Hey readers, today we are going to revise “building block of life” i.e. Cells. So, be ready to get the picture of our basic and functional unit of life.


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  • The cell was discovered by Robert Hooke in 1665 while, its theory was formulated in 1838 by Matthias Schleiden and Theodor Schwann.
  • The branch of biology and medicine concerned with structure and function of cell is called as cytology. The term cyto means cell.


Cells are mainly classified into two categories – Prokaryotic and Eukaryotic. Following is the table showing their characteristics and difference between each other.[/responsivevoice]

Difference Cells


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Now we will discuss sub cellular components and their functions.


Cell Membrane or Plasma membrane

All the cells are surrounded by a cell membrane. It is like a bag containing all cell material and regulates the movement of molecules in and out of the cell through the presence of holes in the membrane.

  • The cell membrane is made up of phospholipids and proteins. Proteins are present around the holes, aiding the movements of molecules in and out of the cell .


Cell wall

It is present in plant cells only and a few other organisms. It is rigid as it acts as shield for the cell.

  • It is made up of cellulose and chitin.
  • There are small holes in cell walls, called plasmodesmata, which enables the cell membranes of other cells to connect.



It is the fluid present inside the cell membrane. It was discovered by Dujardin in 1835 and named it as “sarcode” and the term “Protoplasm” was given by J.E. Purkinje in 1839. It is divided into two parts – nucleoplasm and cytoplasm.

  • Nucleoplasm found inside the nuclear membrane while cytoplasm found outside the nuclear membrane.
  • It is made up of water, ion, salts and organic molecules.


Cell Nucleus

It is like the “brain of the cell”, which controls all the activities of the cell. It is also known as “control room of the cell”. It was discovered by Robert Brown. Within nucleoplasm, nucleolus and chromatin material is present.

  • Nucleolus is made up of protein and RNA while the chromatin material is comprised of DNA and histon protein.
  • During cell division, chromatin breaks into pieces and forms chromosome. Hereditary characteristics from parents to offspring are transferred by chromatin.



It is a threadlike structure found inside the nucleus of animal and plant cell. They carry all the information used to help a cell grow, thrive, and reproduce. A bead like structure on chromosome is called gene.

  • Each chromosome is made up of two chromatids.
  • Chromatin is made up of DNA, proteins, RNA and other macromolecules.



Every animal cell has two small organelles called centrioles. It was discovered by Edouard van Beneden in 1883 and described by Theodor Boveri in 1888.

  • They help the cell at the time of cell division which occurs by the process of mitosis and meiosis.
  • Centrioles are made up of Microtubules.
  • There are threads attached to centrioles called mitotic spindle.



These are the “protein builders” of the cell. Protein is needed for many cell functions such as repairing damage or directing chemical processes. These were discovered by George Emil Palade.

  • Ribosome is found attached to the endoplasmic reticulum or floating in cytoplasm.
  • It is made up of ribonucleic acid (RNA).



It is known as the “powerhouse of the cell”.  It was discovered by Richard Altmann in 1890 and named it as “bioblast”. The term “mitochondria” was coined by Carl Benda in 1898.

  • These are rod shaped structure found in cytoplasm. It is surrounded by double layered membrane. Inner membrane has folds, called cristae. The fluid present in mitochondria is called matrix.
  • The key function of mitochondria is to perform cellular respiration. It takes nutrients from the cell, breaks it down, and turns it into energy during the production of adenosine triphosphate (ATP).



These are found in plant cell only and of three types viz. chroloplast, chromoplast and leucoplast. The term “plastid” was coined by Ernst Haeckel in 1866 but Andreas Schimper gave the clear definition to plastid in 1883.

  • Chroloplast – These are the “kitchen of the cell” or “food producers of the cell”. Chroloplasts convert light energy from the sun into sugar, which is used by the cell. It takes part in the process of photosynthesis and provides green color to plant.
  • Chromoplast – It imparts various colors to plants. It also synthesizes and accumulate carotenoid pigments.
  • Leucoplast – They involved in the storage of various materials like carbohydrates, fats, oils and proteins.
  • Plastids storing carbohydrates are called amyloplasts.
  • Plastids storing fats and oils are called elaioplasts.
  • Plastids storing protein are called proteinoplasts.


Endoplasmic Reticulum (ER)

It is the “manufacturing and packaging system” of the cell. It is the network of membranes found in cytoplasm and connected to the nucleus. It helps in the distribution of the material.

  • There are two types of ER – Rough and smooth. Rough ER is called rough because it has ribosomes attached to its surface.
  • Smooth ER (SER) acts as a storage organelle. It is important in the creation and storage of lipids and steroids.
  • The double membranes of smooth and rough ER form sacs called cisternae.


Golgi Apparatus or Golgi Bodies

It is also the packaging organelle like ER. It was discovered by Camillo Golgi. These are made up of tubes, vesicles and vacuoles.

  • It gathers simple molecules and combines them to make molecules that are more complex. It then takes those big molecules, packages them in vesicles, and either stores them for later use or sends them out of the cell.



These are fluid filled single membrane bounded, dead organelles of the cell. In plants, they are present in large size as compare to animal size.

  • It helps in osmoregulation and also stores toxic metabolic waste so the rest of the cell is protected from contamination.



The purpose of the lysosome is to digest things. These were discovered by De duve.

  • It contains an enzyme named hydrolytic enzyme, which may digest the entire cell. So it is also known as “suicidal bag”.



They have a single membrane that contains digestive enzymes for breaking down toxic materials in the cell.

  • Lysosomes have enzymes that work in oxygen-poor areas and lower pH.



With this, we have completed this topic. Hope you have learned today.

We will post Quiz on Cells in Today’s Cracking Session at 5 p.m. 

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