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Cell - The Unit Of Life

Cell - The Unit Of Life

The cell is the smallest unit and the building block of all living organisms. An organism is made up of one cell, like bacteria or trillions of cells, like humans. It is the basic unit of life. The structure of the cell contains various organelles that perform necessary functions.

Table of Contents:

  • What Is A Cell?
  • Cell Theory
  • Prokaryotic Cells
  • Eukaryotic Cells
  • Cell Organelles
  • Difference between Plant Cell and Animal Cell
  • Practice Problems
  • Frequently Asked Questions

What Is A Cell?

A cell is the structural and functional unit of all living beings. There are unicellular and multicellular organisms in the environment. All the cells are not similar. They are divided into plant and animal cells. The cell also varies in size and shape. The largest cell is the egg or the ovum. The smallest cell is the granule cell present in the human cerebellum. Cell Biology is the study structure, function and life history of a cell.

Cell Theory

The cell theory is formulated by Matthias Schleiden and Theodor Schwann. They proposed that:

  • All living organisms are made up of cells and cell products.
  • All the cells are formed from existing cells through cell division.
  • The body of living organisms is made up of one or more cells.

Prokaryotic Cells

Prokaryotic cells are present in unicellular microorganisms. There are many types of prokaryotic cells, such as extremophiles and photoautotrophic, which can produce nutrients from the energy of the Sun. It is made up of single membrane-bound organelles; thus, all the reaction takes place within the cytoplasm of the cell. They are free-living organisms and found in the gut of other animals, such as ruminants of cows.

Eukaryotic Cells

Eukaryotic cells are present in multicellular microorganisms, and they come under Eukaryota. Eukaryotic cells have a membrane-bound nucleus. They are larger than prokaryotic cells. They have various organelles to perform various functions.

Cell Organelles

All eukaryotic cells contain different types of organelles to perform various functions of the cell. Some of the cell organelles are listed below:

  • Cell or Plasma membrane
  • Cell wall
  • Mitochondria 
  • Plastids
  • Ribosomes
  • Cytoskeletons
  • Centrosome
  • Centrioles
  • Nucleus
  • Microbodies
  • Cilia and Flagella
  • Endomembrane 

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Difference between Plant Cell and Animal Cell

Plant Cell

Animal cell

The cell wall is present 

The cell wall is absent

Centrioles are absent 

Centrioles are present

Plastids are present 

Plastids are absent

Have large vacuole

Have small vacuole

Practice Problems

Q1. Which of the following is absent in the animal cell?

A. Centrioles
B. Mitochondria
C. Cell wall
D. None of the above

Ans: C. Cell Wall

Animal cells, unlike plant cells, lack a cell wall and are surrounded by a plasma membrane, which works as a selective barrier, giving structure, protection, and preserving the cell's internal environment.

Q2. ______ is the basic unit of life.

A. Cell
B. Tissues
C. Plasma membrane
D. None of the above

Ans: A. Cell

Cells are vital life-sustaining elements in all living species, from simple single-celled organisms to complex multicellular animals. They carry out essential processes like nutrition uptake, reproduction, stimulus-response, and homeostasis.

Q3. Which of the following is absent in the plant cell?

A. Centrioles
B. Mitochondria
C. Cell wall
D. None of the above

Ans: A. Centrioles

Plant cells lack centrioles because plant cells have evolved other systems, such as Microtubule Organising Centres (MTOCs) and the cell plate, to achieve cell division and preserve the cell's fundamental activities.

Frequently Asked Questions

Q1. Why is Mitochondria called the ‘Powerhouse of the cell’?
Answer:
Mitochondria are called the ‘Powerhouse of the cell’ because it generates chemical energy that is required for the cell's biochemical reactions.

Q2. What is the function of the Golgi apparatus?
Answer: 
The Golgi apparatus plays an important role in transporting, modifying and carrying out the proteins to vesicles to reach the targeted destinations.

Q3. What is Chloroplast?
Answer: 
The Chloroplast is the green-coloured plastids containing chlorophyll. It is a double membrane organelle present in the plant cell.

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