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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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FAQs on Short Note: Cell- Structure and Function - Class 8

1. What is the basic structure of a cell?
Ans. The basic structure of a cell consists of a cell membrane, cytoplasm, and a nucleus. The cell membrane is a protective layer that surrounds the cell and controls the movement of substances in and out of the cell. The cytoplasm is a jelly-like substance that fills the cell and contains various organelles. The nucleus is the control center of the cell and contains the genetic material.
2. What are the functions of the cell membrane?
Ans. The cell membrane has several important functions. It controls the movement of substances in and out of the cell, allowing nutrients to enter and waste products to exit. It also helps to maintain the shape and structure of the cell. Additionally, the cell membrane plays a role in cell communication and recognition, allowing cells to interact with each other and with their environment.
3. What are organelles? Give some examples and their functions.
Ans. Organelles are specialized structures within cells that perform specific functions. Examples of organelles include the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus. The nucleus contains the cell's genetic material and controls cell activities. Mitochondria are responsible for producing energy for the cell. The endoplasmic reticulum is involved in protein synthesis and lipid metabolism. The Golgi apparatus processes and packages proteins for transport within the cell or secretion outside the cell.
4. What is the role of the cytoplasm in a cell?
Ans. The cytoplasm fills the cell and provides a medium for cellular processes to occur. It contains various organelles and is involved in important cellular activities such as protein synthesis, metabolism, and cell division. The cytoplasm also helps to maintain the shape and structure of the cell and provides support for the organelles.
5. How does the nucleus control cell activities?
Ans. The nucleus controls cell activities by containing the cell's genetic material in the form of DNA. DNA carries the instructions for making proteins, which are essential for cell functions. The nucleus regulates protein synthesis by controlling the transcription and translation processes. It also regulates cell division by controlling the replication and distribution of DNA during cell division. Overall, the nucleus plays a crucial role in controlling and coordinating cell activities.
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