Question

Stem modified into flattened photosynthetic structure is
A. Phyllode
B. Bulbil
C. Phylloclade
D. Tendril

Answer 1

Hint: A stem is part of the plant that is present above the ground that develops from the plumule of the embryo. It bears terminal buds for growth in length. These structures are generally modified into different structures so as to satisfy the needs like storage of food, reproductive growth, photosynthesis, etc.

Complete answer-
Stem is usually the above- ground erect ascending part of the plant body that develops from the plumule, bear leaves and flowers, grows by means of a terminal bud and shows distinction of nodes and internodes. The node bears leaves having axillary buds. Modifications are changes in form and function to suit varied needs like storage of food, reproductive growth and survival through unfavourable seasons, vegeative propagation, mechanical support, protection, photosynthetic etc.
Let us first study about the options given above:
A. PHYLLODES- They are a flattened petiole or rachis of a leaf which perform the function of photosynthesis. They do not arise in the axis of a leaf as it itself is a leafy structure. It bears an axillary bud and they are not differentiated into nodes and internodes. They are generally flattened, foliaceous petioles that carry the functions of the lamina. They are usually vertical in position and are seldom succulent.
B. BULBIL- It is a small, young plant that is produced vegetatively from axillary buds on the parent's stem. They are generally clones of the parent as they are identical to them with respect to the genetic material. They are produced by asexual reproduction and can eventually form up a new plant.
C. PHYLLOCLADES- They are flattened or cylindrical green stems of unlimited growth which have taken place over the function of photosynthesis. They arise from the axil of a leaf and do not bear an axillary bud. They have unlimited growth in them and bear up leaves, branches and flowers. They act as a succulent and help in storage of food and water in many cases.
D. TENDRILS- In some weak plants, leaves are modified into thin, sensitive, wiry structures called tendrils. This kind of modification usually helps the plant to climb up by coiling around a support. They show nutation movement for climbing. They are generally unbranched and scale leaves do not occur on the tendrils. Buds do not occur on the tendrils and they develop in the position of the leaf or its parts.

Phylloclade is the modification of a stem that also helps in the process of photosynthesis. So, the correct answer is option C, Phylloclades.

NOTE-
Formation of phylloclades helps plants to grow in dry habitats because transpiration is little from the stem. Each segment develops in the axil of the caducous leaf which falls down and leaves behind a scar. It has many raised areas called areroles which are called nodes.