Chapter
2
Cell: The Building
Block of Life
It is widely accepted amongst the scientific community that life
originated in water. Some researchers believe that life may have
originated in small water pools with changing environmental
Think It Over conditions rather than in the oceans. Hot springs are examples
of such environments. In India, the hot springs of Puga Valley in
y Where does a cell Ladakh maintain very high temperatures (nearly at the boiling
come from? point of water) even in a cold climate. These environmental
y How have conditions seem to be similar to those on the early Earth, about
technological 3.5 billion years ago. The organisms living in these hot springs
interventions are mostly heat-loving bacteria called thermophiles, which are
facilitated the
unicellular.
creation of new
knowledge in Scientists from the Birbal Sahni Institute of Palaeosciences,
understanding the Lucknow, studied these hot springs and found that calcium carbonate
world beyond the formed rapidly around them. These deposits may have protected
naked eye? early organic molecules from harmful radiation and extreme
y How is the cell conditions, and they may have also helped in the formation of the
structural and first protective membrane — the barrier that defines a cell.
functional unit of
life? All living organisms are made up of cells. The cell represents the
basic level at which life exists. Some organisms, such as bacteria or
y How does a cell
multiply? yeast consist of only one cell (unicellular), while others like plants,
fish, birds or humans are made up of millions of cells (multicellular)
that work together. A group of similar cells performing similar
, Cell: The Building Block of Life 9
functions forms tissues. Different tissues
are organised to form an organ and several 1 km
organs work together to form organ systems.
Such as, nasal pores, nasal cavity, trachea
and lungs form respiratory system. 100 m
Even when cells are organised into Rocket
tissues, organs, and organ systems the cell
Neem Tree
remains the fundamental unit of structure 10 m
and function in all living organisms. This
Unaided eye
makes us wonder how such tiny cells
perform so many different activities. What Human height
1m
Great Indian Bustard
are the different components of a cell? How
do cells in our body communicate with each
other? Do cells live forever, or do they die? In 0.1 m
this chapter, we will explore the answers to Chicken egg
these questions as we enter the fascinating
world of cells!
1 cm
2.1 How to Study Cells?
What do we call the ability of the human Fish egg
eye to see two very close objects as separate 1 mm
and distinct? Imagine two tiny dots drawn Amoeba
on a piece of paper. As the dots are moved
Light microscope
closer, there comes a point at which they 100 µm
can no longer be seen as separate. When Most plant and
viewed from about 25 cm (the near point of animal cells
human eye), two points separated by about 10 µm
0.1 mm can be seen as distinct; otherwise, Nucleus
they appear as a single point. This is called Most bacteria
the limit of resolution of the human eye, Mitochondrion
1 µm
which is 0.1 mm.
Electron microscope
A cell is usually too small to be seen
Smallest bacteria
by the unaided eye (Fig. 2.1). This raises
100 nm
an important question — how have cell Viruses
biologists studied the structure and function
of cells that are much smaller than the limit Ribosomes
of resolution of the human eye? 10 nm
Proteins
You have learnt about Grade 8
convex lens. A convex lens or a Chapter 10
Curiosity Lipids
combination of lenses, i.e., an 1 nm
objective lens and an eyepiece are used for Small molecules
the magnification of an object (Fig. 2.1) to
C
make it appear larger. 0.1 nm Atoms
Robert Hooke was the first Grade 8
person to observe a cell in 1665 Curiosity Fig. 2.1: Size of the objects and its visibility through
Chapter 2 unaided to aided eye
using a self-designed microscope
(capable of about 200–300X magnification). While examining a thin slice
of cork, he observed small box-like compartments and named them ‘cells’.
In school laboratories, light microscopes are used to observe objects using
, Course adjustment Eye piece
different objective lenses (e.g., 10X, 40X) to achieve
knob
better magnification and resolution under visible
light. Explore different parts of a microscope
Body tube (Fig. 2.2) in your school laboratory and Grade 8
use it to observe fine structures of various Curiosity
Objective Chapter 9
Fine adjustment materials. Under the microscope, you
knob lens
will see a magnified image of an object. Can you
Handle estimate its actual size?
Stage
Mirror Activity 2.1: Let us estimate the size of a cell
Base 1. Take a transparent ruler with millimetre (mm)
markings.
Fig. 2.2: Structure of a light microscope 2. Place the ruler on the stage of microscope, focus
on it using the adjustment knob and observe the
diameter of the circular field of view through
Ready to Go Beyond the eyepiece and measure it in mm.
3. Convert the diameter from mm to micrometre
(µm). Suppose the diameter of the visible field
is 5 mm, meaning 5 × 1000 = 5000 µm.
4. Remove the ruler and place an onion peel slide
on the stage of the microscope.
Fig. 2.3: An electron microscope 5. Focus on the slide and count the number of cells
present along the diameter of the field of view in
Apart from light microscopes, one straight line.
scientists also use powerful electron
microscopes that reveal the fine details 6. Estimate the real size of the cell using the
of a cell structure. These instruments formula:
use a beam of electrons instead of light
to produce highly magnified images,
allowing us to see cell structure at
Unit conversion:
the nanometre scale with remarkable
clarity (a nanometre is one-billionth of 1 millimetre (mm) = 1000 micrometre (µm)
a metre).
Diameter of the visible field in micrometre
Estimated size of the onion peel cell =
Number of cells along the diameter
Suppose, 25 cells are seen along the diameter. In that case, the size of one
onion cell would be 5000 µm/25 = 200 µm.
If the estimated size of an onion peel cell is 200 µm, how much does a
light microscope magnify this cell? The total magnification of a microscope
depends on its magnifying power of the eyepiece and the objective lens. If
both the eyepiece and the objective lens have the magnifying power of 10X,
then the total magnification will be 100X. This means that a cell with an
estimated size of 200 µm will appear 100 times larger.
Thus, a microscope allows us to see very small structures clearly and is an
essential tool for studying the cell structure. Over the years, scientists have
improved the microscope by improving its three main features — resolution
(measure of clarity), contrast (the difference in brightness between various
10 Exploration|Grade 9
2
Cell: The Building
Block of Life
It is widely accepted amongst the scientific community that life
originated in water. Some researchers believe that life may have
originated in small water pools with changing environmental
Think It Over conditions rather than in the oceans. Hot springs are examples
of such environments. In India, the hot springs of Puga Valley in
y Where does a cell Ladakh maintain very high temperatures (nearly at the boiling
come from? point of water) even in a cold climate. These environmental
y How have conditions seem to be similar to those on the early Earth, about
technological 3.5 billion years ago. The organisms living in these hot springs
interventions are mostly heat-loving bacteria called thermophiles, which are
facilitated the
unicellular.
creation of new
knowledge in Scientists from the Birbal Sahni Institute of Palaeosciences,
understanding the Lucknow, studied these hot springs and found that calcium carbonate
world beyond the formed rapidly around them. These deposits may have protected
naked eye? early organic molecules from harmful radiation and extreme
y How is the cell conditions, and they may have also helped in the formation of the
structural and first protective membrane — the barrier that defines a cell.
functional unit of
life? All living organisms are made up of cells. The cell represents the
basic level at which life exists. Some organisms, such as bacteria or
y How does a cell
multiply? yeast consist of only one cell (unicellular), while others like plants,
fish, birds or humans are made up of millions of cells (multicellular)
that work together. A group of similar cells performing similar
, Cell: The Building Block of Life 9
functions forms tissues. Different tissues
are organised to form an organ and several 1 km
organs work together to form organ systems.
Such as, nasal pores, nasal cavity, trachea
and lungs form respiratory system. 100 m
Even when cells are organised into Rocket
tissues, organs, and organ systems the cell
Neem Tree
remains the fundamental unit of structure 10 m
and function in all living organisms. This
Unaided eye
makes us wonder how such tiny cells
perform so many different activities. What Human height
1m
Great Indian Bustard
are the different components of a cell? How
do cells in our body communicate with each
other? Do cells live forever, or do they die? In 0.1 m
this chapter, we will explore the answers to Chicken egg
these questions as we enter the fascinating
world of cells!
1 cm
2.1 How to Study Cells?
What do we call the ability of the human Fish egg
eye to see two very close objects as separate 1 mm
and distinct? Imagine two tiny dots drawn Amoeba
on a piece of paper. As the dots are moved
Light microscope
closer, there comes a point at which they 100 µm
can no longer be seen as separate. When Most plant and
viewed from about 25 cm (the near point of animal cells
human eye), two points separated by about 10 µm
0.1 mm can be seen as distinct; otherwise, Nucleus
they appear as a single point. This is called Most bacteria
the limit of resolution of the human eye, Mitochondrion
1 µm
which is 0.1 mm.
Electron microscope
A cell is usually too small to be seen
Smallest bacteria
by the unaided eye (Fig. 2.1). This raises
100 nm
an important question — how have cell Viruses
biologists studied the structure and function
of cells that are much smaller than the limit Ribosomes
of resolution of the human eye? 10 nm
Proteins
You have learnt about Grade 8
convex lens. A convex lens or a Chapter 10
Curiosity Lipids
combination of lenses, i.e., an 1 nm
objective lens and an eyepiece are used for Small molecules
the magnification of an object (Fig. 2.1) to
C
make it appear larger. 0.1 nm Atoms
Robert Hooke was the first Grade 8
person to observe a cell in 1665 Curiosity Fig. 2.1: Size of the objects and its visibility through
Chapter 2 unaided to aided eye
using a self-designed microscope
(capable of about 200–300X magnification). While examining a thin slice
of cork, he observed small box-like compartments and named them ‘cells’.
In school laboratories, light microscopes are used to observe objects using
, Course adjustment Eye piece
different objective lenses (e.g., 10X, 40X) to achieve
knob
better magnification and resolution under visible
light. Explore different parts of a microscope
Body tube (Fig. 2.2) in your school laboratory and Grade 8
use it to observe fine structures of various Curiosity
Objective Chapter 9
Fine adjustment materials. Under the microscope, you
knob lens
will see a magnified image of an object. Can you
Handle estimate its actual size?
Stage
Mirror Activity 2.1: Let us estimate the size of a cell
Base 1. Take a transparent ruler with millimetre (mm)
markings.
Fig. 2.2: Structure of a light microscope 2. Place the ruler on the stage of microscope, focus
on it using the adjustment knob and observe the
diameter of the circular field of view through
Ready to Go Beyond the eyepiece and measure it in mm.
3. Convert the diameter from mm to micrometre
(µm). Suppose the diameter of the visible field
is 5 mm, meaning 5 × 1000 = 5000 µm.
4. Remove the ruler and place an onion peel slide
on the stage of the microscope.
Fig. 2.3: An electron microscope 5. Focus on the slide and count the number of cells
present along the diameter of the field of view in
Apart from light microscopes, one straight line.
scientists also use powerful electron
microscopes that reveal the fine details 6. Estimate the real size of the cell using the
of a cell structure. These instruments formula:
use a beam of electrons instead of light
to produce highly magnified images,
allowing us to see cell structure at
Unit conversion:
the nanometre scale with remarkable
clarity (a nanometre is one-billionth of 1 millimetre (mm) = 1000 micrometre (µm)
a metre).
Diameter of the visible field in micrometre
Estimated size of the onion peel cell =
Number of cells along the diameter
Suppose, 25 cells are seen along the diameter. In that case, the size of one
onion cell would be 5000 µm/25 = 200 µm.
If the estimated size of an onion peel cell is 200 µm, how much does a
light microscope magnify this cell? The total magnification of a microscope
depends on its magnifying power of the eyepiece and the objective lens. If
both the eyepiece and the objective lens have the magnifying power of 10X,
then the total magnification will be 100X. This means that a cell with an
estimated size of 200 µm will appear 100 times larger.
Thus, a microscope allows us to see very small structures clearly and is an
essential tool for studying the cell structure. Over the years, scientists have
improved the microscope by improving its three main features — resolution
(measure of clarity), contrast (the difference in brightness between various
10 Exploration|Grade 9
