MCQ
Q.
Which of the following is NOT a root?
Correct Answer: B
The correct answer is Potato.
Modifications of Root
- For storage of food
- Roots are modified in some plants for storing reserve food materials.
- These modified roots usually are swollen and assume different forms such as spindle-shaped, e.g., radish; top-shaped, e.g., beet, turnip; cone-like, e.g., carrot; indefinite shape, e.g., sweet potatoes.
- Dahlia, Asparagus, Portulaca are some other examples of plants with modified roots for food storage.
- Nodulated roots
- The roots of pea and other leguminous plants have numerous swollen nodules on fine branches of roots.
- These nodules are formed due to the symbiotic association of Rhizobium (bacterium) that live inside the root cortical cells of the roots.
- They fix nitrogen and an active nodule is pink in colour.
- For mechanical support
- Roots are modified to provide mechanical support as seen in a banyan tree which has roots growing vertically/obliquely downwards (prop roots); sugarcane/maize in which roots arise from the nodes in the cluster at the base of the stem (stilt roots) and betel/black pepper in which nodes and internodes bear roots which help in climbing.
- For gaseous exchange
- Pneumatophores or breathing roots are found in plants growing in mangroves or swamps with saline water for exchange of gases.
- They are erect peg-like structures with numerous pores through which air circulates e.g., Rhizophora mangle.
- Modifications of Stem
- For storage of food
- Stems get modified into underground structures for storage of food as seen in potato (tuber), ginger (rhizome), garlic (bulb), yam (corm).
- Presence of an eye (node) in potato, distinct nodes with internodes and scaly leaves in ginger/yam, a cluster of roots at the base of the reduced stem in garlic/ onion, all indicate that these underground plant parts are modified stem.
- For vegetative propagation
- Plants besides reproducing sexually also propagate through vegetative parts.
- For this purpose, stems may be modified into a runner (Cyanodon dactylon, Oxalis). Runners are slender prostrate branches arising from axillary buds;
- stolon (e.g., mint, strawberry) which is a slender lateral branch arising from the base of the stem grows upward and then down to develop new daughter plants;
- offset having a single long horizontal internode growing up to some distance and producing a tuft of leaves above and a cluster of roots below at the apex (Eichornia, Pistia) and
- sucker, which arises from the underground part of the stem, grow obliquely and gives rise to a new shoot. (Chrysanthemum, Banana, Pineapple).
- For protection
- Some modified stem provides protection as thorns which are hard, pointed structures each representing a branch that arises from the axil of a leaf.
- Thorns are found in plants like Duranta, Pomegranate, Acacia, Ber, Prosopis, Bougainvillea, Citrus, etc.
- For support
- Tendrils are modifications of the stem to provide support to plants, e.g., Vitis, passionflower, Bignonia etc.
- For photosynthesis
- Stems are also modified into Phylloclade, to facilitate photosynthesis.
- Phylloclades are flattened/cylindrical stem or branches of unlimited growth (Cactus).
