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• Cell: Basic unit of living organisms
• Unicellular organisms (Uni – Single): Living organism made up of single cell
• Multicellular organisms (Multi – Many): Living organism made of number of cells.
• Cell organelles : Components of cell
• Comparison between prokaryotic and eukaryotic cell
  

  Prokaryotic Cell	Eukaryotic Cell
  Nucleus is absent	Nucleus is present
  Do not contain membrane bound organelles	Contains membrane bound organelles
  Are mostly unicellular	Are multicellular
  E.g. E.coli, Streptococcus,etc.	E.g. Plants, animals, etc.

• Cells have different shapes and can perform different functions. E.g. Nerve cells in human beings have branches forming a network to send and receive signals between body parts and nervous system.
• Size of cell: Size of cells can be different and usually are in micrometres. E.g. bacterial cell is smallest cell of size 0.1 to 0.5 micrometre. Some cells can be in centimetres like ostrich egg is of size 17 cm × 13 cm.
• Cell structures:
  

  Prokaryotic Cell	Eukaryotic Cell
  Nucleus is absent	Nucleus is present
  Do not contain membrane bound organelles	Contains membrane bound organelles
  Are mostly unicellular	Are multicellular
  E.g. E.coli, Streptococcus,etc.	E.g. Plants, animals, etc.

• Cell structures:
  

  Name	Structure	Functions
  Plasma Membrane	Outermost covering of animal cell Flexible Composed of lipids and proteins Acts as semipermeable membrane	Exchanges material between cell and its surrounding
  Cell Wall	Outermost covering of plant cell Composed of cellulose	Acts as covering to plasma membrane Allows passage of large molecules like lipids, proteins, etc.
  Nucleus	Covered with nuclear membrane having pores Contains rod shaped chromosomes Chromosomes contains condensed structure called DNA Functional segments of DNA is called as genes DNA is present in form of chromatin in indivisible cell	Pores in nuclear membrane transports material outside the nucleus Play important role in division of single cell to number of cells during process of reproduction
  Cytoplasm	Fluid material present in cell Cell organelles like endoplasmic reticulum, golgi body, mitochondria, etc, are placed in it	It acts as site for various chemical reactions Helps in exchange of material
  Endoplasmic reticulum	Rough endoplasmic reticulum (RER) are flattened sac like structure. Ribosomes are present on it Smooth endoplasmic reticulum(SER) are tube like structure.	Proteins are manufactured at rough endoplasmic reticulum Lipids are manufactured at smooth endoplasmic reticulum Provides surface for some biochemical activities
  Golgi Apparatus	Flattened sac like structure, arranged in parallel fashion Cisterns are membrane bound vesicles	Cisterns keep material inside the apparatus separated from outside cytoplasm Golgi apparatus package and process material in and out of cell
  Lysosomes	Are membrane bound Spherical in shape	Digest waste inside the cell If cell gets damaged, lysosome burst and digest its own cell
  Mitochondria	Outer membrane separates internal part from other cell organelles Inner membrane is made up folded structure cristae Fluid is made up of matrix containing DNA, ribosomes, etc.	Stores energy in form of ATP Ribosome makes proteins for mitochondria
  Plastids	Found only in plant cell Contains large numbers of layers called stroma Have DNA and ribosomes Present in two types: chloroplast and leucoplast	Chloroplast manufacture food by the process of photosynthesis Leucoplast stores starch, oil, proteins, etc
  Vacuoles	Fluid filled sac of cell Plant cell have large vacuole Animal cell have small vacuole	Stores food material Removes excess water and waste material Stores materials like proteins, amino acids, etc.

• Comparison between plant cell and animal cell
  

  Component	Plant Cell	Animal Cell
  Cell Membrane	Present	Present
  Nucleus	Present	Present
  Nuclear Membrane	Present	Present
  Cytoplasm	Present	Present
  Cell Wall	Present	Absent
  Plastids	Present	Absent
  Vacuole	Present (Usually a large central vacuole)	Usually absent but if present then these are smaller in size
  Shape of cell	Fixed	Do not have fixed shape