NCERT INSIDER
• Biology is the study of living organisms.
• Cell biology is the branch of biology studying the structure, function, behaviour & life cycle of cells.
• The living organisms differ in their form & appearance showing diversity.
• This diversity in living organisms is united by “Cell Theory”
• The physico-chemical approach to study and understand living organisms is called Reductionist Biology.
When we observe our surroundings, we see living and non-living things.
‘What is it that makes an organism living, or what is it that an inanimate thing does not have which a living thing has’?
The answer to this is the presence of the basic unit of life - the cell in all living organisms.
Cell
A cell is the fundamental structural and functional unit of life. All organisms are composed of cells.
(a) Unicellular organisms are capable of
• Independent existence
• Performing the essential functions of life.
(b) 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.
Drona NEET (XI) Module - 1 • Botany 1
, Basic Component of a Cell
Fig: Basic structure of a Cell
Discovery of Cell
Observed thin slice of cork using a simple
1 Robert Hooke (1665) microscope and saw box-like compartments
and named them cells.
Actually, observed dead cells (cell wall).
Was the first to observe living cells such as
2 Antonie van Leeuwenhoek (1674) bacteria, protozoa, spermcells, and red blood
cells using his self-designed microscope. He called
them “animalcules.”
Discovered the nucleus in cells.
3 Robert Brown (1831)
The invention of the microscope and its improvement leading to the electron microscope reveal all the structural details of
the cell.
Drona NEET (XI) Module - 1 • Botany 2
, Microscope Breakdown
Device Resolution
Simple microscope Basic Camera
Fig: Compound microscope
Compound microscope HD Camera
Electron microscope 4K Ultra HD
Fig: Electron microscope
• In 1838, Matthias Jakob 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, Theodor 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.
• He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character
of the plant cells.
• Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of
cells.
• Schleiden and Schwann together formulated the cell theory. This theory however, did not explain how new
cells were formed.
Drona NEET (XI) Module - 1 • Botany 3
, • In 1855, Rudolf Virchow explained that cells divide and new cells are formed from pre-existing cells Omnis-
cellula-e-cellula).
• He modified the hypothesis of Schleiden and schwann and gave the cell theory its final shape.
Cell Theory (Modern Form)
• All living organisms are composed of cells and products of cells.
• All cells arise from pre-existing cells.
Add-Ons
• Viruses do not easily fit into the parameters of a true cell.
• These are an exception to cell theory as they are not made of cells.
• They lack a membrane, cytoplasm, and organelles.
• They cannot replicate without a host cell.
• They do not produce their own energy or carry out chemical processes.
• Therefore, they are not considered either living or non - living. Fig: Virus
1. Which statement best explains the phrase “No Cell = No Life”?
(a) All cells contain DNA
(b) Cells are the smallest living units capable of life processes
(c) Cells are visible only under microscope
(d) Cells are present only in animals
2. Division of labour among cells is seen in
(a) Unicellular (b) Multicellular organisms (c) Viruses (d) Bacteria only
3. Arrange the following discoveries in the correct chronological order:
(i) Discovery of nucleus
(ii) Discovery of living cells
(iii) Discovery of cells in cork
(a) iii ii i (b) ii iii i (c) i ii iii (d) ii i iii
4. The statement “Omnis-cellula-e-cellula” was proposed by
(a) Robert Hooke (b) Rudolf Virchow (c) Schwann (d) Robert Brown
Drona NEET (XI) Module - 1 • Botany 4
• Biology is the study of living organisms.
• Cell biology is the branch of biology studying the structure, function, behaviour & life cycle of cells.
• The living organisms differ in their form & appearance showing diversity.
• This diversity in living organisms is united by “Cell Theory”
• The physico-chemical approach to study and understand living organisms is called Reductionist Biology.
When we observe our surroundings, we see living and non-living things.
‘What is it that makes an organism living, or what is it that an inanimate thing does not have which a living thing has’?
The answer to this is the presence of the basic unit of life - the cell in all living organisms.
Cell
A cell is the fundamental structural and functional unit of life. All organisms are composed of cells.
(a) Unicellular organisms are capable of
• Independent existence
• Performing the essential functions of life.
(b) 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.
Drona NEET (XI) Module - 1 • Botany 1
, Basic Component of a Cell
Fig: Basic structure of a Cell
Discovery of Cell
Observed thin slice of cork using a simple
1 Robert Hooke (1665) microscope and saw box-like compartments
and named them cells.
Actually, observed dead cells (cell wall).
Was the first to observe living cells such as
2 Antonie van Leeuwenhoek (1674) bacteria, protozoa, spermcells, and red blood
cells using his self-designed microscope. He called
them “animalcules.”
Discovered the nucleus in cells.
3 Robert Brown (1831)
The invention of the microscope and its improvement leading to the electron microscope reveal all the structural details of
the cell.
Drona NEET (XI) Module - 1 • Botany 2
, Microscope Breakdown
Device Resolution
Simple microscope Basic Camera
Fig: Compound microscope
Compound microscope HD Camera
Electron microscope 4K Ultra HD
Fig: Electron microscope
• In 1838, Matthias Jakob 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, Theodor 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.
• He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character
of the plant cells.
• Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of
cells.
• Schleiden and Schwann together formulated the cell theory. This theory however, did not explain how new
cells were formed.
Drona NEET (XI) Module - 1 • Botany 3
, • In 1855, Rudolf Virchow explained that cells divide and new cells are formed from pre-existing cells Omnis-
cellula-e-cellula).
• He modified the hypothesis of Schleiden and schwann and gave the cell theory its final shape.
Cell Theory (Modern Form)
• All living organisms are composed of cells and products of cells.
• All cells arise from pre-existing cells.
Add-Ons
• Viruses do not easily fit into the parameters of a true cell.
• These are an exception to cell theory as they are not made of cells.
• They lack a membrane, cytoplasm, and organelles.
• They cannot replicate without a host cell.
• They do not produce their own energy or carry out chemical processes.
• Therefore, they are not considered either living or non - living. Fig: Virus
1. Which statement best explains the phrase “No Cell = No Life”?
(a) All cells contain DNA
(b) Cells are the smallest living units capable of life processes
(c) Cells are visible only under microscope
(d) Cells are present only in animals
2. Division of labour among cells is seen in
(a) Unicellular (b) Multicellular organisms (c) Viruses (d) Bacteria only
3. Arrange the following discoveries in the correct chronological order:
(i) Discovery of nucleus
(ii) Discovery of living cells
(iii) Discovery of cells in cork
(a) iii ii i (b) ii iii i (c) i ii iii (d) ii i iii
4. The statement “Omnis-cellula-e-cellula” was proposed by
(a) Robert Hooke (b) Rudolf Virchow (c) Schwann (d) Robert Brown
Drona NEET (XI) Module - 1 • Botany 4
