Textbook: Life Processes in Living Organisms Part -1 | Science and Technology Class 10 (Maharashtra SSC Board) PDF Download

 Page 1


12
Ø    Living Organisms & Life Processes Ø Living Organisms & Energy                     
              Production
Ø Some Nutrients & Energy Efficiency  Ø Cell Division- A Life Process
2. Life Processes in Living Organisms Part -1 
1. How are the food stuffs and their nutrient contents useful   
 for body?
2. What is the importance of balanced diet for body?
3. Which different functions are performed by muscles in body?
1. What is respiration? How does it occur?
4. What is the importance of digestive juices in digestive system?
5. Which system is in action for removal of waste materials produced in human body?
6. What is the role of circulatory system in energy production?
7. How are the various processes occurring in human body controlled? In how many   
 ways ?
Living Organisms and Life Processes
 Various organ-systems are continuously performing their functions in human body. 
Along with the various systems like digestive, respiratory, circulatory, excretory and control 
systems, different external and internal organs are performing their functions independently 
but through a complete co-ordination. This overall system is in action in more or less same 
way in all the organisms. Those are in need of continuous source of energy for this purpose. 
Carbohydrates, fats and lipids are the main sources of this energy and it is harvested by the 
mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy 
production but oxygen is also necessary. All these i.e. food stuffs and oxygen are transported 
up to the cell via circulatory system. Besides, it is coordinated by the control system of the 
body. i.e. each life process contributes in its own way in the process of energy production. 
Functioning of all these life processes also requires the energy. 
 Human and other animals consume the fruits and vegetables. Plants are autotrophs. 
They prepare their own food. They utilize some of the food for themselves whereas remaining 
is stored in various parts like fruits, leaves, stem, roots, etc. We consume all these various 
plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, 
minerals, etc. Which food materials do we consume to obtain these nutrients?
 We obtain the carbohydrates from milk, fruits, jaggary, cane sugar, vegetables, 
potatoes, sweet potatoes, sweetmeats and cereals like wheat, maize, ragi, jowar, millet, 
rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which 
this energy is obtained.
 Many players are seen consuming some food stuffs during breaks of the game. 
Can you recall?
Use your brain power
Why may be the players consuming these food stuffs?
Can you recall?
Page 2


12
Ø    Living Organisms & Life Processes Ø Living Organisms & Energy                     
              Production
Ø Some Nutrients & Energy Efficiency  Ø Cell Division- A Life Process
2. Life Processes in Living Organisms Part -1 
1. How are the food stuffs and their nutrient contents useful   
 for body?
2. What is the importance of balanced diet for body?
3. Which different functions are performed by muscles in body?
1. What is respiration? How does it occur?
4. What is the importance of digestive juices in digestive system?
5. Which system is in action for removal of waste materials produced in human body?
6. What is the role of circulatory system in energy production?
7. How are the various processes occurring in human body controlled? In how many   
 ways ?
Living Organisms and Life Processes
 Various organ-systems are continuously performing their functions in human body. 
Along with the various systems like digestive, respiratory, circulatory, excretory and control 
systems, different external and internal organs are performing their functions independently 
but through a complete co-ordination. This overall system is in action in more or less same 
way in all the organisms. Those are in need of continuous source of energy for this purpose. 
Carbohydrates, fats and lipids are the main sources of this energy and it is harvested by the 
mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy 
production but oxygen is also necessary. All these i.e. food stuffs and oxygen are transported 
up to the cell via circulatory system. Besides, it is coordinated by the control system of the 
body. i.e. each life process contributes in its own way in the process of energy production. 
Functioning of all these life processes also requires the energy. 
 Human and other animals consume the fruits and vegetables. Plants are autotrophs. 
They prepare their own food. They utilize some of the food for themselves whereas remaining 
is stored in various parts like fruits, leaves, stem, roots, etc. We consume all these various 
plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, 
minerals, etc. Which food materials do we consume to obtain these nutrients?
 We obtain the carbohydrates from milk, fruits, jaggary, cane sugar, vegetables, 
potatoes, sweet potatoes, sweetmeats and cereals like wheat, maize, ragi, jowar, millet, 
rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which 
this energy is obtained.
 Many players are seen consuming some food stuffs during breaks of the game. 
Can you recall?
Use your brain power
Why may be the players consuming these food stuffs?
Can you recall?
13
Observe and Label the diagram given beside.
In living organisms, respiration occurs at 
two levels as body and cellular level. 
Oxygen and carbon dioxide are exchanged 
between body and surrounding in case of 
respiration occurring at body level. In case 
of respiration at cellular level, foodstuffs 
are oxidized either with or without help of 
oxygen.
Observe 
Living organism and Energy production
2.1  Human respiratory system
Can you tell?
1. How many atoms of C, H and O are 
respectively present in a molecule of 
glucose?
2. Which types of chemical bonds are 
present between all these atoms?
3. In terms of Chemistry what happens 
actually when a molecule is oxidized?
 Carbohydrates of the food that we consume everyday are mainly utilized for production 
of energy required for daily need. This energy is obtained in the form of ATP. For this 
purpose, glucose, a type of carbohydrates is oxidized step by step in the cells. This is 
called as cellular respiration. Cellular respiration occurs among the living organisms by 
two methods. Those two methods are aerobic respiration (oxygen is involved) and 
anaerobic respiration (oxygen is not involved). In aerobic respiration, glucose is oxidized 
in three steps. 
1. Glycolysis 
 Process of glycolysis occurs in cytoplasm. A molecule of glucose is oxidized step by 
step in this process and two molecules of each i.e. pyruvic acid, ATP, NADH
2 
and water 
are formed. 
 Molecules of pyruvic acid formed in this process are converted into molecules of 
Acetyl-Coenzyme-A. Two molecules of NADH
2
 and two molecules of  CO
2
 are released 
during this process.
2. Tricarboxylic acid cycle (Krebs cycle) 
 Both molecules of acetyl-CoA enter the mitochondria. Cyclic chain of reactions called 
as tricarboxylic acid cycle is operated on it in the mitochondria. Acetyl part of acetyl-CoA 
is completely oxidized through this cyclical process and molecules CO
2
, H
2
O, NADH
2
, 
FADH
2
 are derived. 
Page 3


12
Ø    Living Organisms & Life Processes Ø Living Organisms & Energy                     
              Production
Ø Some Nutrients & Energy Efficiency  Ø Cell Division- A Life Process
2. Life Processes in Living Organisms Part -1 
1. How are the food stuffs and their nutrient contents useful   
 for body?
2. What is the importance of balanced diet for body?
3. Which different functions are performed by muscles in body?
1. What is respiration? How does it occur?
4. What is the importance of digestive juices in digestive system?
5. Which system is in action for removal of waste materials produced in human body?
6. What is the role of circulatory system in energy production?
7. How are the various processes occurring in human body controlled? In how many   
 ways ?
Living Organisms and Life Processes
 Various organ-systems are continuously performing their functions in human body. 
Along with the various systems like digestive, respiratory, circulatory, excretory and control 
systems, different external and internal organs are performing their functions independently 
but through a complete co-ordination. This overall system is in action in more or less same 
way in all the organisms. Those are in need of continuous source of energy for this purpose. 
Carbohydrates, fats and lipids are the main sources of this energy and it is harvested by the 
mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy 
production but oxygen is also necessary. All these i.e. food stuffs and oxygen are transported 
up to the cell via circulatory system. Besides, it is coordinated by the control system of the 
body. i.e. each life process contributes in its own way in the process of energy production. 
Functioning of all these life processes also requires the energy. 
 Human and other animals consume the fruits and vegetables. Plants are autotrophs. 
They prepare their own food. They utilize some of the food for themselves whereas remaining 
is stored in various parts like fruits, leaves, stem, roots, etc. We consume all these various 
plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, 
minerals, etc. Which food materials do we consume to obtain these nutrients?
 We obtain the carbohydrates from milk, fruits, jaggary, cane sugar, vegetables, 
potatoes, sweet potatoes, sweetmeats and cereals like wheat, maize, ragi, jowar, millet, 
rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which 
this energy is obtained.
 Many players are seen consuming some food stuffs during breaks of the game. 
Can you recall?
Use your brain power
Why may be the players consuming these food stuffs?
Can you recall?
13
Observe and Label the diagram given beside.
In living organisms, respiration occurs at 
two levels as body and cellular level. 
Oxygen and carbon dioxide are exchanged 
between body and surrounding in case of 
respiration occurring at body level. In case 
of respiration at cellular level, foodstuffs 
are oxidized either with or without help of 
oxygen.
Observe 
Living organism and Energy production
2.1  Human respiratory system
Can you tell?
1. How many atoms of C, H and O are 
respectively present in a molecule of 
glucose?
2. Which types of chemical bonds are 
present between all these atoms?
3. In terms of Chemistry what happens 
actually when a molecule is oxidized?
 Carbohydrates of the food that we consume everyday are mainly utilized for production 
of energy required for daily need. This energy is obtained in the form of ATP. For this 
purpose, glucose, a type of carbohydrates is oxidized step by step in the cells. This is 
called as cellular respiration. Cellular respiration occurs among the living organisms by 
two methods. Those two methods are aerobic respiration (oxygen is involved) and 
anaerobic respiration (oxygen is not involved). In aerobic respiration, glucose is oxidized 
in three steps. 
1. Glycolysis 
 Process of glycolysis occurs in cytoplasm. A molecule of glucose is oxidized step by 
step in this process and two molecules of each i.e. pyruvic acid, ATP, NADH
2 
and water 
are formed. 
 Molecules of pyruvic acid formed in this process are converted into molecules of 
Acetyl-Coenzyme-A. Two molecules of NADH
2
 and two molecules of  CO
2
 are released 
during this process.
2. Tricarboxylic acid cycle (Krebs cycle) 
 Both molecules of acetyl-CoA enter the mitochondria. Cyclic chain of reactions called 
as tricarboxylic acid cycle is operated on it in the mitochondria. Acetyl part of acetyl-CoA 
is completely oxidized through this cyclical process and molecules CO
2
, H
2
O, NADH
2
, 
FADH
2
 are derived. 
14
Fatty acids 
Mitochondrial 
Matrix
Outer 
Membrane 
Inner 
Membrane 
Pyruvic acid 
2.2 Mitochondria and Tri-carboxylic acid cycle 
ATP: Adenosine triphosphate is 
energy-rich molecule and energy is 
stored in the bonds by which phosphate 
groups are attached to each other. 
These molecules are stored in the cells 
as per need. Chemically, ATP is 
triphosphate molecule formed from 
adenosine ribonucleoside. It contains 
a nitrogenous compound-adenine, 
pentose sugar- ribose and three 
phosphate groups. As per the need, 
energy is derived by breaking the 
phosphate bond of ATP; hence ATP is 
called as ‘energy currency’ of the cell.
Energy released 
Adenine 
Ribose 
Phosphate bonds with 
more energy  
Inorganic Phosphate 
ATP ADP
3.3 ATP: Energy Currency
3. Electron transfer chain 
reaction 
 Molecules of NADH
2
 and 
FADH
2
 formed during all above 
processes participate in electron 
transfer chain reaction. Due to 
this, 3 molecules of ATP are 
obtained from each NADH
2 
molecule and 2 molecules of ATP 
from each FADH
2
 molecule. 
Besides ATP, water molecules 
are also formed in this reaction. 
Electron transfer chain reaction is 
operated in mitochondria only.
 Thus, a molecule of glucose 
is completely oxidized in aerobic 
respiration and molecules of CO
2 
and H
2
O are produced along with 
energy.
NAD  -  Nicotinamide Adenine 
 dinucleotide 
FAD  -  Flavin adenine dinucleotide  
 
Both coenzymes are formed in the cells 
and used in cellular respiration.
 If there is insufficient amount of carbohydrates in body due to exceptional 
conditions like fasting and hunger, then lipids and proteins are used for energy production. 
In case of lipids, they are converted into fatty acids whereas proteins into amino acids. 
Fatty acids and amino acids are converted into acetyl-CoA and energy is obtained 
through complete oxidation of acetyl-CoA by the process of Krebs cycle in mitochondria.
Adenine 
Ribose 
Always Remember. 
TCA
Cycle
Acetyl Co A
Page 4


12
Ø    Living Organisms & Life Processes Ø Living Organisms & Energy                     
              Production
Ø Some Nutrients & Energy Efficiency  Ø Cell Division- A Life Process
2. Life Processes in Living Organisms Part -1 
1. How are the food stuffs and their nutrient contents useful   
 for body?
2. What is the importance of balanced diet for body?
3. Which different functions are performed by muscles in body?
1. What is respiration? How does it occur?
4. What is the importance of digestive juices in digestive system?
5. Which system is in action for removal of waste materials produced in human body?
6. What is the role of circulatory system in energy production?
7. How are the various processes occurring in human body controlled? In how many   
 ways ?
Living Organisms and Life Processes
 Various organ-systems are continuously performing their functions in human body. 
Along with the various systems like digestive, respiratory, circulatory, excretory and control 
systems, different external and internal organs are performing their functions independently 
but through a complete co-ordination. This overall system is in action in more or less same 
way in all the organisms. Those are in need of continuous source of energy for this purpose. 
Carbohydrates, fats and lipids are the main sources of this energy and it is harvested by the 
mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy 
production but oxygen is also necessary. All these i.e. food stuffs and oxygen are transported 
up to the cell via circulatory system. Besides, it is coordinated by the control system of the 
body. i.e. each life process contributes in its own way in the process of energy production. 
Functioning of all these life processes also requires the energy. 
 Human and other animals consume the fruits and vegetables. Plants are autotrophs. 
They prepare their own food. They utilize some of the food for themselves whereas remaining 
is stored in various parts like fruits, leaves, stem, roots, etc. We consume all these various 
plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, 
minerals, etc. Which food materials do we consume to obtain these nutrients?
 We obtain the carbohydrates from milk, fruits, jaggary, cane sugar, vegetables, 
potatoes, sweet potatoes, sweetmeats and cereals like wheat, maize, ragi, jowar, millet, 
rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which 
this energy is obtained.
 Many players are seen consuming some food stuffs during breaks of the game. 
Can you recall?
Use your brain power
Why may be the players consuming these food stuffs?
Can you recall?
13
Observe and Label the diagram given beside.
In living organisms, respiration occurs at 
two levels as body and cellular level. 
Oxygen and carbon dioxide are exchanged 
between body and surrounding in case of 
respiration occurring at body level. In case 
of respiration at cellular level, foodstuffs 
are oxidized either with or without help of 
oxygen.
Observe 
Living organism and Energy production
2.1  Human respiratory system
Can you tell?
1. How many atoms of C, H and O are 
respectively present in a molecule of 
glucose?
2. Which types of chemical bonds are 
present between all these atoms?
3. In terms of Chemistry what happens 
actually when a molecule is oxidized?
 Carbohydrates of the food that we consume everyday are mainly utilized for production 
of energy required for daily need. This energy is obtained in the form of ATP. For this 
purpose, glucose, a type of carbohydrates is oxidized step by step in the cells. This is 
called as cellular respiration. Cellular respiration occurs among the living organisms by 
two methods. Those two methods are aerobic respiration (oxygen is involved) and 
anaerobic respiration (oxygen is not involved). In aerobic respiration, glucose is oxidized 
in three steps. 
1. Glycolysis 
 Process of glycolysis occurs in cytoplasm. A molecule of glucose is oxidized step by 
step in this process and two molecules of each i.e. pyruvic acid, ATP, NADH
2 
and water 
are formed. 
 Molecules of pyruvic acid formed in this process are converted into molecules of 
Acetyl-Coenzyme-A. Two molecules of NADH
2
 and two molecules of  CO
2
 are released 
during this process.
2. Tricarboxylic acid cycle (Krebs cycle) 
 Both molecules of acetyl-CoA enter the mitochondria. Cyclic chain of reactions called 
as tricarboxylic acid cycle is operated on it in the mitochondria. Acetyl part of acetyl-CoA 
is completely oxidized through this cyclical process and molecules CO
2
, H
2
O, NADH
2
, 
FADH
2
 are derived. 
14
Fatty acids 
Mitochondrial 
Matrix
Outer 
Membrane 
Inner 
Membrane 
Pyruvic acid 
2.2 Mitochondria and Tri-carboxylic acid cycle 
ATP: Adenosine triphosphate is 
energy-rich molecule and energy is 
stored in the bonds by which phosphate 
groups are attached to each other. 
These molecules are stored in the cells 
as per need. Chemically, ATP is 
triphosphate molecule formed from 
adenosine ribonucleoside. It contains 
a nitrogenous compound-adenine, 
pentose sugar- ribose and three 
phosphate groups. As per the need, 
energy is derived by breaking the 
phosphate bond of ATP; hence ATP is 
called as ‘energy currency’ of the cell.
Energy released 
Adenine 
Ribose 
Phosphate bonds with 
more energy  
Inorganic Phosphate 
ATP ADP
3.3 ATP: Energy Currency
3. Electron transfer chain 
reaction 
 Molecules of NADH
2
 and 
FADH
2
 formed during all above 
processes participate in electron 
transfer chain reaction. Due to 
this, 3 molecules of ATP are 
obtained from each NADH
2 
molecule and 2 molecules of ATP 
from each FADH
2
 molecule. 
Besides ATP, water molecules 
are also formed in this reaction. 
Electron transfer chain reaction is 
operated in mitochondria only.
 Thus, a molecule of glucose 
is completely oxidized in aerobic 
respiration and molecules of CO
2 
and H
2
O are produced along with 
energy.
NAD  -  Nicotinamide Adenine 
 dinucleotide 
FAD  -  Flavin adenine dinucleotide  
 
Both coenzymes are formed in the cells 
and used in cellular respiration.
 If there is insufficient amount of carbohydrates in body due to exceptional 
conditions like fasting and hunger, then lipids and proteins are used for energy production. 
In case of lipids, they are converted into fatty acids whereas proteins into amino acids. 
Fatty acids and amino acids are converted into acetyl-CoA and energy is obtained 
through complete oxidation of acetyl-CoA by the process of Krebs cycle in mitochondria.
Adenine 
Ribose 
Always Remember. 
TCA
Cycle
Acetyl Co A
15
Introduction To   Scientists
 Process of glycolysis was discovered by three scientists 
Gustav Embden, Otto Meyerhof, and Jacob Parnas along with 
their colleagues. For this purpose, they performed experiments on 
muscles. Hence, glycolysis is also called as Embden-Meyerhof- 
Parnas pathway (EMP pathway).
 The cyclical reactions of tricarboxylic acid cycle were 
discovered by Sir Hans Krebs. Hence, this cyclical process is also 
called as Krebs cycle. He has been awarded the Nobel Prize in 
1953 for this discovery.                                                              
Sir Hans Krebs  
 (1900-1981)
Lipids Carbohydrates
Proteins 
Fatty acids
Glycolysis
Amino acids
Pyruvic acid
Acetyl-CoA
Krebs Cycle
CO
2 
 + H
2
O + Energy
Pyruvic 
acid
Pyruvic 
acid
Pyruvic acid 
Glycolysis
Glucose
Fermentation 
Fermentation
Fermentation
Alcohol 
Yeast
Different 
Products
Ex: Vinegar, 
Vitamins, etc.
Various 
Microbes
Lactic acid
Erythrocytes, 
Muscle cells,
Energy Production in Microorganisms through Anaerobic Respiration
 Some organisms cannot live in presence of oxygen. Ex. Many bacteria. Such living 
organisms have to perform anaerobic respiration for energy production. Glycolysis and 
fermentation are two steps of anaerobic respiration. Glucose is incompletely oxidized and 
less amount of energy is obtained in this type of respiration.  Pyruvic acid produced through 
glycolysis is converted into other organic acids or alcohol with the help of some enzymes 
in this process. This is called as fermentation. Some higher plants, animals and aerobic 
microorganisms also perform anaerobic respiration instead of aerobic respiration if there 
is depletion in oxygen level in the surrounding.
Ex. Seeds perform anaerobic respiration if the soil is submerged under water during 
germination. Similarly, our muscle cells also perform anaerobic respiration while 
performing the exercise. Due to this, less amount of energy is produced in our body and 
lactic acid accumulates due to which we feel tired.
Process of energy production through
aerobic respiration of carbohydrates, 
proteins and fats.
Anaerobic respiration in living 
organisms/ cells
Page 5


12
Ø    Living Organisms & Life Processes Ø Living Organisms & Energy                     
              Production
Ø Some Nutrients & Energy Efficiency  Ø Cell Division- A Life Process
2. Life Processes in Living Organisms Part -1 
1. How are the food stuffs and their nutrient contents useful   
 for body?
2. What is the importance of balanced diet for body?
3. Which different functions are performed by muscles in body?
1. What is respiration? How does it occur?
4. What is the importance of digestive juices in digestive system?
5. Which system is in action for removal of waste materials produced in human body?
6. What is the role of circulatory system in energy production?
7. How are the various processes occurring in human body controlled? In how many   
 ways ?
Living Organisms and Life Processes
 Various organ-systems are continuously performing their functions in human body. 
Along with the various systems like digestive, respiratory, circulatory, excretory and control 
systems, different external and internal organs are performing their functions independently 
but through a complete co-ordination. This overall system is in action in more or less same 
way in all the organisms. Those are in need of continuous source of energy for this purpose. 
Carbohydrates, fats and lipids are the main sources of this energy and it is harvested by the 
mitochondria present in each cell. It is not like that only foodstuff is sufficient for energy 
production but oxygen is also necessary. All these i.e. food stuffs and oxygen are transported 
up to the cell via circulatory system. Besides, it is coordinated by the control system of the 
body. i.e. each life process contributes in its own way in the process of energy production. 
Functioning of all these life processes also requires the energy. 
 Human and other animals consume the fruits and vegetables. Plants are autotrophs. 
They prepare their own food. They utilize some of the food for themselves whereas remaining 
is stored in various parts like fruits, leaves, stem, roots, etc. We consume all these various 
plant materials and obtain different nutrients like carbohydrates, fats, proteins, vitamins, 
minerals, etc. Which food materials do we consume to obtain these nutrients?
 We obtain the carbohydrates from milk, fruits, jaggary, cane sugar, vegetables, 
potatoes, sweet potatoes, sweetmeats and cereals like wheat, maize, ragi, jowar, millet, 
rice, etc. We get 4Kcal energy per gram of carbohydrates. Let us study the way by which 
this energy is obtained.
 Many players are seen consuming some food stuffs during breaks of the game. 
Can you recall?
Use your brain power
Why may be the players consuming these food stuffs?
Can you recall?
13
Observe and Label the diagram given beside.
In living organisms, respiration occurs at 
two levels as body and cellular level. 
Oxygen and carbon dioxide are exchanged 
between body and surrounding in case of 
respiration occurring at body level. In case 
of respiration at cellular level, foodstuffs 
are oxidized either with or without help of 
oxygen.
Observe 
Living organism and Energy production
2.1  Human respiratory system
Can you tell?
1. How many atoms of C, H and O are 
respectively present in a molecule of 
glucose?
2. Which types of chemical bonds are 
present between all these atoms?
3. In terms of Chemistry what happens 
actually when a molecule is oxidized?
 Carbohydrates of the food that we consume everyday are mainly utilized for production 
of energy required for daily need. This energy is obtained in the form of ATP. For this 
purpose, glucose, a type of carbohydrates is oxidized step by step in the cells. This is 
called as cellular respiration. Cellular respiration occurs among the living organisms by 
two methods. Those two methods are aerobic respiration (oxygen is involved) and 
anaerobic respiration (oxygen is not involved). In aerobic respiration, glucose is oxidized 
in three steps. 
1. Glycolysis 
 Process of glycolysis occurs in cytoplasm. A molecule of glucose is oxidized step by 
step in this process and two molecules of each i.e. pyruvic acid, ATP, NADH
2 
and water 
are formed. 
 Molecules of pyruvic acid formed in this process are converted into molecules of 
Acetyl-Coenzyme-A. Two molecules of NADH
2
 and two molecules of  CO
2
 are released 
during this process.
2. Tricarboxylic acid cycle (Krebs cycle) 
 Both molecules of acetyl-CoA enter the mitochondria. Cyclic chain of reactions called 
as tricarboxylic acid cycle is operated on it in the mitochondria. Acetyl part of acetyl-CoA 
is completely oxidized through this cyclical process and molecules CO
2
, H
2
O, NADH
2
, 
FADH
2
 are derived. 
14
Fatty acids 
Mitochondrial 
Matrix
Outer 
Membrane 
Inner 
Membrane 
Pyruvic acid 
2.2 Mitochondria and Tri-carboxylic acid cycle 
ATP: Adenosine triphosphate is 
energy-rich molecule and energy is 
stored in the bonds by which phosphate 
groups are attached to each other. 
These molecules are stored in the cells 
as per need. Chemically, ATP is 
triphosphate molecule formed from 
adenosine ribonucleoside. It contains 
a nitrogenous compound-adenine, 
pentose sugar- ribose and three 
phosphate groups. As per the need, 
energy is derived by breaking the 
phosphate bond of ATP; hence ATP is 
called as ‘energy currency’ of the cell.
Energy released 
Adenine 
Ribose 
Phosphate bonds with 
more energy  
Inorganic Phosphate 
ATP ADP
3.3 ATP: Energy Currency
3. Electron transfer chain 
reaction 
 Molecules of NADH
2
 and 
FADH
2
 formed during all above 
processes participate in electron 
transfer chain reaction. Due to 
this, 3 molecules of ATP are 
obtained from each NADH
2 
molecule and 2 molecules of ATP 
from each FADH
2
 molecule. 
Besides ATP, water molecules 
are also formed in this reaction. 
Electron transfer chain reaction is 
operated in mitochondria only.
 Thus, a molecule of glucose 
is completely oxidized in aerobic 
respiration and molecules of CO
2 
and H
2
O are produced along with 
energy.
NAD  -  Nicotinamide Adenine 
 dinucleotide 
FAD  -  Flavin adenine dinucleotide  
 
Both coenzymes are formed in the cells 
and used in cellular respiration.
 If there is insufficient amount of carbohydrates in body due to exceptional 
conditions like fasting and hunger, then lipids and proteins are used for energy production. 
In case of lipids, they are converted into fatty acids whereas proteins into amino acids. 
Fatty acids and amino acids are converted into acetyl-CoA and energy is obtained 
through complete oxidation of acetyl-CoA by the process of Krebs cycle in mitochondria.
Adenine 
Ribose 
Always Remember. 
TCA
Cycle
Acetyl Co A
15
Introduction To   Scientists
 Process of glycolysis was discovered by three scientists 
Gustav Embden, Otto Meyerhof, and Jacob Parnas along with 
their colleagues. For this purpose, they performed experiments on 
muscles. Hence, glycolysis is also called as Embden-Meyerhof- 
Parnas pathway (EMP pathway).
 The cyclical reactions of tricarboxylic acid cycle were 
discovered by Sir Hans Krebs. Hence, this cyclical process is also 
called as Krebs cycle. He has been awarded the Nobel Prize in 
1953 for this discovery.                                                              
Sir Hans Krebs  
 (1900-1981)
Lipids Carbohydrates
Proteins 
Fatty acids
Glycolysis
Amino acids
Pyruvic acid
Acetyl-CoA
Krebs Cycle
CO
2 
 + H
2
O + Energy
Pyruvic 
acid
Pyruvic 
acid
Pyruvic acid 
Glycolysis
Glucose
Fermentation 
Fermentation
Fermentation
Alcohol 
Yeast
Different 
Products
Ex: Vinegar, 
Vitamins, etc.
Various 
Microbes
Lactic acid
Erythrocytes, 
Muscle cells,
Energy Production in Microorganisms through Anaerobic Respiration
 Some organisms cannot live in presence of oxygen. Ex. Many bacteria. Such living 
organisms have to perform anaerobic respiration for energy production. Glycolysis and 
fermentation are two steps of anaerobic respiration. Glucose is incompletely oxidized and 
less amount of energy is obtained in this type of respiration.  Pyruvic acid produced through 
glycolysis is converted into other organic acids or alcohol with the help of some enzymes 
in this process. This is called as fermentation. Some higher plants, animals and aerobic 
microorganisms also perform anaerobic respiration instead of aerobic respiration if there 
is depletion in oxygen level in the surrounding.
Ex. Seeds perform anaerobic respiration if the soil is submerged under water during 
germination. Similarly, our muscle cells also perform anaerobic respiration while 
performing the exercise. Due to this, less amount of energy is produced in our body and 
lactic acid accumulates due to which we feel tired.
Process of energy production through
aerobic respiration of carbohydrates, 
proteins and fats.
Anaerobic respiration in living 
organisms/ cells
16
1. Which type of cellular respiration performs complete          
 oxidation of glucose?
2. Which cell organelle is necessary for complete oxidation of 
 glucose?
Energy from different food components
 Excess of the carbohydrates are stored in liver and muscles in the form of glycogen. 
What is the source of proteins? What are they made up of?
 Proteins are the macromolecules formed by bonding together many amino acids. 
Proteins of animal origin are called as ‘first class’ proteins. We get 4 Kcal of energy per 
gram of proteins. Amino acids are obtained after digestion of proteins. Those amino acids 
are absorbed in the body and transported up to each organ and cell via blood. From these 
amino acids, organs and cells produce various proteins necessary for themselves and the 
whole body. Those examples are given in the following diagram.
 Excess of amino acids 
obtained from proteins are not 
stored in the body. They are 
broken down and the ammonia 
formed is eliminated out of the 
body. If necessary, excess of 
proteins are converted into other 
useful substances like glucose 
through the process of 
gluconeogenesis.
 Plants produce the necessary 
amino acids from minerals denovo 
and thereby produce different 
proteins. An enzyme RUBISCO 
present in the plant chloroplasts is 
most abundant protein found in 
nature.
Always remember
Amino 
Acids 
Skin: 
Melanin , 
keratin
Bones: Ossein
Cells : 
various proteins of 
cell membrane, 
various enzymes
Pancreas:
Insulin,
Trypsin
Pituitary Gland : 
Various 
hormones
Muscles:
Actin and 
Myosin flexible 
proteins 
Blood:
Haemoglobin, 
Antibodies
2.4 Proteins and different amino  acids obtained 
Can you tell?
Can you recall?
From where do we obtain the lipids?
       The substances formed by specific chemical bond between fatty acids and alcohol are 
called as lipids. Digestion of lipids consumed by us is nothing but their conversion into 
fatty acids and alcohol. Fatty acids are absorbed up and distributed everywhere within 
the body. From those fatty acids, different cells produce various substances necessary to 
themselves. Ex. the molecules called as phospholipids which are essential for producing 
plasma membrane are formed from fatty acids. Besides, fatty acids are used for producing 
hormones like progesterone, estrogen, testosterone, aldosterone, etc. and the covering 
around the axons of nerve cells. We get 9 KCal of energy per gram of lipids. Excess of 
lipids are stored in adipose connective tissue in the body.