The fundamental unit of life refers to nothing but a cell. However, do you know why a cell is a crucial structural and functional unit of life? It is because a cell is the smallest and individual living entity that carries on various life functions. The chapter – The Fundamental Unit of Life, deals with cells and other characteristics related to them.
Cell and Its History
Cells are referred to as the building blocks of all living organisms. One cannot stress enough the importance of cells in the existence and sustenance of life on earth. Talking about its history, a scientist named Robert Hooke introduced the term cell in 1665. He took a slice of cork under his compound microscope. What he observed changed the entire history of science.
When he observed the cock slice under his microscope, he observed numerous small blocks that looked like the blocks of honeycomb. They were nothing but cells. It led to the discovery of cells, the fundamental unit that is essential to make life possible on earth.
Features of a Cell
Our bodies consist of numerous types of cells. Each cell contributes to the overall functioning of the body. Some characteristic properties of a cell are –
- A cell is the smallest and basic unit of life.
- A cell is not visible to the naked eye because of its minute size.
- A cell can have different shapes and sizes within the same organism.
- Every organism possesses different types of cells.
- All the active cells show and exhibit specific functions. These functions include respiration, reproduction, growth, and many more.
- From Cell Theory, we know that every cell comes from a pre-existing cell. It means a single cell divides further from new cells.
- New cells not only perform the same activity as their parent cells but also carry the same genetic material.
- A characteristic feature of all cells is their ability to divide and form new cells.
What is Cellular Respiration?
Cellular respiration refers to the process through which energy is released by the mitochondria of a cell. The glucose that we get from our food is absorbed by the cell and utilized to produce energy. In turn, the body receives energy in the form of ATP.
Also See: NCERT Solutions for Class 9 Science Fundamental Unit of Life
What are the Two Different Types of Cells Based on Their Number?
Cells are diverse in nature. It means there are numerous types of cells within our universe. The two broad categories of living cells found in an organism are –
- Unicellular Organisms
These are the organisms that are made above only a single cell. Most of these organisms are made up of prokaryotic cells, cells that don’t have membrane-bound organelles or a true nucleus. For example – most microorganisms like bacteria are made up of a single cell only.
- Multicellular Organisms
Multicellular organisms are a more advanced and well-structured category of organisms. The cells in a multicellular organism show better structure and shape as compared to unicellular organisms. These multicellular organisms are made up of eukaryotic cells, the cells which have membrane-bound organelles and a nucleus with a nuclear membrane.
Also Read:
Difference Between Unicellular and Multicellular Organisms
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Do you know which is the smallest cell in the human body? |
What are the Two Main Types of Cells Based on their Structural Organization?
The structural organization refers to the structures present inside the cell and their arrangement. Following the above criteria, we have two main types of cells –
- Prokaryotic Cells
These types of cells lack membrane-bound organelles like mitochondria, chloroplast, Golgi bodies, and others. Apart from this, the nucleus inside the prokaryotic cell does not have a nuclear membrane, which means that all the genetic material of the nucleus remains spread throughout the cytoplasm.
- Eukaryotic Cells
These cells contain the most defined structures. They have membrane-bound organelles and a defined nuclear membrane. Eukaryotic cells are considered to be advanced and more sophisticated than prokaryotic cells.
Cell organelles Inside a Cell
There are several cell organelles found inside the cytoplasm of a cell. Each cell organelle looks and performs in a different manner. Below is a list of different cell organelles with their specific functions.
Cell membrane or plasma membrane is identified as the outermost covering of a cell. This structure provides shape to the cell and protection to all the cell organelles present inside it.
The plasma membrane only permits certain types of substances through it. It hints at the selective permeability of the cell membrane.
Diffusion is a natural phenomenon associated with the cell membrane. It happens when there is a movement of molecules across a cell membrane. These molecules generally flow from a region of high concentration to a region of low concentration. Gases like carbon dioxide and oxygen move across the plasma membrane through the phenomena called diffusion.
Osmosis refers to the passage of water molecules through a semipermeable membrane. In osmosis, water molecules move across a semipermeable membrane from a low solute concentration region to a high solute concentration region.
It means if the surroundings of a cell have more water than the inside of the cell, the water molecules will flow from the surroundings to the inside of the cell and vice versa.
Also Read: Difference between Diffusion and Osmosis
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What do you understand about the functions of a plasma membrane?
The cell wall is a structure that is peculiar to only plant cells. It means animal cells do not have a cell wall.
The presence of a cell wall is a major difference between a plant cell and an animal cell. A cell wall is composed of cellulose or other biomolecules depending on the organism. The main function of a cell wall is to provide protection and rigidity to a plant cell.
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Which is the outermost layer of a plant cell? Is it a cell wall or a cell membrane?
The nucleus is the storage centre for all the genetic material inside a cell. And it is why it is also known as the brain of a cell.
The nucleus is enclosed by a layer called a nuclear membrane. It covers the nucleus that contains chromatin fibres and proteins. Chromatin fibres form chromosomes during cell division.
The nucleus plays a significant role in the initiation and completion of a cell cycle (meiosis or mitosis).
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What is the common difference between chromatin fibres and chromosomes? |
The cytoplasm is a fluid-like substance found throughout the surface of a cell. All the cell organelles are found suspended in this fluid, cytoplasm. Just like a cell membrane, the cytoplasm also supports the formation of the structure of a cell.
The cytoplasm is the place where different cell organelles are found. On the other hand, various biochemical reactions like glycolysis take place inside the cytoplasm.
The endoplasmic reticulum is a structure that is formed as a continuation of the nuclear membrane.
The two types of endoplasmic reticulum are –
Smooth Endoplasmic Reticulum (SER)
SER is characterized by the absence of ribosomes found on the surface of ER. Although they are not involved in protein synthesis, they assist in the manufacturing of lipid and fat molecules.
Rough Endoplasmic Reticulum (RER)
RER has ribosomes on their surface and hence appear to be rough. The ribosomes are involved in protein synthesis. Therefore, the rough endoplasmic reticulum is involved with the modification and folding of the protein.
Golgi Apparatus
This cell organelle appears as an arrangement of membrane-bound vesicles placed parallel to each other. This structure is involved in the storage and transportation of complex molecules across the cytoplasm.
Lysosomes
Lysosomes are the cell organelle that is responsible for maintaining the cleanliness of the cell. It is why they are called suicide bags.
They are referred to as the disposal system of a cell that helps to clean by digesting any foreign material and other old cell organelles.
They do this because of the presence of powerful enzymes that are capable of breaking down large organic materials.
Because mitochondria is a cell organelle that is responsible for generating energy, it is known as the powerhouse of the cell.
The glucose found in our food is further processed inside a cell to generate energy from it in the form of ATP.
Mitochondria is a membrane-bound cell organelle that has its own genetic material.
Curiously enough
Are you aware that ATP is referred to as the currency of a cell? Try to find out why it is so? |
This is a collective term used for cell organelles that are present in plant cells only. Plastids refer to chloroplasts and chromoplasts.
Chloroplasts are the cell structures that contain chlorophyll. Thus, involved in photosynthesis.
Chromoplasts are the cell structures that provide colour to the parts of the plant, like flowers, leaves, and fruits.
There are storage vesicles placed inside the cell, which are known as vacuoles. These vacuoles contain solid or liquid materials that indirectly help the cell to maintain its shape.
While animal cells have smaller vacuoles, the vacuoles present in plant cells are large.
Did you know?
The vacuoles present in a plant cell occupies about 90% of the total cell volume. Most vacuoles in a plant cell contain cell sap. |
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What are the two cell organelles that contain their own genetic material? |
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Frequently Asked Questions About- The Fundamental Unit of Cell
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