A is acted upon by enzyme succinyl-Co-A synthetase to form succinate (a 4C compound). The reaction releases sufficient energy to
form ATP (in plants) or GTP (in animals) by substrate-level phosphorylation. GTP can form ATP through a coupled reaction. Succinyl \(\mathrm{Co}-\mathrm{A}+\mathrm{GDP} / \mathrm{ADP}+\mathrm{H}_{3}\)
\(\mathrm{PO}_{4}\) synthetase. Succinyl Co-A Succinate +Co-A+GTP/ATP.

Hint

(a) Conversion of glucose to glucose-6-phosphate during glycolysis is catalysed by the enzyme hexokinase. During this step, glucose is phosphorylated to glucose-6-phosphate
by ATP. It is the first step of the activation phase of glycolysis.

Hint

(c) Respiratory Electron Transport System (ETS) in plants is located in the inner mitochondrial membrane. It serves as the site of oxidative phosphorylation through the action of ATP synthase.

Hint

(a) The \(\mathrm{RQ}\) value of tripalmitin is \(0.7\). It can be calculated as follows
Respiratory Quotient (RQ)
\(
\begin{aligned}
&=\frac{\text { Amount of } \mathrm{CO}_{2} \text { released }}{\text { Amount of } \mathrm{O}_{2} \text { Consumed }} \\
&2\left(\mathrm{C}_{51} \mathrm{H}_{98} \mathrm{O}_{6}\right)+145 \mathrm{O}_{2} \rightarrow 102 \mathrm{CO}_{2}+98 \mathrm{H}_{2} \mathrm{O}
\end{aligned}
\)

Tripalmitin
\(
\mathrm{RQ}=\frac{102 \mathrm{CO}_{2}}{1450 \mathrm{O}_{2}}=0.7
\)
It is to note that RQ of common fats is usually less than 1 under aerobic conditions.

Hint

(d) Oxidative phosphorylation is the process of ATP formation due to the transfer of electrons from NADH or \(\mathrm{FADH}{ }_{2}\) to oxygen molecule \(\left(\mathrm{O}_{2}\right)\) by a series of electron carriers. This process occurs in the inner mitochondrial membrane because of its less permeability, presence of ETC proteins, and ATP synthase.

The rest three statements are correct.

Hint

(b) \(\mathrm{NAD}^{+}\)functions as an electron carrier in cellular respiration. NAD is an oxidising agent which accepts electrons and then transfers them to the Electron Transport System(ETS). As a result, 3ATP molecules are formed.

Hint

(c) Krebs’ cycle starts with the condensation of an acetyl group (acetyl CoA) with oxaloacetate to form a tricarboxylic, 6-carbon compound called citric acid.

Hint

(a) In the mesophyll cells cytoplasm of \(\mathrm{C}_{4}\) plants like sugarcane, maize, sorghum etc. PEP is \(3 \mathrm{C}\) compound which serves as primary \(\mathrm{CO}_{2}\) acceptor.

Hint

(d) Carbohydrates are usually first converted into glucose before they are used for respiration. Fats are broken down into glycerol and fatty acids first. If fatty acids were to be respired they would first be degraded to acetyl CoA and enter the pathway. Glycerol would enter the pathway after being converted to 3-phosphoglyceraldehyde (PGAL). The proteins are degraded by proteases to individual amino acids (after deamination) and depending on their structure enter the pathway within the Krebs’ cycle or as pyruvate or acetyl CoA. Thus, acetyl CoA is the common metabolite of all three (carbohydrates, proteins, and fats).

Hint

(d) Oxidative phosphorylation is the synthesis of energy-rich ATP molecules with the help of energy liberated during oxidation of reduced co-enzymes \(\left(\mathrm{NADH}, \mathrm{FADH}_{2}\right)\) produced in respiration. The enzyme required for this synthesis is called ATP synthase. It is located in \(F_{1}\) or headpiece of \(F_{0}-F_{1}\) or elementary particles present in the inner mitochondrial membrane. \(F_{1}\) particle is capable of ATP synthesis. ATP synthase becomes active in ATP formation only when there is a proton gradient having higher concentration of \(\mathrm{H}^{+}\)or protons on the \(\mathrm{F}_{0}\) side as compared to \(\mathrm{F}_{1}\) side.This higher concentration creates an electric potential across the mitochondrial membrane. The proton gradient and membrane electric potential together form proton motive force (PMF). The flow of protons through the \(F_{0}\) channel which induces \(F_{1}\) particle to function as ATP synthase. The energy of the proton gradient is used in attaching a phosphate radicle to ADP by high-energy bond. This produces ATP.

Hint

(a) Cytochrome is a group of proteins, each with an iron-containing haeme group. They are a part of the electron transport chain in mitochondria (present in cristae) and chloroplasts (in thylakoids).

Hint

(d) Anaerobic respiration or fermentation can be of two types, i.e., lactate fermentation and ethanol fermentation. Lactate fermentation produces lactic acid only as pyruvic acid produced in glycolysis is directly reduced by NADH to form lactic acid and no \(\mathrm{CO}_{2}\) is produced. Alcoholic (ethanol) fermentation involves the conversion of pyruvate to acetaldehyde, hence, \(\mathrm{CO}_{2}\) is released.

Hint

(b) Carbohydrates are usually first converted into glucose before they are used for respiration. Fats are broken down into glycerol and fatty acids first. If fatty acids were to be respired they would first be degraded to acetyl CoA and enter the pathway. Glycerol would enter the pathway after being converted to 3-phosphoglyceraldehyde ( \(\mathrm{PGAL})\). The proteins are degraded by proteases to individual amino acids (after deamination) and depending on their structure enter the pathway within the Krebs’ cycle or as pyruvate or acetyl CoA. Thus, acetyl CoA is the common metabolite of all three (carbohydrates, proteins, and fats).

Hint

(d) In the given diagram, pathway A represents glycolysis, pathway B represents Krebs’ cycle and pathway \(\mathrm{C}\) represents oxidative phosphorylation. Arrows numbered 4,8 and 12 can all be ATP.

Hint

(c) In respiration, protons accumulate in the intermembrane space of the mitochondria when electrons move through the ETS.

Hint

(b) Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates and using an endogenous electron acceptor not external or exogenous, which is usually an organic compound, as opposed to respiration where electrons are donated to an exogenous electron acceptor, such as oxygen via an electron transport chain.

Hint

(b) A biochemical pathway that serves both anabolic and catabolic process is known as the amphibolic pathway. The aerobic respiration involves both catabolism of carbohydrates and fatty acids and the synthesis of anabolic precursors for amino acid synthesis, various intermediatory metabolic products, and secondary metabolites. Thus it is called as amphibolic pathway rather than a catabolic pathway.

Hint

(a) The chemiosmotic coupling hypothesis of oxidative phosphorylation proposed by Mitchell, explains the process of ATP formation and states that it is linked to the development of a proton gradient across a membrane. ATP synthase, required for ATP synthesis is located in \(F_{1}\) particles present in the inner mitochondrial membrane and becomes active only when there is high concentration of proton on \(\mathrm{F}_{0}\) side as compared to \(\mathrm{F}_{1}\) side. The flow of proton through \(\mathrm{F}_{0}\) channel induces \(\mathrm{F}_{1}\) particle to function as ATP synthase and the energy of proton gradient produces ATP by attaching a phosphate radical to ADP.

Hint

(b) In germinating seeds, fatty acids are degraded exclusively in the glyoxysomes.
Glyoxylate cycle occurs in tissues rich in fats, such as those of germinating seeds; the enzymes involved in the cycle, which have not been found in mammals, are contained in organelles called glyoxysomes.

Hint

(d) Respiration is an energy liberating enzymatically controlled multistep catabolic process of step-wise breakdown of organic substances (hexose sugar) inside the living cells. Aerobic respiration includes the 3 major processes, glycolysis, Krebs’ cycle, and electrons transport chain. The substrate is completely broken down to form \(\mathrm{CO}_{2}\) and water. A large amount of energy is released stepwise in the form of ATP.

Hint

(c) Mitochondrion is the organelle which bears various enzymes participating in Krebs’ cycle. Each mitochondrion is covered by double membrane. The inner membrane is selectively permeable and forms foldings called cristae. The inner membrane bears oxysomes, enzymes of fatty acids, succinate dehydrogenase (of Krebs’ cycle), and an electron transport system. All other enzymes of Krebs’ cycle are present in the mitochondrial matrix.

Hint

(d) One mole of ATP liberates \(12 \mathrm{kcal}\) of energy. So \(686 \mathrm{kcal}\) will be liberated by \(686 / 12=57.1 \mathrm{ATP}\) molecules.

Hint

(a) Clostridium botulinum is an obligate anaerobe i.e. it normally lives in the absence of oxygen. Facultative anaerobes are those who generally live in oxygen but may live without oxygen in a suitable medium. Obligate aerobes can only live in the presence of oxygen while facultative aerobes generally live in oxygen but can also live without oxygen.

Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking.

Hint

(d) The last step of aerobic respiration is the oxidation of reduced coenzymes, i.e., \(\mathrm{NADH}_{2}\) and \(\mathrm{FADH}_{2}\) by molecular oxygen through FAD, ubiquinone, Cyt \(b\), Cyt \(c\), Cyt \(c_{1}\), Cyt \(a\) and Cyt \(a_{3}\). By oxidation of 1 molecule of \(\mathrm{NADH}_{2}, 3 \mathrm{ATP}\) molecules are produced and by oxidation of 1 molecule of \(\mathrm{FADH}_{2}, 2\) ATP molecules are produced. In glycolysis \(2 \mathrm{ATP}\) molecules are produced from ADP. Further \(2 \mathrm{NADH}_{2}\) produced, give \(2 \times 3=6\) ATP, on oxidative phosphorylation. Similarly in Krebs’ cycle 2 ATP molecules are produced. So the greatest number of ATP molecules are produced in the electron transport chain.

Hint

(d) Chemiosmotic hypothesis for oxidative phosphorylation (ATP synthesis) was proposed by Peter Mitchell in 1961, for this he was awarded Nobel Prize in 1978. This theory is based on the proton gradient.

Hint

(c) During glycolysis, NAD (Nicotinamide adenine dinucleotide) removes electrons from 1 , 3 -diphosphoglyceric acid using diphosphoglyceraldehyde dehydrogenase. NAD changes to \(\mathrm{NADH}_{2}\) and this is either utilized as such in anaerobic respiration or in the presence of oxygen.

Hint

(c) TCA cycle is so-called because the first stable product formed in the cycle is a tricarboxylic acid molecule, that is, citric acid. Hence, the name citric acid cycle. It is also called the Krebs cycle as it was discovered by Krebs.

Hint

(b) In alcohol fermentation triose phosphate is the electron donor while acetaldehyde is the electron acceptor.

In alcoholic fermentation, the pyruvic acid from glycolysis loses one carbon in the form of carbon dioxide to form acetaldehyde, which is reduced to ethyl alcohol by NADH. When acetaldehyde is reduced to ethyl alcohol, NADH becomes NAD+ (is oxidized). This is the fermentation that commonly occurs in yeast.

Hint

(c) Energy gain in one complete cycle of aerobic respiration is:

In aerobic respiration complete oxidation of one glucose molecule produces 38 ATP molecules. But the number of ATP molecules so produced may vary depending upon the mode of entry of \(\mathrm{NADH}_{2}\) in the mitochondria.

If the electrons of \(\mathrm{NADH}_{2}\) are accepted by malate then each molecule of \(\mathrm{NADH}_{2}\) yields \(3 \mathrm{ATP}\) molecules and the total would be 38 ATP molecules. But if the electrons of \(\mathrm{NADH}_{2}\) are accepted by FAD it yields only 2 ATP molecules making the total of 36 ATP molecules. This type of shuttle occurs in most of the eukaryotic cells.

Hint

(b) Chemoautotrophs are organisms that are capable of manufacturing their organic food utilizing chemical energy released in oxidation of some inorganic substances. The process of manufacture of food in such organisms is called chemosynthesis. It includes some aerobic bacteria. Photoautotroph obtain energy for their synthesis of food from light.

Fungi living on dead or decaying plant or animal remains and also growing on the dung of herbivores are saprophytes.

Hint

(b) Cytochromes are electron transferring proteins often regarded as enzymes. They contain iron porphyrin or copper porphyrin as prosthetic groups. Cytochrome \(a, b\) and \(c\) are harmo-chromogens widely occurring in cells and acting as oxygen carriers during cellular respiration.

Hint

(c) Lignin is a complex polymer of phenylpropane units, which are cross-linked to each other with a variety of different chemical bonds.

Lignin and its related metabolism play important roles in the growth and development of plants. As a complex phenolic polymer, lignin enhances plant cell wall rigidity, and hydrophobic properties and promotes minerals transport through the vascular bundles in plants.

Hint

(d) During aerobic respiration, 38 ATP molecules are gained. If specifically aerobic respiration in eukaryote is asked, then the answer would be 36 ATP because 2 ATP molecules are produced by FADH \({ }_{2}\) which accepts the H \({ }^{+}\)from 2 \(\mathrm{NADH}\) molecules produced in glycolysis.

Hint

(b) Cytochrome is not a coloured cell, instead, this is a respiratory pigment-mixture of iron and protein which are electron acceptors. Cytochrome are membrane-bound
hemeproteins contain heme groups and are primarily responsible for the generation of ATP via electron transport.

Hint

(a) The energy yield during aerobic respiration (36 ATP) is 18 times of that during anaerobic respiration (2 ATP).

Hint

(a) Cytochrome \(P_{450}\) is a host of enzymes that use iron to oxidise, often as part of the body’s strategy to dispose of potentially harmful substances making them more water-soluble. These are found in plants, animals, and microbes and are involved in a variety of oxidative reaction in cells. These catalyse a variety of reactions including epoxidation, \(N\)-dialkylation, \(o\) dialkylation, \(S\)-oxidation and hydroxylation. A typical cytochrome \(\mathrm{P}_{450}\) catalysed reactions is
\(
\mathrm{NADPH}+\mathrm{H}^{+}+\mathrm{O}_{2}+\mathrm{RH} \rightarrow \mathrm{NADP}^{+}+\mathrm{H}_{2} \mathrm{O}+\mathrm{R}-\mathrm{OH}
\)

Hint

(b) During glycolysis pyruvic acid is produced from glucose and is oxidatively decarboxylated to form acetyl CoA. This formation of acetyl CoA from pyruvic acid needs a multienzyme complex and 5 essential cofactors, i.e. lipoic acid, \(\mathrm{CoA}, \mathrm{Mg}^{2+}, \mathrm{NAD}\) and TPP (thiamine pyrophosphate). It results in production of 2 molecules of \(\mathrm{CO}_{2}\) and 2 molecules of \(\mathrm{NADH}_{2}\). This acetyl CoA enters mitochondria and is completely oxidised during Krebs’ cycle. Thus acetyl CoA acts as the linker of glycolysis and Krebs’ cycle.

Hint

(b) During Krebs’ cycle when succinic acid is oxidised to fumaric acid then the precipitation of FAD as electron acceptor occurs. It is the only Krebs’ cycle oxidation that does not employ a pyridine nucleotide. In this, succinate is dehydrogenated by succinate dehydrogenase. This enzyme removes two hydrogen ions and two electrons from succinate and these are then used to reduce \(\mathrm{FAD}\) to \(\mathrm{FADH}_{2}\).

Hint

(d) When oxygen is not available (anaerobic condition) yeast and some other microbes convert pyruvic acid into ethyl alcohol. It is a two-step process. In the first step pyruvic acid is decarboxylated to yield acetaldehyde and \(\mathrm{CO}_{2}\).

Hint

(d) Last step of aerobic respiration is oxidation of reduced co-enzymes, i.e., \(\mathrm{NADH}_{2}\) and \(\mathrm{FADH}_{2}\) by molecular oxygen through FAD, CoQ (ubiquinone), Cyt. \(b\), Cyt. \(c_{1}\), Cyt. \(c\), Cyt. \(a\) and Cyt \(a_{3}\). Two hydrogen atoms or electrons move from \(\mathrm{NADH}_{2}\) and travel through this ETS chain and finally combine with half molecule of \(\mathrm{O}_{2}\) to form water.

During this electron transport FAD and Fe of different cytochromes are successively reduced and oxidised and at certain points, enough energy is released which is used to bind ADP with Pi to form ATP.

Hint

(c) In chemiosmotic- coupling hypothesis, outward pumping of protons across the inner chloroplast or mitochondrial membrane results in the accumulation of protons between the outer membrane and inner membrane. A proton gradient is thus established. As protons now flow back passively down the gradient, the proton motive force is utilised to synthesise ATP.

Hint

(c) Mesosomes are the invaginations of the plasma membrane that can form into vesicles. They are found to be present in both gram-positive and gram-negative bacteria.

Mesosomes may play a role in cell wall formation during cell division and/or chromosome replication and distribution and/or electron transfer systems of respiration.

Hint

(d) End products of fermentation are ethyl alcohol, lactic acid, and \(\mathrm{CO}_{2}\).

Hint

(d) The end product of glycolysis is pyruvate. It enters mitochondria and is oxidatively decarboxylated to acetyl CoA before entering into the Krebs cycle.

Hint

(d) In the absence of \(\mathrm{O}_{2}\), fermentation or anaerobic respiration occurs. In this process pyruvic acid forms ethyl alcohol and \(\mathrm{CO}_{2}\).

Hint

(c) Glycolysis or EMP pathway is the breakdown of glucose into two molecules of pyruvic acid through a series of enzyme-mediated reactions releasing energy. Pyruvic acid is a 3 -carbon compound. In glycolysis net gain of 2 ATP and 2 \(\mathrm{NADH}_{2}\) molecules occurs.
It can be represented in equation form as:
\(
\begin{aligned}
&\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+2 \mathrm{ADP}+2 \mathrm{Pi}+2 \mathrm{NAD} \rightarrow \\
&2 \mathrm{CH}_{3} \mathrm{COCOOH}+2 \mathrm{ATP}+2 \mathrm{NADH}_{2}
\end{aligned}
\)

Hint

(c) ATP is adenosine triphosphate. It was discovered by Lohmann in 1929. It consists of a purine, adenine, a pentose sugar (ribose), and a row of three phosphates out of which the last two are attached by high energy bonds. The last phosphate bond yields an energy equivalent of \(7 \mathrm{kcal}\).

Hint

(d) In oxidative phosphorylation ATP is formed as the electrons are transferred from \(\mathrm{NADH}\) or \(\mathrm{FADH} \mathrm{H}_{2}\) to \(\mathrm{O}_{2}\) by a series of electron carriers, located in the inner membrane of mitochondria.

Hint

(a) Krebs’ cycle occurs inside the matrix of mitochondria. The cycle is also named as citric acid cycle or tricarboxylic acid cycle. It includes stepwise oxidative and cyclic degradation of activated acetate derived from pyruvic acid.

Hint

(b) Fermentation is defined as the anaerobic breakdown of carbohydrates and other organic compounds to form aldehyde, alcohol, and organic acids (lactic acid) with the help of microorganisms or their enzymes.

Hint

(c) Competitive inhibition is the reversible inhibition of enzyme activity due to the presence of substrate analogues. Non-competitive inhibition is the reduction of enzyme activity by a factor that has no real structural similarity with the substrate. Allosteric inhibition is reversible noncompetitive inhibition occurring in the case of allosteric enzymes. Herein, the inhibitors are the products or intermediates of reactions are catalyzed by the enzymes. Hence, it is also called end product inhibition or feedback inhibition.

Hint

(d) The oxidative decarboxylation of pyruvate into acetyl Co-A involves the presence of at least five essential co-factors and an enzyme complex. The co-factors involved are Mg ions, Thiamine Pyrophosphate (TPP), \(\mathrm{NAD}^{+}\), Coenzyme-A (Co-A), and lipoic acid.

Hint

(b) Active transport is the uphill movement of materials across the membrane where the solute particles move against their chemical concentration or electrochemical gradient. Hence the transport requires energy in the form of ATP. Metabolic inhibitors like cyanide inhibit the absorption of solutes by lowering the rate of respiration. Consequently, less ATP are formed. However, by adding ATP, active transport is facilitated.

It occurs in plants as in climacteric fruits and under cold stress. ATP synthesis does not occur. Reducing power present in reduced coenzymes is oxidised to produce heat energy. Therefore, the heat liberation pathway of terminal oxidation is cyanide resistant. In normal aerobic respiration, the effect of cyanide poisoning can be minimised by the immediate supply of ATP.

Hint

(c) Glucose is the chief respiratory substrate that fields maximum number of ATP molecules. Glucose is the most common substrate in glycolysis. Any other carbohydrate is first converted into glucose. During glycolysis it changes to pyruvic acid and the net gain is of \(2 \mathrm{ATP}\) and \(2 \mathrm{NADH}_{2}\) molecules. And later on, during the Krebs cycle, 30 molecules of ATP are produced. So a total of 38 ATP molecules are produced from \(1 \mathrm{~mol}\) of glucose during aerobic respiration.

Hint

(a) When oxygen is not available (anaerobic condition) yeast and some other microbes convert pyruvic acid into ethyl alcohol. It is a two-step process. In the first step pyruvic acid is decarboxylated to yield acetaldehyde and \(\mathrm{CO}_{2}\). Pyruvic acid is a \(3-\mathrm{C}\) compound and acts as an electron donor while acetaldehyde is the electron acceptor.

Hint

(a) The 1992 Nobel prize for medicine was awarded to Edmond H. Fischer and Edwin J. Krebs for their work concerning reversible protein phosphorylation as biological regulation mechanism. The winners of the 1992 Noble Prize in Physiology and Medicine discovered a ‘life switch” that turns on and off a variety of biological functions of the cell, including the breakdown of fats and the generation of chemical energy. The prize-winning discovery is known as “reversible protein phosphorylation”.

Hint

(c) Glycolysis is the first step of glucose breakdown in both animals and plants. During glycolysis 6-carbon glucose molecule is converted into 2 molecules of 2 carbon pyruvic acid. In this process net gain of \(2 \mathrm{ATP}\) and \(2 \mathrm{NADH}_{2}\) occurs. It is a common pathway for both aerobic and anaerobic modes of respiration.

Hint

(d) Kornberg and Krebs (1957) gave glyoxylate cycle in Pseudomonas bacteria. It involves the conversion of insoluble fats into soluble sugars. This occurs in germinating fatty seeds because plants are not able to transport fats from the endosperm to the root and shoot tissues of the germinating seedling, so they must convert stored lipids to a more mobile form of carbon, generally sucrose.

Hint

(a) Cyanide is a deadly poison. It stops respiration by inhibiting electron flow from cyt.-b tocyt.- \(c_{1}\). ATP is the energy currency of cell is injected in cyanide poisoning because it is necessary for cellular functions.

Hint

(a) Fats or lipids are second to carbohydrates as a source of energy. By weight, each gram mol of fat yields about \(9.3 \mathrm{kcal}\) of energy, i.e. more than
double of that yielded by glucose.

Hint

(d) Yeast cells undergo alcoholic fermentation in which glucose is first converted into pyruvic acid. In the presence of pyruvic decarboxylase, it is changed into acetaldehyde. Alcohol dehydrogenase changes it to ethyl alcohol and \(\mathrm{CO}_{2}\).

Hint

(d) Anaerobic respiration (absence of oxygen) takes place in anaerobic bacteria and in plant seeds. Anaerobic respiration occurs in the organism which can live without oxygen. In this respiration, only glycolysis takes place due to the absence of oxygen.

Hint

(a) During respiratory chain, complete degradation of one glucose molecule produced 38 ATP molecules. \(\mathrm{NAD}\) and \(\mathrm{FAD}\) is reduced to \(\mathrm{NADH} / \mathrm{FADH}_{2}\).

Hint

(d)  The end product of glycolysis is pyruvic acid whereas acetyl \(\mathrm{CoA}\) is the connecting link between glycolysis and Krebs’ cycle. The TCA cycle was first described by Krebs, 1937 as a cyclic process in which acetyl coA is oxidised to \(\mathrm{CO}_{2}\) and water. Acetyl \(\mathrm{CoA}\) combines with oxalo acetic acid to form citric acid. After a series of cyclic reactions, OAA is recycled back.

Hint

(c) Respirometer is an instrument used for measuring R.Q. and rate of respiration. The apparatus consists of a graduated tube attached at right angles to a bulbous respiratory chamber in its upper end. Desired plant material whose R.Q. is to be determined is placed in the respiratory chamber.

Hint

(b) Aerobic respiration is the process of complete oxidation of organic foods into carbon dioxide and water in presence of oxygen. It has three steps: Glycolysis – occurs in the cytoplasm, common in both aerobic and anaerobic respiration. One glucose molecule is broken into two molecules of pyruvates. The net ATP produced is 8 . Krebs cycle – it is the citric acid cycle and the process of oxidation and degradation of acetate which is obtained from pyruvate. The net ATP produced is 24 ATP. Terminal oxidation – It has different carriers of electrons which creates an electron gradient in the membranous matrix. So, the correct option is 38 ADP molecules and 38 ATP molecules.

Hint

(c) In the electron transport system the hydrogen donated by succinate is accepted by FAD which is reduced to \(\mathrm{FADH}_{2}\). This hydrogen dissociates into electrons and protons and then passes through a series of carriers involving the phenomenon of oxidation and reduction. During this flow, ATP synthesis occurs at different steps and the phenomenon is called as oxidative phosphorylation.

Hint

(a) The plants can perform photosynthesis on a range of temperature, while some cryophytes can do photosynthesis at \(35^{\circ} \mathrm{C}\). Usually the plants can perform photosynthesis between \(10^{\circ} \mathrm{C}-40^{\circ} \mathrm{C}\). The optimum temperature ranges between \(25^{\circ} \mathrm{C}-30^{\circ} \mathrm{C}\). At high temperature the enzymes are denatured and hence the photosynthetic rate declines.

Hint

(c) The food substances in living cells are oxidised in presence of oxygen, it is called aerobic respiration. Complete oxidation of food matter ( 1 mole of glucose) occurs releasing \(686 \mathrm{Kcal}\) of energy. The end of products formed are \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}_{\text {. }}\)

Hint

(d) Krebs’ cycle is intimately related to fat metabolism. Dihydroxy acetone phosphate produced in glycolysis may be converted into glycerol via glycerol – 3 – phosphate and vice-versa. Glycerol is an important constituent of fats. After \(\beta\)-oxidation, fatty acids give rise to active \(2-\mathrm{C}\) units, the acetyl-CoA which may enter the Krebs’ cycle. Thus, Acetyl-CoA is a link between glycolysis, Krebs’ cycle, and \(\)\beta\(\) oxidation of fatty acid or carbohydrate and fat metabolism.

Hint

(b) During respiration, 36 ATP molecules are produced per glucose molecule. 2 molecules of ATP are produced outside mitochondria i.e., during glycolysis and the other 34 molecules of ATP are produced inside mitochondria from Krebs’ cycle.

Hint

(d) Cytochrome \(a_{3}\) helps in the transfer of electrons to oxygen. The oxygen has a great affinity to accept the electrons and in presence of protons, a water molecule is formed.

Hint

(d) The end product of glycolysis is a three-carbon molecule of pyruvic acid. Pyruvic acid is first converted to acetyl coenzyme A by a link reaction. This acetyl coenzyme \(\mathrm{A}\) is a two-carbon molecule. This reaction results in the decarboxylation of the pyruvic acid. The acetyl coenzyme A thus formed enters the Krebs cycle and along with oxaloacetic acid forms a 6 C molecule citric acid.

Hint

(b) EMP (Embden-Meyerhof Paranas Pathway) refers to glycolysis, in which one molecule of glucose is broken down to two molecules of pyruvic acid. In this process there is a gain of \(2 \mathrm{NADH}\) \((2 \times 3\) ATP \()\) and 2 ATP, i.e. total 8 ATP.

Hint

(b) The ratio of the volume of \(\mathrm{CO}_{2}\) released to the volume of \(\mathrm{O}_{2}\) absorbed in the respiratory process is termed as the respiratory ratio or Respiratory Quotient.
R. Q. \(=\frac{\text { Volume of } \mathrm{CO}_{2} \text { evolved }}{\text { Volume of } \mathrm{O}_{2} \text { absorbed }}\)
The value of R.Q. varies from one respiratory substrate to another, e.g., R.Q. of carbohydrates is equal to 1, R.Q. of lipids and proteins are less than 1, and that of organic acid is greater than 1.

Hint

(b) During glycolysis one molecule of glucose is broken down into two molecules of pyruvic acid in the cytoplasm. Glycolysis is the common path of aerobic and anaerobic respiration.

Hint

(c) Respiratory Quotient (RQ) is the ratio of the volume of \(\mathrm{CO}_{2}\) evolved to the volume of oxygen consumed per unit time per unit weight. Therefore, \(\mathrm{RO}=\mathrm{CO}_{2} / \mathrm{O}_{2}\). It is useful in knowing the type of respiration, major transformations, and respiratory substrate.

Hint

(a) HMP pathway generates NADPH molecules which are used as reductants in the biosynthetic process under conditions when NADPH molecules are not generated by photosynthesis. It is, therefore, important in non-photosynthetic tissues such as in differentiating tissues, generating seeds, and during periods of darkness. The production of NADPH is not linked to ATP generation in the pentose phosphate pathway.

Hint

(b) Glycolysis is the sequence of enzyme-mediated reactions by which glucose is
degraded anaerobically into pyruvic acid in the cell cytoplasm. The net gain of
molecules of ATP during glycolysis is two.