Chapter 5 Fundamental Unit Of Life Notes | Study Science - Short Notes Class IX - Class 9

 Page 1


Chapter 5 Fundamental Unit of Life 
Cell – The structural and functional unit of life. Largest cell unfertilized ostrich egg (17cm*13cm) while 
smaller cells and most cells are of few micrometers. (10
-6
m). 
Cells were discovered by Robert Hooke in 1665 in a cork slice. Leeuwenhoek observed first free living cells 
(microorganisms) in 1674 in pond water. 
Cell theory 
Given by Schleiden and Schwann in 1838-39 and further expanded by Virchow in 1855 
1. All plants and animals are made up of cells 
2. Cell is the basic structural and functional unit of life. 
3. New cells arise from the pre-existing cells. 
 
Microscope – An optical instrument used to see cells (the one which are not very small and not visible to our 
naked eyes). 
 
 
 
 
 
 
 
 
                    Fig. A simple dissecting microscope        Fig. A compound microscope 
 
 
 
 
 
 
 
  Fig. Onion peel as seen under a compound microscope 
1. Variation in cells 
a. Number of cells 
Different organisms can have different number of cells. For e.g. Microorganisms are usually made of 
a single cell while humans are made of billions of cells.   
Unicellular organisms (uni – single; cellular – cell) – Organisms that are made of a single cell are 
called unicellular organisms. E.g. Amoeba, bacteria etc. 
Page 2


Chapter 5 Fundamental Unit of Life 
Cell – The structural and functional unit of life. Largest cell unfertilized ostrich egg (17cm*13cm) while 
smaller cells and most cells are of few micrometers. (10
-6
m). 
Cells were discovered by Robert Hooke in 1665 in a cork slice. Leeuwenhoek observed first free living cells 
(microorganisms) in 1674 in pond water. 
Cell theory 
Given by Schleiden and Schwann in 1838-39 and further expanded by Virchow in 1855 
1. All plants and animals are made up of cells 
2. Cell is the basic structural and functional unit of life. 
3. New cells arise from the pre-existing cells. 
 
Microscope – An optical instrument used to see cells (the one which are not very small and not visible to our 
naked eyes). 
 
 
 
 
 
 
 
 
                    Fig. A simple dissecting microscope        Fig. A compound microscope 
 
 
 
 
 
 
 
  Fig. Onion peel as seen under a compound microscope 
1. Variation in cells 
a. Number of cells 
Different organisms can have different number of cells. For e.g. Microorganisms are usually made of 
a single cell while humans are made of billions of cells.   
Unicellular organisms (uni – single; cellular – cell) – Organisms that are made of a single cell are 
called unicellular organisms. E.g. Amoeba, bacteria etc. 
 
 
 
Fig. Amoeba 
Multicellular Organisms (multi -many; cellular – cell) – Organisms that are made up of more than one 
cell are known as multicellular organisms. E.g. Plants, animals. 
 
b. Shape of cells 
Different types of cells have different shapes. For e.g. Red blood cells are round while the nerve 
cells are branched. Amoeba keeps on changing its shape while bacteria can be of different shapes 
such as round, cylindrical or comma. 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometers (one millionth of a meter) or 1*10
-6
m to a few 
centimeters. The smallest cell is 0.1 to about 0.5 micrometer in bacteria while ostrich egg is the 
largest cell measuring about 17cmx13cm. 
 
 
d. Functions 
In unicellular organisms, all the functions are performed by a single cell. Functions in multicellular 
organisms are distributed among different types of cells. For example: 
a. The nerve cells transmit the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Fig. Some parts of cells in onion peel under a microscope 
 
Pseudopodia 
Page 3


Chapter 5 Fundamental Unit of Life 
Cell – The structural and functional unit of life. Largest cell unfertilized ostrich egg (17cm*13cm) while 
smaller cells and most cells are of few micrometers. (10
-6
m). 
Cells were discovered by Robert Hooke in 1665 in a cork slice. Leeuwenhoek observed first free living cells 
(microorganisms) in 1674 in pond water. 
Cell theory 
Given by Schleiden and Schwann in 1838-39 and further expanded by Virchow in 1855 
1. All plants and animals are made up of cells 
2. Cell is the basic structural and functional unit of life. 
3. New cells arise from the pre-existing cells. 
 
Microscope – An optical instrument used to see cells (the one which are not very small and not visible to our 
naked eyes). 
 
 
 
 
 
 
 
 
                    Fig. A simple dissecting microscope        Fig. A compound microscope 
 
 
 
 
 
 
 
  Fig. Onion peel as seen under a compound microscope 
1. Variation in cells 
a. Number of cells 
Different organisms can have different number of cells. For e.g. Microorganisms are usually made of 
a single cell while humans are made of billions of cells.   
Unicellular organisms (uni – single; cellular – cell) – Organisms that are made of a single cell are 
called unicellular organisms. E.g. Amoeba, bacteria etc. 
 
 
 
Fig. Amoeba 
Multicellular Organisms (multi -many; cellular – cell) – Organisms that are made up of more than one 
cell are known as multicellular organisms. E.g. Plants, animals. 
 
b. Shape of cells 
Different types of cells have different shapes. For e.g. Red blood cells are round while the nerve 
cells are branched. Amoeba keeps on changing its shape while bacteria can be of different shapes 
such as round, cylindrical or comma. 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometers (one millionth of a meter) or 1*10
-6
m to a few 
centimeters. The smallest cell is 0.1 to about 0.5 micrometer in bacteria while ostrich egg is the 
largest cell measuring about 17cmx13cm. 
 
 
d. Functions 
In unicellular organisms, all the functions are performed by a single cell. Functions in multicellular 
organisms are distributed among different types of cells. For example: 
a. The nerve cells transmit the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Fig. Some parts of cells in onion peel under a microscope 
 
Pseudopodia 
1. Cell membrane or Plasma membrane 
? Outermost layer of a cell 
? Separates the content of the cell from the external environment 
? Semi-permeable – it allows the entry and exit of only some materials in and out of the cell 
? Diffusion – the movement of gases such as carbon dioxide from a region of higher concentration 
to lower concentration.  
Diffusion is used by plants and animals in exchange of gases such as oxygen and carbon dioxide. 
? Osmosis – the movement of water from a region of higher concentration to a region of lower 
concentration through a semi-permeable membrane. 
Osmosis is used by plants to absorb water from the soil and it is used in our body for the 
movement of water in and out of the cell. 
 
Hypotonic solution – A type of solution which has lower concentration of salts or higher 
concentration of water as compared to, inside of the cell.  
Since, the concentration of water is more in the solution it will move inside the cell by osmosis 
and the cell swells. An animal cell can burst is large amount of water keep entering inside the 
cell such as in case of distilled water, which do not have any salts. 
Hypertonic solution - A type of solution which has higher concentration of salts or lower 
concentration of water as compared to, inside of the cell. 
Since, the concentration of water is more in the solution it will move outside the cell by osmosis 
and the cell shrinks. 
Isotonic solution – A type of solution which has same concentration of water and  
salts as is inside the cell. 
Since, the concentration of water is same on both sides of the plasma membrane there is no net 
movement of water and the cell remains of same size. 
 
Although the water moves both inside and outside the cells in all the three cases (hypotonic, hypertonic and 
isotonic solutions) but the net movement is different in all of them. 
 
Page 4


Chapter 5 Fundamental Unit of Life 
Cell – The structural and functional unit of life. Largest cell unfertilized ostrich egg (17cm*13cm) while 
smaller cells and most cells are of few micrometers. (10
-6
m). 
Cells were discovered by Robert Hooke in 1665 in a cork slice. Leeuwenhoek observed first free living cells 
(microorganisms) in 1674 in pond water. 
Cell theory 
Given by Schleiden and Schwann in 1838-39 and further expanded by Virchow in 1855 
1. All plants and animals are made up of cells 
2. Cell is the basic structural and functional unit of life. 
3. New cells arise from the pre-existing cells. 
 
Microscope – An optical instrument used to see cells (the one which are not very small and not visible to our 
naked eyes). 
 
 
 
 
 
 
 
 
                    Fig. A simple dissecting microscope        Fig. A compound microscope 
 
 
 
 
 
 
 
  Fig. Onion peel as seen under a compound microscope 
1. Variation in cells 
a. Number of cells 
Different organisms can have different number of cells. For e.g. Microorganisms are usually made of 
a single cell while humans are made of billions of cells.   
Unicellular organisms (uni – single; cellular – cell) – Organisms that are made of a single cell are 
called unicellular organisms. E.g. Amoeba, bacteria etc. 
 
 
 
Fig. Amoeba 
Multicellular Organisms (multi -many; cellular – cell) – Organisms that are made up of more than one 
cell are known as multicellular organisms. E.g. Plants, animals. 
 
b. Shape of cells 
Different types of cells have different shapes. For e.g. Red blood cells are round while the nerve 
cells are branched. Amoeba keeps on changing its shape while bacteria can be of different shapes 
such as round, cylindrical or comma. 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometers (one millionth of a meter) or 1*10
-6
m to a few 
centimeters. The smallest cell is 0.1 to about 0.5 micrometer in bacteria while ostrich egg is the 
largest cell measuring about 17cmx13cm. 
 
 
d. Functions 
In unicellular organisms, all the functions are performed by a single cell. Functions in multicellular 
organisms are distributed among different types of cells. For example: 
a. The nerve cells transmit the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Fig. Some parts of cells in onion peel under a microscope 
 
Pseudopodia 
1. Cell membrane or Plasma membrane 
? Outermost layer of a cell 
? Separates the content of the cell from the external environment 
? Semi-permeable – it allows the entry and exit of only some materials in and out of the cell 
? Diffusion – the movement of gases such as carbon dioxide from a region of higher concentration 
to lower concentration.  
Diffusion is used by plants and animals in exchange of gases such as oxygen and carbon dioxide. 
? Osmosis – the movement of water from a region of higher concentration to a region of lower 
concentration through a semi-permeable membrane. 
Osmosis is used by plants to absorb water from the soil and it is used in our body for the 
movement of water in and out of the cell. 
 
Hypotonic solution – A type of solution which has lower concentration of salts or higher 
concentration of water as compared to, inside of the cell.  
Since, the concentration of water is more in the solution it will move inside the cell by osmosis 
and the cell swells. An animal cell can burst is large amount of water keep entering inside the 
cell such as in case of distilled water, which do not have any salts. 
Hypertonic solution - A type of solution which has higher concentration of salts or lower 
concentration of water as compared to, inside of the cell. 
Since, the concentration of water is more in the solution it will move outside the cell by osmosis 
and the cell shrinks. 
Isotonic solution – A type of solution which has same concentration of water and  
salts as is inside the cell. 
Since, the concentration of water is same on both sides of the plasma membrane there is no net 
movement of water and the cell remains of same size. 
 
Although the water moves both inside and outside the cells in all the three cases (hypotonic, hypertonic and 
isotonic solutions) but the net movement is different in all of them. 
 
 
 
 
Cell Wall 
? Another membrane present in plant cells outside the plasma membrane 
? Made up of cellulose. Cellulose is a polymer. 
? It provides mechanical strength to the plants 
? Plant cells do not burst when kept in a hypotonic solution because of the cell wall. 
? When kept in a hypertonic solution the cell shrink and the cell wall move away from the cell 
wall. This process is known as plasmolysis. 
 
2. Nucleus 
It is an organelle usually present in the center and act as the control center of the cell. It is bounded by a 
double layered nuclear membrane, which is porous and allows the movement of selected materials 
between the cytoplasm and the nucleus. 
A spherical body called nucleolus is present inside the nucleus, which has an intermediate function in 
protein synthesis.  
The nucleus contain rod shaped structures called chromosomes that pass hereditary characters from 
parents to offspring. 
The chromosomes are made up of DNA or deoxyribonucleic acid.  
Genes – The functional part of DNA or chromosomes that can produce protein is called a gene. 
Page 5


Chapter 5 Fundamental Unit of Life 
Cell – The structural and functional unit of life. Largest cell unfertilized ostrich egg (17cm*13cm) while 
smaller cells and most cells are of few micrometers. (10
-6
m). 
Cells were discovered by Robert Hooke in 1665 in a cork slice. Leeuwenhoek observed first free living cells 
(microorganisms) in 1674 in pond water. 
Cell theory 
Given by Schleiden and Schwann in 1838-39 and further expanded by Virchow in 1855 
1. All plants and animals are made up of cells 
2. Cell is the basic structural and functional unit of life. 
3. New cells arise from the pre-existing cells. 
 
Microscope – An optical instrument used to see cells (the one which are not very small and not visible to our 
naked eyes). 
 
 
 
 
 
 
 
 
                    Fig. A simple dissecting microscope        Fig. A compound microscope 
 
 
 
 
 
 
 
  Fig. Onion peel as seen under a compound microscope 
1. Variation in cells 
a. Number of cells 
Different organisms can have different number of cells. For e.g. Microorganisms are usually made of 
a single cell while humans are made of billions of cells.   
Unicellular organisms (uni – single; cellular – cell) – Organisms that are made of a single cell are 
called unicellular organisms. E.g. Amoeba, bacteria etc. 
 
 
 
Fig. Amoeba 
Multicellular Organisms (multi -many; cellular – cell) – Organisms that are made up of more than one 
cell are known as multicellular organisms. E.g. Plants, animals. 
 
b. Shape of cells 
Different types of cells have different shapes. For e.g. Red blood cells are round while the nerve 
cells are branched. Amoeba keeps on changing its shape while bacteria can be of different shapes 
such as round, cylindrical or comma. 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometers (one millionth of a meter) or 1*10
-6
m to a few 
centimeters. The smallest cell is 0.1 to about 0.5 micrometer in bacteria while ostrich egg is the 
largest cell measuring about 17cmx13cm. 
 
 
d. Functions 
In unicellular organisms, all the functions are performed by a single cell. Functions in multicellular 
organisms are distributed among different types of cells. For example: 
a. The nerve cells transmit the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Fig. Some parts of cells in onion peel under a microscope 
 
Pseudopodia 
1. Cell membrane or Plasma membrane 
? Outermost layer of a cell 
? Separates the content of the cell from the external environment 
? Semi-permeable – it allows the entry and exit of only some materials in and out of the cell 
? Diffusion – the movement of gases such as carbon dioxide from a region of higher concentration 
to lower concentration.  
Diffusion is used by plants and animals in exchange of gases such as oxygen and carbon dioxide. 
? Osmosis – the movement of water from a region of higher concentration to a region of lower 
concentration through a semi-permeable membrane. 
Osmosis is used by plants to absorb water from the soil and it is used in our body for the 
movement of water in and out of the cell. 
 
Hypotonic solution – A type of solution which has lower concentration of salts or higher 
concentration of water as compared to, inside of the cell.  
Since, the concentration of water is more in the solution it will move inside the cell by osmosis 
and the cell swells. An animal cell can burst is large amount of water keep entering inside the 
cell such as in case of distilled water, which do not have any salts. 
Hypertonic solution - A type of solution which has higher concentration of salts or lower 
concentration of water as compared to, inside of the cell. 
Since, the concentration of water is more in the solution it will move outside the cell by osmosis 
and the cell shrinks. 
Isotonic solution – A type of solution which has same concentration of water and  
salts as is inside the cell. 
Since, the concentration of water is same on both sides of the plasma membrane there is no net 
movement of water and the cell remains of same size. 
 
Although the water moves both inside and outside the cells in all the three cases (hypotonic, hypertonic and 
isotonic solutions) but the net movement is different in all of them. 
 
 
 
 
Cell Wall 
? Another membrane present in plant cells outside the plasma membrane 
? Made up of cellulose. Cellulose is a polymer. 
? It provides mechanical strength to the plants 
? Plant cells do not burst when kept in a hypotonic solution because of the cell wall. 
? When kept in a hypertonic solution the cell shrink and the cell wall move away from the cell 
wall. This process is known as plasmolysis. 
 
2. Nucleus 
It is an organelle usually present in the center and act as the control center of the cell. It is bounded by a 
double layered nuclear membrane, which is porous and allows the movement of selected materials 
between the cytoplasm and the nucleus. 
A spherical body called nucleolus is present inside the nucleus, which has an intermediate function in 
protein synthesis.  
The nucleus contain rod shaped structures called chromosomes that pass hereditary characters from 
parents to offspring. 
The chromosomes are made up of DNA or deoxyribonucleic acid.  
Genes – The functional part of DNA or chromosomes that can produce protein is called a gene. 
In a non-dividing cell these rod shaped chromosomes are present as threads bounded with proteins to 
form chromatin material. Chromatin material makes the packaging of DNA inside a very small 
nucleus, easier. 
 
 
 
 
 
 
 
     Chromatin material        Chromosome  DNA (deoxyribonucleic acid) 
 
Types of cells based on nucleus 
Eukaryotic cells Prokaryotic cells 
Eu means true and karyon means nucleus 1. Pro –primitive; karyon means nucleus 
Nucleus has a membrane called the nuclear 
membrane 
2. The nuclear material is not bounded by 
a membrane. The region containing the 
chromatin material is called nucleoid. 
Membrane bound organelles such as 
mitochondria, chloroplast are present. 
3. Membrane bound organelles are absent 
Example – All other organisms such as fungi, 
plants and animals. 
4. Examples – Bacteria, blue green algae