Answer

Process of glycolysis is summarised as follow

Thinking Process

Krebs’ cycle is amphibolic (Gk. amphi -both, bole-throw). There is the involvement of both anabolic and catabolic reactions in this cycle.

Answer

Glucose is the favourite sulphate for respiration as carbohydrates are first converted into glucose. Prior to used for respiration. Fats are acetyl CO-A are broken down into glycerol and fatty acid which is further degraded into acetyl Co-A, while protein is degraded into, smaller units anino acids.

Respiratory process involves the breaking down of substrate is catabolic proceses. Sometime the fatty acid is required them synthesis of it occurs by withdrawing acetly Co-A. This synthesising phase is the anabolic process.

Thus, respiratory pathway involves the catabolic process (break down) and anabolic pathway synthesis of molecules using respiratory intermediates frant link, it is called as an amphibolic pathway.

Answer

An energy carrier is a highly specialised molecule that transfers, recieves and stores energy within the cell. This energy is then used to facilitate the chemical reactions within the cell. The three major types of energy carriers are ATP, NADPH and NADH.

Answer

Substrate-level phosphorylation is a type of metabolic reaction that results in the formation of Adenosine Triphosphate (ATP) or Guanosine Triphosphate (GTP) by the direct transfer and donation of a phosphoryl $\left(\mathrm{PO}_{3}\right)$ group to Adenosine Diphosphate (ADP) or Guanosine Diphosphate (GDP) from a phosphorylated reactive intermediate.

In glycolysis substrate level phosphorylation occurs in following two reactions

(i) 2 molecules of 1, 3-diphosphoglyceric acid react with 2 molecules of ADP to form 2 molecules of 3-phosphoglyceric acid and 2 molecules of ATP .

$ \underset{\text{(2 molecules)}}{\text{1,3 -diphosphoglyceric acid}} +\text{2 ADP} \xrightarrow[{\mathrm{Mg^{2+}}}]{\text { Phosphotransferase }} \underset{\text{(2 molecules)}}{\text{2-phosphoglyceric acid}} +\text{2 ATP}$

(ii) 2 molecules of phosphoenolpyruvic acid reacts with 2 molecules of ADP to form 2 molecules of pyruvic acid and 2 ATP.

$\underset{\text { (2 molecules) }}{2-\text { phosphoenolpyruvic acid 2ADP }} \xrightarrow[{\mathrm{Mg}^{2+}}]{\text { Pyruvic kinase }} \underset{(2 \text { molecules })}{\text { Pyruvic acid }+2 A T P}$

Answer

In an intermediate reaction of TCA cycle, succinyl Co-A is converted to succinic acid and one GTP molecule is synthesised through substrate level phosphorylation.

GTP formed in this reaction gives rise to ATP as follows

$$ \mathrm{GTP}+\mathrm{ADP} \rightarrow \mathrm{GDP}+\mathrm{ATP} $$

Thinking Process

All heterotrophs depend on food synthesised by autotrophs, such as cyanobacteria or green plants.

Answer

Cyanobacteria are unicellular prokaryotic organisms. Besides, some primitive cellular cell organelles, they have photosynthetic lamellae where photosynthetic pigments are present. There are chlorophyll-a c, phycocyanin and phycoerythrin.

These coloured pigments impart typical blue green colour to the bacteria and enable them to manufacture food for themselves and aquatic animals. Green plants are multicellular organisms capable of making food by using $CO_{2}, H_{2} {O}$ and light energy in special cell organelles called chloroplast.

So, bacteria and green plants make food for living organisms on earth.

Answer

The process of aerobic respiration is divided into four phases-glycolysis, TCA cycle, ETS and oxidative phosphorylation. The process of respiration and production of ATP in each phase takes place in a step-wise manner.

The product of one pathway forms the substrate of the other pathway and these substrates enter or withdrawn from the pathway according to the necessity ATP gets utilised wherever required and enzymatic rates are generally controlled. Thus, the step-wise released of energy makes the system more efficient is extracting and storing energy.

Answer

Respiration always does not require $O_{2}$. There are organisms which respire even in absence of $O_{2}$ through anaerobic respiration.

The first cells of earth i.e., chemosynthetic bacteria are the primitive organisms of early life on earth. Obtained energy by breaking down inorganic molecules like $H_{2} \mathrm{~S}, NO_{2}^{-}$, etc.

e.g., chemosynthesis occured in sulphur bacteria in the following way

$12 \mathrm{H} _2 \mathrm{S}+6 \mathrm{CO} _2 \rightarrow \mathrm{C} _6 \mathrm{H _{12}} \mathrm{O} _6+6 \mathrm{H} _2 \mathrm{O}+12 \mathrm{S} \downarrow$

Answer

There are basically two kinds of muscle fibers (i) Red muscles (ii) White muscles

Red muscles work for a longer time continuously because

(i) These muscle fibres are dark red which is due to the presence of red haemoprotein called myoglobin. Myoglobin binds and stores oxygen as oxymyoglobin in the red fibres. Oxymyoglobin releases oxygen for utilisation during muscle contraction.

(ii) Mitochondria are more in number, hence they work for long periods of time.

(iii) Red muscles have less sarcoplasmic reticulum.

(iv) They carry out considerable aerobic oxidation without accumulating much lactic acid. Thus, red muscle fibres can contract for a longer period without fatigue.

(v) These muscle fibres have slow rate of contraction for long periods. e.g., extensor muscles of the human back.

Thinking Process

Respiration is a catabolic process occurring in all living cells providing them energy to stay alive and to remain metabolically active.

Answer

The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration is as given

Answer

RuBP Carboxylase This is a part of dark reaction of photosynthesis. It catalyses the fixing of $CO_{2}$ in $C_{3}$ cycle.

PEPcase This is a part of photosynthesis of $C_{4}$ plants. It catalyses the reaction of fixing of $CO_{2}$ to form first stable product oxaloacetate. 4 carbon compound.

Pyruvate dehydrogenase It is involved in aerobic respiration and catalyses the reaction of formation of acetyl Co-A from pyruvic acid. It requires the participation of NAD and Co-enzyme-A.

$ \text { Pyruvic acid }+\mathrm{Co}-\mathrm{A}+\mathrm{NAD}^{+} \xrightarrow[{\text { Pyruvate dehydrogenase }}]{\mathrm{Mg}^{2+}} \text { Acetyl } \mathrm{Co}-\mathrm{A}+\mathrm{CO}_{2}+\mathrm{NADH}+\mathrm{H}^{+} $

ATPase It is a part of both respiration and photosynthesis. Both these processes uses electron transport chain and associated proton pump and ATP synthase as a key part of process. ETC uses the energy to pump hydrogen ions across a membrane.

The protons flows back through ATP synthase, driving the production of ATP.

Cytochrome Oxidase This is involved in both respiration and photosynthesis. It is an electron carrier in the electron transport chain.

Hexokinase This enzyme is also involved in, respiration. In glycolysis, it catalyses the first reaction, i.e., formation of glucose -6- phosphate from glucose molecule. It uses one ATP molecule which transfers $\mathrm{PO}_{4}$ group to glucose molecules.

Lactate Dehydrogenase

This enzyme is involved in anaerobic respiration in bacteria Lactobacillus.

Pyruvic acid formed at the end of glycolysis is converted to lactic acid by homo-fermentative lactic acid bacteria. Hydrogen from NADH molecule is transferred to pyruvate is transferred to pyruvate molecule lactic acid molecule leading formation of acid.

$ \underset{\text { Pyruvic acid }}{CH_{3} \mathrm{COCOOH}}+\mathrm{NADH} . \quad \xrightarrow[{\text { Dehydrogenase }}]{\text { Lactate }} \underset{\text { Lactic acid }}{C_{3} H_{6} O_{3}} +\mathrm{NAD} $

Thinking Process

Gaseous exchange is an important phenomenon in plants. Plants take up $CO_{2}$ for photosynthesis and release $O_{2}$ as by product. They have devised structural adaptations in them to carry out this phenomenon.

Answer

The old tree trunk is covered by dead woody tissue called cork. The epidermal layers of such tree get ruptured and outer cortical cells are loosely arranged. These structures are called as lenticels.

These are the sites of gases exchange and transpiration.

Answer

The following figure shows the process of glycolysis, and sites for yielding energy during glycolysis

Thus, ATP is produced during degradation of 1,3 biphosphoglyceric acid into 3-phosphoglyceric acid and during degradation of 2-phosphoenol pyruvate into pyruvic acid.

Answer

Pyruvate is synthesised in cytoplasm of the cell by the process of glycolysis. 1 molecule of glucose forms 2 molecules of pyruvate through a series of reactions.

Pyruvic acid dehydrogenase catalyses the reaction in which pyruvate forms acetyl Co-A. It requires $\mathrm{NAD}^{+}$, Co-enzyme $\mathrm{A}$ and $\mathrm{Mg}^{2+}$ ions for its activity. The reaction is as follows

$ \text { Pyruvic acid }+\mathrm{Co}-\mathrm{A}+\mathrm{NAD}^{+} \xrightarrow[{\text { Pyruvate Dehydrogenase }}]{\mathrm{Mg}^{2+}} \text { Acetyl } \mathrm{Co}-\mathrm{A}+\mathrm{NADH}+\mathrm{H}^{+}+\mathrm{CO}_{2} \uparrow $

Answer

Living cells obtain energy through respiration. It is the process of generating energy in the form of ATP molecules by breaking down food molecules like glucose, fats, etc.

The process starts with glycolysis which occurs in cytoplasm producing pyruvic acid. It is then converted to acetyl Co-A, which enters mitochondrial matrix. This initiates the tricarboxylic acid cycle.

This cycle is said to be amphibolic because many intermediate compounds formed in this cycle act as precursors for biosynthesis of many important biological molecules, i.e., co-enzymes, vitamins, hormones. Besides this, many molecules, i.e., fatty acids, aminoacids, co-enzymes etc, can enter this cycle directly.

Acetyl Co-A is related to synthesis and breakdown of fatty acids, steroids, carotenoids terpenes and aromatic compounds. $\alpha$ - ketoglutarate and oxaloacetate are row materials for synthesis of amino acids like glutamate and aspartate and also pyrimidines and alkaloids. Succinyl forms pyrroole compunds like cytochrome and chlorophyll.

So, it is the cycle where both breakdown and synthesis reactions keep on going simultaneously. the following figure shows interrelationship among netabolic pathway showing respiration mediated break down of different organic molecule.

Answer

Krebs’ cycle occurs in the matrix of mitochondria. It is depicted in the following series of reactions

Electron transport chain is carried out in the inner mitochondria membrane

The inner mitochondrial membrane is specific about possessing proton $\left(\mathrm{H}^{+}\right)$and electron $\left(e^{-}\right)$acceptors in a particular sequence called electron transport chain. It has four enzyme complexes.

The electrons either follow the pathway of complexes I, III and IV or II, III and IV depending upon the substrates from Krebs’ cycle.

The transfer of electrons and hydrogen atoms takes place in the following way

Complex I Consists of flavoproteins of NADH dehydrogenase ( $F P_{N}$ ) of which FMN is the prosthetic group. Combined with the flavoprotein is non-heme iron of NADH dehydrogenase. This complex spans inner mitochondrial membrane and is able to translocate protons across it from matrix side to outer side.

Complex II Consists of flavoprotein of succinate dehydrogenase, of which FAD is the prosthetic group. Combined with the flavoprotein is non-heme iron of succinate dehydrogenase.

Between complexes II and III is the mobile carrier coenzyme-Q (Co-Q) or ubiquinone (UQ).

Complex III Consists of cytochrome-b and cytochrome- $c_{1}$. Associated with cytochrome- $b$ is non-heme iron of complex III. Between complexes III and IV is the mobile carrier cytochrome-c.

Complex IV Consists of cytochrome-a and cytochrome- $a_{3}$, and bound copper that are required for this complex reaction to occur. This cytochrome also called cytochrome oxidase, is the only electron carrier in which the heme iron has a free ligand that can react directly with molecular oxygen.

Thus, hydride ions are transferred from the substance to be oxidised to $\mathrm{NAD}^{+}$. From NAD the hydrogen atoms are transferred to FMN of flavoprotein 1 (Fp’N). After FMN the hydrogen atom undergoes ionisation, i.e., it splits into an electron and a proton.

In further stages there is no longer a transfer of hydrogens but of electrons. The electron passes to co-enzyme- $Q$, and from co-enzyme $Q$ to cytochromes- $b, c_{1}, c, a$ and $a_{3}$. The proton is released free.

As the hydrogen atom or electron passes down by $F_{0}-\mathrm{F}_{1}$ particle the chain, there is simultaneous oxidation of one coenzyme and reduction at another steps. Oxygen is able to diffuse indside the mitochondria.

It is converted to anionic form $O_{2}^{-}$, combines with $2 \mathrm{H}^{+}$and forms metabolic water reduced co-enzyme $\mathrm{NADH}+\mathrm{H}^{+}$helps in pushing out three pairs of $\mathrm{H}^{+}$to outer chamber while $\mathrm{FADH}_{2}$ sends two pairs of $\mathrm{H}^{+}$to outer chamber.

Oxidative phosphorylation is the synthesis of energy rich ATP molecules, with the help of energy liberated during oxidation of reduced co-enzyme $\left(NADH_{2}, FADH_{2}\right)$ produced in respiration. The enzyme required for this synthesis is called ATP synthase present in inner mitochondria membrane.

The following figures shows this process

Thinking Process

The pyruvic acid is the end product of glycolysis. It is further broken down depending on the circumstances and requirement of the cell.

Answer

The metabolic pathway given in the figure is fermentation. The products marked as $a, b, c$ and $d$ represents

a-Glyceraldehyde 3 phosphate,

b-Phosphoenol pyruvic acid

c-Ethanol,

d-Lactic acid

The fermentation is of two types

(i) Alcohol Fermentation in Yeast Fermentation is an incomplete oxidation of glucose under anaerobic condition. Alcohol fermentation in yeast occurs in 2 sets of reaction thus, converting pyruvic acid into ethanol and $\mathrm{CO}_{2}$.

A. In the first step, pyruvic acid is decarboxylated (equation I), resulting in the formation of acetaldehyde and $\mathrm{CO}_{2}$.

$ \underset{\text { Pyruvic acid }}{2 CH_{3} \mathrm{COCOOH}} \xrightarrow{\text { Pyruvic decarboxylase }} \underset{\text { Acetaldehyde }}{2 CH_{3} \mathrm{CHO}} \quad \quad \quad \quad\quad \text{(i)} $

B. In the second step acetaldehyde is reduced to alcohol by $\mathrm{NADH}_{2}$ (equation (ii))

(ii) Lactic Acid Fermentation in Muscles

In animal tissue like muscles, during exercise, when oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is $\mathrm{NADH} \mathrm{HH}^{+}$which is reoxidised to $\mathrm{NAD}^{+}$in the subsequent processes.

Two applications of fermentation process are

(i) It helps in manufacture of ethyl alcohol.

(ii) It also helps in curdling of milk to make curd aided by bacteria Lactobacillus.

Thinking Process

Phosphorylation of ATP from ADP $+\mathrm{Pi}$ is an important step occurring in every cell to obtain energy. This process takes place in the inner mitochondrial membrane

Answer

Symbol A, B, C, D and E in the diagram represents

A______ATP

B______ $F_{1}$ particle

C______ Pi

D______ $2 \mathrm{H}^{+}$

E______ inner mitochondria membrane.

Answer

Role of $\mathrm{O}_{2}$ in Aerobic Respiration

The respiration of glucose starts with glycolysis in cytoplasm, followed by in Krebs’ cycle and finally Electron Transport Chain (ETC) in inner mitochondrial membrane. The requirement of $\mathrm{O}_{2}$ is at the end of ETC.

Where, it acts as final hydrogen acceptor. $\mathrm{O}_{2}$ is responsible for removing electrons from the system. If oxygen is not available, electrons could not be passed through the co-enzymes, inturn proton pump will not be established and ATP will not be produced via oxidative phosphorylation. Thus Oxygen play a critical role in aerobic respiration in mitochondrial matrix.

Answer

The calculations of the net gain of ATP for every glucose molecule oxidised can be made on the following assumptions

(i) There is sequential pathway that follows, i.e., glycolysis, TCA cycle and ETS in cytoplasm, mitochondrial matrix and inner mitochondrial membrane respectively.

(ii) NADH, synthesised in glycolysis enters in to ETC for phosphorylation.

(iii) None of the intermediates in the pathway are utilised to synthesise any other compound.

(iv) Glucose forms respiratory substrate.

These assumptions are not valid for a living system because of following reasons

(i) These all pathways work simultaneously and do not take place one after the other.

(ii) ATP is utilised when needed.

(iii) Rate of enzyme actions is controlled by multiple means.

Comparisan between fermentation and aerobic respiration are as follows