Back to Lesson

• Cell: Living organisms are made up of basic unit called cell.
• Unicellular organisms (Uni – Single): Living organism made up of single cell
• Multicellular organisms (Multi – Many): Living organism made of number of cells.
• Prokaryotic organisms: Organisms in which nuclear membrane is absent are called prokaryotic organisms or prokaryotes. E.g. E. coli, Streptococcus, streptomyces, etc
• Eukaryotic organisms: Organisms in which nuclear membrane is present are called as eukaryotic organisms or eukaryotes. E.g. Fungi, plants, etc.
• 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.

• 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.

• Transportation of material through plasma membrane:
  • Plasma membrane exchange material between cell and surrounding.
    Click here to watch video on Plasma Membrane.
  • Material is transfer by diffusion through the process of osmosis.
  • Osmosis: Solvent from higher concentration, moves through a semipermeable membrane, towards lower concentration area of solvent.
  • Hypotonic solution: If medium surrounding the cell has high water concentration, more amount of water moves inside cell by the process of osmosis. Such a solution is called hypotonic solution.
  • Isotonic solution: If the water concentration of medium and cell is same, equal amount of water travels on both side. Hence, there is no net movement across the cell. Such a solution is isotonic solution.
  • Hypertonic solution: If medium surrounding the cell is of low water concentration, more water moves out of cell. Such a solution is called as hypertonic solution.
  • Plasmolysis: Plant cell when placed in hypertonic solution undergo osmosis, and content of cell shrinks away from the cell wall. This is process of plasmolysis.
• Endocytosis (Endo- inside, Cytosis: Movement of molecules): A process of engulfing food into body of unicellular organism due to flexibility of plasma membrane.
• Exocytosis (Exo – out, Cytosis: Movement of molecules): A process of removing material outside the body of unicellular organism due to flexibility of plasma membrane.