In Opuntia the stem is modified into a flattened green structure to perform the function of leaves (i.e., photosynthesis). Cite some other examples of modifications of plant parts for the purpose of photosynthesis.

$\rightarrow$ Opuntia is a xerophytic plant, in which leaves are modified into spines and reduce the rate of transpiration and they can't perform photosynthesis. So the photosynthesis is done by stem in opuntia. Which is a thick, fleshy and flat structure. It possesses chlorophyll and stores food. Such structure is called phylloclade.

$\rightarrow$ Sometimes stems get modified into internodes leaf like structure and performs photosynthesis e.g. Asparagus. They are in the level of scaly leaves. While true leaves are modified into either scaly leaves or spines.

$\rightarrow$ Similarly in some plants, there are assimilatory roots. Eg. Trapa and Tinospora.

$\rightarrow$ These roots develop outside the soil and bears chloroplasts and performs function of photosynthesis.