NEET Biology Notes Morphology of Flowering Plants Root
Root
- Root is generally non-green, underground, positively geotropic (only main root), positively hydrotropic and often negatively phototropic descending cylindrical axis of the plant body.
- The root which develops from the radicle of the embryo is called primary root. Primary root bears lateral roots called secondary roots, which are further branched into tertiary roots and so on, e.g. many dicot plants. Primary roots and its branches constitute tap root system. In monocot plants, the primary root is short lived and is replaced by a large number of roots originated from the base of stem and constitute the fibrous roots, e.g. wheat, rice, etc. In grasses, Monstera and the banyan tree, roots arise from parts of the plant other than radicle and are known as adventitious roots. A typical root consists of a cap-like structure called root cap (root pockets in hydrophytes like Lemna, Eichhomia and Pistia) region, i.e. the region of meristematic activity, the region of cell elongation and region of maturation.
- Root hair are found in the region of maturation, which absorb water and minerals from the soil.
General Functions of Root
- Anchor the plant in the ground. .
- Absorb water and minerals from the soil.
- Store extra-sugars manufactured during photosynthesis.
- Transport water, minerals, sugars and hormones to and from the shoot.
- Produce some hormones.
- Interact with soil fungi and microorganisms that provide nutrients to the plant.
Specialised Functions of Roots
- Mangrove plants such as Rhizophora have upright, aerial roots called pneumatophores, which are exposed at low tide and function in gas exchange for aerobic respiration. They are negatively geotropic and positively phototropic.
- In rice, cortical root cells breakdown to form large air spaces, which are required for gas exchange when the soil is flooded.
- In epiphytic orchids, (grow on other plants for support) the epidermis known as velamen covers all root but the absorptive tip of the orchid root is thick and multilayered, preventing water loss.
- Roots of carrot (Daucus carota) and sweat potato (Ipomoea batatas) act as storage organs.
- Root nodules found in legumes (family-Fabaceae) and wattles (family-Mimosaceae) contain nitrogen fixing bacteria, which convert inert nitrogen gas from the atmosphere to organic nitrogenous compounds that are then available to the host plant.
- Coralloid roots, found in the roots of the sheoaks, alder [Alnus] and cycads (e.g. Macrozamia and Cycas) have cyanobacteria, which are involved in nitrogen fixation.
- Mycorrhizae are symbiotic association between roots of higher plants and fungi, which aid the root in absorption of nutrients, particularly phosphorus from the soil.
- Some other roots performing special functions are as follows. Assimilatory root in Tinospora, Trapa, contractile roots in Crocus, Allium cepa and mycorrhizal roots in Pinus.
