Biology · Morphology of Flowering Plants · NEET
NCERT gives a single clear line: roots in some plants get modified for (1) storage of food, (2) mechanical support, and (3) respiration. Storage roots swell with reserve food (carrot, turnip, sweet potato). Support roots hold the plant up (prop roots of banyan, stilt roots of maize/sugarcane). Respiratory roots grow up out of soil to take in oxygen (pneumatophores in mangroves). Remember these three jobs - most NEET questions are just asking which job a given example does.
Sweet potato is a modified ROOT - a tuberous adventitious root that stores food. This is a very common NEET trap. Do not confuse it with potato, which is a modified STEM (stem tuber with eyes/buds). NEET 2018 asked exactly this: 'Sweet potato is a modified ___' and the answer is adventitious root, because it arises from parts other than the radicle, not from the tap root.
Both give mechanical support but grow from different places. Prop roots hang DOWN from big horizontal branches and become pillar-like on reaching the soil (classic example: banyan tree). Stilt roots grow OUT and down from the lower nodes of the main stem in a slanting way (examples: maize, sugarcane). Simple rule: prop roots come from branches above, stilt roots come from the basal nodes of the stem.
Pneumatophores are respiratory roots. They are negatively geotropic - they grow vertically UPWARD, out of the soil or water, so the plant can take in oxygen. They occur in plants growing in swampy, oxygen-poor, salty soil - the halophytes / mangroves, such as Rhizophora. NEET 2018 answer to 'Pneumatophores occur in' is halophytes. A deeper page on this is linked below.
Carrot, radish, turnip and beet are modified TAP ROOTS that store food (they swell up from the primary root). This is different from sweet potato, which is a modified ADVENTITIOUS root. So storage roots can come from either the tap root (carrot, turnip) or adventitious roots (sweet potato) - NEET may test whether you know the origin, not just the function.
Normally roots are positively geotropic - they grow down toward gravity. But pneumatophores are negatively geotropic and grow upward. The reason is oxygen: mangrove soil is waterlogged and has almost no oxygen for the roots to respire. So the plant sends special roots up into the air with tiny pores (lenticels) to breathe. This is a common 'assertion-reason' style point in NEET.
Sweet potato is a modified:
Pneumatophores occur in:
Identify the correct set of statements: (a) Leaflets are modified into thorns in Citrus and Bougainvillea (b) Axillary buds form tendrils in cucumber and pumpkin (c) Stem is flattened and fleshy in Opuntia doing leaf work (d) Rhizophora shows vertically upward roots for respiration (e) Sub-aerial stems in grasses and strawberry help vegetative propagation.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Storage of food (carrot, turnip, sweet potato), mechanical support (prop roots of banyan, stilt roots of maize and sugarcane), and respiration (pneumatophores in mangroves).
Pneumatophores. They are negatively geotropic respiratory roots found in mangroves (Rhizophora) growing in oxygen-poor swampy soil.
No. Potato is a modified STEM (stem tuber with buds/eyes). Sweet potato is the modified root. This swap is a very common NEET trap.
No. Prop roots hang down from branches to the ground (banyan). Stilt roots grow slanting out from the lower nodes of the stem (maize, sugarcane). Both give support.
Some do (carrot, turnip, radish are modified tap roots). But sweet potato is a modified adventitious root. So storage roots can be either type - always check the origin.
