(a) A terminal method to prevent pregnancy in humans is called sterilisation or surgical methods ( Vasectomy in Males and Tubectomy in females). Surgical intervention blocks gamete transport and thus prevents conception.
(b) The procedure of the terminal method carried in human male and human female are as follows:
a) Tubectomy (in females): A small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through the vagina.
b) Vasectomy (in males) : A small part of the vas deferens is removed or tied up through a small incision on the scrotum.
No, not all pollen grains remain viable for the same length of time.
Two suitable examples of the same are:
a) Some cereals like rice have pollen grains that lose viability within 30 minutes of their release.
b) Some members of family Leguminoseae, have pollen grains that have viability for a few months.
'Pollen Banks' store pollen grains for a period of time in viable conditions. These can be used for different studies and crop breeding techniques. It preserves the biodiversity by preserving genetic material.
The pollen grains can be stored by two methods.
1) Short term storage of pollen grains :
a) Low temperature and low humidity -
In this method pollen can be stored for shorter period of time.
b) In an organic solvent -
Pollen grains are dried over silica and stored in organic solvents after which they are maintained in deep freezer.
2) Long term storage of pollen :
a) Storage of vacuum-dried pollen grains -
The pollen grains are stored at subzero temperature with gradual removal of water (in freeze-drying) or simultaneous cooling (in vacuum drying). By this method, pollen grains can be stored for a long period of time.
b) Cryopreservation -
Pollen grains are dried by 'Pollen Drier' that helps in bringing down the water content below a threshold level and then the pollen grains are stored in liquid nitrogen.
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