In mycorrhizal association, the advantage of plant is :

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Correct — D, Increased mineral absorption and diseases protection. A mycorrhiza is the mutualistic association between a fungus and the root of a green plant, named in 1885 by the German botanist A. B. Frank, and the whole question turns on getting the direction of the exchange right. The plant photosynthesises and hands organic molecules — sugars and lipids — down to the root and on to its fungal partner; the fungus, which cannot photosynthesise at all, hands back water and mineral nutrients taken from the soil, phosphorus above all, and also nitrogen and zinc. So food travels from plant to fungus, and minerals from fungus to plant. Both halves of option (d) are on the plant's side of that ledger, and both are real. The mineral half works for two reasons, one physical and one chemical. Physically, fungal hyphae are much finer than the smallest root or root hair, so they thread into soil pores that a root can never enter and vastly extend the absorbing surface; the plant recruits them precisely when it senses phosphorus starvation. Chemically, fungal membranes and secretions differ from a root's — the hyphae release organic acids that dissolve or chelate ions and free nutrients that are physically or chemically immobilised, phosphate ions and micronutrients such as iron being the standard examples, so a mycorrhizal plant can obtain phosphate that an unaided root simply cannot reach. The protection half is equally well established: mycorrhizal plants are more resistant to soil-borne microbial disease, the fungus excretes enzymes toxic to soil organisms such as nematodes, and colonisation primes the plant's own immune system so that its defence responses fire faster and harder when a pathogen does arrive. That is exactly the ground on which the Commission upheld this key when it disposed of objections — the hyphal network supplying nutrients and water, and the fungus both shielding the root from pathogens and inducing systemic resistance in the plant. Alongside these come drought tolerance, relief from salinity stress and tolerance of heavy metals, which is why mycorrhizal inoculation is standard practice in rehabilitating degraded and mined land.

Why the other options are wrong — (a) True but incomplete, and in a question that offers a fuller correct option an incomplete one is wrong. The fungus does protect the root — a physical mantle in ectomycorrhizas, enzymes toxic to nematodes, and a primed immune response. But protection is the secondary service. The association is initiated by the plant's phosphorus hunger, and nutrient uptake is the benefit that explains why roughly four-fifths of all plant species maintain it.  (b) The direction is reversed, and this is the single misconception the question is built to expose. Fungi are heterotrophs with no chlorophyll; the mycorrhizal fungus gets its constant supply of carbohydrates — glucose and sucrose, translocated from the leaves down through the root — from the plant. The plant is the food provider here, not the beneficiary. Arbuscular mycorrhizal fungi are in fact obligate biotrophs, wholly dependent on their host for carbon.  (c) The designed trap: it welds one true item to one reversed item and therefore cannot stand. Protection is a genuine gain for the plant, but 'food' is what the plant gives up, not what it receives, so the pair is half wrong and the combination fails. Option (d) states both real plant-side benefits — mineral absorption and disease protection — without smuggling in the fungus's side of the bargain.

Concept: Mycorrhiza literally means 'fungus-root', and it is the rule rather than the exception: mycorrhizas are present in about 92% of the plant families that have been studied and in roughly 80% of plant species, and fossil and genetic evidence puts the partnership back 400 to 460 million years, to the moment plants colonised land, when fungi effectively served as the first root systems. Two structural types dominate. In an ectomycorrhiza the fungus never enters a living cell: it wraps the root tip in a hyphal sheath called the mantle and pushes a lattice of hyphae, the Hartig net, between the cortical cells, with an extensive mycelium spreading outward into soil and leaf litter. Ectomycorrhizas involve only about 10% of plant families and some 2% of plant species, but those species are the dominant woody ones — pine, oak, birch, eucalyptus, dipterocarps — so they account for a huge share of forest biomass. In an arbuscular mycorrhiza the hyphae do penetrate the cortical cells, invaginating the cell membrane to form finely branched, tree-like arbuscules that maximise the exchange surface, often with balloon-like storage vesicles as well. Arbuscular fungi belong to a single phylum, Glomeromycota, are obligate biotrophs, and occur in about 85% of plant families. Ericoid and orchid mycorrhizas are the specialised remainder — and every orchid is dependent on a fungus at some stage, because orchid seeds carry no food reserve at all.

State PCS 2025 Q150 — Science & Technology PYQ with Answer

State PCS 2025 Q150 — Science & Technology PYQ with Answer