Question

diffrence between thorn and a tendril

Answer 1

These are homologous organs means they have same origin but perform different functions.
These are modified branches and are axillary in position. It means axillary branches in Bougainvillea are modified into thorns for protection from burrowing animals and in Cucurbita into tendrils for climbing.

Answer 2

Thorns are the sharp points on some plants and trees, for example on a rose bush.

Tendrils are thin stems which grow on some plants so that they can attach themselves to supports such as walls or other plants.