In Australian acacia, which part performs photosynthesis?

Formation of roots from the lenticular hyperhydric tissue is of great advantage to a plant in:

Although potato tuber is an underground part,it is considered as a stem. Give two reasons.

The swollen underground structure in an onion is known as .........

Nodes are the regions of the stem where:

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.