IMPORTANCE OF DIODE

A diode is a two-terminal electronic component with asymmetric conductance, it has low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other.A diode is a one way valve for electricity. It will allow current to flow in one direction but not in the opposite direction.

Diode is a Two terminal device which allows flow of curent in forward direction that means it converts DC to AC.A diode is a semiconductor meaning it will conduct from anode to cathode if the anode is held positive. Reversing the polarity Will in effect block current flow.A diode is an electronic component with two terminals that conduct asymmetrically. Although there are different types of diodes with different invention histories, the thermionic diodes were first described by Frederick Guthrie in 1873.

Forward biasing means to give the p-region of a p-n junction higher potential w.r.t the n-region. Thus the potential barrier for an electron is reduced. so they can easily diffuse across the junction.Similarly holes move through the n-region into the negative terminal of the source.this constitutes a current (diffusion current).when positive terminal of the battery connected to positive terminal of diode it is aid to be in forward bias.

The diode will have two polarities anode and cathode .take multimeter and set it in buzer mode or resistance mode and connect the positive terminal of multimeter to anode of diode and negative to the cathode the multimeter shows the resistance say 500-700ohms 

if it working and doesn't show any impedance i.e, very high impedance in reverse bias i.e, by connecting the positive terminal of multimeter to cathode of diode and negative terminal to anode,and in no working condition it shows same characteristics as in reverse bias connected. 
the simple way of checking diode is connect the 2v led in series with the diode to the battery of 3v the led will glow if the diode is connected in forward bias in circuit and it doesn't glow if the diode is connected in reverse bias in circuit /diode is damaged .
A: a diode will conduct from cathode [negative ] to anode [positive] A stripe at one end is the cathode or a stripe on the arrow is the cathode. By applying the proper voltage it will conduct and show low resistance and a voltage from .6v to .7v. Reversing the lead it will show relatively hi resistance.

Forward biasing means to give the p-region of a p-n junction higher potential w.r.t the n-region. Thus the potential barrier for an electron is reduced. so they can easily diffuse across the junction.Similarly holes move through the n-region into the negative terminal of the source.this constitutes a current (diffusion current).when positive terminal of the battery connected to positive terminal of diode it is aid to be in forward bias.