NCERT Textbook: Cellular Organelles | Biotechnology for Class 11 - NEET PDF Download

 Page 1


Cell Organelles 
and Biomolecules
Unit II
Chapter 2 
Cellular Organelles
Chapter 3
Biomolecules
Chapter 4
Enzymes and Bioenergetics
Chapter 5
Cellular Processes
Being the structural and functional unit of a living 
organism, cell has got a very important place in 
understanding the entire functioning of a living 
system. Therefore, it is required to have a thorough 
understanding of the structure and functions of a cell. 
This unit gives a detailed description of the  general 
characteristics of cell, its structure and growth. Cell 
theory, which will be explained in Chapter 2 of this 
unit, offered an intriguing explanation of the living 
phenomena. It ??lled the researchers with wonder 
and compelled them to investigate the molecular 
structure and physiochemical characteristics of a 
cell. Chapter 3 deals with details of the molecular 
compounds responsible for carrying out various 
cellular processes and sustaining living systems. 
Central to the various molecular processes are the 
biocatalysts, which help in carrying out various 
biochemical reactions in a living system effectively.   
The importance of biocatalysts and their mechanism 
of action will be discussed in Chapter 4. The concepts 
and mechanisms of some of the important cellular 
processes have been dealt with in Chapter 5. 
Chapter 2 Cellular Organelles.indd   23 09/01/2025   15:23:12
Reprint 2025-26
Page 2


Cell Organelles 
and Biomolecules
Unit II
Chapter 2 
Cellular Organelles
Chapter 3
Biomolecules
Chapter 4
Enzymes and Bioenergetics
Chapter 5
Cellular Processes
Being the structural and functional unit of a living 
organism, cell has got a very important place in 
understanding the entire functioning of a living 
system. Therefore, it is required to have a thorough 
understanding of the structure and functions of a cell. 
This unit gives a detailed description of the  general 
characteristics of cell, its structure and growth. Cell 
theory, which will be explained in Chapter 2 of this 
unit, offered an intriguing explanation of the living 
phenomena. It ??lled the researchers with wonder 
and compelled them to investigate the molecular 
structure and physiochemical characteristics of a 
cell. Chapter 3 deals with details of the molecular 
compounds responsible for carrying out various 
cellular processes and sustaining living systems. 
Central to the various molecular processes are the 
biocatalysts, which help in carrying out various 
biochemical reactions in a living system effectively.   
The importance of biocatalysts and their mechanism 
of action will be discussed in Chapter 4. The concepts 
and mechanisms of some of the important cellular 
processes have been dealt with in Chapter 5. 
Chapter 2 Cellular Organelles.indd   23 09/01/2025   15:23:12
Reprint 2025-26
G.N. Ramachandran
(1922–2001) 
He was born in a small town near Cochin 
on the Southwestern coast of India. 
His father taught mathematics at a 
local college and profoundly in??uenced 
Ramachandran’s interest in mathematics. 
Ramachandran completed his graduation 
in physics in the year 1942 and was the 
top-ranking student at his college. He 
received a doctoral degree in 1949 from 
Cambridge University. His meeting with 
Linus Pauling considerably directed his 
attention towards solving the intricate 
structure of collagen. In 1954, his study on 
the Triple Helical Structure of Collagen was 
published in the Nature. Ramachandran 
was the founder of ‘Madras School’ of 
conformational analysis of biopolymers.  
His work on the analysis of the allowed 
conformations of proteins through the use 
of  ‘Ramachandran  plot’ is considered to be 
one of the most outstanding contributions 
in structural biology. 
Chapter 2 Cellular Organelles.indd   24 09/01/2025   15:23:14
Reprint 2025-26
Page 3


Cell Organelles 
and Biomolecules
Unit II
Chapter 2 
Cellular Organelles
Chapter 3
Biomolecules
Chapter 4
Enzymes and Bioenergetics
Chapter 5
Cellular Processes
Being the structural and functional unit of a living 
organism, cell has got a very important place in 
understanding the entire functioning of a living 
system. Therefore, it is required to have a thorough 
understanding of the structure and functions of a cell. 
This unit gives a detailed description of the  general 
characteristics of cell, its structure and growth. Cell 
theory, which will be explained in Chapter 2 of this 
unit, offered an intriguing explanation of the living 
phenomena. It ??lled the researchers with wonder 
and compelled them to investigate the molecular 
structure and physiochemical characteristics of a 
cell. Chapter 3 deals with details of the molecular 
compounds responsible for carrying out various 
cellular processes and sustaining living systems. 
Central to the various molecular processes are the 
biocatalysts, which help in carrying out various 
biochemical reactions in a living system effectively.   
The importance of biocatalysts and their mechanism 
of action will be discussed in Chapter 4. The concepts 
and mechanisms of some of the important cellular 
processes have been dealt with in Chapter 5. 
Chapter 2 Cellular Organelles.indd   23 09/01/2025   15:23:12
Reprint 2025-26
G.N. Ramachandran
(1922–2001) 
He was born in a small town near Cochin 
on the Southwestern coast of India. 
His father taught mathematics at a 
local college and profoundly in??uenced 
Ramachandran’s interest in mathematics. 
Ramachandran completed his graduation 
in physics in the year 1942 and was the 
top-ranking student at his college. He 
received a doctoral degree in 1949 from 
Cambridge University. His meeting with 
Linus Pauling considerably directed his 
attention towards solving the intricate 
structure of collagen. In 1954, his study on 
the Triple Helical Structure of Collagen was 
published in the Nature. Ramachandran 
was the founder of ‘Madras School’ of 
conformational analysis of biopolymers.  
His work on the analysis of the allowed 
conformations of proteins through the use 
of  ‘Ramachandran  plot’ is considered to be 
one of the most outstanding contributions 
in structural biology. 
Chapter 2 Cellular Organelles.indd   24 09/01/2025   15:23:14
Reprint 2025-26
2.1 Plasma 
Membrane 
2.2 Cell Wall
2.3 Endomembrane 
System
2.4 Mitochondria
2.5 Plastids
2.6 Ribosomes
2.7 Microbodies
2.8 Cytoskeleton
2.9 Cilia and Flagella
2.10 Centrosome and 
Centrioles
2.11 Nucleus
2.12 Chromosome
Overview Our body does large number of tasks at a given point 
of time for example, food digestion, sending electrical 
messages through nerves, pumping blood from the heart, 
circulating nutrients, synthesising proteins, ??ltering urine 
and many more. All this is possible because of cells which 
are  considered to be the basic unit of life. Each cell is 
equipped with different machineries known as organelles 
responsible for different functions. You also know that 
cells present in organisms (unicellular or multicellular) 
have been broadly characterised into two main categories, 
based on the nuclear organisation and membrane-bound 
cell organelles, i.e., prokaryote and eukaryote. Some of 
the components are common to both prokaryotic and 
eukaryotic cell. These are plasma membrane, cytoplasm, 
ribosomes, DNA, etc. Prokaryotic cells are without an 
organised nucleus and contain numerous ribosomes, 
mesosomes (folds in plasma membrane) besides having 
locomotory structures such as ??agella in some of them. 
While a eukaryotic cell has a well-organised nucleus, cell 
Cellular 
Organelles
Chapter 2
Chapter 2 Cellular Organelles.indd   25 09/01/2025   15:23:14
Reprint 2025-26
Page 4


Cell Organelles 
and Biomolecules
Unit II
Chapter 2 
Cellular Organelles
Chapter 3
Biomolecules
Chapter 4
Enzymes and Bioenergetics
Chapter 5
Cellular Processes
Being the structural and functional unit of a living 
organism, cell has got a very important place in 
understanding the entire functioning of a living 
system. Therefore, it is required to have a thorough 
understanding of the structure and functions of a cell. 
This unit gives a detailed description of the  general 
characteristics of cell, its structure and growth. Cell 
theory, which will be explained in Chapter 2 of this 
unit, offered an intriguing explanation of the living 
phenomena. It ??lled the researchers with wonder 
and compelled them to investigate the molecular 
structure and physiochemical characteristics of a 
cell. Chapter 3 deals with details of the molecular 
compounds responsible for carrying out various 
cellular processes and sustaining living systems. 
Central to the various molecular processes are the 
biocatalysts, which help in carrying out various 
biochemical reactions in a living system effectively.   
The importance of biocatalysts and their mechanism 
of action will be discussed in Chapter 4. The concepts 
and mechanisms of some of the important cellular 
processes have been dealt with in Chapter 5. 
Chapter 2 Cellular Organelles.indd   23 09/01/2025   15:23:12
Reprint 2025-26
G.N. Ramachandran
(1922–2001) 
He was born in a small town near Cochin 
on the Southwestern coast of India. 
His father taught mathematics at a 
local college and profoundly in??uenced 
Ramachandran’s interest in mathematics. 
Ramachandran completed his graduation 
in physics in the year 1942 and was the 
top-ranking student at his college. He 
received a doctoral degree in 1949 from 
Cambridge University. His meeting with 
Linus Pauling considerably directed his 
attention towards solving the intricate 
structure of collagen. In 1954, his study on 
the Triple Helical Structure of Collagen was 
published in the Nature. Ramachandran 
was the founder of ‘Madras School’ of 
conformational analysis of biopolymers.  
His work on the analysis of the allowed 
conformations of proteins through the use 
of  ‘Ramachandran  plot’ is considered to be 
one of the most outstanding contributions 
in structural biology. 
Chapter 2 Cellular Organelles.indd   24 09/01/2025   15:23:14
Reprint 2025-26
2.1 Plasma 
Membrane 
2.2 Cell Wall
2.3 Endomembrane 
System
2.4 Mitochondria
2.5 Plastids
2.6 Ribosomes
2.7 Microbodies
2.8 Cytoskeleton
2.9 Cilia and Flagella
2.10 Centrosome and 
Centrioles
2.11 Nucleus
2.12 Chromosome
Overview Our body does large number of tasks at a given point 
of time for example, food digestion, sending electrical 
messages through nerves, pumping blood from the heart, 
circulating nutrients, synthesising proteins, ??ltering urine 
and many more. All this is possible because of cells which 
are  considered to be the basic unit of life. Each cell is 
equipped with different machineries known as organelles 
responsible for different functions. You also know that 
cells present in organisms (unicellular or multicellular) 
have been broadly characterised into two main categories, 
based on the nuclear organisation and membrane-bound 
cell organelles, i.e., prokaryote and eukaryote. Some of 
the components are common to both prokaryotic and 
eukaryotic cell. These are plasma membrane, cytoplasm, 
ribosomes, DNA, etc. Prokaryotic cells are without an 
organised nucleus and contain numerous ribosomes, 
mesosomes (folds in plasma membrane) besides having 
locomotory structures such as ??agella in some of them. 
While a eukaryotic cell has a well-organised nucleus, cell 
Cellular 
Organelles
Chapter 2
Chapter 2 Cellular Organelles.indd   25 09/01/2025   15:23:14
Reprint 2025-26
BiOteChnOlOgy
26
membrane and membrane-bound cell organelles such as 
endoplasmic reticulum, Golgi apparatus, mitochondria, 
plastids, vacuole, lysosomes, peroxisomes, and many 
more. Advancement in microscopic techniques played a 
very crucial role in exploring  the detailed structure of cell.
Let us now look at an individual cell to understand 
the structure and functioning, along with the role in 
establishing cell functioning and life.
2.1 Plasma m embrane Plasma membrane forms the boundary of the cytoplasm 
being guarded from outside by extracellular matrix. The 
membrane is responsible for the relationship of a cell with 
its surrounding. It is semipermeable in nature. Major 
breakthrough in understanding the detailed structure of 
cell membrane was realised only after understanding the 
chemical composition (lipid and protein mainly)  and the 
invention of electron microscope. A widely accepted model 
for the organisation of plasma membrane was proposed by 
Seymour Jonathan Singer and Garth L. Nicolson (1972) as 
‘The Fluid Mosaic Model’ (Fig. 2.1). The model suggests 
plasma membrane to be lipid bilayer surrounding the 
cell with mosaic of globular proteins. Composition of lipid 
and protein varies in different cells, for example, human 
erythrocyte membrane contains approximately 52 per cent 
protein and 40 per cent lipids. Lipid bilayer makes the cell 
boundary in a quasi??uid state and it is dynamic in nature.  
Due to the ??uid nature, lipids and proteins can freely diffuse 
laterally across the membrane. Phospholipids (the major 
membrane lipid) is composed of hydrophilic head facing the 
exterior and long hydrophobic tail of hydrocarbon chains 
occupying the interior of a lipid bilayer. Two different types 
of proteins have been identi??ed in the plasma membrane 
based on their location and association i.e., peripheral 
and integral membrane proteins. Peripheral membrane 
proteins are mainly involved in cell signalling and these are 
super??cially attached to lipid bilayer. Integral membrane 
proteins are partially or fully buried in the plasma membrane. 
Transmembrane proteins are the most abundant type of 
integral membrane protein. Structurally, prokaryotic cell 
membrane is similar to that of eukaryotes.
Chapter 2 Cellular Organelles.indd   26 09/01/2025   15:23:14
Reprint 2025-26
Page 5


Cell Organelles 
and Biomolecules
Unit II
Chapter 2 
Cellular Organelles
Chapter 3
Biomolecules
Chapter 4
Enzymes and Bioenergetics
Chapter 5
Cellular Processes
Being the structural and functional unit of a living 
organism, cell has got a very important place in 
understanding the entire functioning of a living 
system. Therefore, it is required to have a thorough 
understanding of the structure and functions of a cell. 
This unit gives a detailed description of the  general 
characteristics of cell, its structure and growth. Cell 
theory, which will be explained in Chapter 2 of this 
unit, offered an intriguing explanation of the living 
phenomena. It ??lled the researchers with wonder 
and compelled them to investigate the molecular 
structure and physiochemical characteristics of a 
cell. Chapter 3 deals with details of the molecular 
compounds responsible for carrying out various 
cellular processes and sustaining living systems. 
Central to the various molecular processes are the 
biocatalysts, which help in carrying out various 
biochemical reactions in a living system effectively.   
The importance of biocatalysts and their mechanism 
of action will be discussed in Chapter 4. The concepts 
and mechanisms of some of the important cellular 
processes have been dealt with in Chapter 5. 
Chapter 2 Cellular Organelles.indd   23 09/01/2025   15:23:12
Reprint 2025-26
G.N. Ramachandran
(1922–2001) 
He was born in a small town near Cochin 
on the Southwestern coast of India. 
His father taught mathematics at a 
local college and profoundly in??uenced 
Ramachandran’s interest in mathematics. 
Ramachandran completed his graduation 
in physics in the year 1942 and was the 
top-ranking student at his college. He 
received a doctoral degree in 1949 from 
Cambridge University. His meeting with 
Linus Pauling considerably directed his 
attention towards solving the intricate 
structure of collagen. In 1954, his study on 
the Triple Helical Structure of Collagen was 
published in the Nature. Ramachandran 
was the founder of ‘Madras School’ of 
conformational analysis of biopolymers.  
His work on the analysis of the allowed 
conformations of proteins through the use 
of  ‘Ramachandran  plot’ is considered to be 
one of the most outstanding contributions 
in structural biology. 
Chapter 2 Cellular Organelles.indd   24 09/01/2025   15:23:14
Reprint 2025-26
2.1 Plasma 
Membrane 
2.2 Cell Wall
2.3 Endomembrane 
System
2.4 Mitochondria
2.5 Plastids
2.6 Ribosomes
2.7 Microbodies
2.8 Cytoskeleton
2.9 Cilia and Flagella
2.10 Centrosome and 
Centrioles
2.11 Nucleus
2.12 Chromosome
Overview Our body does large number of tasks at a given point 
of time for example, food digestion, sending electrical 
messages through nerves, pumping blood from the heart, 
circulating nutrients, synthesising proteins, ??ltering urine 
and many more. All this is possible because of cells which 
are  considered to be the basic unit of life. Each cell is 
equipped with different machineries known as organelles 
responsible for different functions. You also know that 
cells present in organisms (unicellular or multicellular) 
have been broadly characterised into two main categories, 
based on the nuclear organisation and membrane-bound 
cell organelles, i.e., prokaryote and eukaryote. Some of 
the components are common to both prokaryotic and 
eukaryotic cell. These are plasma membrane, cytoplasm, 
ribosomes, DNA, etc. Prokaryotic cells are without an 
organised nucleus and contain numerous ribosomes, 
mesosomes (folds in plasma membrane) besides having 
locomotory structures such as ??agella in some of them. 
While a eukaryotic cell has a well-organised nucleus, cell 
Cellular 
Organelles
Chapter 2
Chapter 2 Cellular Organelles.indd   25 09/01/2025   15:23:14
Reprint 2025-26
BiOteChnOlOgy
26
membrane and membrane-bound cell organelles such as 
endoplasmic reticulum, Golgi apparatus, mitochondria, 
plastids, vacuole, lysosomes, peroxisomes, and many 
more. Advancement in microscopic techniques played a 
very crucial role in exploring  the detailed structure of cell.
Let us now look at an individual cell to understand 
the structure and functioning, along with the role in 
establishing cell functioning and life.
2.1 Plasma m embrane Plasma membrane forms the boundary of the cytoplasm 
being guarded from outside by extracellular matrix. The 
membrane is responsible for the relationship of a cell with 
its surrounding. It is semipermeable in nature. Major 
breakthrough in understanding the detailed structure of 
cell membrane was realised only after understanding the 
chemical composition (lipid and protein mainly)  and the 
invention of electron microscope. A widely accepted model 
for the organisation of plasma membrane was proposed by 
Seymour Jonathan Singer and Garth L. Nicolson (1972) as 
‘The Fluid Mosaic Model’ (Fig. 2.1). The model suggests 
plasma membrane to be lipid bilayer surrounding the 
cell with mosaic of globular proteins. Composition of lipid 
and protein varies in different cells, for example, human 
erythrocyte membrane contains approximately 52 per cent 
protein and 40 per cent lipids. Lipid bilayer makes the cell 
boundary in a quasi??uid state and it is dynamic in nature.  
Due to the ??uid nature, lipids and proteins can freely diffuse 
laterally across the membrane. Phospholipids (the major 
membrane lipid) is composed of hydrophilic head facing the 
exterior and long hydrophobic tail of hydrocarbon chains 
occupying the interior of a lipid bilayer. Two different types 
of proteins have been identi??ed in the plasma membrane 
based on their location and association i.e., peripheral 
and integral membrane proteins. Peripheral membrane 
proteins are mainly involved in cell signalling and these are 
super??cially attached to lipid bilayer. Integral membrane 
proteins are partially or fully buried in the plasma membrane. 
Transmembrane proteins are the most abundant type of 
integral membrane protein. Structurally, prokaryotic cell 
membrane is similar to that of eukaryotes.
Chapter 2 Cellular Organelles.indd   26 09/01/2025   15:23:14
Reprint 2025-26
Cellular  Organelles 27
Edwin Gorter and F. Grendel in the year 1925 collected blood cells (chromocytes) from 
the artery or vein of mammals. The chromocytes were separated from plasma by several 
washes with saline solution and extracted using acetone. They obtained lipids that 
exactly covered the entire surface area of chromocytes like a two-molecular thick layer. 
They observed all the cells, either prokaryotic or eukaryotic, to be enclosed with well-
de??ned plasma membrane, which maintains cell identity by preserving its internal 
constituents from the environment. This evidence was further supported by high 
magni??cation electron micrograph referring plasma membrane as a ‘railroad track’, 
with two densely stained lines of polar heads groups of phospholipids and a lightly 
stained portion representing hydrophobic fatty acid chain. Its molecular organisation 
was still rudimentary. On the basis of this, they proposed the bilayer structure of plasma 
membrane rather than a monolayer, using mammalian RBCs as a model.
Fig. 2.1: Schematic diagram showing ??uid mosaic model of plasma membrane
Cholesterol
Integral
membrane
protein
Membrane channel Peripheral
membrane
protein
Peripheral membrane
protein
Inside of cell
Outside of cell
Glycoprotein
Glycolipid
Lipid 
bilayer
Hydrophillic
head
Hydrophillic 
head
Hydrophobic 
tails
Box 1
A special membranous structure is formed by 
extension of plasma membrane in the cell, this structure 
called mesosome, which is in the form of vesicle, tubules 
and lamellae. Mesosomes increase the surface of plasma 
membrane. 
The quasi??uid nature of membrane is useful for different 
cellular functions such as cell division, cell growth, 
Chapter 2 Cellular Organelles.indd   27 09/01/2025   15:23:14
Reprint 2025-26