UNIT 3
CELL: STRUCTURE AND FUNCTIONS
Chapter 8 Biology is the study of living organisms. The detailed description of
Cell: The Unit of Life their form and appearance only brought out their diversity. It is the
cell theory that emphasised the unity underlying this diversity of forms,
Chapter 9 i.e., the cellular organisation of all life forms. A description of cell
Biomolecules structure and cell growth by division is given in the chapters comprising
this unit. Cell theory also created a sense of mystery around living
Chapter 10 phenomena, i.e., physiological and behavioural processes. This mystery
Cell Cycle and was the requirement of integrity of cellular organisation for living
Cell Division phenomena to be demonstrated or observed. In studying and
understanding the physiological and behavioural processes, one can
take a physico-chemical approach and use cell-free systems to
investigate. This approach enables us to describe the various processes
in molecular terms. The approach is established by analysis of living
tissues for elements and compounds. It will tell us what types of organic
compounds are present in living organisms. In the next stage, one can
ask the question: What are these compounds doing inside a cell? And,
in what way they carry out gross physiological processes like digestion,
excretion, memory, defense, recognition, etc. In other words we answer
the question, what is the molecular basis of all physiological processes?
It can also explain the abnormal processes that occur during any
diseased condition. This physico-chemical approach to study and
understand living organisms is called ‘Reductionist Biology’. The
concepts and techniques of physics and chemistry are applied to
understand biology. In Chapter 9 of this unit, a brief description of
biomolecules is provided.
2020-21
, G.N. RAMACHANDRAN, an outstanding figure in the field of protein
structure, was the founder of the ‘Madras school’ of
conformational analysis of biopolymers. His discovery of the triple
helical structure of collagen published in Nature in 1954 and his
analysis of the allowed conformations of proteins through the
use of the ‘Ramachandran plot’ rank among the most outstanding
contributions in structural biology. He was born on October 8,
1922, in a small town, not far from Cochin on the southwestern
coast of India. His father was a professor of mathematics at a
local college and thus had considerable influence in shaping
Ramachandran’s interest in mathematics. After completing his
school years, Ramachandran graduated in 1942 as the top-
ranking student in the B.Sc. (Honors) Physics course of the
University of Madras. He received a Ph.D. from Cambridge
University in 1949. While at Cambridge, Ramachandran met
Linus Pauling and was deeply influenced by his publications on
models of the α-helix and β-sheet structures that directed his
attention to solving the structure of collagen. He passed away at
G.N. Ramachandran the age of 78, on April 7, 2001.
(1922 – 2001)
2020-21
, C HAPTER 8
C ELL: THE U NIT OF LIFE
8.1 What is a Cell? When you look around, you see both living and non-living things. You
8.2 Cell Theory must have wondered and asked yourself – ‘what is it that makes an
organism living, or what is it that an inanimate thing does not have which
8.3 An Overview of
a living thing has’ ? The answer to this is the presence of the basic unit of
Cell
life – the cell in all living organisms.
8.4 Prokaryotic Cells All organisms are composed of cells. Some are composed of a single
8.5 Eukaryotic Cells cell and are called unicellular organisms while others, like us, composed
of many cells, are called multicellular organisms.
8.1 W HAT IS A CELL?
Unicellular organisms are capable of (i) independent existence and
(ii) performing the essential functions of life. Anything less than a complete
structure of a cell does not ensure independent living. Hence, cell is the
fundamental structural and functional unit of all living organisms.
Anton Von Leeuwenhoek first saw and described a live cell. Robert
Brown later discovered the nucleus. The invention of the microscope and
its improvement leading to the electron microscope revealed all the
structural details of the cell.
8.2 C ELL THEORY
In 1838, Matthias Schleiden, a German botanist, examined a large number
of plants and observed that all plants are composed of different kinds of
cells which form the tissues of the plant. At about the same time, Theodore
2020-21
CELL: STRUCTURE AND FUNCTIONS
Chapter 8 Biology is the study of living organisms. The detailed description of
Cell: The Unit of Life their form and appearance only brought out their diversity. It is the
cell theory that emphasised the unity underlying this diversity of forms,
Chapter 9 i.e., the cellular organisation of all life forms. A description of cell
Biomolecules structure and cell growth by division is given in the chapters comprising
this unit. Cell theory also created a sense of mystery around living
Chapter 10 phenomena, i.e., physiological and behavioural processes. This mystery
Cell Cycle and was the requirement of integrity of cellular organisation for living
Cell Division phenomena to be demonstrated or observed. In studying and
understanding the physiological and behavioural processes, one can
take a physico-chemical approach and use cell-free systems to
investigate. This approach enables us to describe the various processes
in molecular terms. The approach is established by analysis of living
tissues for elements and compounds. It will tell us what types of organic
compounds are present in living organisms. In the next stage, one can
ask the question: What are these compounds doing inside a cell? And,
in what way they carry out gross physiological processes like digestion,
excretion, memory, defense, recognition, etc. In other words we answer
the question, what is the molecular basis of all physiological processes?
It can also explain the abnormal processes that occur during any
diseased condition. This physico-chemical approach to study and
understand living organisms is called ‘Reductionist Biology’. The
concepts and techniques of physics and chemistry are applied to
understand biology. In Chapter 9 of this unit, a brief description of
biomolecules is provided.
2020-21
, G.N. RAMACHANDRAN, an outstanding figure in the field of protein
structure, was the founder of the ‘Madras school’ of
conformational analysis of biopolymers. His discovery of the triple
helical structure of collagen published in Nature in 1954 and his
analysis of the allowed conformations of proteins through the
use of the ‘Ramachandran plot’ rank among the most outstanding
contributions in structural biology. He was born on October 8,
1922, in a small town, not far from Cochin on the southwestern
coast of India. His father was a professor of mathematics at a
local college and thus had considerable influence in shaping
Ramachandran’s interest in mathematics. After completing his
school years, Ramachandran graduated in 1942 as the top-
ranking student in the B.Sc. (Honors) Physics course of the
University of Madras. He received a Ph.D. from Cambridge
University in 1949. While at Cambridge, Ramachandran met
Linus Pauling and was deeply influenced by his publications on
models of the α-helix and β-sheet structures that directed his
attention to solving the structure of collagen. He passed away at
G.N. Ramachandran the age of 78, on April 7, 2001.
(1922 – 2001)
2020-21
, C HAPTER 8
C ELL: THE U NIT OF LIFE
8.1 What is a Cell? When you look around, you see both living and non-living things. You
8.2 Cell Theory must have wondered and asked yourself – ‘what is it that makes an
organism living, or what is it that an inanimate thing does not have which
8.3 An Overview of
a living thing has’ ? The answer to this is the presence of the basic unit of
Cell
life – the cell in all living organisms.
8.4 Prokaryotic Cells All organisms are composed of cells. Some are composed of a single
8.5 Eukaryotic Cells cell and are called unicellular organisms while others, like us, composed
of many cells, are called multicellular organisms.
8.1 W HAT IS A CELL?
Unicellular organisms are capable of (i) independent existence and
(ii) performing the essential functions of life. Anything less than a complete
structure of a cell does not ensure independent living. Hence, cell is the
fundamental structural and functional unit of all living organisms.
Anton Von Leeuwenhoek first saw and described a live cell. Robert
Brown later discovered the nucleus. The invention of the microscope and
its improvement leading to the electron microscope revealed all the
structural details of the cell.
8.2 C ELL THEORY
In 1838, Matthias Schleiden, a German botanist, examined a large number
of plants and observed that all plants are composed of different kinds of
cells which form the tissues of the plant. At about the same time, Theodore
2020-21
