Cell is the smallest unit of life capable of performing all living functions.

Properties of cell

  • It is the smallest living unit of life.
  • It is so small that it is not visible to the naked eye.
  • The shape varies in different organisms and within an organism.
  • Size also differs.
  • All living cells exhibit certain basic properties like respiration, growth,
  • metabolism etc.
  • Originate from a pre-existing cell. A mother cell divides to produce daughter cells.

Invention of Microscope

  • The first, simple microscope was constructed by Antony van Leeuwenhoek.
  • He used biconvex lens to make the microscope.
  • The invention of compound microscope was done by Robert Hooke.
  • These compound microscopes consisted of concave lens.
  • The modern compound microscopes are a modification of one made by Robert Hooke. Their magnification power has been improved up to 2,000 times.
  • Electron microscopes are the one that use electronic beams to magnify the objects. Their magnification power is over 2,00,000 times.

Cell theory

  • All plants and animals are composed of cells.
  • It is the basic unit of life.
  • This was further expanded by Virchow by suggesting that all cells arise from pre-existing cells.

Classification of Cell on the basis of their cellular complexity

Prokaryotic Cells

  • The nuclear region is poorly defined;
  • membrane-bound organelles are absent.
  • The undefined nuclear region containing only nucleic acid called nucleoid.
  • Prokaryotes are unicellular organisms.

Eukaryotic Cells

  • Eukaryotes are usually multicellular organisms.
  • Yeast is exceptionally a unicellular eukaryote.
  • Nuclear region is well defined, bounded by nuclear membrane.
  • Other membrane-bound organelles are also present.
  • Also read Structure of Chromosomes

Components of the cell

Cell membrane

  • It is the protective layer that surrounds the cell.
  • Cell membrane selectively allows the entry of only some substances.
  • prevents the movement of other materials. Hence, it checks the transport of substances in and out of the cell.

Cell wall

  • In plants, an extra protective covering of a polysaccharide, cellulose is present.
  • It is called cell wall that protects plant cells from environmental variations.


  • It is a jelly-like substance present between cell membrane and nucleus.
  • It contains various cell organelles such as mitochondria, Golgi bodies, lysosomes etc.


  • It is a dense spherical body located at the centre of the cell.
  • It is surrounded by porous nuclear membrane.
  • It contains spherical body called nucleolus.
  • It also contains thread-like structures called chromosomes.
  • Chromosomes are the structures that carry genes and play an important role in inheritance.
  • Genes are the structural and functional unit of inheritance.
  • The entire living substance in a cell is known as protoplast.


  • Vacuoles are fluid-filled membrane-bound structures in the cell.
  • In plant cells, a single large vacuole is present.
  • In animal cells, numerous small vacuoles are present.
  • Also Read Genetics


  • They are present only in plant cells.
  • Plastids that contain green colour pigment chlorophyll are known as chloroplasts. It is the chlorophyll that gives green colour to the leaves.


  • Vacuoles are fluid-filled membrane-bound structures in the cell.
  • In plant cells, a single large vacuole is present.
  • In animal cells, numerous small vacuoles are present.
  • The membrane of the vacuole is called tonoplast. This membrane encloses a
    fluid called cell sap.


  • They are present in plant cells.
  • Chloroplast is a plastid containing green pigment called chlorophyll that is required in photosynthesis.
  • Plastids are of two types – leucoplasts and chromoplasts
  • Leucoplasts are colourless and are used to store food while chromoplasts are plastids containing pigments. Chloroplasts are a type of chromoplasts.
  • Chloroplasts consist of two regions – grana (stacks of sac like membrane bound structures that contain pigment chlorophyll) and stroma (ground substance containing enzymes and starch grains)

Endoplasmic Reticulum (ER)

They are of two types:

  • Rough Endoplasmic Reticulum (RER) is important for synthesis and packaging of proteins.
  • Smooth Endoplasmic Reticulum (SER) acts as storage organelle. It also helps in lipid (fat) synthesis.

Golgi Apparatus

  • It is made up of parallel arranged membrane-bound vesicles called cisternae.
  • It helps in storage, modification, and packaging of products in vesicles.
  • It helps in formation of glycoproteins and glycolipids.


  • It is a membrane-bound structure that holds variety of enzymes.
  • Rich in all types of hydrolytic enzymes, which are active at acidic pH.
  • It is involved in the digestion of carbohydrates, proteins, lipids, and nucleic acids.


  • It is a double membrane-bound structure.
  • The inner membrane of mitochondria is deeply folded to form cristae.
  • Cristae increase the surface area in the organelle.
  • It is the site of cellular respiration and hence known as ‘power house of cell’.
  • They have their own circular DNA.
  • They divide by fission.

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