Unit 7 – Bioenergetics (Exercise Questions)

ANSWER THE FOLLOWING QUESTIONS.
Q.1. How would you define bioenergetics while relating it to the oxidation-reduction reactions in living system?
Q.2. Interpret that ATP is the chief energy currency of all cells.
Q.3 Why is said that all life forms are dependent on photosynthesis?
Q.4. What is the role of chlorophyll and light in photosynthesis?
Q.5. Outline the process involved in photosynthesis?
Q.6. What structures and phenomena are involved in the intake of carbon dioxide and water by plants?
Q.7. State how the varying light intensity, carbon dioxide concentration and temperature affect the rate of photosynthesis.
Q.8. What is the importance of anaerobic respiration?
Q.9. Outline the mechanism of respiration while defining Glycolysis, Krebs cycle and electron transport chain?
Q.10. Draw a comparison of aerobic and anaerobic respiration.
Q.11. In what way the respiratory energy is used in the body of organisms?
Q.12. How will you compare respiration and photosynthesis?
Q.13. How the leaf is structurally adapted for photosynthesis?
SHORT QUESTIONS – TEXT EXERCISE
Q.1. Why is it said that all life forms are dependent on photosynthesis?
Q.2. What structures and phenomena are involved in the intake of carbon dioxide arid water by plants?
Q.3. In what ways the respiratory energy is used in the body of organisms?
Q.4. What is the importance of anaerobic respiration?

Q.1. How would you define bioenergetics while relating it to the oxidation-reduction reactions in living system?
Answer:
Definition
The quantitative study of energy relationships & conversions in different forms is called Bioenergetics.
For example, the solar energy is converted into chemical energy by the plants in the process of photosynthesis. Similarly, this chemical energy is utilized in to some metabolic reaction producing heat of some other form of
energy etc.
Thus these energy conversions obey the laws of thermodynamics.
How and Why Organisms Need Energy?
How?
For any organism, the ultimate source of energy is its food obtained by any means. This food is when, metabolized in the body release some energy which was previously present in the form of Potential Energy in the bonds of food particles/ molecules. When the food is catabolized this potential energy is converted to kinetic energy. Some of this released energy is converted to chemical energy (ATP) so that it can be stored in the body. This chemical energy is actually a form of potential energy. So when body requires energy for performing some task / activity, this potential energy is converted again to kinetic energy by the hydrolysis of ATP.
Why?
All organisms. need free energy for performing different activities & running the various processes of metabolism.
For Example
(i) For the synthesis of proteins
(ii) Active Transport
(iii) Phagocytosis
(iv) Pinocytosis
(v) Mechanical work
(vi) Maintaining temperature of body
(vii) Nerve impulse etc.
Role of Redox reactions:
Redox
The term Redox is a combination of two processes Reduction & Oxidation. So, a redox reaction involves’ both these
processes simultaneously.
Oxidation Reduction:
Oxidation-reduction can be defined as
(i) Gain of oxygen
(ii) Loss of Hydrogen
(iii) Loss of electrons
Where as reduction is referred to
(i) Loss of oxygen
(ii) Gain of Hydrogen
(iii) Gain of electrons
These two processes are constantly involved in flow of energy. Is the energy generation & utilization go in cyclic manner by these reactions.

Q.2. Interpret that ATP is the chief energy currency of all cells.
Answer:
ATP:
Adenosine Triphosphate A P is the cells immediate source of energy. It was 6 ATP is a kind of chemical discovered by Karl Lehman (1919) Fitz link between catabolism & Lipmann (1941) proposed that ATP is the major energy source in the cell & he got Nobel Prize.
Composition
Its name indicates that it contains adenosine and three-phosphate group. Adenosine is formed of a nitrogenous base called adenine and a sugar called ribose. In A TP three phosphate groups are attached to
the adenosine in a series one after the other.
Adenosine’ PO₄  PO ∼ PO₄
Examples of cell’s Reactions, which ATP drive.
(i) Anabolism of macromolecules (e.g., nucleic acids, carbohydrates, proteins, lipids etc).
(ii) Movement.
(iii) Transmission of nerve impulse.
(iv) Exo & Endocytosis
(v) Active Transport
ATP Hydrolysis & Generation
Is the symbol used for the high-energy covalent bond between two phosphates & termed as tilde.
Hydrolysis
On hydrolysis, A TP becomes ADP as one-terminal phosphate group (P i) is removed releasing about 7.3 k cal /mole. When the cell requires more energy & other sources of energy not easily available, then this ADP further breaks down & result into AMP, as follows.
Hydrolysis
ADP + H₂0⇔ ADP + P i + (7.3 K cal/ mole)
Generation  Energy
Hydrolysis
ATP + H₂0 ⇔AMP + P i + (7.3 K cal/ mole)
Generation
Thus the ATP hydrolysis & generation takes place during the metabolic reaction on cell’s demand.

Q.3 Why is said that all life forms are dependent on photosynthesis?
Answer:
Water &CO₂ are the essential raw material, plants use to make glucose.
Sources of Raw Material:
The roots of plants are adapted to absorb water & mineral from soil by the process of diffusion Active / Passive Transport and Osmosis to facilitate “the movement of water & minerals, roots provides large surface area by having root lairs, which penetrate the soil very deep. Root lairs are present in large number so that providing water & minerals to move from soil (High conc.) to root lairs (low conc.)
Water and Mineral Movement:
When water moves from soil to root, the root sap becomes diluted & the concentration of minerals in the root becomes low facilitating their osmosis, from soil to roots. Thus as the water moves from roots to stem (upward
movement) the minerals also move in same manner by the help of xylem vessels. Then through these vessels “the sap (Water + Minerals) gets transported to leaves so that there, they can be utilized for driving Photosynthesis .
C02
CO2 enters the leaves from air through pores in leaves. These pores are called Stomata (stoma ~ singular). The water present in the thin layer outside the mesophyll cells which absorbs the CO₂ from air by diffusion. And then, CO₂ diffuses into the mesophyll cells from water.

Q.4. What is the role of chlorophyll and light in photosynthesis?
Answer:
Light:
It is the driving energy of photosynthesis
Light is visible part of solar radiations. Light behaves as waves as well as short of energy called photons. The visible light ranges from about 389 to 750nm in wavelength. The amount of energy of a photon is inversely related to the wavelength of the light. Thus, a photon of violet light has nearly twice as much energy as a photon of red light. However in photosynthesis, number of quanta (photons) is more effective than the energy of quanta.
As the sunlight comprises of wide range of wavelengths. Only the rays of suitable wavelengths are. absorbed by the chlorophylls.
Absorption spectrum of chlorophylls indicates that absorption, is maximum in blue and red parts of the spectrum.
On absorption of light the electrons of chlorophyll get excited. The electron carries of ETC (Electron Transport Chain) then transport them &during their transport Chemiosmosis or formation of ATP & reduction of NADP to
NADPH takes place.
Chlorophyll
These are different kinds of chlorophylls. The chlorophyll a, b, c and d are found in eukaryotic photosynthetic plants and algae while the other are found in photosynthetic bacteria and are known as bacterial chlorophylls.
Chlorophylls absorb mainly violet-blue and orange red wavelengths. Green and yellow wave lengths are least absorbed by chlorophylls and are transmitted or reflected, although the yellow are often masked by dark green colour, hence plants appear green.
Action spectrum
Chlorophyll a is the must abundant and the must important photosynthetic pigment as it takes part directly in the light all photosynthetic organisms except photosynthetic bacteria.
Chlorophyll -b is’ found along with chlorophyll a in all green plants and green algae. Chlorophylls are insoluble in water but soluble in organic solvents.
Carotenoids – accessory pigments
Carotenoids are yellow’ and red to orange pigments that absorb strongly the blue violet range different wavelengths than the chlorophyll absorbs. So they broaden the spectrum of light that provides energy for photosynthesis. Thus chlorophyll b is called accessory pigment because it absorbs light and transfers the energy to chlorophyll a, which then initiates the light reaction. It is generally believed that the order of transfer of energy is:
Carotenoids → Chlorophyll b ) →Chlorophyll a
Some carotenoids protect chlorophyll from intense light by absorbing and dissipating excessive light energy, rather than transmitting energy to chlorophyll.

Q.5. Outline the process involved in photosynthesis?
Answer:
Respiration
The gaseous exchange in plant is not very evident during the daytime “as the products of respiration ie. carbon dioxide and water are the reactants in the process of photosynthesis. So the carbon dioxide and water produced in the respiration are utilized in photosynthesis, occurring in the daylight. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant form outside for photosynthesis.
In the daytime the plant therefore, takes in carbon dioxide and expel out oxygen. The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria.

Q.6. What structures and phenomena are involved in the intake of carbon dioxide and water by plants?
Answer:
Water and Mineral Movement:
When water moves from soil to root, the root sap becomes diluted & the concentration of minerals in the root becomes low facilitating their osmosis, from soil to roots. Thus as the water moves from roots to stem (upward
movement) the minerals also move in same manner by the help of xylem vessels. Then through these vessels “the sap (Water + Minerals) gets transported to leaves so that there, they can be utilized for driving Photosynthesis .
C0₂
CO2 enters the leaves from air through pores in leaves. These pores are called Stomata (stoma ~ singular). The water present in the thin layer outside the mesophyll cells which absorbs the CO₂ from air by diffusion. And then, CO₂ diffuses into the mesophyll cells from water.

Q.7. State how the varying light intensity, carbon dioxide concentration and temperature affect the rate of photosynthesis.
Answer:
Limiting factor can be any environmental factor e.g., absence of some metabolic reaction or deficiency of light or in avail ability of suitable temperature, CO₂, water etc.
Effect of Absence! Deficiency of light:
The rate of photosynthesis is proportional to light intensity up to a certain limit. As the light intensity increases the rate of reaction also increases but at very high light intensity the rate of reaction doesn’t change.
Effect of suitable temperature availability:
The process of photosynthesis goes well in certain range of temperature. If temperature exceeds this range the reaction retards / stops. Decrease in temperature decreases the rate of reaction.
Effect of C0₂ Amount Provided:
CO₂ is the major reactant of photosynthesis. So, it’s high amount will induce rate of photosynthesis to increase only when other factors are ideally present / available.
Rubisco
is an enzyme, which catalyzes the first step of photosynthesis. It has affinity both for CO2 & O2 So in the presence of large amount of CO₂, it binds O₂ when large concentration of O2 is available (to bring about respiration).
That mean in presence of large amount of oxygen, Rubisco will not be available to catalyze fixation of CO₂
In contrast, if concentration of available CO₂ exceeds the threshold .level, the stomata get closed & thus rate of photosynthesis declines.

Q.8. What is the importance of anaerobic respiration?
Answer:
Definition: Living organisms need energy, which is provided by the phenomenon of respiration. It is the process by which organism’s breakdown’ complex compounds containing carbon to get a maximum of usable energy. Generally respiration means the exchange of respiratory. gases (C0₂ and O₂) between the organism and its environment. This
exchange is called external respiration, which is followed by cellular respiration. Cellular respiration is the process. by which energy is made available to cells in a step-be-step breakdown of C-chain molecules in the cells.
AEROBIC RESPIRATION
In most of the higher and larger organisms, the glucose etc. is oxidized by using molecular oxygen. This type of respiration is known as aerobic respiration.
In aerobic respiration a mole of glucose is oxidized completely into carbon dioxide and water releasing enormous amount of energy. One glucose molecule in this respiration produces 686, 000 calories of energy. Aerobic
respiration ,thus produces 20 times more energy than the anaerobic respiration.
There are two stages of aerobic respiration.
(i) External respiration (ii) Internal respiration
(i) External respiration
In this stage the organisms take the air (containing oxygen) into then bodies. This stage includes the transport of oxygen obtained from the inhaled oxygen to each cell of the body.
(ii) Internal respiration
The second stage, which is called internal respiration, consists of the oxidation of glucose, amino acid and fatty acids etc., with molecular oxygen. This respiration is also known as cellular respiration as it occurs within cells.
In the internal or cellular respiration glucose and other compounds art passed through such enzymatic reactions, which release the chemical energy gradually in small amounts, with the help of which’ ATP molecule! are.
There are two, methods of respiration in the organisms.
Anaerobic respiration
Some organisms oxidize their food without using any molecular oxygen. This is known as anaerobic respiration. In this type of respiration considerably less amount of energy is produced as compared with the other type of respiration. It is also called fermentation.
In anaerobic respiration, a glucose molecule is broken down into two molecules of lactic acid with a release of only 47,000 calories of energy.
Glucose →2Lactic acid + Energy (47,000 calories)
(i) Alcoholic Fermentation
In primitive cells and in some eukaryotic cells such as yeast, pyruvic acid is further broken down by alcoholic fermentation into alcohol (C₂H₅ OH) and CO₂
2(C₃ H₄O₃)             2(C₂H₅OH)    +   2CO2
Pyruvic acid              Alcohol
(ii) Lactic acid Fermentation
In lactic acid fermentation, each pyruvic acid molecule is converted into lactic acid C) H603 in the absence of oxygen gas.
2(C₃H₄O₃)     +        4H                   2(C₃HO₃)
Pyruvic acid                                        Lactic acid
Both alcoholic and lactic acid fermentations yield about 2% of the energy present within the chemical bonds of glucose, which’ is converted into adenosine triphosphate (ATP).

Q.9. Outline the mechanism of respiration while defining Glycolysis, Krebs cycle and electron transport chain?
Answer:
Cellular Respiration:
It is divided into few stages
Glycolysis
Pyruvic acid oxidation
Krebs’s cycle /citric acid cycle
Respiratory chain
(i) Glycolysis:
Glyco means “Glucose” & lysis means “break down”. So this is the process of glucose break down & formation of pyruvic acid, It can take place in absence/ presence of oxygen, both resulting in same product. A series of steps involved in glycolysis require specific enzymes.
Glycolysis can be divided into two phases:
Preparatory phase
Oxidative phase
Preparatory phase
The first step in glycolysis is the transfer of phosphate group from ATP to the 6th carbon atom of glucose; as a result a molecule of glucose 6 phosphate is formed. An enzyme catalyzes the conversion of glucose 6 phosphate to its isomer, fructose 6 phosphate. At this stage another ATP molecule transfer a second phosphate group at l^st carbon atom of the glucose. The product is fructose-I, 6- bisphosphate. The next step in glycolysis is the enzymatic splitting of fructose-I, 6-di phosphate into 3-phospoglyceraldehye and dihydroxy acetone phosphate. These two molecules are isomers and are readily interconnected by enzymes.
Oxidative phase
In this phase two electrons or two hydrogen atoms are removed from the molecule of3-phosphoglyceraldehde (PGAL) and transferred to a molecule 0f NAD. During this reaction of second phosphate group is donated to the
molecule, which resulted in the formation of 1,3-diphosphoglyceric acid (DPGA). The oxidation of PGAL is an energy yielding process. At the very next step in glycolysis ATP is formed. The end product of this reaction is3-phosphoglyceric acid. In the next step 3-phosphoglyceric acid is converted to 2phosphoglyceric acid. From 2-phosphoglyceric acid a molecule of water is removed and the product is phosphoenol pyruvic acid (PEP). PEP
then gives up its high-energy phosphate to convert a second molecule of ADP to ATP. The product is pyruvic acid (C₃ H₄O₃).
(ii) PYRUVIC ACID OXIDATION
Pyruvic acid, the end product of glycolysis does not enter the Krebs cycle directly. The pyruvic acid is first changed into 2-carbon acetic acid molecule. One carbon is released as CO2. Acetic acid on entering the mitochondrion unites with coenzymes A (CoA) to form acetyl CoA. In addition more hydrogen is transferred to NAD.

(iii) Krebs’s cycle:
Sir Hans Krebs discovered, Krebs’s cycle. It starts after the formation of Acetyl CO-A. Krebs cycle takes place in mitochondrial membrane & comprises of following steps:
1- The union of acetyle CoA with oxaloacetate to form citrate. In this process molecule of CoA is regenerated and one molecule of water is used.
Oxaloacetate is a 4-carbon acid with two carboxyl groups. Citrate thus has 6-carbo atoms and three carboxyl groups.
2- In the next reactions NAD mediated oxidation takes place and citrate is changed into ketoglutarate.
3- Ketoglutarate is then oxidized & decarboxylated simultaneously. Thus a new product Succinate is formed. One ATP molecule is also synthesized.
4- The next step in the Krebs cycle is the oxidation of succinate to fumarate. Once again, two hydrogen atoms are removed, but this time. the oxidizing agent is a coenzyme called flavin adenine dinucloetide (FAD), which is reduced to FADH₂.
5- With the addition of another molecule of water, fumigate is converted to malate.
6- Anther NAD mediated oxidation of malate produces oxaloacetate, the original 4-carbon molecule.
(iv) Respiratory Chain.
NADH formed in Krebs’s cycle transfers its hydrogen atom to the electron carriers of respiratory’ chains. This transfer brings about transport of electron down to all carriers resulting, in a series or reduction oxidation process & ultimately releasing O₂ & water is formed. Electron carriers are
(i) Coenzyme Q
(ii) Series of cytochromes enzymes
(iii) Molecular oxygen
The repiratory electron transport chain and its coupling with oxidative phosphorylation.

Q.10. Draw a comparison of aerobic and anaerobic respiration.
Answer:

Q.11. In what way the respiratory energy is used in the body of organisms?
Answer:
For any organism, the ultimate source of energy is its food obtained by any means. This food is when, metabolized in the body release some energy which was previously present in the form of Potential Energy in the bonds
of food particles/ molecules. When the food is catabolized this potential energy is converted to kinetic energy. Some of this released energy is converted to chemical energy (ATP) so that it can be stored in the body.
This chemical energy is actually a form of potential energy. So when body requires energy for performing some task / activity, this potential energy is converted again to kinetic energy by the hydrolysis of ATP.
Why?
All organisms. need free energy for performing different activities & running the various processes of metabolism.

Q.12. How will you compare respiration and photosynthesis?
Answer:
Respiration
The gaseous exchange in plant is not very evident during the daytime as the products of respiration i.e. carbon dioxide and water are the reactants in the process of photosynthesis. So the carbon dioxide and water produced in the respiration are utilized in photosynthesis, occurring in the daylight. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant form outside for photosynthesis.
In the daytime the plant therefore, takes in carbon dioxide and expel out oxygen. The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria.

Q.13. How the leaf is structurally adapted for photosynthesis?
Answer:
In aerobic respiration the organisms utilize the environmental oxygen to oxidize their organic compounds as a result of which carbon dioxide is produced. The carbon dioxide is toxic to the organism and it is, therefore,
necessary that the organism should expel the carbon dioxide out of their bodies in some way.
The aerobic organisms in the process of respiration take up oxygen from their environment and eliminate carbon dioxide from their bodies to the environment.
The exchange of gases of between the organisms and their environment form the first stage of aerobic respiration.
SHORT QUESTIONS – TEXT EXERCISE

Q.1. Why is it said that all life forms are dependent on photosynthesis?
Answer:
All organisms need free energy for performing different activities & running the various processes of metabolism.
For Example
(i) For the synthesis of proteins
(ii) Active Transport
(iii) Phagocytosis
(iv) Pinocytosis
(v) Mechanical work
(vi) Maintaining temperature of body
(vii) Nerve impulse etc.

Q.2. What structures and phenomena are involved in the intake of carbon dioxide arid water by plants?
Answer:
Intake of Water and Carbon dioxide
Water and carbon dioxide are the raw materials of photosynthesis. Plants have mechanisms or the intake and transport of these raw materials. Water, present in soil, is absorbed by roots and root hairs through osmosis. This water is eventually transported to leaves through xylem vessels.
The air that enters leaf through tiny pores (stomata) reaches into the air spaces present around mesophyll cells. This air carries CO2, which gets absorbed in the thin layer of water surrounding
mesophyll cells. From here, the carbon dioxide diffuses into mesophyll cells.

Q.3. In what ways the respiratory energy is used in the body of organisms?
Answer:
(i) Respiratory Energy
Organisms utilize oxygen for the breakdown of C-H bonds- present in the food in their cells. This breakdown yields energy which is transformed into ATP.
(ii) A TP is the cell’s currency
Because it stores chemical energy in its phosphate bonds & its hydrolysis (i.e. removal of phosphate groups) results in immediate source of kinetic energy available to drive any metabolic process ..
Each phosphate bond stores about 7.3 Kcal/mole.

Q.4. What is the importance of anaerobic respiration?
Answer:
(i) Source of energy for anaerobic organisms.
(ii) Source of energy for aerobic organisms in short supply of O₂
(iii) Source of many products ethanol, cheese etc.