EPFO EO/AO 2023 General Ability Test · Question 52 of 120

Correct — B, (b) Epiphytic root. Velamen is the spongy sheath that covers the hanging aerial roots of epiphytic orchids, and it exists to solve a problem peculiar to plants that live on other plants. An epiphyte grows perched on the trunk or branch of a tree, using it purely for support and taking nothing from it — which is what separates an epiphyte from a parasite. The arrangement buys light in a shaded forest and costs the plant its access to soil. Its roots hang in the air, so there is no soil water to draw on and no soil solution to draw it from; what is available is rain, the drip from the canopy, and dew, all of it arriving suddenly and draining away just as fast. Velamen is the adaptation to that. It is a thick, multiple-layered covering of dead, empty cells that replaces the ordinary root epidermis and behaves like blotting paper: when rain arrives, the cells fill by capillary action within moments, holding a reserve of water against the living root beneath, which then absorbs it at leisure. Between showers the same dead layer works the other way, insulating the root cortex against evaporation and shielding it from mechanical damage and strong light. Vanda, the orchid of Indian textbooks, is the standard example, with thick greenish-white roots dangling from the branch that carries it. A caveat for accuracy, which does not affect the answer: velamen has been recorded in the roots of a number of ground-dwelling monocots as well, so it is not exclusive to epiphytes in nature. Of the four kinds of root the question offers, however, only the epiphytic root is defined by the aerial, soil-free habit that velamen answers, and it is the association every textbook makes.

• (a)Tap root — A tap root is the persistent primary root of a dicotyledonous plant, growing vertically downward into the soil and giving off lateral branches. It is an underground organ, bathed in soil water, and it absorbs through root hairs — fine, short-lived extensions of single epidermal cells that give an enormous absorbing surface. Nothing in that setting calls for a water-storing sheath, and a thick jacket of dead cells would only get in the way of the root hairs. Its own modifications run in a different direction altogether, towards storage: the conical root of the carrot, the fusiform root of the radish and the napiform root of the turnip.
• (c)Fibrous root — The fibrous system, characteristic of monocotyledons such as wheat, rice and the grasses, is a cluster of slender roots of roughly equal thickness arising from the base of the stem. Like the tap root it is an underground, soil-absorbing structure that works through root hairs, and it has no velamen. Its business is holding a shallow, fast-growing plant firmly in the topsoil and exploiting the moisture there, which is the opposite of the problem an aerial root faces.
• (d)Respiratory root — The most instructive wrong answer, because it is a genuine root modification with a genuine special tissue — and the tissue answers a different need. Respiratory roots, or pneumatophores, are the spike-like roots that grow vertically UPWARD out of the waterlogged saline mud of a mangrove swamp, as in Rhizophora and Avicennia. Their pores admit air to root tissue that would otherwise suffocate, so the adaptation is to a shortage of oxygen. Velamen is an adaptation to a shortage of water. Both are aerial and both look unusual, which is why they are offered together.

Roots are classified first by origin and then by modification. By origin there are tap root systems, in which the primary root of the seedling persists and dominates, and fibrous or adventitious systems, in which roots arise from the stem or from other organs rather than from the radicle. Modifications are then read as answers to environmental problems, which is the way to learn them. For storage: the conical root of carrot, fusiform of radish, napiform of turnip, and the tuberous roots of sweet potato and dahlia. For support: the prop roots that descend from the branches of the banyan, and the stilt roots that brace maize and sugarcane. For climbing: the clinging roots of money plant and betel. For gas exchange: the pneumatophores of mangroves. For nutrition in unusual settings: the haustoria of the parasitic dodder, the nodules of leguminous plants that house nitrogen-fixing bacteria, and the assimilatory green roots of Tinospora. And for life in the air: the epiphytic roots of orchids, coated in velamen. Each pairing of an organ with a habitat is a one-line question waiting to be asked.

The general science block of this paper asks botany as vocabulary — a named tissue or structure, and where it is found. That makes it a memory test, but a structured one, because almost every term in the syllabus is the solution to an environmental problem, and remembering the problem regenerates the term. The habit rewarded is asking what difficulty the plant faces before choosing between options: a plant with no soil needs water, a plant in mud needs air, a plant in a shady forest needs light, and the modifications follow.

• Velamen is a spongy, multi-layered covering of dead cells on the aerial roots of epiphytic orchids.
• It absorbs rain and moisture rapidly, holds it for the living root beneath, and checks evaporation between showers.
• An epiphyte grows on another plant for support only and takes no nourishment from it, which distinguishes it from a parasite.
• Vanda is the standard Indian textbook example of an epiphytic orchid with velamen-covered roots.
• Pneumatophores or respiratory roots grow upward out of marshy saline soil in mangroves and carry pores for gaseous exchange.
• Tap root systems belong to dicotyledons; fibrous root systems to monocotyledons.
• Ordinary soil roots absorb through root hairs, which are extensions of single epidermal cells.
• Velamen has also been recorded in a number of terrestrial monocots, so it is not confined to epiphytes in nature.

• Confusing an epiphyte with a parasite, and concluding that the aerial root draws sap from the host.
• Choosing the respiratory root because it is also aerial and also has a special tissue, without asking whether the need is for water or for air.
• Assuming a spongy tissue must be for storage of food rather than of water.
• Attaching velamen to any orchid rather than to the aerial roots that hang free.

Botany items in EO/AO papers are one-line pairings — a tissue and its location, a modification and its plant, a deficiency and its symptom. The reliable preparation is the list of root, stem and leaf modifications with one named example each, since the same handful of examples supplies the options in every question of this family.

No directly related past PYQ was found.

• practice — not a real PYQ

  Pneumatophores are found in plants growing in :

  • (a)Deserts
  • (b)Marshy and saline soil
  • (c)Alpine meadows
  • (d)Dry deciduous forests

  Answer(b) Marshy and saline soil

• practice — not a real PYQ

  Prop roots that grow downward from branches to the ground are characteristic of :

  • (a)Maize
  • (b)Banyan
  • (c)Radish
  • (d)Money plant

  Answer(b) Banyan