Chapter 8 Cell- Structure and Function Class 8 Notes | EduRev

Science - Short Notes for Class 8th

Created by: Sushil Solanki

Class 8 : Chapter 8 Cell- Structure and Function Class 8 Notes | EduRev

 Page 1


Chapter 8 Cell – Structure and function 
 
Cell – The smallest structural and functional unit of life. All living organisms, plants animals and even 
microorganisms are made up of cells. 
Robert Hooke discovered cell in 1665 while observing a cork under a magnifying device.  
Microscope is a magnifying device that is used to magnify very small things such as cells. 
 
 
 
 
 
 
 
          
A microscope    Cells as seen in an onion peel under a microscope. 
 
Cells combine to form tissues, tissues combine to form organs, and organs form organ system, and organ system 
for complex organisms such as humans. 
 
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. 
Pseudopodia 
Page 2


Chapter 8 Cell – Structure and function 
 
Cell – The smallest structural and functional unit of life. All living organisms, plants animals and even 
microorganisms are made up of cells. 
Robert Hooke discovered cell in 1665 while observing a cork under a magnifying device.  
Microscope is a magnifying device that is used to magnify very small things such as cells. 
 
 
 
 
 
 
 
          
A microscope    Cells as seen in an onion peel under a microscope. 
 
Cells combine to form tissues, tissues combine to form organs, and organs form organ system, and organ system 
for complex organisms such as humans. 
 
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. 
Pseudopodia 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometer (one millionth of a meter) or 1*10
-6
m to a few 
centimeter. 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 transmits the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Organelle – the structures of cells that perform various function essential for life. Examples are nucleus, 
mitochondria, Golgi bodies etc. 
 
 
 
 
 
 
 
Fig. Some parts of cells in onion peel under a microscope 
 
1. Nucleus 
It is an organelle usually present in the center and act as the control center of the cell. It is a bounded by 
a nuclear membrane, which is porous and allows the movement of selected materials between the 
cytoplasm and the nucleus. 
 
Page 3


Chapter 8 Cell – Structure and function 
 
Cell – The smallest structural and functional unit of life. All living organisms, plants animals and even 
microorganisms are made up of cells. 
Robert Hooke discovered cell in 1665 while observing a cork under a magnifying device.  
Microscope is a magnifying device that is used to magnify very small things such as cells. 
 
 
 
 
 
 
 
          
A microscope    Cells as seen in an onion peel under a microscope. 
 
Cells combine to form tissues, tissues combine to form organs, and organs form organ system, and organ system 
for complex organisms such as humans. 
 
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. 
Pseudopodia 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometer (one millionth of a meter) or 1*10
-6
m to a few 
centimeter. 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 transmits the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Organelle – the structures of cells that perform various function essential for life. Examples are nucleus, 
mitochondria, Golgi bodies etc. 
 
 
 
 
 
 
 
Fig. Some parts of cells in onion peel under a microscope 
 
1. Nucleus 
It is an organelle usually present in the center and act as the control center of the cell. It is a bounded by 
a 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 chromosomes that carry genes, which helps in inheritance of 
characters from parents to offspring. 
 
 
 
 
2. Cell membrane  
Cell membrane, also called the plasma membrane is the outer layer of the cell that encloses all its other 
components inside it. In plants another membrane, called the cell wall is present around the cell 
membrane, which provides additional strength to the plant cells. 
 
 
3. Cytoplasm  
It is a jelly like substance present between the cell membrane and the nucleus. All the other organelles 
such as the mitochondria, Golgi bodies, lysosomes etc. and nutrients, molecules floats inside the 
cytoplasm. 
 
4. Organelles 
The structures of cells that perform various function essential for life. Examples are nucleus, 
mitochondria, Golgi bodies etc. 
 
a. Mitochondria is the powerhouse of the cell. It produces energy. 
b. Chloroplast is found in plant cells and produces food by photosynthesis. 
c. Golgi bodies helps in packaging of the nutrients. 
  
Types of cells 
Prokaryotic cells Eukaryotic cells 
1. Pro –primitive; karyon means nucleus Eu means true and karyon means nucleus 
2. The nuclear material is not bounded 
by a membrane  
Nucleus has a membrane called the nuclear 
membrane 
3. Membrane bound organelles are 
absent 
Membrane bound organelles such as 
mitochondria, chloroplast are present. 
4. Examples – Bacteria, blue green algae Example – All other organisms such as fungi, 
plants and animals. 
 
 
Page 4


Chapter 8 Cell – Structure and function 
 
Cell – The smallest structural and functional unit of life. All living organisms, plants animals and even 
microorganisms are made up of cells. 
Robert Hooke discovered cell in 1665 while observing a cork under a magnifying device.  
Microscope is a magnifying device that is used to magnify very small things such as cells. 
 
 
 
 
 
 
 
          
A microscope    Cells as seen in an onion peel under a microscope. 
 
Cells combine to form tissues, tissues combine to form organs, and organs form organ system, and organ system 
for complex organisms such as humans. 
 
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. 
Pseudopodia 
 
  
Red blood cells    Nerve cells   Amoeba 
 
c. Cell Size 
The size of cells can vary from a few micrometer (one millionth of a meter) or 1*10
-6
m to a few 
centimeter. 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 transmits the messages between brain and other organs 
b. Muscle cells helps in movement. 
c. Skin cells helps to feel touch. 
Structure of cells  
Organelle – the structures of cells that perform various function essential for life. Examples are nucleus, 
mitochondria, Golgi bodies etc. 
 
 
 
 
 
 
 
Fig. Some parts of cells in onion peel under a microscope 
 
1. Nucleus 
It is an organelle usually present in the center and act as the control center of the cell. It is a bounded by 
a 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 chromosomes that carry genes, which helps in inheritance of 
characters from parents to offspring. 
 
 
 
 
2. Cell membrane  
Cell membrane, also called the plasma membrane is the outer layer of the cell that encloses all its other 
components inside it. In plants another membrane, called the cell wall is present around the cell 
membrane, which provides additional strength to the plant cells. 
 
 
3. Cytoplasm  
It is a jelly like substance present between the cell membrane and the nucleus. All the other organelles 
such as the mitochondria, Golgi bodies, lysosomes etc. and nutrients, molecules floats inside the 
cytoplasm. 
 
4. Organelles 
The structures of cells that perform various function essential for life. Examples are nucleus, 
mitochondria, Golgi bodies etc. 
 
a. Mitochondria is the powerhouse of the cell. It produces energy. 
b. Chloroplast is found in plant cells and produces food by photosynthesis. 
c. Golgi bodies helps in packaging of the nutrients. 
  
Types of cells 
Prokaryotic cells Eukaryotic cells 
1. Pro –primitive; karyon means nucleus Eu means true and karyon means nucleus 
2. The nuclear material is not bounded 
by a membrane  
Nucleus has a membrane called the nuclear 
membrane 
3. Membrane bound organelles are 
absent 
Membrane bound organelles such as 
mitochondria, chloroplast are present. 
4. Examples – Bacteria, blue green algae Example – All other organisms such as fungi, 
plants and animals. 
 
 
   
 Plant cell     Animal Cell    *ncert class VIII 
Plant cells Animal cells 
Plant cells have an extra layer outside the cell 
membrane called cell wall. 
Cell wall is absent in animals 
Plant cells have large vacuoles to store food 
material 
Animal cells have smaller vacuoles. 
 
Chloroplasts are present in plant cells that 
helps in photosynthesis. 
Chloroplasts is absent in animal cells. 
Plastids are organelles that give color to plant 
e.g. chloroplast 
Plastids are absent in animals 
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