How do leaves get modified?

How do leaves get modified ? Describe some of the important modifications of the leaf that you have studied giving suitable examples.
How do die various leaf modifications help plants ?

The normal functions of leaves are photosynthesis, respiration and transpiration. Besides these functions the leaves have to perform other functions. Hence they modify themselves in different ways as follows:
1.Tendril: In some plants, the entire leaf or part of it gets modified into coiled thread like structure called ‘tendril’. Tendrils help the plants climb up. e.g., Pea, Gloriosa, Clematis.
2.Spine : In many plants, the leaves or their apices are modified into thin, sharp and pointed structure, known as spines. They help in defence, e.g., Opuntia, Ziziphus, Yucca etc.
3.Scale leaves : In onion, mostly all the leaves are present in the form of fleshy scale leaves.
4.Pitcher: It is the modification of leaf in insectivorous plant in which the lamina takes the form of a pitcher, apex in the form of a lid to trap the insects. There are number of digestive glands in the inner walls of the pitcher. These glands secrete a fluid which digests insects, e.g… Nepenthes (Pitcher plant).
5.Phyllode : The petiole becomes green, flattened and leaf-like and is called phyllode. e.g., Austrialian Acacia (Acacia auriculiformis).