Lecture 9 - Introduction to cell | Cell Biology- Botany PDF Download

 Page 1


Introduction to Cell 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Lesson: Introduction to cell 
Lesson Developer: Manju A.Lal 
College/Department: Kirori Mal College, University of Delhi 
Page 2


Introduction to Cell 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Lesson: Introduction to cell 
Lesson Developer: Manju A.Lal 
College/Department: Kirori Mal College, University of Delhi 
 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
 
Chapter: Introduction to Cell           
? Cell is unit of life 
? Characteristics of a living cell 
? History of Cell Biology 
? Cell is the basic unit of structure and function 
? Cell size 
? Cell types 
?  Prokaryotic cell 
?  Characteristics 
? Diversity of prokaryotes 
? Eukaryotic cell 
? Infective particles 
? Viruses   
? Viroids 
? Prions  
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
Page 3


Introduction to Cell 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Lesson: Introduction to cell 
Lesson Developer: Manju A.Lal 
College/Department: Kirori Mal College, University of Delhi 
 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
 
Chapter: Introduction to Cell           
? Cell is unit of life 
? Characteristics of a living cell 
? History of Cell Biology 
? Cell is the basic unit of structure and function 
? Cell size 
? Cell types 
?  Prokaryotic cell 
?  Characteristics 
? Diversity of prokaryotes 
? Eukaryotic cell 
? Infective particles 
? Viruses   
? Viroids 
? Prions  
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
Institute of Lifelong Learning, University of Delhi 2 
Cell is unit of life  
When you see the world around you, a distinction between living and nonliving can be made 
immediately. Let us see, how do you distinguish between these two? 
The organisms, which are living, are able to grow (i.e., there is increase either in size of the 
organism, or in their mass), they can utilize energy from their surrounding for their growth, 
and they are able to reproduce i.e. they produce the progeny of their kind. 
 
Figure: You see a great diversity of living organisms both in size, as well as in shape. 
Source: http://cimg1.ck12.org/datastreams/f-
d%3A0517ff938b6d399c6c915fba103f142ed29e82bf4e8d71e7deccf02e%2BIMAGE%2BIMA
GE.1 (CC-BY-SA) 
Some of the living organisms are so small that you are not able to see them with your 
unaided eyes, These are smaller than 0.1 mm and are called microorganisms. Others can be 
as big as 300 meters e.g. redwood trees. 
Microscopic study of all organisms suggests that they are made up of cells. Like a house, in 
which bricks are the basic unit of structure, cells are the basic unit of structure and 
function of all the living beings. Some organisms are made up of single cell and are called 
unicellular, while others have many cells, so are called multicellular. 
In this chapter you will learn about: - 
1. The characteristics of a living cell. 
2. Discoveries that led to understanding of cell structure and cell 
function. 
3. How did the concept of cell biology evolve? 
Page 4


Introduction to Cell 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Lesson: Introduction to cell 
Lesson Developer: Manju A.Lal 
College/Department: Kirori Mal College, University of Delhi 
 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
 
Chapter: Introduction to Cell           
? Cell is unit of life 
? Characteristics of a living cell 
? History of Cell Biology 
? Cell is the basic unit of structure and function 
? Cell size 
? Cell types 
?  Prokaryotic cell 
?  Characteristics 
? Diversity of prokaryotes 
? Eukaryotic cell 
? Infective particles 
? Viruses   
? Viroids 
? Prions  
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
Institute of Lifelong Learning, University of Delhi 2 
Cell is unit of life  
When you see the world around you, a distinction between living and nonliving can be made 
immediately. Let us see, how do you distinguish between these two? 
The organisms, which are living, are able to grow (i.e., there is increase either in size of the 
organism, or in their mass), they can utilize energy from their surrounding for their growth, 
and they are able to reproduce i.e. they produce the progeny of their kind. 
 
Figure: You see a great diversity of living organisms both in size, as well as in shape. 
Source: http://cimg1.ck12.org/datastreams/f-
d%3A0517ff938b6d399c6c915fba103f142ed29e82bf4e8d71e7deccf02e%2BIMAGE%2BIMA
GE.1 (CC-BY-SA) 
Some of the living organisms are so small that you are not able to see them with your 
unaided eyes, These are smaller than 0.1 mm and are called microorganisms. Others can be 
as big as 300 meters e.g. redwood trees. 
Microscopic study of all organisms suggests that they are made up of cells. Like a house, in 
which bricks are the basic unit of structure, cells are the basic unit of structure and 
function of all the living beings. Some organisms are made up of single cell and are called 
unicellular, while others have many cells, so are called multicellular. 
In this chapter you will learn about: - 
1. The characteristics of a living cell. 
2. Discoveries that led to understanding of cell structure and cell 
function. 
3. How did the concept of cell biology evolve? 
 
Institute of Lifelong Learning, University of Delhi 3 
4. Cell types and cell sizes. 
5. Some of the acellular structures. 
Characteristics of living cells 
All the living cells have following characteristics:- 
? Presence of a membrane around the cell, which restricts entry to only certain 
molecules, besides allowing free passage to water and to some of the gases such as 
oxygen and carbon-di-oxide. The membrane is able to separate the inside space of 
the cell from the surroundings. This helps in keeping the environment of the cell at 
optimal level suitable for various chemical reactions occurring inside the living cell. 
? The cell has its own energy generating system. The energy, which is produced by the 
cell, is conserved in the form of ATP and it is this form of energy, which is utilized for 
various life functions. 
? A cell has its own genetic information, which it has received from its parent cell. 
? The cell has its own machinery by which it can copy, and translate the genetic 
information, which is present in it in the form of polymer of nitrogen bases. This 
information is translated to the sequence of amino acids of a protein molecule by the 
cell machinery.  
? The cell is able to produce its own kind i.e. the cell is capable of forming new 
daughter cells. In plants this capacity of cell division is limited to the meristematic 
tissues, such as stem meristems, root meristems and intercalary meristems.  
History of Cell Biology  
Discovery of the cell was dependent on the invention and improvement of the microscope, 
the equipment used to observe the structures having dimensions lesser than 0.1 mm. 
Janssen had invented the first compound microscope in 1590 with the magnification of 9X. 
Robert Hooke used it in 1665 for the first time to observe a thin section of cork (cork was 
the piece of bark, which is outer dead layer of tree and it was being used as a stopper of the 
bottles). He observed that the section was like a honeycomb structure. It had a number of 
compartments, which were separated by a wall. He considered the wall as a living structure, 
which was enclosing the empty space. These empty spaces were called as „Cells?. He 
thought these cells to be the containers of „noble juices? or „fibrous threads? of once living 
Page 5


Introduction to Cell 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
Lesson: Introduction to cell 
Lesson Developer: Manju A.Lal 
College/Department: Kirori Mal College, University of Delhi 
 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
 
Chapter: Introduction to Cell           
? Cell is unit of life 
? Characteristics of a living cell 
? History of Cell Biology 
? Cell is the basic unit of structure and function 
? Cell size 
? Cell types 
?  Prokaryotic cell 
?  Characteristics 
? Diversity of prokaryotes 
? Eukaryotic cell 
? Infective particles 
? Viruses   
? Viroids 
? Prions  
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
 
 
 
 
 
 
Institute of Lifelong Learning, University of Delhi 2 
Cell is unit of life  
When you see the world around you, a distinction between living and nonliving can be made 
immediately. Let us see, how do you distinguish between these two? 
The organisms, which are living, are able to grow (i.e., there is increase either in size of the 
organism, or in their mass), they can utilize energy from their surrounding for their growth, 
and they are able to reproduce i.e. they produce the progeny of their kind. 
 
Figure: You see a great diversity of living organisms both in size, as well as in shape. 
Source: http://cimg1.ck12.org/datastreams/f-
d%3A0517ff938b6d399c6c915fba103f142ed29e82bf4e8d71e7deccf02e%2BIMAGE%2BIMA
GE.1 (CC-BY-SA) 
Some of the living organisms are so small that you are not able to see them with your 
unaided eyes, These are smaller than 0.1 mm and are called microorganisms. Others can be 
as big as 300 meters e.g. redwood trees. 
Microscopic study of all organisms suggests that they are made up of cells. Like a house, in 
which bricks are the basic unit of structure, cells are the basic unit of structure and 
function of all the living beings. Some organisms are made up of single cell and are called 
unicellular, while others have many cells, so are called multicellular. 
In this chapter you will learn about: - 
1. The characteristics of a living cell. 
2. Discoveries that led to understanding of cell structure and cell 
function. 
3. How did the concept of cell biology evolve? 
 
Institute of Lifelong Learning, University of Delhi 3 
4. Cell types and cell sizes. 
5. Some of the acellular structures. 
Characteristics of living cells 
All the living cells have following characteristics:- 
? Presence of a membrane around the cell, which restricts entry to only certain 
molecules, besides allowing free passage to water and to some of the gases such as 
oxygen and carbon-di-oxide. The membrane is able to separate the inside space of 
the cell from the surroundings. This helps in keeping the environment of the cell at 
optimal level suitable for various chemical reactions occurring inside the living cell. 
? The cell has its own energy generating system. The energy, which is produced by the 
cell, is conserved in the form of ATP and it is this form of energy, which is utilized for 
various life functions. 
? A cell has its own genetic information, which it has received from its parent cell. 
? The cell has its own machinery by which it can copy, and translate the genetic 
information, which is present in it in the form of polymer of nitrogen bases. This 
information is translated to the sequence of amino acids of a protein molecule by the 
cell machinery.  
? The cell is able to produce its own kind i.e. the cell is capable of forming new 
daughter cells. In plants this capacity of cell division is limited to the meristematic 
tissues, such as stem meristems, root meristems and intercalary meristems.  
History of Cell Biology  
Discovery of the cell was dependent on the invention and improvement of the microscope, 
the equipment used to observe the structures having dimensions lesser than 0.1 mm. 
Janssen had invented the first compound microscope in 1590 with the magnification of 9X. 
Robert Hooke used it in 1665 for the first time to observe a thin section of cork (cork was 
the piece of bark, which is outer dead layer of tree and it was being used as a stopper of the 
bottles). He observed that the section was like a honeycomb structure. It had a number of 
compartments, which were separated by a wall. He considered the wall as a living structure, 
which was enclosing the empty space. These empty spaces were called as „Cells?. He 
thought these cells to be the containers of „noble juices? or „fibrous threads? of once living 
 
Institute of Lifelong Learning, University of Delhi 4 
cork trees. He published his observations made with the microscope in the book 
Micrographia. 
 
Figure: Robert Hooke  (1665) used the first compound microscope to observe the cells  ( 
cork) . 
Source: http://historymicrobio.files.wordpress.com/2012/07/robert-hooke.jpg?w=252&h=300, 
http://blogs.scientificamerican.com/history-of-geology/files/2013/07/HOOKE_1665_Micrographia_Cell.jpg 
 
Anton Van Leeuwenhoek improved the lens system. Using the improved lens, he observed a 
number of moving structures in a drop of pond water, which he called ‘ an i ma l cul e s’. 
Similarly, Nehemiah Grew studied the sections of plant tissues and concluded that all the 
tissues consist of cells.  
A brief historical account of the landmark researches is given in the table. 
Table: History of Cell Biology 
Source: Author 
Year Name of the Scientist Contribution 
1590 Janssen Invented the compound 
microscope, which combines 
two lenses for greater 
magnification. 
1665 Robert Hooke Published Micrographia, in 
which he describes and