NCERT Textbook: The Invisible Living World: Beyond Our Naked Eye | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


8
Curiosity — Textbook of Science for Grade 8
2
The Invisible Living 
World: Beyond Our 
Naked Eye
Probe and ponder
 z Have you ever wondered what you might see if the invisible 
world around you became visible?
 z How do you think your observation of this hidden world might 
change the way you think about size, complexity, or even what 
counts as ‘living’?
 z Have you thought how these tiny living beings interact with 
each other?
 z Share your questions  
  ?
Chapter 2.indd   8 Chapter 2.indd   8 6/30/2025   4:19:34 PM 6/30/2025   4:19:34 PM
Page 2


8
Curiosity — Textbook of Science for Grade 8
2
The Invisible Living 
World: Beyond Our 
Naked Eye
Probe and ponder
 z Have you ever wondered what you might see if the invisible 
world around you became visible?
 z How do you think your observation of this hidden world might 
change the way you think about size, complexity, or even what 
counts as ‘living’?
 z Have you thought how these tiny living beings interact with 
each other?
 z Share your questions  
  ?
Chapter 2.indd   8 Chapter 2.indd   8 6/30/2025   4:19:34 PM 6/30/2025   4:19:34 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
9
The human eye can only see objects that are above a certain 
size. For a long time, many tiny things around us remained 
unknown. Long ago, people discovered that a curved piece of 
glass could make small things look bigger. The piece of glass 
was shaped like a lentil seed — thick in the middle and thin at 
the edge — hence they called it a lens. Over time, lenses were 
improved to become more powerful. Each new tool, from simple 
magnifying glasses to microscopes, helped humans see what 
their eyes could not. The invention of the microscope opened 
a fascinating hidden world filled with tiny living creatures. We 
will explore some of these life forms in this chapter.
You have already learnt about the amazing variety of living 
beings. Just look around — there are so many beautiful plants 
and animals! They are of all shapes, sizes, and colours. Some 
living beings are tiny, while others are really big. They differ not 
only in their structure but also in many other features. All these 
living beings, whether plants or animals, are called organisms. 
Have you ever noticed the smallest organism around you that is 
visible to the naked eye? Think about it — how small a thing can 
your eyes actually see? 
You might have seen some people using reading glasses. How 
does it help them see better? Or what happens when we use a 
magnifying glass to observe something?
Activity 2.1: Let us observe
 z Take a round-bottom flask made up of glass as shown in 
Fig. 2.1. Fill it with water.
 z Close the mouth of the flask with a cork.
 z Now, place the flask on an open book and look at 
the letters through it.
Do you notice something interesting? The letters 
appear larger when seen through the flask! This 
happens because the flask filled with water acts like a 
magnifying glass. Now, use a real magnifying glass to 
look at small organisms, like an ant. Were you able to 
see the details of its body more clearly?
For a long time, people were curious to explore the 
tiny organisms around them, but they could not see them 
with their naked eyes. So, how did we finally discover 
this invisible world? Do you know which scientific 
discovery helped us see the tiny world for the first time? Fig. 2.1: Round-bottom flask
Chapter 2.indd   9 Chapter 2.indd   9 6/30/2025   4:19:35 PM 6/30/2025   4:19:35 PM
Page 3


8
Curiosity — Textbook of Science for Grade 8
2
The Invisible Living 
World: Beyond Our 
Naked Eye
Probe and ponder
 z Have you ever wondered what you might see if the invisible 
world around you became visible?
 z How do you think your observation of this hidden world might 
change the way you think about size, complexity, or even what 
counts as ‘living’?
 z Have you thought how these tiny living beings interact with 
each other?
 z Share your questions  
  ?
Chapter 2.indd   8 Chapter 2.indd   8 6/30/2025   4:19:34 PM 6/30/2025   4:19:34 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
9
The human eye can only see objects that are above a certain 
size. For a long time, many tiny things around us remained 
unknown. Long ago, people discovered that a curved piece of 
glass could make small things look bigger. The piece of glass 
was shaped like a lentil seed — thick in the middle and thin at 
the edge — hence they called it a lens. Over time, lenses were 
improved to become more powerful. Each new tool, from simple 
magnifying glasses to microscopes, helped humans see what 
their eyes could not. The invention of the microscope opened 
a fascinating hidden world filled with tiny living creatures. We 
will explore some of these life forms in this chapter.
You have already learnt about the amazing variety of living 
beings. Just look around — there are so many beautiful plants 
and animals! They are of all shapes, sizes, and colours. Some 
living beings are tiny, while others are really big. They differ not 
only in their structure but also in many other features. All these 
living beings, whether plants or animals, are called organisms. 
Have you ever noticed the smallest organism around you that is 
visible to the naked eye? Think about it — how small a thing can 
your eyes actually see? 
You might have seen some people using reading glasses. How 
does it help them see better? Or what happens when we use a 
magnifying glass to observe something?
Activity 2.1: Let us observe
 z Take a round-bottom flask made up of glass as shown in 
Fig. 2.1. Fill it with water.
 z Close the mouth of the flask with a cork.
 z Now, place the flask on an open book and look at 
the letters through it.
Do you notice something interesting? The letters 
appear larger when seen through the flask! This 
happens because the flask filled with water acts like a 
magnifying glass. Now, use a real magnifying glass to 
look at small organisms, like an ant. Were you able to 
see the details of its body more clearly?
For a long time, people were curious to explore the 
tiny organisms around them, but they could not see them 
with their naked eyes. So, how did we finally discover 
this invisible world? Do you know which scientific 
discovery helped us see the tiny world for the first time? Fig. 2.1: Round-bottom flask
Chapter 2.indd   9 Chapter 2.indd   9 6/30/2025   4:19:35 PM 6/30/2025   4:19:35 PM
10
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
In 1665, a scientist named Robert Hooke 
published a book called Micrographia. He 
was a careful observer, and a skilled artist. 
In this book, he showed detailed drawings 
of tiny things that people had never seen 
before — things he saw using a tool we now 
call a microscope.
His microscope made things look 200 
to 300 times bigger, than what one could 
see with the unaided eye. One day, he 
looked at a thin slice of cork and saw it 
was made of many small, empty spaces. 
These compartments reminded him of a 
honeycomb. He drew what he saw and 
called each small space a cell. This was the 
first time the word cell was used in science 
to describe the basic unit of life.
Around the same time in 1660s, Antonie 
van Leeuwenhoek, a Dutch scientist, made 
better lenses that allowed him to build more 
useful microscopes. He was the first person 
to clearly see and describe tiny living things 
like bacteria and blood cells.  Because of this, 
he is known as the Father of Microbiology.
Fig. 2.2: (a) Micrographia book; (b) Microscope of Robert Hooke; 
(c) Cork cells as published in the Micrographia
MICROGRAPHIA:
OR SOME
Physiological Descriptions
OF
MINUTE BODIES
MADE BY
MAGNIFYING GLASSES.
WITH
OBSERVATIONS and INQUIRIES thereupon.
By R. HOOKE, Fellow of the ROYAL SOCIETY
Non poifis oculo quantum contendere 
Lincent, Non tamen idcirco contemnas 
Lippus inungi. Horat. Ep. lib. 1.
LONDON, Printed by 7o. Martyn, and 7a. 
Alleftry, Printers to the ROYAL SOCIETY, 
and are to be fold at their Shop at the Bell 
in S. Paul’s Church-yard. M DC LX V.
(a)
(b)
(c)
2.1 What Is a Cell?
All living beings are made up of cells. You might wonder what 
cells actually look like. Let us take a closer look at the basic 
structure of a cell using a microscope.
Chapter 2.indd   10 Chapter 2.indd   10 6/30/2025   4:19:38 PM 6/30/2025   4:19:38 PM
Page 4


8
Curiosity — Textbook of Science for Grade 8
2
The Invisible Living 
World: Beyond Our 
Naked Eye
Probe and ponder
 z Have you ever wondered what you might see if the invisible 
world around you became visible?
 z How do you think your observation of this hidden world might 
change the way you think about size, complexity, or even what 
counts as ‘living’?
 z Have you thought how these tiny living beings interact with 
each other?
 z Share your questions  
  ?
Chapter 2.indd   8 Chapter 2.indd   8 6/30/2025   4:19:34 PM 6/30/2025   4:19:34 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
9
The human eye can only see objects that are above a certain 
size. For a long time, many tiny things around us remained 
unknown. Long ago, people discovered that a curved piece of 
glass could make small things look bigger. The piece of glass 
was shaped like a lentil seed — thick in the middle and thin at 
the edge — hence they called it a lens. Over time, lenses were 
improved to become more powerful. Each new tool, from simple 
magnifying glasses to microscopes, helped humans see what 
their eyes could not. The invention of the microscope opened 
a fascinating hidden world filled with tiny living creatures. We 
will explore some of these life forms in this chapter.
You have already learnt about the amazing variety of living 
beings. Just look around — there are so many beautiful plants 
and animals! They are of all shapes, sizes, and colours. Some 
living beings are tiny, while others are really big. They differ not 
only in their structure but also in many other features. All these 
living beings, whether plants or animals, are called organisms. 
Have you ever noticed the smallest organism around you that is 
visible to the naked eye? Think about it — how small a thing can 
your eyes actually see? 
You might have seen some people using reading glasses. How 
does it help them see better? Or what happens when we use a 
magnifying glass to observe something?
Activity 2.1: Let us observe
 z Take a round-bottom flask made up of glass as shown in 
Fig. 2.1. Fill it with water.
 z Close the mouth of the flask with a cork.
 z Now, place the flask on an open book and look at 
the letters through it.
Do you notice something interesting? The letters 
appear larger when seen through the flask! This 
happens because the flask filled with water acts like a 
magnifying glass. Now, use a real magnifying glass to 
look at small organisms, like an ant. Were you able to 
see the details of its body more clearly?
For a long time, people were curious to explore the 
tiny organisms around them, but they could not see them 
with their naked eyes. So, how did we finally discover 
this invisible world? Do you know which scientific 
discovery helped us see the tiny world for the first time? Fig. 2.1: Round-bottom flask
Chapter 2.indd   9 Chapter 2.indd   9 6/30/2025   4:19:35 PM 6/30/2025   4:19:35 PM
10
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
In 1665, a scientist named Robert Hooke 
published a book called Micrographia. He 
was a careful observer, and a skilled artist. 
In this book, he showed detailed drawings 
of tiny things that people had never seen 
before — things he saw using a tool we now 
call a microscope.
His microscope made things look 200 
to 300 times bigger, than what one could 
see with the unaided eye. One day, he 
looked at a thin slice of cork and saw it 
was made of many small, empty spaces. 
These compartments reminded him of a 
honeycomb. He drew what he saw and 
called each small space a cell. This was the 
first time the word cell was used in science 
to describe the basic unit of life.
Around the same time in 1660s, Antonie 
van Leeuwenhoek, a Dutch scientist, made 
better lenses that allowed him to build more 
useful microscopes. He was the first person 
to clearly see and describe tiny living things 
like bacteria and blood cells.  Because of this, 
he is known as the Father of Microbiology.
Fig. 2.2: (a) Micrographia book; (b) Microscope of Robert Hooke; 
(c) Cork cells as published in the Micrographia
MICROGRAPHIA:
OR SOME
Physiological Descriptions
OF
MINUTE BODIES
MADE BY
MAGNIFYING GLASSES.
WITH
OBSERVATIONS and INQUIRIES thereupon.
By R. HOOKE, Fellow of the ROYAL SOCIETY
Non poifis oculo quantum contendere 
Lincent, Non tamen idcirco contemnas 
Lippus inungi. Horat. Ep. lib. 1.
LONDON, Printed by 7o. Martyn, and 7a. 
Alleftry, Printers to the ROYAL SOCIETY, 
and are to be fold at their Shop at the Bell 
in S. Paul’s Church-yard. M DC LX V.
(a)
(b)
(c)
2.1 What Is a Cell?
All living beings are made up of cells. You might wonder what 
cells actually look like. Let us take a closer look at the basic 
structure of a cell using a microscope.
Chapter 2.indd   10 Chapter 2.indd   10 6/30/2025   4:19:38 PM 6/30/2025   4:19:38 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
11
Activity 2.2: Let us study a cell  
(Teacher demonstration activity)
 z Take an onion bulb from your kitchen or garden and wash it 
thoroughly with water.
 z Cut the onion bulb vertically into pieces.
 z Take one piece of onion and pull out the thin, transparent 
layer from its inner surface with the help of forceps. This 
layer is called the onion peel.
 z Place the peel in a petri dish containing a few drops of 
safranin (red-coloured stain) for 30 seconds. This will give 
a pinkish colour to the cells and help us see them clearly.  
 z With the help of thin brush transfer the onion peel to another 
petri dish containing water to rinse 
the peel and remove extra stain.
 z Now, carefully place the stained 
onion peel on the glass slide using 
a thin brush, ensuring it does not 
break or fold.
 z Put a drop of glycerin over the 
onion peel on the slide. The 
glycerin will prevent drying of the 
cells and improve clarity for better 
visualisation of cells. 
 z Slowly place a coverslip over the 
peel using a needle, such that no 
air bubbles get trapped.
 z Use blotting paper to gently wipe 
off any extra glycerin around the 
edges of the coverslip.
 z View the slide under a microscope 
or a foldscope. Compare it with 
Fig. 2.3c.
 z What similarities do you find in 
Fig. 2.3c and Fig. 2.3d?
You will observe nearly rectangular 
structures under the microscope. These 
are the cells of the onion peel, which 
are closely arranged without any space 
between them. Try to observe the peels 
of the leaves of different plants around 
you. You will find that all plants are 
made up of cells. What do you think 
the body of an animal is made of?
Fig. 2.3: (a) Removing 
onion peel from an 
onion bulb
(c)
(d)
Fig. 2.3: (b) Mounting the onion peel in glycerin 
using a needle; (c) Structure of onion peel under the 
microscope; and (d) A wall made of  brick
Cell wall
Cytoplasm
Nucleus
Cell 
membrane
(b)
(1)
(5)
One drop of 
safranin
Glycerin
Microscope
Onion peel
Cover slip
45°
(2)
(6)
(3) (4)
Chapter 2.indd   11 Chapter 2.indd   11 6/30/2025   5:26:03 PM 6/30/2025   5:26:03 PM
Page 5


8
Curiosity — Textbook of Science for Grade 8
2
The Invisible Living 
World: Beyond Our 
Naked Eye
Probe and ponder
 z Have you ever wondered what you might see if the invisible 
world around you became visible?
 z How do you think your observation of this hidden world might 
change the way you think about size, complexity, or even what 
counts as ‘living’?
 z Have you thought how these tiny living beings interact with 
each other?
 z Share your questions  
  ?
Chapter 2.indd   8 Chapter 2.indd   8 6/30/2025   4:19:34 PM 6/30/2025   4:19:34 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
9
The human eye can only see objects that are above a certain 
size. For a long time, many tiny things around us remained 
unknown. Long ago, people discovered that a curved piece of 
glass could make small things look bigger. The piece of glass 
was shaped like a lentil seed — thick in the middle and thin at 
the edge — hence they called it a lens. Over time, lenses were 
improved to become more powerful. Each new tool, from simple 
magnifying glasses to microscopes, helped humans see what 
their eyes could not. The invention of the microscope opened 
a fascinating hidden world filled with tiny living creatures. We 
will explore some of these life forms in this chapter.
You have already learnt about the amazing variety of living 
beings. Just look around — there are so many beautiful plants 
and animals! They are of all shapes, sizes, and colours. Some 
living beings are tiny, while others are really big. They differ not 
only in their structure but also in many other features. All these 
living beings, whether plants or animals, are called organisms. 
Have you ever noticed the smallest organism around you that is 
visible to the naked eye? Think about it — how small a thing can 
your eyes actually see? 
You might have seen some people using reading glasses. How 
does it help them see better? Or what happens when we use a 
magnifying glass to observe something?
Activity 2.1: Let us observe
 z Take a round-bottom flask made up of glass as shown in 
Fig. 2.1. Fill it with water.
 z Close the mouth of the flask with a cork.
 z Now, place the flask on an open book and look at 
the letters through it.
Do you notice something interesting? The letters 
appear larger when seen through the flask! This 
happens because the flask filled with water acts like a 
magnifying glass. Now, use a real magnifying glass to 
look at small organisms, like an ant. Were you able to 
see the details of its body more clearly?
For a long time, people were curious to explore the 
tiny organisms around them, but they could not see them 
with their naked eyes. So, how did we finally discover 
this invisible world? Do you know which scientific 
discovery helped us see the tiny world for the first time? Fig. 2.1: Round-bottom flask
Chapter 2.indd   9 Chapter 2.indd   9 6/30/2025   4:19:35 PM 6/30/2025   4:19:35 PM
10
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
In 1665, a scientist named Robert Hooke 
published a book called Micrographia. He 
was a careful observer, and a skilled artist. 
In this book, he showed detailed drawings 
of tiny things that people had never seen 
before — things he saw using a tool we now 
call a microscope.
His microscope made things look 200 
to 300 times bigger, than what one could 
see with the unaided eye. One day, he 
looked at a thin slice of cork and saw it 
was made of many small, empty spaces. 
These compartments reminded him of a 
honeycomb. He drew what he saw and 
called each small space a cell. This was the 
first time the word cell was used in science 
to describe the basic unit of life.
Around the same time in 1660s, Antonie 
van Leeuwenhoek, a Dutch scientist, made 
better lenses that allowed him to build more 
useful microscopes. He was the first person 
to clearly see and describe tiny living things 
like bacteria and blood cells.  Because of this, 
he is known as the Father of Microbiology.
Fig. 2.2: (a) Micrographia book; (b) Microscope of Robert Hooke; 
(c) Cork cells as published in the Micrographia
MICROGRAPHIA:
OR SOME
Physiological Descriptions
OF
MINUTE BODIES
MADE BY
MAGNIFYING GLASSES.
WITH
OBSERVATIONS and INQUIRIES thereupon.
By R. HOOKE, Fellow of the ROYAL SOCIETY
Non poifis oculo quantum contendere 
Lincent, Non tamen idcirco contemnas 
Lippus inungi. Horat. Ep. lib. 1.
LONDON, Printed by 7o. Martyn, and 7a. 
Alleftry, Printers to the ROYAL SOCIETY, 
and are to be fold at their Shop at the Bell 
in S. Paul’s Church-yard. M DC LX V.
(a)
(b)
(c)
2.1 What Is a Cell?
All living beings are made up of cells. You might wonder what 
cells actually look like. Let us take a closer look at the basic 
structure of a cell using a microscope.
Chapter 2.indd   10 Chapter 2.indd   10 6/30/2025   4:19:38 PM 6/30/2025   4:19:38 PM
Chapter 2?—?The Invisible Living World: Beyond Our Naked Eye
11
Activity 2.2: Let us study a cell  
(Teacher demonstration activity)
 z Take an onion bulb from your kitchen or garden and wash it 
thoroughly with water.
 z Cut the onion bulb vertically into pieces.
 z Take one piece of onion and pull out the thin, transparent 
layer from its inner surface with the help of forceps. This 
layer is called the onion peel.
 z Place the peel in a petri dish containing a few drops of 
safranin (red-coloured stain) for 30 seconds. This will give 
a pinkish colour to the cells and help us see them clearly.  
 z With the help of thin brush transfer the onion peel to another 
petri dish containing water to rinse 
the peel and remove extra stain.
 z Now, carefully place the stained 
onion peel on the glass slide using 
a thin brush, ensuring it does not 
break or fold.
 z Put a drop of glycerin over the 
onion peel on the slide. The 
glycerin will prevent drying of the 
cells and improve clarity for better 
visualisation of cells. 
 z Slowly place a coverslip over the 
peel using a needle, such that no 
air bubbles get trapped.
 z Use blotting paper to gently wipe 
off any extra glycerin around the 
edges of the coverslip.
 z View the slide under a microscope 
or a foldscope. Compare it with 
Fig. 2.3c.
 z What similarities do you find in 
Fig. 2.3c and Fig. 2.3d?
You will observe nearly rectangular 
structures under the microscope. These 
are the cells of the onion peel, which 
are closely arranged without any space 
between them. Try to observe the peels 
of the leaves of different plants around 
you. You will find that all plants are 
made up of cells. What do you think 
the body of an animal is made of?
Fig. 2.3: (a) Removing 
onion peel from an 
onion bulb
(c)
(d)
Fig. 2.3: (b) Mounting the onion peel in glycerin 
using a needle; (c) Structure of onion peel under the 
microscope; and (d) A wall made of  brick
Cell wall
Cytoplasm
Nucleus
Cell 
membrane
(b)
(1)
(5)
One drop of 
safranin
Glycerin
Microscope
Onion peel
Cover slip
45°
(2)
(6)
(3) (4)
Chapter 2.indd   11 Chapter 2.indd   11 6/30/2025   5:26:03 PM 6/30/2025   5:26:03 PM
12
Curiosity — Textbook of Science for Grade 8
Activity 2.3: Let us investigate
 z Rinse your mouth with clean water.
 z Use the blunt end of a clean toothpick, and gently scrape the 
inside of your cheek.
 z Place the scraped material in a drop of water on a clean glass 
slide and spread it evenly.
 z Add a drop of methylene blue (a blue-coloured stain) over 
the material on slide. Adding stain improves the visibility of 
the material under the microscope by increasing contrast.
 z After one minute, add a drop of glycerin over the material on 
the slide to prevent the cells from drying.
 z Now, carefully place a clean coverslip on the material, and 
remove the excess glycerin from the edges of the coverslip 
using blotting paper.
 z Observe the slide under a microscope and draw what you 
see in your notebook.
What did you observe? You will observe a polygon-
shaped structure as shown in Fig. 2.4. These are cheek 
cells, which form the inner lining of your mouth.
What similarities and differences did you observe 
between the cells of onion peel in Activity 2.2 and 
human cheek cells in Activity 2.3? 
You have observed that cells have three main parts  
— a thin outer lining, a central region, and a small 
round structure inside it. The outer layer is called the 
cell membrane. The round structure in the middle is 
the nucleus, which is also covered by a thin membrane. The space 
between the cell membrane and nucleus is filled with cytoplasm. 
These three — cell membrane, cytoplasm, and nucleus — are the 
basic parts of a cell. Some cells, like onion peel cells, have an 
extra outer layer called the cell wall. What is the importance of 
these structures in a cell? What functions do they perform? Are 
these functions important for the maintenance of life?
The cell membrane encloses the cytoplasm and nucleus. The 
cell membrane separates one cell from another. It is porous and 
allows the entry of materials essential for life processes and the 
exit of waste material.
Cytoplasm contains other components of the cell and 
compounds, such as carbohydrates, proteins, fats, and mineral 
salts. Most of the life processes take place within the cytoplasm.
Fig. 2.4: Mount of human cheek cells
Nucleus
Cytoplasm
Cell membrane
Chapter 2.indd   12 Chapter 2.indd   12 6/30/2025   4:19:39 PM 6/30/2025   4:19:39 PM