Fundamental unit of life

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The fundamental unit of life


Chapter1
Class 9
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What is cell ?

• Cell is a latin word which means a little room.
• All living organism are made up of small small
  tiny units called cell
• Living organism are made up of either one cell
  (unicellular).or made up of many cells
  (multicellular).

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As home is made up of bricks an organism made up
of cells
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Discovery of cell

• Cell is discovered by robert hooke in 1665.
• Robert hooke is an english physicist.looked at a
  slice of cork through a microscopic lens and
  noticed some pores in it.
• Robert hooke believed that this pores served as a
  container for the plant juice, he called this
  pores as cell meaning little room

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Feature common to all cell.

• All cells have a definite boundary or cell
  membrane .
• The structure of the cell membrane is same in
  all cell.
• All cell have genetic material(DNA OR RNA).
• Mechanism of energy production is same in all
  cell.
• All cell transfer genetic material to its
  successor cell.
• Exchange of energy, material and other basic
  metabolic processes are also same.

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Cell theory of schleiden and schwann (1839)

• All living beings are composed of cell. All cell
  basically similar in chemical composition and
  metabolic activities.
• New cell develop inside the old ones (cytoblast)
• Cell could be generated spontaneously like a
  crystal.

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Modern cell theory or cell principle proposed by
r.virchow(1855)

• He stated omnis cellula e cellula which means
  new cells always arise from pre-existing cell
  this proposal was called theory of lineage.
• Two important feactures of modern cell theory
  are
• 1.all living cell are composed of cell and their
  product.
• 2.all cells arise from pre-existing cell.

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Exceptions of cell theory.

• 1.There are many cell which do not have nucleus
  eg.bacteria,mycoplasma etc.
• 2.Virus do not have cell structure,inspite of
  this it can show some living properties.
• 3.Mammalian RBC,sieve tube cell of plants do not
  have any nucleus.
• 4.Many fungi and algae have cells that contain
  many nuclei.

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Unicellular
multicellular
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Shape and size of cells

• Every organism have different kinds of cell,which
  is differ in shape ,size and function.
• The variation in different cells is mainly due to
  their different specific function.

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Remember it.

• Smallest known cell is PPLO(pleuro pneumonia like
  organism)
• Largest cell -ostrich egg cell
• Longest cell- nerve cell
• Largest cell in human body - ovum cell

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Types of cell
1.prokaryotic 2.eukaryotic

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Prokaryotic cells

• The cells in which a true nucleus absent and
  membranous organelles are absent are called
  prokaryotic cells.
• Instead a primitive nucleus is present.
• Pro means primitive,karyon means nucleus.
• Eg. bacteria,mycoplasma,cyanobacteria etc.
• .

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A typical prokaryotic cell
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Important feature of prokaryotic cell are

• Absence of a true nucleus.
• Absence of nuclear membrane.
• The genetic material lie inside the cytoplasm.
• Other membrane bound organelles such as golgi
  complex ,ER and mitochondria are also absent.
• The ribosomes are70S types.
• Cell wall does not contain cellulose and chitin.
• Genetic material represented by single circular
  DNA molecule,have plasmid
• Since mitochondria are absent the plasma membrane
  forms some infoldings,called mesosomes
• Cells divide by simple methods like binary and
  multiple fission.
• Spindle formation is absent.

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Eukaryotic cell

• These are well developed and advance cells with a
  true nucleus and membrane bound cell organelles.
• All higher organism are composed of eukaryotic
  cell.
• Eu means true, karyon means nucleus.

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Important feature of eukaryotic cells

• Nucleus is well developed, surrounded by a
  doubled walled true nuclear membrane.
• DNA and genetic material is located in nucleus.
• DNA is not circular in nature .
• DNA is associated with histone proteins.
• Ribosome are usually attached to ER.
• Ribosomes are of 80s types.
• Membrane bounded organelles are present .
• Formation of spindle fibres takes place here.
• Mitochondria are present .

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• Thank you