Biology For Class IX - Chapter No.6 - ENZYMES - Questions and Answers

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CHAPTER 6
ENZYMES

By Mrs. Ayesha Arif
(Jauhar Progressive School)

Q.1: Define metabolic reactions and metabolism?
Ans: METABOLIC REACTIONS AND METABOLISM:
Life is another name of activity, therefore thousands of chemical reactions take place in the body of an organism. These reactions of an organism are collectively called metabolic reactions and This phenomenon of chemical activity called metabolism.

Q.2: A: Briefly describe the types of metabolic activities?
Ans: TYPES OF METABOLIC ACTIVITIES:
The metabolic activities are always of two types:

1. Anabolism or Constructive Reaction
2. Catabolism or Destructive Reaction

Anabolism or Constructive Reaction:
In constructive reactions large molecules are formed to form a structure of cell or body. These reactions are called anabolic reactions and this type of metabolism is called anabolism.

Catabolism or Destructive Reaction:
The destructive reaction in which large molecules breakdown in small molecules to produce energy or to re-utilize further or to discard called catabolic reactions. The type of this metabolic activity is called catabolism.

Q.3: What is activation energy? Or Define activation energy?
Ans: ACTIVATION ENERGY:
Definition:
The minimum amount of energy require to activate a reaction called activation energy.

OR

Living body requires some facilitators. These facilitators help to perform biochemical reactions at low energy. This minimum amount of energy is called activation energy.

e.g. the activation energy needed to break a glucose molecule initially requires energy of 2 ATP molecules. If this amount is high the difficult will be the reaction or vice versa.

Explanation:
The chemical reaction requires particular conditions to carry down at proper rate, especially temperature and pressure. The conditions of temperature and pressure inside cell or organism are generally found not suitable for chemical reactions e.g. inside human body normal temperature remain 37 °C and pressure is 120/80 mm of Hg. These conditions of temperature and pressure are not enough to perform any chemical reactions. The activation energy needed to perform such biochemical or metabolic reactions without altering these conditions.

Q.4: What are enzymes?
Ans: ENZYMES: (En=inside, zyme = yeast)
The name was coined due to observation when yeast was introduced in fruit sap which converted it into alcohol.
Definition:
The high amount of activation energy cannot be provided by organism itself therefore they require some facilitators to reduce this activation energy. These facilitators are special molecules made up of mostly protein called enzymes. Thus the enzymes are the biocatalyst which facilitate chemical reaction by lowering activation energy.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

OR

The molecules which facilitate biochemical reaction by reducing activation energy called enzymes. Enzymes are biocatalyst made up of mostly proteins and therefore are three dimensionally folded chains of amino acids with a specific shape.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

Q.5: Describe characteristics of enzymes.
Ans: CHARACTERISTICS OF ENZYMES:

1. Nature:
   Enzymes are biocatalyst, made up of mostly proteins and have three dimensionally folded chains of amino acids with a specific shape, held together by Hydrogen bonds.
   
   
2. Speed Up:
   Enzymes speed up reactions by bringing reactants together and reducing the activation energy required to start the reaction (enzymatic reaction).
   
   
3. Catalyst:
   When an enzyme starts a chemical reaction, catalyzes the reaction hence does not utilized itself which means even a single or little amount of enzyme can start a reaction and catalyze fastly. Their presence does not affect the nature or properties of end products.
   
   
4. Substrate:
   Reactants of enzyme are called substrate.
   They are very specific in their action; a single enzyme catalyzes only a single chemical reaction or a group of related reactions.
   
   
5. Active site:
   A small portion of enzyme where substrate attaches with enzyme is called active site. The shape of active site is complementary to shape of the substrate.
   
   
6. Sensitive:
   They are sensitive to even a minor change in pH, temperature and substrate concentration.
   
   
7. Co-factors:
   Some enzymes require cofactor for their functioning; a cofactor is a non-protein substance which may be organic or inorganic. Inorganic cofactors are Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹, the organic cofactors are NADP, NAD and FAD are used in enzymes as cofactors.
   
   
8. Regulation of Metabolic Pathway:
   Many enzymes work in a sequential manner to produce a specific product. This pathway is called metabolic pathway.
   
   
9. Regulation of enzyme activity:
   Activity of enzymes can be enhanced by activator and can be decreased by inhibitors.
   An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

Q.6: Define: (i) Substrate (ii) Active site (iii) Activator
Ans: (i) SUBSTRATE:
Reactants of enzymes are called substrate.

(ii) ACTIVE SITE:
A small portion of enzymes, where substrate attaches with enzymes is called active site.

(iii) ACTIVATOR:
Enzyme activators are molecules that can bind with an enzyme to increase its activity.

Q.7: Define cofactor?
Ans: COFACTOR:
A cofactor is a non-protein substance which may be organic or inorganic. 

• Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹ are inorganic cofactors.
• NADP, NAD and FAD are organic cofactors used in enzymes.

Cofactor can be categorized into:

• Prosthetic group (if organic cofactors are tightly bound to an enzyme) and
• Coenzymes (if organic cofactors are loosely attached with an enzyme)

Q.8: What are enzymes inhibitor?
Ans: ENZYME INHIBITOR:
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

Q.9: Define use of enzymes in industries?
Ans: USES OF ENZYMES:
Many enzymes are used commercially in industries. The most common industries are:

• Paper industry- To get cellulose for paper making.
• Food industry- For making bakery products and pizza.
• Brewing industry- For conversion of sugar into alcohol.
• Bio-detergents- Use to remove different type of stains.

Q.10: Explain the factors affecting the activity of an enzyme?
Ans: FACTORS AFFECTING THE ACTIVITY OF AN ENZYME:
The main factors which affecting the activity of an enzyme are as follows:
Substrate Concentration:
The enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum after which further increase in the substrate concentration produces no significant change in the reaction rate.
Conclusion:
The enzyme molecules are saturated with substrate. The excess substrate molecules cannot react until the substrate already bound to the enzymes has reacted and been released or been released without reacting.

Temperature:
The protein nature of the enzymes makes them extremely sensitive to thermal changes. Enzyme activity occurs within a narrow range of temperatures compared to ordinary chemical reactions.
Enzymes catalyses by randomly colliding with substrate molecules, increasing temperature and increases collision which also increases the rate of reaction, forming more product. However, increasing temperature also increases the vibrations and structure of enzymes is lost i.e denature enzyme. These changes decreases the rate of enzyme action or it may seized completely.
Conclusion:
As temperature increases, initially the rate of reaction will increase, because of increased kinetic energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.

pH:
Enzymes are also sensitive to pH due to their protien nature. All enzymes work at their maximum rate at narrow range of pH. The point where the enzyme is most active is known as optimum pH. Forexample, pepsin works at a low pH i.e. it is highly acidic, while trypsin works at a high pH i.e. it is basic. Most enzymes work at neutral pH 7.4.
Conclusion:
Small changes in pH above or below the optimum do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to denature and permanently lose their function.

Q.11: Describe the models explaining the mechanism of enzyme action? OR Describe mechanism of enzymes and the models to explain enzyme action?
Ans: MECHANISM OF ENZYME ACTION:

Enzyme catalyzes the reaction by attaching to substrate which ends to the product formation. Enzyme exposes its active site to attract specific substrate, makes enzyme substrate complex (ESC) after which the product is formed and enzyme is detached from it and used again for the same reaction.

Model Or Theories for Action of Enzyme:
There are two models or theories to explain enzyme action:

1. Lock and key model
2. Induced fit model

1. The lock and key model:
This theory was first postulated by Emil Fischer in 1894 shows the high specificity of enzymes.
The “Lock and Key” model tells that enzymes and substrates fit together. Each enzymes fits specifically to a certain substrate.
This theory explains that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another like a key into a lock, only the correct size and shape of the substrate (the key) would fit into active site (the key hole) of the enzyme (the lock). However, it does not explain the stabilization of the transition state that the enzyme achieve.
For example:
Lipase fits together with lipids to break them down.

2. Induced fit model:
The induced fit model suggested by Daniel Koshland in 1958. It explains that active site continuously changes it shape until the substrate bind to it. It also says that active site of enzyme is flexible (lock and key theory doesnot explain it).

Q.12: What do you know about specificity of enzyme? OR Why enzymes are specific in nature?
Ans: SPECIFICITY OF ENZYME:
In the human body there are more than 1000 known enzymes and all work with their own substrates. These substrate are reactants used in reaction and are responsible for enzymes specificity.
Enzymes are specific in nature therefore a particular enzyme can only bind to its specific substrate  and it's all due to its active site.  Active site of the enzyme possesses some geometric shape and as the enzymes are made up of proteins and proteins contain different type of amino acids which carry different charges/nature like acidic, basic, hydrophilic etc hence active site is highly specific to its substrate. 
Some of the enzymes catalyzes the reaction by recognizing the bond formed between the molecules, the functional group present in the molecules or the geometric shape of the molecules.
In general, the Absolute specificity - the enzyme will catalyze only one reaction.
For example:

• Proteases are the enzymes which catalyzes the proteins only.
• Lipase acts on lipids only.

It means the enzymes are bond specific, so lipase can act an ester bond in lipids/fats substances.

Q.13: Briefly describe the categories of enzymes?
Ans: Categories Of Enzymes:
There are TWO categories of enzymes:

1. Intracellular and
2. Extracellular.

1. Intracellular: enzymes work inside the cell such as ATPase, cytochrome C reductase etc.
2. Extracellular enzymes work outside the cells such as pepsin, lipase etc.

Source: Special Thanks To Sir Syed Arif Ali

CLICK HERE TO DOWNLOAD PDF FILE OF Questions And Answers:
Enzymes

Biology For Class IX - Chapter No.6 - ENZYMES - Text Book Exercise

GO TO INDEX
CHAPTER 6
ENZYMES
Review Questions

By Mrs. Ayesha Arif
(Jauhar Progressive School)

1. Encircle the correct answer:
(i) All are characters of enzymes except:
(a) Enzyme speed up a biochemical reaction.
(b) Enzymes are sensitive to minor change in pH
(c) Enzyme activity enhanced by inhibitors ✔
(d) Enzyme portion where substrate attach called active site

(ii) Enzymes are:
(a) Steroid in nature
(b) Protein in nature ✔
(c) Lipid in nature
(d) Carbohydrate in nature

(iii) Metabolic reactions are:
(I) Constructive reactions
(II) Destructive reactions
(III) Inhibiting reactions
(a) I only
(b) I and II only ✔
(c) I, II and III
(d) II and III only

(iv) The point where the enzyme is most active is known as:
(a) Neutral pH
(b) Acidic pH
(c) Basic pH
(d) Optimum pH ✔

(v) Active site continuously changes it shapes until the substrate do not bind to it, is statement of:
(a) Induce fit model ✔
(b) Lock and key model
(c) Fluid mosaic model
(d) Both “a” and “b”

(vi) Select the mismatched:
(a) Proteases → Carbohydrate
(b) Lipases → Lipids
(c) Trypsin → Protein
(d) All are correctly matched ✔

(vii) Chemical reaction requires particular conditions to carry down at proper rate, especially:
(a) Temperature and Nature
(b) Nature and Pressure
(c) Nature and Structure
(d) Temperature and Pressure ✔

(viii)All are factors affecting enzyme activity except:
(a) pH
(b) Substrate concentration
(c) Organic solvent ✔
(d) Temperature

(ix) Rate of reaction will increase when temperature:
(a) Increases ✔
(b) Decreases
(c) Below 10°C
(d) Both “a” and “c”

(x) Choose the correct statement regarding lock and key model.
(a) Enzyme and substrate posses' specific complementary geometric shapes. ✔
(b) Active site of enzyme is flexible
(c) Active site continuously changes
(d) All above statements are correct.

2. Fill in the blanks:
(i) There are two types of metabolic reactions.
(ii) Enzymes catalyze chemical reaction by lowering the activation energy.
(iii) Presence of enzyme does not affect the nature or properties of products.
(iv) In constructive reaction large molecules are formed.
(v) Activity of enzymes can be enhanced by activator.
(vi) Small portion of enzyme where substrate attach with enzyme called active site.
(vii) Enzyme activity decreased by inhibitors.
(viii) As temperature increases, initially the rate of reaction will increase.
(ix) Enzyme changes in pH can cause enzymes to denature.
(x) In the human body there are more than 1000 known enzymes.

3. Define the following terms:

1. Substrate
2. Active site
3. Inhibitor
4. Activator
5. Anabolism
6. Catabolism
7. Activation energy
8. Cofactor
9. Prosthetic group
10. Coenzymes

Ans: (i) SUBSTRATE:
Reactants of enzymes are called substrate.
In other words, A substrate is a molecule acted upon by an enzyme. A substrate is loaded into the active 

site of the enzyme, or the place that allows weak bonds to be formed between the two molecules.

(ii) ACTIVE SITE:
A small portion of enzymes, where substrate attaches with enzymes is called active site. It is the site where the catalytic "action" happens. A substrate enters the active site of the enzyme. This forms the enzyme-substrate complex.

(iii) INHIBITOR:
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

OR

Inhibitor is a substance which slows down or prevents a particular chemical reaction or other process. An inhibitor reduces the activity of a particular enzyme.

(iv) ACTIVATOR:
Enzyme activators are molecules that can bind with an enzyme to increase its activity.

OR

Activators are molecules that bind to enzymes and increase their activity. In some cases, when a substrate binds to one catalytic subunit of an enzyme, this can trigger an increase in the substrate affinity as well as catalytic activity in the enzyme's other subunits, and thus the substrate acts as an activator.

(v) ANABOLISM:
In constructive reactions large molecules are formed to form a structure of cell or body. These reactions are called anabolic reactions and this type of metabolism is called anabolism.

OR

Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. Anabolism is the building-up aspect of metabolism.

(vi) CATABOLISM:
The destructive reaction in which large molecules breakdown in small molecules to produce energy or to re-utilize further or to discard called catabolic reactions. The type of this metabolic activity is called catabolism.

OR

The sequences of enzyme-catalyzed reactions by which relatively large molecules in living cells are broken down, or degraded is called catabolism. Part of the chemical energy released during catabolic processes is conserved in the form of energy-rich compounds.

(vii) ACTIVATION ENERGY:
The minimum amount of energy require to activate a reaction called activation energy (E_A).
e.g. the activation energy needed to break a glucose molecule initially requires energy of 2 ATP molecules. If this amount is high the difficult will be the reaction or vice versa.

OR

Living body requires some facilitators. These facilitators help to perform biochemical reactions at low energy. This minimum amount of energy is called activation energy (E_A).
e.g. the activation energy needed to break a glucose molecule initially requires energy of 2 ATP molecules. If this amount is high the difficult will be the reaction or vice versa.

(viii) COFACTORS:
Some enzymes require cofactor for their functioning; a cofactor is a non-protein substance which may be organic or inorganic. Inorganic cofactors are Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹, the organic cofactors are NADP, NAD and FAD are used in enzymes as cofactors.

OR

A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes. Cofactors can be considered "helper molecules” that assist in biochemical transformations.

(ix) PROSTHETIC GROUP:
A prosthetic group is a tightly bound, specific non-polypeptide unit required for the biological function of some proteins. The prosthetic group may-be organic (such as a vitamin, sugar, or lipid) or inorganic (such as a metal ion), but is not composed of amino acids.

OR

A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being covalently linked to the apoprotein. OR we can say that Prosthetic group is a tightly bound, specific non-polypeptide unit required for the biological function of some enzymes.

(x) COENZYME:
A coenzyme is an organic non-protein compound that binds with an enzyme to catalyze a reaction. Coenzymes are often broadly called cofactors, but they are, chemically different. A coenzyme cannot function alone, but can be reused several times when paired with an enzyme.

OR

Coenzymes are small molecules. They cannot by themselves catalyze a reaction but they can help enzymes to do so. In technical terms, coenzymes are organic non protein molecules that bind with the protein molecule to form the active enzyme.

4. Distinguish between the following in tabulated form:
(i) Activator and Inhibitor
(ii) Anabolism and Catabolism
Ans: Difference Between Activator And Inhibitor

S.No.	Activator	Inhibitor
1.	Enzyme activators are molecules that can bind with an enzyme to increase its activity.	Enzyme inhibitors are molecules that combined with an enzyme to decrease its activity.
2.	They can be either proteins, peptides, lipids, small organic molecules or ions.	Two main types of inhibitors are reversible and irreversible inhibitors.
3.	Some important examples include hexokinase - I and glucokinase	Some typical examples include drugs, ribonucleic inhibitor, etc.

(ii) Difference Between Anabolism And Catabolism

S.No.	Anabolism	Catabolism
1.	It is a metabolic chemical process used to build molecules required for the energy to do different activities by the body.	It is a metabolic chemical process used for breakdown of complex molecules to simple small molecules.
2.	In this state body requires energy to keep body in anabolic state. Nutrition is the main source.	In this state body releases energy in different activities.
3.	In anabolism state, energy is converted from kinetic energy to potential energy.	In catabolism state, energy is converted from potential energy to kinetic energy.
4.	Anabolism helps in furnishing and preserving tissues and results in muscle growth.	Catabolism helps in burning fats and calories.
5.	Anabolism requires less oxygen compared to catabolism.	Catabolism uses oxygen.
6.	Anabolism is in function during rest or sleep.	Catabolism is in function during activities.
7.	The main role is construction in metabolism.	The main role is destruction in metabolism.
8.	Hormones involved in the process are adrenaline, cytokine, glucagon and cortisol.	Hormones involved in the process are estrogen, testasterone, growth
9.	Example of catabolic processes are proteins become amino acid, glycogen breaks down into glucose and triglycerides break down into fatty acid.	Examples include the formation of polypeptides from amino acid, glucose forming glycogen and fatty acid forming triglyceides.

5. Write short answers of following questions:
(i) Why enzymes are specific in nature?
Ans: Enzymes are specific in nature therefore a particular enzyme can only bind to its specific substrate and it's all due to its active site. Active site of the enzyme possesses some geometric shape and as the enzymes are made up of proteins and proteins contain different type of amino acids which carry different charges/nature like acidic, basic, hydrophilic etc hence active site is highly specific to its substrate.
Some of the enzymes catalyzes the reaction by recognizing the bond formed between the molecules, the functional group present in the molecules or the geometric shape of the molecules.
In general, the Absolute specificity - the enzyme will catalyze only one reaction.
For example:

• Proteases are the enzymes which catalyze the proteins only.
• Lipase acts on lipids only. It means the enzymes are bond specific, so lipase can act an ester bond in lipids/fats substances.

(ii) How enzyme reduces the amount of activation energy?
Ans: Enzymes can lower the activation energy of a chemical reaction in several ways.

• The enzymes lower activation energy by binding two of the substrate molecules and orient them in a correct and precise manner to encourage a reaction.
• Enzyme can also lower the activation energy by rearranging the electrons in the substrate so that there are areas that carry partial positive and partial negative charges which favor a reaction to occur.
• The enzymes may alter the shape of substrate. It can strain the bound substrate which forces it to transition state that favors a reaction and reduce the requirement of energy needed to make the reaction occur.

(iii) Why presence of enzymes does not effect on the nature and properties of end product?
Ans: The enzyme itself is not a component of the chemical reaction and is the same molecule at the beginning of the reaction as it is at the end. That is why their presence does not affect the nature or properties of end products.

OR

Ans: An enzyme does not effect on the nature and properties of end product because enzymes act as catalyst. They only effect the speed of the reaction and remain unchanged themselves.

(iv) How substrate concentrations affect enzyme activity?
Ans: It has been shown experimentally that if the amount of the enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum after which further increase in the substrate concentration produces no significant change in the reaction rate.

OR

Ans: The concentration of substrate affects the enzyme activity in three ways:

1. Increase In Substrate Concentration:
   If enzyme molecules are available in a reaction, increase in the substrate concentration increases the rate of reaction.
   
2. Constant Enzyme concentration:
   If enzyme concentration is kept constant and the amount of substrate is increased a point is reached where any further increase in the substrate does not increase the rate of reaction any more.
   
3. Saturation:
   When the active sites of all enzymes are occupied at high substrate concentrations any more substrate molecule do not find free active sites. This state is called saturation of active sites and reaction rate does not increase.

(v) How enzymes are uses in industries?
Ans: Uses of enzymes:
Many enzymes are used commercially in industries. The most common industries are:

1. Paper industry- To get cellulose for paper making.
2. Food industry- For making bakery products and pizza.
3. Brewing industry- For conversion of sugar into alcohol.
4. Bio-detergents- Use to remove different type of stains.

6. Write detailed answers of the following questions:
(i) What are enzymes? Describes characteristics of enzymes.
Ans: ENZYMES: (En=inside, zyme = yeast)
The name was coined due to observation when yeast was introduced in fruit sap which converted it into alcohol.
Definition:
The high amount of activation energy cannot be provided by organism itself therefore they require some facilitators to reduce this activation energy. These facilitators are special molecules made up of mostly protein called enzymes. Thus the enzymes are the biocatalysts which facilitate chemical reaction by lowering activation energy.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

OR

The molecules which facilitate biochemical reaction by reducing activation energy called enzymes. Enzymes are biocatalyst made up of mostly proteins and therefore are three dimensionally folded chains of amino acids with a specific shape.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

CHARACTERISTICS OF ENZYMES:

1. Nature:
   Enzymes are biocatalyst, made up of mostly proteins and have three dimensionally folded chains of amino acids with a specific shape, held together by Hydrogen bonds.
   
   
2. Speed Up:
   Enzymes speed up reactions by bringing reactants together and reducing the activation energy required to start the reaction (enzymatic reaction).
   
   
3. Catalyst:
   When an enzyme starts a chemical reaction, catalyzes the reaction hence does not utilized itself which means even a single or little amount of enzyme can start a reaction and catalyze fastly. Their presence does not affect the nature or properties of end products.
   
   
4. Substrate:
   Reactants of enzyme are called substrate.
   They are very specific in their action; a single enzyme catalyzes only a single chemical reaction or a group of related reactions.
   
   
5. Active site:
   A small portion of enzyme where substrate attaches with enzyme is called active site. The shape of active site is complementary to shape of the substrate.
   
   
6. Sensitive:
   They are sensitive to even a minor change in pH, temperature and substrate concentration.
   
   
7. Co-factors:
   Some enzymes require cofactor for their functioning; a cofactor is a non-protein substance which may be organic or inorganic. Inorganic cofactors are Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹, the organic cofactors are NADP, NAD and FAD are used in enzymes as cofactors.
   
   
8. Regulation of Metabolic Pathway:
   Many enzymes work in a sequential manner to produce a specific product. This pathway is called metabolic pathway.
   
   
9. Regulation of enzyme activity:
   Activity of enzymes can be enhanced by activator and can be decreased by inhibitors.
   An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

(ii) Describe factors affecting enzyme activity.
Ans: FACTORS AFFECTING THE ACTIVITY OF AN ENZYME:
The main factors which affecting the activity of an enzyme are as follows:
Substrate Concentration:
The enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum after which further increase in the substrate concentration produces no significant change in the reaction rate.
Conclusion:
The enzyme molecules are saturated with substrate. The excess substrate molecules cannot react until the substrate already bound to the enzymes has reacted and been released or been released without reacting.

Temperature:
The protein nature of the enzymes makes them extremely sensitive to thermal changes. Enzyme activity occurs within a narrow range of temperatures compared to ordinary chemical reactions.
Enzymes catalyses by randomly colliding with substrate molecules, increasing temperature and increases collision which also increases the rate of reaction, forming more product. However, increasing temperature also increases the vibrations and structure of enzymes is lost i.e denature enzyme. These changes decreases the rate of enzyme action or it may seized completely.
Conclusion:
As temperature increases, initially the rate of reaction will increase, because of increased kinetic energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.

pH:
Enzymes are also sensitive to pH due to their protein nature. All enzymes work at their maximum rate at narrow range of pH. The point where the enzyme is most active is known as optimum pH. For example, pepsin works at a low pH i.e. it is highly acidic, while trypsin works at a high pH i.e. it is basic. Most enzymes work at neutral pH 7.4.
Conclusion:
Small changes in pH above or below the optimum do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to denature and permanently lose their function.

Source: Special Thanks To Sir Syed Arif Ali

CLICK HERE TO DOWNLOAD PDF FILE OF Question & Answers:
Enzymes

Biology For Class IX - Chapter No.6 - ENZYMES - MCQs and Fill In the Blanks

GO TO INDEX
CHAPTER 6: ENZYMES
Multiple Choice Questions (MCQs)

By Mrs. Ayesha Arif
(Jauhar Progressive School

1. Encircle the correct answer:
(i) All are characters of enzymes except:
(a) Enzyme speed up a biochemical reaction.
(b) Enzymes are sensitive to minor change in pH
(c) Enzyme activity enhanced by inhibitors ✔
(d) Enzyme portion where substrate attach called active site

(ii) Enzymes are:
(a) Steroid in nature
(b) Protein in nature ✔
(c) Lipid in nature
(d) Carbohydrate in nature

(iii) Metabolic reactions are:
(I) Constructive reactions
(II) Destructive reactions
(III) Inhibiting reactions
(a) I only
(b) I and II only ✔
(c) I, II and III
(d) II and III only

(iv) The point where the enzyme is most active is known as:
(a) Neutral pH
(b) Acidic pH
(c) Basic pH
(d) Optimum pH ✔

(v) Active site continuously changes it shapes until the substrate do not bind to it, is statement of:
(a) Induce fit model ✔
(b) Lock and key model
(c) Fluid mosaic model
(d) Both “a” and “b”

(vi) Select the mismatched:
(a) Proteases → Carbohydrate
(b) Lipases → Lipids
(c) Trypsin → Protein
(d) All are correctly matched ✔

(vii) Chemical reaction requires particular conditions to carry down at proper rate, especially:
(a) Temperature and Nature
(b) Nature and Pressure
(c) Nature and Structure
(d) Temperature and Pressure ✔

(viii) All are factors affecting enzyme activity except:
(a) pH
(b) Substrate concentration
(c) Organic solvent ✔
(d) Temperature

(ix) Rate of reaction will increase when temperature:
(a) Increases ✔
(b) Decreases
(c) Below 10°C
(d) Both “a” and “c”

(x) Choose the correct statement regarding lock and key model.
(a) Enzyme and substrate posses' specific complementary geometric shapes. ✔
(b) Active site of enzyme is flexible
(c) Active site continuously changes
(d) All above statements are correct.

11. Reactions of an organism are collectively called:
a) Metabolic reactions ✔
b) Anabolic reactions
c) Catabolic reactions
d) complex reactions

12. The phenomenon of chemical activity in an organism is called:
a) disjunction
b) Terminalization
c) Anabolism
d) Metabolism ✔

13. The metabolic activities are always of:
a) Two types ✔
b) Three types
c) Four types
d) Five types

14. In constructive reactions, large molecules are formed to form a structure of cell or body. These reaction ere called:
a) Metabolic reactions
b) Anabolic reactions ✔
c) Catabolic reactions
d) complex reaction

15. In destructive reactions, large molecules breakdown in small molecules to produce energy is called:
a) metabolic reactions
b) anabolic reactions
c) catabolic reactions ✔
d) complex reaction

16. The minimum amount of energy, a reaction requires to initiate, is called:
a) metabolic energy
b) anabolic energy
c) catabolic energy
d) activation energy ✔

17. The bio-catalysts which facilitate chemical reaction by lowering activation energy is called:
a) enzymes ✔
b) hormones
c) inhibitors
d) substrate

18. Its action allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism:
a) substrate
b) hormones
c) enzymes ✔
d) inhibitor

19. Enzymes are bio-catalyst made up of mostly:
a) chitin
b) carbohydrates
c) lipid
d) protein ✔

20. Enzymes have specific shape with three dimensionally folded chains of:
a) ether
b) amino acid ✔
c) amide
d) ester

21. Reactants of enzyme are called:
a) substrate ✔
b) inhibitor
c) hormones
d) yeast

22. A small portion of enzyme where substrate attaches with enzyme is called:
a) substrate
b) inhibitor
c) hormones
d) active site ✔

23. Enzymes are sensitive to a minor change in:
a) pH, pressure and density
b) PH, temperature and pressure
c) pH, substrate concentration and pressure
d) pH, temperature and substrate concentration ✔

24. Activity of enzymes can be enhanced by:
a) inhibitors
b) cofactor
c) activator ✔
d) hormones

25. By inhibitor, the activity of enzymes can be:
a) increased
b) decreased ✔
c) remained the same
d) first increased & then decreased

26. If the amount of the enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will:
(a) decrease
(b) increase
(c) decrease until it reaches a maximum
(d) increase until it reaches a maximum ✔

27. The protein nature of the enzymes makes them extremely sensitive to:
(a) thermal changes ✔
(b) pressure changes
(c) density changes
(d) substrate changes

28. Enzymes activity occurs within a:
(a) narrow range of pressures
(b) wide range of pressures
(c) narrow range of temperatures ✔
(d) wide range of temperatures

29. The protein nature of the enzymes makes them sensitive to:
(a) pressure changes
(b) pH ✔
(c) density changes
(d) Kinetic energy

30. All enzymes work at their maximum rate at:
(a) wide range of pressure
(b) narrow range of pressure
(c) wide range of pH
(d) narrow range of pH ✔

31. The point where the enzyme is most active is known as:
(a) active pH
(b) maximum pH
(c) optimum pH ✔
(d) cutoff pH

32. It works at a low pH i.e., it is highly acidic.
(a) Pepsin✔
(b) Trypsin
(c) proteases
(a) lipase

33. It works at a high pH is:
(2) Pepsin
(b) Trypsin ✔
(c) proteases
(d) lipase

34. Most enzymes work at neutral pH:
(a) 6.2
(b) 6.4
(c) 7.2
(d) 7.4 ✔

35. In 1894, the lock and key model theory was first postulated by:
(a2) Zachanan Janson
(b) Walter Fleming
(c) Emil Fischer ✔
(d) Daniel Koshland

36. In 1958, the induced fit model suggested by:
(a) Zachanan Janson
(b) Walter Fleming
(c) Emil Fischer
(d) Daniel Koshland ✔

37. In the human body, the number of known enzymes is more than:
(a) 1000 ✔
(b) 700
(c) 500
(d) 100

38. These are the enzymes which catalyzes the proteins.
(a) Lipase
(b) Proteases ✔
(c) Pepsin
(d) Trypsin

39. This enzyme acts on lipids only.
(a) Lipase ✔
(b) Proteases
(c) Pepsin
(4) Trypsin

2. Fill in the blanks:
(i) There are two types of metabolic reactions.
(ii) Enzymes catalyze chemical reaction by lowering the activation energy.
(iii) Presence of enzyme does not affect the nature or properties of end products.
(iv) In constructive reaction large molecules are formed.
(v) Activity of enzymes can be enhanced by activator.
(vi) Small portion of enzyme where substrate attach with enzyme called active site.
(vii) Enzyme activity decreased by inhibitors.
(viii) As temperature increases, initially the rate of reaction will increase.
(ix) Enzyme changes in pH can cause enzymes to denature.
(x) In the human body there are more than 1000 known enzymes.
11. Reactions occur in living organisms called metabolic reaction.
12. Anabolism reactions are constructive reactions.
13. Catabolic reactions are destructive reactions.
14. The biochemical reaction requires high amount activation energy.
15. The molecules which facilitate biochemical reaction by reducing activation energy called enzymes.
16.Activity of Enzymes can be Enhanced by activator and declined by inhibitors.
17. Many enzymes are used commercially in industries, like paper, food, brewery, bio-detergents industries.
18. The enzymes attach with Substrate form enzymes substrate complex (ESC) after completion enzyme detached while product is formed.
19. There are two models to explain enzyme action: (i) Lock and Key model (ii) Induce fit model.

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Biology For Class IX - Chapter No.7 - BIOENERGETICS - Questions and Answers

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CHAPTER 7
BIOENERGETICS

Q.1: Define energy?
Ans: ENERGY:
Energy is the capacity for doing work. The only source of energy on earth is Sun. Energy can neither be created nor be destroyed but it can change from one form to another form. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms.

Q.2: From where does the energy come in fuel and food molecules?
Ans: Source Of Energy:
The only source of energy on earth is Sun. Energy of the Sun reaches earth in the form of light (light energy). This light energy is converted into chemical energy by living organisms or in heat energy stored by non-living things.

Conversion Of Energy:
Law of conservation of energy or first law of thermodynamics states that:
"energy can neither be created nor be destroyed but it can change from one form to another form.
Thus the heat energy of light converts in:

• K.E. energy which flows water. This K.E. of water in dams is converted into mechanical energy when falls on turbine. This mechanical energy converts into light energy in bulbs and LED lights or again in mechanical energy in our fans.
• Light energy when falls on green parts of plant is captured, It is:
  (a) Converted into chemical energy. This chemical energy is stored as food energy in plants. When these parts of plant are eaten by animal this energy transferred into them.
  (b) When the organisms buried and remain under pressure inside earth crust for millions of year their chemical energy is converted into fossil fuel.

Q.3: Define bioenergetics?
Ans: BIOENERGETICS:

"The study about conversion of free energy into different forms by living organisms is called Bioenergetics."

Bioenergetics can also be defined as:

"The study of energy relationships, energy transformation and transmission in living organisms."

It is the part of biology, Physics and chemistry concerned with the energy involved in making and breaking of chemical bonds found in the molecules of organisms.

Q.4: Describe the chemical process of energy transmission in living organisms?
Ans: CHEMICAL PROCESS OF ENERGY TRANSMISSION:
In living organisms the energy is transferred through gain or loss of electrons during formation and breaking of chemical bonds. There are two chemical processes where it occurs, known with the name of oxidation and reduction.

The Oxidation Reactions:
are those reactions in which loss of electron (e^-) and proton (H⁺) occurs. These electrons carry energy from the molecules from where they release to the molecules where they added. e.g.
Iron reacts with oxygen to form a chemical called rust, in this reaction iron (Fe) loses some e- which transfer to oxygen. In this reaction Fe is oxidized and it transfers its energy to oxygen through electrons.

The Reduction Reactions:
are those reaction in which gain of e^- and H⁺ occur. This gain of e^- also brings energy which is stored in it.

Redox Reaction:
In living organisms these oxidation - reduction (Redox) reactions occur continuously to transfer energy from one molecule to other molecule, without these reactions energy transfer becomes impossible in living system.

Q.5: What is energy currency of cell? OR Describe the formation of ATP?
Ans: Energy Currency in living organism:
The major energy currency of all cells of living organism is a nucleotide called adenosine triphosphate (ATP) because it acts as the main energy source for majority of the cellular functions.

Formation Of Adenosine Tri-Phosphate (ATP):
As all living organisms have system to store energy. This energy is stored in a special molecule called Adenosine Tri-Phosphate (ATP). In organisms, energy is liberated during any oxidation reaction; this energy is utilized by molecules called Adenosine Di-Phosphate (ADP) to form a bond with phosphate (P). As a result the ADP become ATP, energy of oxidation is now stored in ATP.

Use Of Energy Stored In ATP:
The amount of energy stored is 7.3 Kcal / mole, this stored energy in ATP will be utilized by living organism for performing any type of work e.g. transport of molecules against the concentration gradient. The energy is now become free (liberated) by breaking ATP molecule.

ATP → ADP + P + Energy (7.3 K Cal / mole)

So the formation of ATP is endergonic (energy intake) process and breakdown of ATP is exergonic (energy liberating) process.

Q.6: Define and describe the process of photosynthesis and write down its importance?
Ans: PHOTOSYNTHESIS:
Word photo means light and synthesis means to prepare.
Photosynthesis is the fundamental process in which basic organic molecules and O₂ are produced for all bio-molecules and living organisms. Photosynthesis converts light energy into chemical energy.
Definition:
Plants utilize simple inorganic molecules carbon dioxide (CO₂) and water (H₂O) which react by using light energy in the presence of pigments like Chlorophyll to form glucose and oxygen.

OR

Photosynthesis is a biochemical process by which green part of plant manufactures their own food (Glucose C₆H₁₂O₁₂) by combining carbon dioxide and water in the presence of sunlight and chlorophyll. During this process oxygen is liberated.

Photosynthetic Organism:
This process is carried out by chlorophyll containing organisms like plants, algae, some protozoan and some bacteria.
Equation:

IMPORTANCE OR SIGNIFICANCE OF PHTOSYNTHESIS:
(i) Role Of Glucose:
The fundamental molecule produced during photosynthesis is simple sugar i.e. Glucose. Glucose utilizes in most of the metabolism of plant to produce secondary products like starch and other polysaccharides. Plants also use carbohydrates to form fats, proteins and other chemical like Nucleic Acids. This glucose is also used in respiration as reactant to produce energy for the metabolism of living organisms.

(ii) Essential In Food Chain:
Plants are not the only organisms which depend on photosynthesis but animals (Heterotrophs) also depend on phototrophs (i.e plants). Animals utilize the molecules of phototrophs as food molecules. If an animal is herbivorous it feeds directly on plants. If an animal is carnivorous it depends on herbivores (those animals which feed on plants). These feeding sequences and relationship are called Food Chains.

(iii) Role Of Oxygen:
Photosynthesis is the only process which produces free O₂ by splitting water. This O₂ is utilized by all living organisms for respiration to produced energy for metabolism. Without O₂ living organisms cannot survive.

(iv) Quantity Of CO₂ and O₂ In nature Is Maintained:
During Photosynthesis plants fix CO₂ and release O₂ in environment. CO₂ has a property to absorb heat of sun. If its quantity increases in environment, there will be increase in an environmental temperature on earth called Global warming. Thus photosynthesis keeps the quantity of CO₂ to maintain the temperature of earth.

Q.7: What is chloroplast and chlorophyll? OR Define chloroplast and chlorophyll?
Ans: CHLOROPLAST:
Green part of plants and algae contain special cell which contain special organelle called chloroplast. The chloroplast is a double membraned organelle. Within the double membrane is a gel-like substance (semi fluid protein) called stroma. Stroma contains enzymes for photosynthesis. Suspended in the stroma are stack-like structures called grana (singular = granum). Each granum is a stack of thylakoid discs.

Chlorophyll:
The chlorophyll molecules are green pigments, found on the surface of the thylakoid discs in chloroplast. It captures a specific part of visible light only from sun, therefore it is not a reactant but absorbs energy needed to drive the photosynthetic reaction.

Q.8: Describe the Process Of Photosynthesis? Or How many phases of photosynthesis are there describe each with suitable diagram?
Ans: PROCESS OF PHOTOSYNTHESIS:
The simple looking reaction of photosynthesis is not as simple. It involves number of chemical reactions which are catalyzed by number of enzymes, either in non cyclic or cyclic ways. Each reaction occurs at different site in chloroplast.

PHASES OF PHOTOSYNTHESIS:
Processes of Photosynthesis is mainly divided into phases or reactions.

1. Light Reaction or Light Dependent reaction
2. Dark Reaction or Light Independent reaction

1. Light Reaction or Light Dependent Reaction:
Definition:
Reaction in which light energy converted into chemical energy and stored in ATP (Adenosine Triphosphate) and NADPH₂ (reduced Nicotine amide Adenosine Dinucleotide Phosphate). This conversion occurs at thylakoid membrane where solar energy is captured by pigments located in harvesting complex. This phase of photosynthesis is called Light Dependent reaction Or Light Reaction.
It is non Cyclic process coupled with breakdown of H₂O molecules i.e. photolysis, takes place also at thylakoid membrane.
Explanation:
The term light reaction or light dependent reaction is used due to the reason that during this phase of photosynthesis light energy is captured and converted into chemical energy.
Photolysis:
Some of the light is utilized to split water into oxygen and H with e^- (electrons), this splitting of water is called Photolysis. Oxygen which is produced during photolysis is released in the environment where as H⁺ together with CO₂ are used in building Glucose.
Photosystem I & II:
In chloroplast, different pigments absorb light of different wave lengths. Among them chlorophyll is the main light capturing molecules in thylakoid membrane which absorbs violet, blue and red light but reflects green therefore it appears green. In the thylakoid membrane other pigments and electron carrier molecules form highly organized assemblies in a series called photosystems. Each thylakoid contains thousands of copies of two different kind of photosystems called photosystems I and II. Each consists of two major parts:

• A light harvesting complex and
• An electron transport system.

The conversion of light energy takes places when the chlorophyll of reaction center receives energy. One of the electrons from chlorophyll “a” molecule leaves and jump over the electron transport system. This energized electron moves from one carrier to next. The electron releases energy, when it comes down, this energy drives reactions and produces two energy rich compounds. These are:

1. ATP (Adenosine Triphosphate)
2. NADPH₂ (Reduced Nicotinamide Adenosine Dinucleotide Phosphate)

Phosphorylation:
ADP is the compound which is already present in cell. It combines with phosphate by using energy of photon released from when moving through e- carriers in photosynthesis. The formation of ATP from ADP by using light energy called phosphorylation

Reduction Of NADP:
NADP also present in chloroplast is reduced into NADPH₂ by accepting Hydrogen ions (H⁺, released from splitting of water.

ATP and NADPH₂ formed, both are energy rich compounds which are utilized in dark reaction.

2. Dark Reaction or Light Independent reaction:
Definition:
Reaction in which captured solar energy transferred to glucose from ATP and NADPH₂. It takes place in stroma, in cyclic manner. This phase of photosynthesis is called Light Independent reaction Or Dark Reaction.
During this phase fixation of atmospheric CO₂ also takes place to form organic molecules.

Explanation:
This phase of photosynthesis does not require energy of photon but it also takes place in day simultaneously with the light reaction.
Calvin-Benson Cycle:
The ATP and NADPH₂ synthesized during the light dependent reaction are dissolved in stroma where, they provide energy to power the synthesis of Glucose from CO₂ and H₂O (i.e. H⁺ and e^- of water).
This Phase occurs independently, without light as long as ATP and NADPH₂ are available. This phase of photosynthesis is cyclic phase. This phase occurs in set of reactions also called Calvin – Benson Cycle due to it's discoverer or the C₃ (three Carbon Containing Compounds formed initially) Cycle.
The C₃ Cycle requires:

1. CO₂ - normally from air some of it also comes from respiration.
2. CO₂ Capturing Sugar - a Pentose Sugar.
3. Enzymes to catalyze all the reactions.
4. Energy from ATP and NADPH₂ come from light dependent reaction.

Q.9: Define limiting factors? Describe the limiting factors of photosynthesis?
Ans: Limiting Factor:
Rate of biochemical reaction dependent on some factors which affect the rate are called limiting factor.
For example: At low light intensity rate of photosynthesis increase continuously but at high light intensity the rate becomes constant.

Limiting Factors For The Rate Of Photosynthesis: are,

1. Light intensity,
2. Carbon dioxide concentration and
3. Temperature

Following graph shows the idea of limiting factor.

• A- At point Z on graph, light intensity is limiting factor.
• B- If light intensity increase to bright light and moderate temperature the concentration of CO₂, in air becomes limiting factor.
• It is clearly observed that the same plant if put into air containing high CO₂ then the rate of photosynthesis becomes high.
• If there is high light intensity and high CO₂ concentration then the temperature becomes the limiting factor but the temperature should not be very high otherwise enzymes become denatured.

Q.10: Find out the effect of light intensity on the rate of photosynthesis by experiment?
Ans: Experiment To Show The Effect Of Light Intensity On The Rate Of Photosynthesis:
Apparatus:

• Large beaker of water,
• Boiling tube,
• Stand and clamp,
• Paper clip,
• Fresh water plant hydrilla,
• Ruler,
• Stopwatch,
• Thermometer,
• Lamp etc.

Procedure:

1. Take a healthy piece of Hydrilla. Place it upside down in a boiling tube of water. It helps to sink the Hydrilla.
2. Clamp the tube to hold it upright in beaker of water. Ensure that the plant is perpendicular to source of light. The beaker of water is needed to maintain a constant temperature.
3. Place a thermometer in water to record the temperature. Turn off the room lights to reduce back ground light and place a bench lamp close to the beaker.
4. Observe the plant for few minutes, you will see the bubbles of gas coming out from the cut end of plant. If no bubbles are seen repeat the experiment by using fresh piece of plant. Count the number of bubbles per minute. If the rate of bubbling is too fast to count, move the lamp away from the breaker until the rate becomes countable.
5. Repeat the counts until you are sure that the rate is constant. Record the rate and the distance of the lamp from the plant.
6. Change the distance of lamp from plant and take more measurement of the rate of bubbling at each distance. Take 3 values at each point.
7. Repeat the counts at different distance from plant keep the temperature of water constant thought out the experiment.

Conclusion:
Suppose that the rate of bubble production is the measure of the rate of photosynthesis.
It is concluded that the rate of photosynthesis decreases at low light intensities. As the lamp is moved away from plant, the intensity of light falling on it also decreases.

Q.11: Define respiration?
Ans: RESPIRATION:
To carry out all the life process cells requires energy. The source of this energy is food or photo assimilates (Products of photosynthesis) in plants.
Definition:

"Cells break food molecules to release their Chemical energy. The breakdown of food molecules to release energy is called respiration."

Usually cells use oxygen to oxide food. It results CO₂ and water as waste products. The main food oxidized is the sugar i.e. Glucose.
Equation:
The overall equation for this chemical reaction is:

Glucose + Oxygen → Carbon dioxide + water + Energy

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Above equation shows that one molecule of glucose reacts with six molecules of oxygen to produce six molecules of carbon dioxide and six molecules of water. The main product is energy which is produced in the form of energy rich molecules called ATP.

Q.12: Write down the difference between breathing and respiration or cellular respiration?
Ans: DIFFERENCE BETWEEN BREATHING AND RESPIRATION OR CELLULAR RESPIRATION:

S.No	Breathing	Cellular Respiration
1.	Breathing is a physical process in which O2 is taken in CO2 is given out.	Respiration is a biochemical process in which food is oxidized into CO2 and H2O.
2.	It occurs outside the cells.	It occurs inside the cells.
3.	There is gradual and stepwise release of energy.	There is no release of energy.
4.	Enzymes are not involved.	Enzymes are involved.
5.	Oxygen is necessary in this process	Oxygen is not necessary in anaerobic respiration.

Q.13: What are the steps of respiration?
Ans: Steps Of Respiration:
Respiration consist of the following two steps:

• Breathing
• Cellular Respiration

Breathing:
Breathing allows the process of gaseous exchange at surface of cells and tissues. It is the movement of air in and out of the organism to supply O₂ and give out CO₂. Breathing is also called Ventilation.

Cellular Respiration:
It is the biochemical reaction in which the oxidation of food takes place within cells with the help of oxygen and enzymes, resulting in the release of energy.

Q.14: How many types of respiration are there? Explain them with the help of chemical equations?
Ans: TYPES OF RESPIRATION:
There are two types of respiration found in living organisms for the production of energy.

1. Anaerobic Respiration or Fermentation
2. Aerobic Respiration

(i) ANAEROBIC RESPIRATION OR FERMENTATION:
Definition:
The primitive type of respiration which takes place in the absence of O₂ or without O₂ is called anaerobic respiration or fermentation.
There are special conditions where O₂ is not available so the organisms adapt themselves to break down their food without oxygen which is called anaerobic respiration or fermentation.
Example:
It takes place in some bacteria, fungi, endoparasite and sometimes in animal.

MECHANISM OF ANAEROBIC RESPIRATION OR FERMENTATION:
During anaerobic respiration, glucose is not broken down completely so less amount of energy (5 to 10% as compared to aerobic respiration) is released but it can sustain life even in the absence of O₂.
It had evolved on earth where there was no O₂ on earth.

Types Of Anaerobic Respiration OR Fermentation
There are two types of anaerobic respiration:

1. Alcoholic Fermentation
2. Acidic fermentation

Alcoholic Fermentation:
The bacteria and fungi respire aerobically but when these organisms are deprived of oxygen they stop respiration aerobically and start respiring anaerobically instead, During this anaerobic respiration they produce ethyl alcohol with CO₂.

Glucose → Ethanol + CO₂ + Some energy
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Some ATP

Acidic Fermentation:
In animals when aerobic respiration is not enough to produced required energy they start anaerobic respiration. During this process glucose breaks down into a substance called lactic acid.

Glucose → Lactic acid + Some energy
C₆H₁₂O₆ → 2C₃H₆O₃

A limited amount of energy is produced as compared to aerobic respiration which is enough to power the athlete's muscles during muscles fatigue.

(ii) AEROBIC RESPIRATION:
Definition:
Type of respiration where food breakdown occurs in the presence of oxygen to produce energy, is called aerobic respiration.
It takes place in the presence of free oxygen, oxidizing the food and releasing the maximum amount of energy i.e. 2827 kj / mole of glucose or 36 ATP molecules/glucose.
Example:
It is a method of respiration found in majority of organisms.
Equation:
The end products of aerobic respiration are CO₂ and H₂O.

Glucose + oxygen → Carbon dioxide + water + Energy (36 ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 36 ATP

MECHANISM OF AEROBIC RESPIRATION:
Aerobic Respiration takes place in 3 steps at different places in the cell.

• Glycolysis
• Kreb's or Citric acid Cycle
• Electron Transport Chain

(a) Glycolysis (Gr. Glyco = Sugar, Lysis = Break down):
First stage is that stage where a molecule of glucose (Six carbon sugar) is broken down into two molecules of pyruvic acid (three carbon acid). It does not require oxygen. It takes place in both aerobic and anaerobic respiration. This splitting of glucose releases small amount of energy of glucose which is enough to generate 2 molecules of ATP. Glycolysis is a complex sequence of reaction all occur in cytosol.

(b) Kreb's or Citric acid Cycle:
The second stage of aerobic respiration in which pyruvic acid produced during glycolysis enters the mitochondria where O₂ available. Cellular respiration uses this O₂ to break pyruvic acid completely into CO₂ and H₂O in a cyclic manner. During Kreb's Cycle some ATP produce and some coenzymes like NAD and FAD are reduced to NADH₂ and FADH₂ . It takes place in matrix of mitochondria.

(c) Electron Transport Chain:
The last stage of aerobic respiration in which NADH₂ (Nicotinamide Adenosine Di-nucleotide) and FADH₂ (Flavinamide Adenosine Di- nucleotide) are oxidized to produce ATP and H₂O. It takes place at the cristae of mitochondria.

Q.15: Write down importance of anaerobic respiration?
Ans: Importance Of Anaerobic Respiration:

1. Anaerobic respiration is the emergency arrangement of energy which has an advantage that organisms can survive without O₂ or can work with same pace for short period.
2. The other products of anaerobic respiration are acids. Vinegars are also organic acids that are produced commercially by acidic formulations.
3. Anaerobic respiration also produces ethyl alcohol. This process is commercially utilized by making alcoholic products like beer, wines and other beverages.
4. Baking industry is also based on it because anaerobic respiration also produces CO₂ which gives fluffy and soft shapes to cakes and breads also break down of starch into complex sugar to form bread and pizza.

Q.16: Describe usage of respiration Energy in the body of organisms?
Ans: Usage Of Respiration Energy In The Body Of Organisms:
Number of Processes requires energy in the body of an organism. Body provides it from respiratory energy. Following are some process which utilize respiratory energy:

• Synthesis of molecules:
  Formation of different molecules as well as large molecules from small molecules requires energy.
• Cell division:
  During cell division formation of large molecules like DNA and protein takes place which require energy as well as movement of chromosome also require energy.
• Growth without cell division:
  Enlargement & growth is not possible and both require formation of molecules which require energy.
• Active transport:
  Movement of ions and molecules from low concentration to high concentration requires energy.
• Muscle Contraction:
  Movement of muscle requires energy which is produced from chemical energy, chemical energy converted into kinetic energy.
• Passage of Nerve impulse:
  Nerve Impulse (message of Neuron) is basically electrical signals moving long nerve fiber by active transport requires energy.
• Maintenance of Body temperature:
  In higher animal's body temperature is maintained at constant level, this temperature maintenance requires energy of respiration.

Q.17: Distinguish between:
Photosynthesis and Respiration
Light and dark reaction
Aerobic and anaerobic respiration
Ans: (i) Difference Between Photosynthesis & Respiration

S.No.	Photosynthesis	Respiration
1.	Photosynthesis is the process where light energy converted in chemical energy.	Respiration is the process where chemical energy converted into energy of ATP.
2.	It occurs only in chlorophyll containing organisms.  OR  It takes place in green part i.e. chlorophyll of the cells of plants only.	It occurs in all organisms. OR  It takes place in all living cells of plants and animals.
3.	It requires light sources i.e occur only in the presence of light. (i.e. during day time only)	It does not requires light source so occurs throughout the life. (i.e. during day and night like.)
4.	It occurs in chloroplast.	It occurs in mitochondria.
5.	The reactants are Carbon dioxide and water.	Reactants are carbohydrates and oxygen usually.
6.	The end products are glucose (simple carbohydrate) and oxygen.	The end products are carbon dioxide and water in the case of aerobic respiration
7.	It is an anabolic process i.e. compounds are formed.	It is catabolic process i.e. compounds are broken down.
8.	Energy is used in this process ans it is stored in the form of food material.	In respiration energy is released from food materials.
9.	During this process carbon dioxide enters in the plant body and oxygen is given out.	During this process oxygen is entered in the body and carbon dioxide releases.
10.	The chemical equation for this process is: 6CO2 + 6H2O → C6H12O6 + 6O2	The chemical equation for this process is: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
11.	During the breakdown of one glucose, 38 ATP molecules are formed.	During the formation of one glucose, 18 ATP molecules are utilized.

Difference Between Light Reaction And Dark Reaction

S.No.	Light Reaction	Dark Reaction
1.	It take place only in the presences of light	It takes place only in presence or absence of sunlight.
2.	It is a photo-chemical phase.	It is a biochemical phase.
3.	It takes place in the grana of the chloroplast	It takes place in the stroma of the chloroplast.
4.	NADP utilizes H+ ions to form NADPH.	The hydrogen of NADPH combines with CO2.
5.	The end products are ATP and NADPH2.	Glucose is the end product. ATP and NADPH2 help in the formation of glucose.
6.	The water molecules split into hydrogen and oxygen.	Glucose is produce. CO2 is utilized in the dark reaction.
7.	Photolysis occurs.	Photolysis does not occur.

Difference Between Aerobic Respiration And Anaerobic Respiration

S.No.	Aerobic Respiration	Anaerobic Respiration
1.	It is that type of respiration in which oxygen is necessary.	It takes place in the absence of oxygen.
2.	It oxidizes the food completely.	It oxidizes the food partially.
3.	During this process large amount of energy is released i.e. 2827 KJ.	In this process, small amount of energy is released i.e. 210 KJ (in bacteria 8 fungi) and 150 KJ (in animals).
4.	Carbon dioxide and water are the end products of this process.	The end products are lactic acid (in animals), Ethanol and carbon dioxide (in bacteria and fungi).

CLICK HERE TO DOWNLOAD PDF FILE OF Question & Answers:
Bioenergetics

By Mrs. Ayesha Arif
(Jauhar Progressive School)

LONG QUESTION & ANSWERS

Q. Write detailed answers of the following questions:

Source: Special Thanks To Sir Syed Arif Ali