1
UNIT 3
CELL: STRUCTURE AND FUNCTIONS
Introduction to Biology and Reductionist Approach--
1. Biology and Diversity
1. Biology is the study of living organisms.
2. The detailed description of their form and appearance only brought out their
diversity.
3. It is the cell theory that emphasised the unity underlying this diversity of forms,
i.e., the cellular organisation of all life forms.
4. A description of cell structure and cell growth by division is given in the chapters
comprising this unit.
2. Mystery of Living Phenomena
1. Cell theory also created a sense of mystery around living phenomena, i.e.,
physiological and behavioural processes.
2. This mystery was the requirement of integrity of cellular organisation for living
phenomena to be demonstrated or observed.
3. Physico-Chemical Approach
1. In studying and understanding the physiological and behavioural processes, one
can take a physico-chemical approach and use cell-free systems to investigate.
2. This approach enables us to describe the various processes in molecular terms.
3. The approach is established by analysis of living tissues for elements and
compounds.
4. It will tell us what types of organic compounds are present in living organisms.
4. Functional Questions
1. In the next stage, one can ask the question:
1) What are these compounds doing inside a cell?And,
2) In what way they carry out gross physiological processes like digestion,
excretion, memory, defense, recognition, etc.
2. In other words, we try to answer the question
what is the molecular basis of all physiological processes?
3. It can also explain the abnormal processes that occur during any diseased
condition.
5. Reductionist Biology
1. This physico-chemical approach to study and understand living organisms is
called ‘Reductionist Biology’.
2. The concepts and techniques of physics and chemistry are applied to understand
biology.
3. In Chapter 9 of this unit, a brief description of biomolecules is provided.
, G.N. Ramachandran 2
(1922 – 2001)
1. Scientific Contributions-
1. G.N. Ramachandran, an outstanding figure in the field of protein structure, was
the founder of the ‘Madras school’ of conformational analysis of biopolymers.
2. His discovery of the triple helical structure of collagen published in Nature in
1954 and
3. His analysis of the allowed conformations of proteins through the use of the
‘Ramachandran plot’ rank among the most outstanding contributions in
structural biology.
2. Early Life-
1. He was born on October 8, 1922, in a small town, not far from Cochin on the
southwestern coast of India.
2. His father was a professor of mathematics at a local college and thus had
considerable influence in shaping Ramachandran’s interest in mathematics.
3. Education-
1. 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.
2. He received a Ph.D. from Cambridge University in 1949.
4. Influences and Research Direction-
1. 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.
5. Later Life-
1. He passed away at the age of 78, on April 7, 2001.
G.N. Ramachandran
(1922 – 2001)
, CHAPTER 8 3
CELL: THE UNIT OF LIFE
Introduction-
Living and Non-living Things-
1. When you look around, you see both living and non-living things.
2. You must have wondered and asked yourself –
1. ‘what is it that makes an organism living, or
2. what is it that an inanimate thing does not have which a living thing has’?
3. The answer to this is the presence of the basic unit of life – the cell in all living
organisms.
Composition of Organisms-
1. All organisms are composed of cells.
2. Some are composed of a single cell and are called unicellular organisms.
3. While others, like us, composed of many cells, are called multicellular organisms.
8.1 WHAT IS A CELL?
Unicellular Organisms-
1. Unicellular organisms are capable of
1. (i) independent existence and
2. (ii) performing the essential functions of life.
2. Anything less than a complete structure of a cell does not ensure independent
living.
3. Hence, cell is the fundamental structural and functional unit of all living
organisms.
Discovery of Cell-
1. Antonie Von Leeuwenhoek first saw and described a live cell.
2. Robert Brown later discovered the nucleus.
3. The invention of the microscope and its improvement leading to the electron
microscope revealed all the structural details of the cell.
Fig 8.3: Development of complex organism from the simplest form
, 8.2 CELL THEORY 4
Studies on Plant Cells
1. 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.
Studies on Animal Cells
1. At about the same time, Theodore Schwann (1839), a German Zoologist, studied
different types of animal cells and reported that
cells had a thin outer layer which is today known as the ‘plasma membrane’.
2. He also concluded, based on his studies on plant tissues, that
the presence of cell wall is a unique character of the plant cells.
3. On the basis of this, Schwann proposed the hypothesis that
the bodies of animals and plants are composed of cells and products of cells.
Formulation of Cell Theory
1. Schleiden and Schwann together formulated the cell theory.
All living organisms are composed of cells and products of cells.
2. This theory however, did not explain as to how new cells were formed.
final form of cell theory
1. Rudolf Virchow (1855) first explained that cells divided and new cells are
formed from pre-existing cells (Omnis cellula-e cellula).
2. He modified the hypothesis of Schleiden and Schwann to give the cell theory a
final shape.
3. Cell Theory as Understood Today
1. All living organisms are composed of cells and products of cells.
2. All cells arise from pre-existing cells.
Fig 8.6: Formation of new cells from pre-existing cells
Fig 8.5: Cell theory
, 5
8.3 AN OVERVIEW OF CELL
Observation of Plant and Animal Cells
1. You have earlier observed cells in an onion peel and/or human cheek cells under
the microscope.Let us recollect their structure.
2. The onion cell, which is a typical plant cell, has a distinct cell wall as its outer
boundary and just within it is the cell membrane.
3. The cells of the human cheek have an outer membrane as the delimiting structure
of the cell.
Nucleus
1. Inside each cell is a dense membrane bound structure called nucleus.
2. This nucleus contains the chromosomes which in turn contain the genetic
material, DNA.
3. Cells that have membrane bound nuclei are called eukaryotic
4. whereas cells that lack a membrane bound nucleus are prokaryotic.
5. Nuclear membrane is found in eukaryotes.
cytoplasm -
1. In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm
occupies the volume of the cell.
2. The cytoplasm is the main arena of cellular activities in both the plant and
animal cells.
3. Various chemical reactions occur in it to keep the cell in the ‘living state’.
Cell Organelles in Eukaryotic and Prokaryotic Cells
1. Besides the nucleus, the eukaryotic cells have other membrane bound distinct
structures called organelles like the
1. endoplasmic reticulum (ER),
2. the golgi complex,
3. lysosomes,
4. mitochondria,
5. microbodies and
6. vacuoles.
2. The prokaryotic cells lack such membrane bound organelles.
non-membrane bound organelles-
a) Ribosomes-
1. Ribosomes are non-membrane bound organelles found in all cells –
both eukaryotic as well as prokaryotic.
2. Within the cell, ribosomes are found not only in the cytoplasm but also
a. within the two organelles –
i. chloroplasts (in plants) and
ii. mitochondria and
b. on rough ER.
3. No organelles, like the ones in eukaryotes, are found in prokaryotic cells
except for ribosomes.
UNIT 3
CELL: STRUCTURE AND FUNCTIONS
Introduction to Biology and Reductionist Approach--
1. Biology and Diversity
1. Biology is the study of living organisms.
2. The detailed description of their form and appearance only brought out their
diversity.
3. It is the cell theory that emphasised the unity underlying this diversity of forms,
i.e., the cellular organisation of all life forms.
4. A description of cell structure and cell growth by division is given in the chapters
comprising this unit.
2. Mystery of Living Phenomena
1. Cell theory also created a sense of mystery around living phenomena, i.e.,
physiological and behavioural processes.
2. This mystery was the requirement of integrity of cellular organisation for living
phenomena to be demonstrated or observed.
3. Physico-Chemical Approach
1. In studying and understanding the physiological and behavioural processes, one
can take a physico-chemical approach and use cell-free systems to investigate.
2. This approach enables us to describe the various processes in molecular terms.
3. The approach is established by analysis of living tissues for elements and
compounds.
4. It will tell us what types of organic compounds are present in living organisms.
4. Functional Questions
1. In the next stage, one can ask the question:
1) What are these compounds doing inside a cell?And,
2) In what way they carry out gross physiological processes like digestion,
excretion, memory, defense, recognition, etc.
2. In other words, we try to answer the question
what is the molecular basis of all physiological processes?
3. It can also explain the abnormal processes that occur during any diseased
condition.
5. Reductionist Biology
1. This physico-chemical approach to study and understand living organisms is
called ‘Reductionist Biology’.
2. The concepts and techniques of physics and chemistry are applied to understand
biology.
3. In Chapter 9 of this unit, a brief description of biomolecules is provided.
, G.N. Ramachandran 2
(1922 – 2001)
1. Scientific Contributions-
1. G.N. Ramachandran, an outstanding figure in the field of protein structure, was
the founder of the ‘Madras school’ of conformational analysis of biopolymers.
2. His discovery of the triple helical structure of collagen published in Nature in
1954 and
3. His analysis of the allowed conformations of proteins through the use of the
‘Ramachandran plot’ rank among the most outstanding contributions in
structural biology.
2. Early Life-
1. He was born on October 8, 1922, in a small town, not far from Cochin on the
southwestern coast of India.
2. His father was a professor of mathematics at a local college and thus had
considerable influence in shaping Ramachandran’s interest in mathematics.
3. Education-
1. 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.
2. He received a Ph.D. from Cambridge University in 1949.
4. Influences and Research Direction-
1. 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.
5. Later Life-
1. He passed away at the age of 78, on April 7, 2001.
G.N. Ramachandran
(1922 – 2001)
, CHAPTER 8 3
CELL: THE UNIT OF LIFE
Introduction-
Living and Non-living Things-
1. When you look around, you see both living and non-living things.
2. You must have wondered and asked yourself –
1. ‘what is it that makes an organism living, or
2. what is it that an inanimate thing does not have which a living thing has’?
3. The answer to this is the presence of the basic unit of life – the cell in all living
organisms.
Composition of Organisms-
1. All organisms are composed of cells.
2. Some are composed of a single cell and are called unicellular organisms.
3. While others, like us, composed of many cells, are called multicellular organisms.
8.1 WHAT IS A CELL?
Unicellular Organisms-
1. Unicellular organisms are capable of
1. (i) independent existence and
2. (ii) performing the essential functions of life.
2. Anything less than a complete structure of a cell does not ensure independent
living.
3. Hence, cell is the fundamental structural and functional unit of all living
organisms.
Discovery of Cell-
1. Antonie Von Leeuwenhoek first saw and described a live cell.
2. Robert Brown later discovered the nucleus.
3. The invention of the microscope and its improvement leading to the electron
microscope revealed all the structural details of the cell.
Fig 8.3: Development of complex organism from the simplest form
, 8.2 CELL THEORY 4
Studies on Plant Cells
1. 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.
Studies on Animal Cells
1. At about the same time, Theodore Schwann (1839), a German Zoologist, studied
different types of animal cells and reported that
cells had a thin outer layer which is today known as the ‘plasma membrane’.
2. He also concluded, based on his studies on plant tissues, that
the presence of cell wall is a unique character of the plant cells.
3. On the basis of this, Schwann proposed the hypothesis that
the bodies of animals and plants are composed of cells and products of cells.
Formulation of Cell Theory
1. Schleiden and Schwann together formulated the cell theory.
All living organisms are composed of cells and products of cells.
2. This theory however, did not explain as to how new cells were formed.
final form of cell theory
1. Rudolf Virchow (1855) first explained that cells divided and new cells are
formed from pre-existing cells (Omnis cellula-e cellula).
2. He modified the hypothesis of Schleiden and Schwann to give the cell theory a
final shape.
3. Cell Theory as Understood Today
1. All living organisms are composed of cells and products of cells.
2. All cells arise from pre-existing cells.
Fig 8.6: Formation of new cells from pre-existing cells
Fig 8.5: Cell theory
, 5
8.3 AN OVERVIEW OF CELL
Observation of Plant and Animal Cells
1. You have earlier observed cells in an onion peel and/or human cheek cells under
the microscope.Let us recollect their structure.
2. The onion cell, which is a typical plant cell, has a distinct cell wall as its outer
boundary and just within it is the cell membrane.
3. The cells of the human cheek have an outer membrane as the delimiting structure
of the cell.
Nucleus
1. Inside each cell is a dense membrane bound structure called nucleus.
2. This nucleus contains the chromosomes which in turn contain the genetic
material, DNA.
3. Cells that have membrane bound nuclei are called eukaryotic
4. whereas cells that lack a membrane bound nucleus are prokaryotic.
5. Nuclear membrane is found in eukaryotes.
cytoplasm -
1. In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm
occupies the volume of the cell.
2. The cytoplasm is the main arena of cellular activities in both the plant and
animal cells.
3. Various chemical reactions occur in it to keep the cell in the ‘living state’.
Cell Organelles in Eukaryotic and Prokaryotic Cells
1. Besides the nucleus, the eukaryotic cells have other membrane bound distinct
structures called organelles like the
1. endoplasmic reticulum (ER),
2. the golgi complex,
3. lysosomes,
4. mitochondria,
5. microbodies and
6. vacuoles.
2. The prokaryotic cells lack such membrane bound organelles.
non-membrane bound organelles-
a) Ribosomes-
1. Ribosomes are non-membrane bound organelles found in all cells –
both eukaryotic as well as prokaryotic.
2. Within the cell, ribosomes are found not only in the cytoplasm but also
a. within the two organelles –
i. chloroplasts (in plants) and
ii. mitochondria and
b. on rough ER.
3. No organelles, like the ones in eukaryotes, are found in prokaryotic cells
except for ribosomes.
