What is a cell in biology?- Structure and their Function

What is a Cell in biology?

A cell is the basic unit of life or a cell is the structural and functional unit of life is determined by Robert Hooke. The body of all livings things is made of cells. Cells were first discovered by Robert Hooke with the help of a microscope in 1665. The number of cells varies in different organisms. Some cells are unicellular (single cell), whereas others are multi-cellular.


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what is a cell in biology
Cell Diagram



In single-celled organisms like paramecium, Amoeba, all the functions (feeding, excretion, respiration, reproduction, movement, etc.) have to be performed by a single cell.

The single-celled organism may be Prokaryotes or Eukaryotes. Multi-cellular organisms develop from a single cell and may have trillions of cells when they grow up.

Study of Cell Cytology
Single Cell Called Zygote
The cell of the Liver is called Hepatic Cell
The cell of the Lungs is called Alveoli
The cell of the Brain is called Neuron
The cell of Kidney is called Nephron


Shapes of cells also vary from being irregular to round, polygonal, cylindrical, etc. The size of cells also varies from 0.1 micrometers to 170 mm x 130 mm.


Cell Theory

All living organisms are made up of cells or products of cells called cell theory. It was given by Schleiden and Schwann. Cell theory, however, did not explain how new cells were formed.

In 1838, Malthias Schleiden (German Botanist) examined a large number of plants. He observed that all plants are composed of different kinds of cells that form the tissues of the plant.

In 1839, Theodore Schwann (British Zoologist) studied different types of animal cells. He reported that cells had a thin outer layer which is today known as the ‘plasma membrane’. He also concluded, based on his studies on plant tissues, that the presence of cell war is a unique character of the plant cells.


Structure of Cell

The cell carries a number of cell organelles suspended in a jelly-like substance called cytoplasm which again is bounded by the cell membrane. Most of the cell organelles are common in animals as well as plants.

Structure of cell



Cell Organelles in Plants and Animals Cells

Various cell organelles and their functions have been given below in brief:

Cell wall

Cell walls are found in only plant cells. In plants, the rigid outer wall is made of cellulose. It gives a definite shape to the cell and provides strength and protection. It is absent in animal cells.


Cell Membrane

It regulates the movement of molecules inside to outside and outside to inside. It is made up of Phospholipids. The semi-permeable membrane that covers the entire cell acts as a gatekeeper allowing only certain things to pass and acting as a barrier for others.



The nucleus is also called the Brain of a cell or manager of the cell. It is the master controller of entire cell functions. It contains chromosomes that contain genes for controlling different functions.

  • The nucleus was discovered by Robert Brown.
  • It is the largest part of the cell.
  • Nucleic acid-like DNA and RNA are present inside the nucleus.
1. The model Of DNA (Deoxy Ribose Nucleic Acid) is given by Watson and crick. 1. Modal of RNA (Ribose Nucleic Acid) is given by Fredrick Mischer.
2. DNA is a double Helix. 2. RNA is a single Helix.
3. It is found in both nucleus and mitochondria. 3. It is found in the nucleus and cytoplasm.
4. DNA is known as genetic material. 4. RNA helps in making protein.


Endoplasmic Reticulum(ER)

The endoplasmic reticulum is a network of the membrane that is found between the nucleus and plasma membrane. It forms a large network of interconnected membranous tubules that connect the nucleus with the cell’s outer boundary. Ribosomes are found attached to it (rough endoplasmic reticulum) where protein synthesis takes place. It also helps to transport materials from the nucleus to outside the cell. The endoplasmic reticular was discovered by Porter.

Types of Endoplasmic Reticulum

  • Rough Endoplasmic Reticulum
  • Smooth Endoplasmic Reticulum


Rough E.R Smooth E.R
1. Rough E.R is found near the nucleus membrane. 1. Smooth E.R is found near the plasma membrane.
2. It is the most stable. 2. It is less stable.
3. A ribosome is present. 3. Ribosome is absent
4. Work = Protein synthesis 4. Work = Lipids/Steroids synthesis



They are responsible for protein synthesis. It was discovered by Palade.

  • Ribosomes are the smallest part of the cell.
  • It is also called the Protein Factory of Cell.
  • It is also called the Engine of cells.



A small dark-colored body in the nucleus that is mainly responsible for the synthesis of protein and RNA.



Vacuoles are absent or of small size in the animal cell but big-sized storage places for plant cells. They also help in secretion and excretion in plant cells.

  • Vacuole was discovered by Antoni van Leeuwenhoek.
  • It is the Empty space of the cell.

Vacuoles = Reserved food+water+minerals

  • It is called a packet of the cell.



The cytoplasm is a jelly-like substance that fills the entire cell and organelles are found embedded in it. It helps to maintain the osmotic concentration of the cells.

  Cytoplasm Diagram



The chloroplast is present in the plant cells only. They contain pigments especially the green-colored chlorophyll that absorbs solar energy and converts it to chemical energy to be used in the process of photosynthesis.


Golgi body

It was discovered by Camallio Golgi. It is called a packer/movers/bundle. The Golgi body is also called the traffic police of the cell and mother of the cell.

Golgi apparatus: They are flattened sac-like structures responsible for the secretion and act as packaging units.



Mitochondria are also called the powerhouse of cells and energy houses of the cell. It is here that the food gets oxidized and energy in the form of ATP molecules is produced.



  • Mitochondrion was discovered by Altman.
  • Mitochondria’s name was given by Benda.
  • It is the second-largest component of the cell.
  • It is the double membrane structure of the cell.



It is also called Suicidal bags of cell and Digestive bags of cell. They contain digestive juices that help to break down the waste or non-performing organelles.

  • It was discovered by Deduve.
  • It is a single membrane structure.
  • Lysosomes are present in saliva.
  • It is more activated in the case of blood cancer.

Why Lysosomes is called Suicidal bags of cells?

Lysosomes having hydrolytic enzymes, these hydrolytic enzymes can digest the Foreign particles but sometimes these hydrolytic enzymes are secreted in huge amounts and they can digest the entire cell. Hence, this is known as the Suicidal bag of the cell.



The centrosome is resent only in animal cells near the nucleus. It is functional during cell division when it helps to form spindle fibers on which chromosomes get attached.


Nuclear membrane

The nuclear membrane is the outer membrane of the nucleus. It is a porous double-membrane structure that helps in transporting substances in and out of the nucleus.


They are made up of DNA, the genetic material that actually controls all the functions of the body and is responsible for the transmission of characters from one generation to the other. In every species, there is a definite number of chromosomes in the nucleus of its cells.

  • It was discovered by Bendon.
  • It becomes visible during the cell division process.
  • Chromosomes are found in pairs.
  • In the human body, 23 pairs of chromosomes are present.

A tissue is formed by a group of similar cells that perform similar functions. Tissues found in human beings are:

  • Epithelial tissue or the covering tissue, which are found on the internal and external surface of every organ and the skin.
  • Muscular tissue, that forms the bulk of the body. They are attached to the bones, internal organs, and blood vessels, and the heart is made of them.
  • Connective tissue (bones, blood, cartilage) that connect, bind, or separates other tissues or organs.
  • Nervous tissue, which is found in the brain, spinal cord, and nerves.

Tissues found in plants are:

  • Meristematic tissue, having cells that keep on dividing and contribute to the growth of plants.
  • Parenchyma tissue, having thin-walled cells with intercellular spaces. This tissue acts as filler and stores food.
  • Collenchymas tissue that has thickened corners of the cells. It provides strength and shape to the plants.
  • Sclerenchyma tissue, the hard woody tissue which is dead but in giving mechanical strength to the plant.
  • Vascular tissue is made of xylem and phloem. Xylem conducts water from roots to all parts of the plants through its hollow xylem vessels and phloem conducts food through its sieve tube cells that are devoid of the nucleus to make room for the food to pass through.

 Some important Link of Biology

  1. The Human Brain
  2. Digestive System
  3. Parts of a Plants


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My Name is Mukesh Kumar. I am a Teacher, Blogger, Educational Content Writer, and Founder of CBSE Digital Education.

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