Which of the following helps some hydrophytes to thrive in wetlands and marshes where the water level fluctuates from time to time?
- (a)Rhizomatous roots
- (b)Submergent roots
- (c)Aerenchyma tissue
- (d)Rhizophores
Correct — C, Aerenchyma tissue.
The keyed answer is Aerenchyma tissue. Aerenchyma is parenchyma riddled with large, connected air spaces. In a hydrophyte it runs through the cortex of roots, stems and petioles, so oxygen from the air and from photosynthesis in the leaves can diffuse down to roots sitting in waterlogged, oxygen-poor mud.
When the water rises, the soil around the roots turns anoxic. A plant with aerenchyma keeps its roots respiring by piping air down from the shoot, and leaks a little of it into the mud, which keeps reduced iron and sulphide away from the root surface.
In rice and maize, flooding itself triggers additional aerenchyma: ethylene builds up in the submerged root and cortical cells die in a programmed way, leaving channels. That inducible response is what lets a plant cope with a water level that changes rather than one that stays put.
The idea to carry away: the wetland problem is oxygen, not water, and aerenchyma is the tissue that solves it. The three distractors name organs; the answer here is the tissue that works inside them.
- (a)Rhizomatous roots — A rhizome is an underground stem, not a root, so the phrase mixes two organs: the roots borne on a rhizome are adventitious.
Typha, Phragmites and lotus do spread by rhizomes, and in an emergent wetland plant that rhizome does carry air down to the roots — but it carries it because it is packed with aerenchyma. The tissue is the adaptation; the rhizome habit is not.
It is the right answer to a modified underground stem for storage and vegetative propagation, as in ginger and turmeric.
- (b)Submergent roots — Submerged hydrophytes such as Hydrilla and Vallisneria typically have thin, reduced roots that mainly anchor the plant, and Ceratophyllum is rootless; absorption happens across the whole plant surface. A root that is itself under water is the thing that needs oxygen, not the thing that supplies it.
It is the right answer to the reduced root system of submerged hydrophytes, which take up water and dissolved gases over their entire surface.
- (d)Rhizophores — Rhizophores are found in Selaginella, a spike-moss of damp, shady ground rather than of standing water.
They are leafless, colourless outgrowths that arise at the forks of the stem, grow downwards and produce roots when their tips reach the soil. The prefix rhizo- and the resemblance to Rhizophora, the mangrove genus, are the hazard here.
It is the right answer to the root-bearing organ of Selaginella, often described as intermediate between a root and a stem.
Hydrophytes are plants that live in water or in waterlogged soil. Their central problem is oxygen rather than water: flooded soil quickly loses its oxygen as microbes use it up, and a root that cannot respire cannot take up ions or grow.
Aerenchyma is parenchyma with large, interconnected air spaces called lacunae. It forms a continuous gas pathway from shoot to root, gives buoyancy to floating leaves and petioles, and reduces the number of living cells the plant has to feed.
Rice forms it constitutively in the root cortex even in drained soil and adds more when flooded, while in maize and wheat it is essentially flooding-induced. Ethylene builds up in the submerged root and triggers programmed death of cortical cells (lysigenous aerenchyma); schizogenous aerenchyma forms instead when neighbouring cells separate from one another.
This sits in plant ecology under adaptations to habitat, alongside xerophytes (sunken stomata, thick cuticle) and halophytes (pneumatophores, vivipary). For wetlands the adaptations to know include aerenchyma, a thin cuticle, stomata on the upper surface of floating leaves, reduced roots and vascular tissue in submerged forms, and rhizomes for perennation in emergents.
The same tissue matters for agriculture: rice tolerates flooded paddies largely because its roots carry aerenchyma, and one trait studied for waterlogging tolerance in maize and wheat is how readily their roots form it. Uttarakhand's first Ramsar site, Asan Conservation Reserve near Dehradun (designated 2020), is the state wetland to pair with this idea.
- Aerenchyma is parenchyma with large, interconnected air spaces (lacunae) in the cortex of roots, stems and petioles of wetland plants.
- It forms a gas pathway from aerial shoot to submerged root, so roots in oxygen-poor mud can keep respiring.
- Oxygen leaking from the root surface (radial oxygen loss) oxidises the rhizosphere and keeps reduced iron and sulphide from harming the root.
- Lysigenous aerenchyma forms by programmed death of cortical cells; schizogenous aerenchyma forms by cells separating from one another.
- In rice and maize roots, flooding raises ethylene, which triggers lysigenous aerenchyma formation.
- Water hyacinth (Eichhornia) floats on swollen petioles packed with aerenchyma; Typha, Nymphaea, Nelumbo and rice also carry it.
- A rhizome is an underground stem with nodes, internodes and scale leaves; ginger, turmeric, Typha and lotus have rhizomes.
- Submerged hydrophytes such as Hydrilla and Vallisneria have reduced roots used mainly for anchorage; Ceratophyllum is rootless.
- Rhizophores are leafless, downward-growing outgrowths of Selaginella that produce roots at their tips.
- Pneumatophores are upward-growing breathing roots of mangroves such as Avicennia and Sonneratia, with lenticels and aerenchyma.
- Asan Conservation Reserve near Dehradun became Uttarakhand's first Ramsar site in 2020.
Aerenchyma is a tissue that moves oxygen inside the plant; the three distractors are organs, and the mangrove root that the word rhizophore evokes — the stilt root of Rhizophora — is a different structure again.
- Reading rhizophore as a water-root: the prefix rhizo- and the mangrove genus Rhizophora pull towards water, but the rhizophore is Selaginella's root-bearing outgrowth.
- Treating rhizomatous roots as one organ: a rhizome is a stem and the roots borne on it are adventitious. Where a rhizome does ventilate a flooded plant, the aerenchyma inside it is doing that work.
- Picking a root option because roots sit in the water: the stem asks what lets the plant thrive when the level fluctuates, which is an oxygen-supply problem solved by a tissue.
- Confusing pneumatophores (breathing roots of Avicennia and Sonneratia) with rhizophores (Selaginella).
- Assuming submerged hydrophytes have strong root systems; their roots are typically reduced and uptake happens over the plant surface.
The idea can arrive as a habitat-to-adaptation match: aerenchyma with hydrophytes, sunken stomata and thick cuticle with xerophytes, pneumatophores and vivipary with mangroves.
It can also come as a tissue-identification item (which parenchyma carries air cavities), as a modified-stem item where the rhizome has to be recognised as a stem, or, as here, as a list that mixes real terms from different chapters so that each one has to be placed in its own chapter first.
No eligible match among this question's citable set.
- practice — not a real PYQ
In rice and other wetland plants, aerenchyma in the root cortex mainly serves to:
- (a)store starch for use in the dry season
- (b)carry oxygen from the shoot down to roots in waterlogged soil
- (c)absorb mineral ions from the soil solution
- (d)anchor the plant firmly in soft mud
Answerb — aerenchyma is an air-space tissue, and its job is gas transport: it forms a continuous pathway so oxygen reaches roots that the flooded soil cannot supply.Option a describes ordinary storage parenchyma, not the air-filled kind. Option c is the work of the root epidermis and root hairs. Option d is what the root as an organ does; an air-filled cortex makes a root lighter, not firmer.
- practice — not a real PYQ
Rhizophores, the leafless outgrowths that produce roots when their tips reach the soil, are characteristic of which of the following?
- (a)Selaginella
- (b)Rhizophora
- (c)Hydrilla
- (d)Typha
Answera — the rhizophore is the root-bearing organ of Selaginella, arising at the forks of the stem and growing downwards.Rhizophora (b) is the mangrove genus with stilt roots; the shared spelling is the trap, not the answer. Hydrilla (c) is a submerged hydrophyte with reduced roots. Typha (d) spreads by rhizomes, which are underground stems.
- practice — not a real PYQ
Which of the following is a modified underground stem rather than a root?
- (a)Rhizome of ginger
- (b)Pneumatophore of Avicennia
- (c)Prop root of banyan
- (d)Tuberous root of sweet potato
Answera — the ginger rhizome has nodes, internodes, scale leaves and axillary buds, the marks of a stem, even though it grows underground.The pneumatophore (b) is a breathing root of mangroves. The prop root of banyan (c) is an adventitious root that descends from the branches. The sweet potato (d) is a swollen adventitious root; the potato, by contrast, would be a stem tuber.
- practice — not a real PYQ
Which one of the following pairs of plant adaptation and habitat is correctly matched?
- (a)Sunken stomata — hydrophytes
- (b)Aerenchyma — xerophytes
- (c)Pneumatophores — mangroves
- (d)Reduced root system — xerophytes
Answerc — pneumatophores are the upward-growing breathing roots of mangroves such as Avicennia and Sonneratia, an answer to anoxic tidal mud.Sunken stomata (a) cut water loss and belong to xerophytes such as Nerium. Aerenchyma (b) is the hydrophyte tissue. Xerophytes (d) typically have deep or widespread roots to reach water; a reduced root system characterises submerged hydrophytes.