Sunday, 12 July 2020

Structure of pollen grain - Class 12, Chap2, Lec-6

Sexual Reproduction In Flowering Plants

Structure Of Pollen grain:
The formation of pollen grain take place from microspore mother cell. pollen is a haploid cell and called as first cell of male gametophyte. Pollen grains are round in shape. Pollen grains are surrounded by two layers, 1st layer is outer side called exine and the 2nd layer is inner side called intine. The exine is a very tough, rigid and ornamented structure.  The exine is formed by cutin and sporopollenin. Sporopollenin is the hardest and non-biodegradable material. The intine of pollen grain is soft, thin and elastic. The intine is formed of pectin and cellulose or pecto-cellulose. The exine is very thin or absent at few places of the outer surface of pollen grain, these places are called as germ pore. The germ pore gives a passage to the intine during the development of pollen tube in a germinating pollen grain. In the pollen grain of insect pollinating plants have oily layer around the pollen grain, it is called pollen kit. Pollen kit is made up of lipids and carotinoids. The bright colour of pollen kit attracts insects and being sticky gets attached to the body surface of insects. The pollen kit material also protects pollen grain from the harmful effects of Ultraviolet rays (UV-rays).
                                        
* Due to the presence of sporopollenin, fossilized pollen grains are found in good condition and indicates the presence of natural resources such as petroleums, coals etc..
* The pollen grains of chenopodium, Parthenium, Sorgum, Amaranths etc. cause allergy ( chronic respiratory disorders like- asthma and bronchitis) and called aero allergens.
* Pollen grains are very nutritious and used as tablets and syrup. 
* Smallest pollen grain - Myosotis.
   Largest pollen grain - Mirabilis.
   Longest pollen grain - Zostera ( Filliform pollen ).

* In India pollen allergy and asthma is caused by Parthenium ( Carrot/Congress grass ).


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