Question

Citrus thorn is actually a modification of
A. Stem
B. Branch
C. Leaf
D. Stipule

Answer 1

Hint: Thorn is a type of plant modification, which is straight, hard and pointed. It is evolved as a protective measure but also checks the transpiration rate. Plants possess such modifications to adapt to their habitat and environment. It improves plant survival rates.

Complete answer:
In Citrus plants, the thorns are developed from a modified stem. In plants, the stems get modified into long, sharp and pointed structures known as thorns. These thorns help in the reduction of the transpiration rate in plants and it also helps plants to protect its fruits from predator animals such as herbivores. It is a modification that helps them to survive in their habitat.
i. Branches are developed from the buds, in the lateral or axillary parts. It bears leaves and supports the leaf in a way to obtain maximum sunlight.
ii. Leaves are modified into many structures. The pointed structures developed from leaves are known as spines, as present in Opuntia. Tendrils are also a type of leaf modification.
iii. Stipule modifications are also known as spines. They are hard and pointed structures. They have a protective function from predators.
Hence, the correct answer is option A.

Note: The other modifications of the stem are rhizomes, present in the ginger plant, which is the modified underground stem for storage of extra food materials. Bulbs in onions, corm present in Colocasia, tuber in potato, runner present in strawberry, sucker, stolon of jasmine and offsets in Pistia. All these structures perform different functions in different plants.