Chapter 12 :Transport in living organisms :1

1) Define transport :
    TRANSPORT : 
                           The movement of substances from one part to another part within the body of an organism is called transport.



2) How transport is done in unicellular organisms?
    TRANSPORT IN UNICELLULAR ORGANISMS :
                           In simple and unicellular living organisms there is no need of any special transport system.The oxygen and dissolved substances from the outside enviroment can diffuse into the protoplasm directly.



3)What is vascular system?
    VASCULAR SYSTEM :
                         In plants the system which is responsible for the transport of material throughout the plant body is called vascular system.Vascular system consists of Xylem and Phloem.
    XYLEM :
                   The vessels which are responsible for the transport of minerals are called xylem vessels.
    PHLOEM :
                   The vessels which are responsible for the transport of food are called phloem vessels.



4) Define passive transport and active transport.
    There are two basic processes responsible for the transport of materials across the cell membrane.They are :
     a) Passive transport        b) Active transport
     PASSIVE TRANSPORT :
                     The movement of the materials across the cell membrane without the expenditure of metabolic energy is called passive transport e.g Diffusion , Osmosis , Plasmolysis etc.
     ACTIVE TRANSPORT :
                     It is defined as the movement of substances across the cell membrane against the concentration difference with the help of energy input.



5) Describe the importance of water in the transport of materials?
    IMPORTANCE OF WATER :
                              Living organisms depend on water for their existance.
    a) MAJOR CONSTITUENT OF THE CELL :
                       The protoplasm of the cell contains 70% to 95% of water , which shows that water is the major constituent of a cell.
    b) UNIVERSAL SOLVENT :
                         Water is said to be the best solvent , capable of dissolvig many substances like sugar , salts or even proteins.This property of water is advantaceous to all living organisms in transport of materials across their cell membrane.
    c) MEDIUM OF TRANSPORT :
                         Water in plants acts as a medium of transport for minerals from roots to leaves of the plant.
    d) WATER AS A METABOLITE :
                           Water acts as a metabolite and is required in many metabolic reactions occuring in the cell.In photosynthesis it provides hydrogen to Carbondioxide for making glucose.
           In hydrolytic reactions water molecules are added to break large molecules into smaller ones.
           In condensation reactions small molecules are joined together by the removal of water molecules to form large molecules.
           Transpiration of water also regulates temperature and help in circulation of nutrients.



  6) Define and explain the process of diffusion.
      DIFFUSION :
                           The movement of molecules or ions from the region of their higher concentration to the region of their lower concentration is known as diffusion.
      EXPLANATION :
                          Diffusion play a very important role in the transport of materials across a cell membrane.water enters a cell through cell membrane and is transported from cell to cell by diffusion.The rate of diffusion depends upon the concentration difference and the nature of the path way the molecules have to take.
     a) DIFFUSION IN PLANTS :
                           Plants during photosynthesis and respiration , are entirely dependent on diffusion for exchange of carbon dioxide and oxygen between the cell and the external enviroment.In transpiration , water diffuses out from leaves through stomata , which helps in the circulation of nutrients.
    b) DIFFUSION IN ANIMALS :
                          Many small animals such as Amoeba and Hydra for obtaining oxygen and getting carbondioxide out depend on diffusion.
       In case of large animal there are special organs for respiration like Lungs , which play imporatant role in respiration and bring fresh supplies of air into body. However even in lungs the final stage in the exchange of gases between air and blood depends on diffusion.



  7) Define and explain osmosis with the help of experiment.
      OSMOSIS :
                        The diffusion of water molecules or any other solvent through semi permiable membrane is known as osmosis.
      EXPLANATION :
                         The process of osmosis play very important role in the transport of material across the cell membrane.
      The plants depend mainly on osmosis for absorption of water through their roots and its translocation from the roots to the leaves.The process of osmosis can be best explained by an experiment which is as follows.
      EXPERIMENT :
                          Take a thistle funnel and tie a piece of cellophane papaer tightly over its mouth.Fill the funnel with concentrated sugar solution.Mark the level of the solution in the funnel.Lower the funnel into a beaker of water so that the liquid levels inside and outside the funnel are the same.Set up a control experiment with distilled water.
               The level of the solution in the funnel gradually rises and then becomes steady.The reason is that the beaker contains 100% pure water , this means that the concentration of water molecules is higher in the beaker than in the sugar solution.Therefore , there is a net flow of water molecules from beaker into sugar solution , raising its level in the stem of thistle funnel.The movement of water molecules from beaker into funnel is called end-osmosis.
               The  sugar solution  exerts a downward pressure by its weight and some water is pushed outside.This movement of water from the inside to the outside is called exosmosis.Inspite of exsosmosis ,the water molecules in the beaker exert pressure on the solution inside the funnel.This pressure is known as osmotic pressure.