LDR : It has a semi-conductor. It depends on light (when there is light, there is no resistance, and when there is no light there is resistance.
Semi-conductor : As the temperature increases, more electrons are free to move. So when photons fall on the LDR, the heat energy causes it to allow free-flow of current.
Thermistor : PTC and NTC are two types.
Transducer : A component that changes energy from one form to another
Piezo-electric transducer : Presence of crystals, which are forced to change shape, causing the piezo-electric effect. This effect leads to a strain energy that presses together +ve and -ve ions, which leads to a small voltage. This is how the crystal acts as a transducer, by changing strain energy to kinetic/electric energy.