Kerala PSC Examination Calendar – JANURY 2013:

Kerala PSC Examination Calendar – JANURY 2013:

       http://www.keralapsc.gov.in/index.php?option=com_docman&task=cat_view&gid=289&Itemid=15

ROOT :

• In most of the dicotyledonous plants, the direct elongation of the radicle leads to the formation of primary root which grows inside the soil.
• The primary roots and its branches constitute  tap root system
• The primary root in monocotyledonous plants is short lived and  is replaced by a large number of roots which are originate from the base of the stem and constitute the fibrous root system.
• In some plants, roots arise from parts of the plant other than the radicle and are called
  

  adventitious roots.

Regions of the Root:

• The root is covered at the apex by a thimble-like structure called the root cap. As  it passes through the soil,it protects the tender apex of the root.

•  A few millimeters above the root cap is the region of meristematic activity. The cells of this region are very small, thin-walled and with dense protoplasm  and  divide repeatedly. 
• The cells proximal to this region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. So region is called the region of elongation.
•  The cells of the elongation zone gradually differentiate and mature. Hence, this zone, proximal to region of elongation, is called the region of maturation.
•  Some of the epidermal cells from this region  form very fine and delicate, thread-like structures called root hairs which absorb water and minerals from the soil.

Functions of the root system:

1. Absorption of water and minerals from the soil.                                                                                                      
2. Providing a proper anchorage to the plant parts.                                                                                   
3. Storing reserve food material.
4. Synthesis of plant growth regulators.

Modifications of Root:
         Modifications of taproot:

• Fusiform : These are  pointed at both  tips and  broad at middle.Eg: radish.

• Napiform : These are spherical in shape in at upper part and sharply tapering towards the tip of he root.Eg:Turnip.  

• Conical    :    It is broad at the base and gradually tapers towards its apex.Eg: Daucas carota (carrot).
• Tubercane :This is  the broad root which has no shape.Eg:Mirabilis                                                                                                                                                                                                                       Modifications of  Adventitious Root (for food storage):                                                                                                                                

•  Tuberous or tubercular root :These are swollen without any definite shape. It is always produced singly and not in clusters. Eg: Ipomoea batotas (Sweet potato).
•  
• Fasciculated roots . E.g: Asparagus, Dahlia.

               In Dahlia and Asparagus a number of adventitious roots arise as a cluster, from almost  the same level at the base of the stem.

• Nodulose roots  Here, the root becomes swollen at its tip. Eg: Curcuma amada, (mango ginger).

• Moniliform or beaded roots

Here, the roots show bead like swellings at frequent intervals. Eg: Momordica.

• Annulated roots

Here, the adventitious roots have a series of ring-like swellings on their surface. Eg: Ipecac.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
  Modifications of    Adventitious Root (for Mechanical Support):

• Prop roots: These are the adventitious roots arise from the horizontal branches and grow vertically downwards. After reaching the soil they become thick and woody. Thus, they function as pillars giving mechanical support to the branches. Hence, they are also known as columnar roots. Eg:Ficus benghalensis (Banyan).
•  Stilt roots :These are the adventitious roots arise from the lower part of the main stem and grow obliquely towards the soil. They serve to keep the plant erect by giving additional support. Eg: Pandanus.
•  Climbing roots or clinging roots: These arise from the nodes and help in attaching the climbing stem firmly to a support like a tree or a wall, by various mechanisms.   Eg: Piper betel, Pothos, etc..                                                      

  Modifications of    Adventitious Root (For Vital Functions):

• Respiratory roots or breathing roots or pneumtophores: Many plants growing in marshy water-logged soils which contain almost no air, develop some branches which grow vertically upwards into the air. these type of  root is provided towards the upper end with numerous pores through which gases diffuse in and out.These roots are called breathing roots or pneumatophores. 
•  Epiphytic roots  : Epiphytes like orchids which grow on other plants  have special adventitious roots called epiphytic roots. The outer region of the root is made up of a special tissue called the velamen. This tissue absorbs moisture from the air and makes it available to the plant. These roots do not penetrate the host tissue like parasitic roots.Eg:Vanda.
•  Haustoria or sucking roots: Parasites develop a kind of root which penetrates into the tissue of the host plant and sucks  nutrients from the host.  Eg: Cuscuta.

NET syllabus

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UGC NET June 2013 Exam Results

UGC NET June 2013 Exam Results

 23,718 candidates have qualified for the eligibility of Lectureship.
 3,684 candidates have qualified for Junior Research Fellowship.

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