Which division of Plantae is called amphibians of plant kingdom ?

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Correct — option (1), Bryophyta. The nickname is an analogy with the amphibians of the animal kingdom, which live on land but must return to water to breed, and it fits the bryophytes — the mosses, liverworts and hornworts — for exactly the same reason. They are land plants: they grow on soil, rock, bark and walls, out of the water, and they are among the first colonisers of bare surfaces. But their sexual reproduction is still tied to water, because the male gametes they produce are flagellated antherozoids that must actually swim to reach the egg in the archegonium, and they can only do that through a continuous film of water — a film supplied by rain, dew or the moisture of a shaded damp place. Without it fertilisation cannot occur at all, so a bryophyte can survive in a dry spell but cannot complete its life cycle in one. Two further features reinforce the halfway position. They have no true vascular tissue, no xylem to conduct water upward under tension and no phloem to distribute food, so water moves largely by capillarity over and between the surfaces of the plant and the whole body must stay small and close to the ground. And they have no true roots, stems or leaves in the anatomical sense, being anchored instead by thread-like rhizoids. Their dominant, green, independent phase is the gametophyte, on which the spore-producing sporophyte remains attached and nutritionally dependent — the reverse of the arrangement in every group above them. Land habit with aquatic reproduction is precisely the amphibian condition.

Why the other options are wrong — (b) Pteridophytes — the ferns and their allies — also require water for fertilisation, since their antherozoids swim in the same way, and that shared dependence makes this the most defensible of the three wrong choices. What separates them is everything else. Pteridophytes possess true vascular tissue, xylem and phloem, and true roots, stems and leaves, which is why they can stand tall and were the dominant vegetation of the Carboniferous forests; and in them the sporophyte is the large independent plant while the gametophyte is reduced to a small separate prothallus. They are conventionally described as the first true vascular land plants, and the amphibian label belongs to the group that lacks the vascular tissue as well as the independence from water.  (c) Gymnosperms have broken the dependence on water for reproduction entirely, which is the opposite of the amphibian condition. Their male gametes reach the ovule inside a pollen grain carried by wind rather than by swimming, and the pollen tube delivers the gamete directly, so fertilisation can take place in a dry environment and even in the freezing conditions where conifers dominate. They are fully vascular, they are woody perennials, and they bear naked seeds — seeds not enclosed in a fruit, which is what the name records. Pines, cycads and the ginkgo belong here.  (d) Angiosperms are the flowering plants and are the most fully terrestrial group of all, so the analogy fits them least. Their seeds are enclosed within a fruit developed from the ovary, they reproduce through pollen carried by wind, water surfaces, insects, birds or bats, and their double fertilisation produces both an embryo and a nutritive endosperm. They possess the most efficient conducting tissue of any plant group, with vessels in the xylem and sieve tubes with companion cells in the phloem, which is part of why they dominate almost every terrestrial habitat on earth today.

Concept: The plant kingdom is arranged as a sequence of steps away from water, and each division marks a further degree of independence from it. Algae are aquatic throughout. Bryophytes make the move onto land but keep an aquatic requirement in reproduction, having neither vascular tissue nor true roots, stems and leaves; their green plant body is the haploid gametophyte, and the diploid sporophyte grows attached to it and depends on it. Pteridophytes add vascular tissue and true organs and reverse the alternation of generations so that the sporophyte becomes the dominant plant, but their flagellated antherozoids still need water to swim in. Gymnosperms remove that last requirement by transferring the male gamete inside a pollen grain and delivering it through a pollen tube, and they protect the embryo in a seed, though the seed is not enclosed in a fruit. Angiosperms enclose the seed in a fruit, add the flower as an apparatus for attracting animal pollinators, and evolve the most efficient conducting tissue, which together account for their dominance of terrestrial vegetation. Reading the sequence as a story of escaping water makes every group's defining feature follow from its position in it, and locates the bryophytes as the amphibious stage.

State PCS 2024 Q58 — Science & Technology PYQ with Answer

State PCS 2024 Q58 — Science & Technology PYQ with Answer