Samacheer Class 11 Bio Botany - Plant Kingdom

Plectostele is a type of stele in which the xylem plates alternate with the phloem plates in a radial arrangement. This arrangement creates a characteristic pattern where vascular tissues are interspersed with one another rather than forming concentric rings. The plectostele is found in certain pteridophytes, particularly in club mosses. A classic example of a plant exhibiting plectostele is Lycopodium clavatum, commonly known as the club moss or stag's horn moss, where this vascular arrangement is clearly observable in cross-sections of the stem.

The correct answer is (ii) be & d. Gemmae formation is not traced in Riella, Ricciocarpus, and Anthoceros. Gemmae are asexual reproductive structures found in certain bryophytes, particularly in liverworts like Marchantia, where they are produced in specialized cup-like structures called gemma cups. However, not all bryophytes produce gemmae. Riella and Ricciocarpus, which are also liverworts, do not form gemmae as a means of reproduction. Anthoceros, which is a hornwort, similarly does not produce gemmae. Therefore, among the four options given, gemmae formation is absent in Riella, Ricciocarpus, and Anthoceros.

(iv) a&b

The correct answer is (d) C-D-B-A. When matching fossil organisms with their respective groups: Fossil bryophytes are represented by Hepaticites and Naiadita (option C), fossil algae are represented by Palaeoporella and Dimorphosiphon (option D), fossil pteridophytes are represented by Calamites and Baragwanthia (option B), and fossil gymnosperms are represented by Lepidodendron and Williamson (option A). These fossil records provide important evidence for understanding the evolutionary history and distribution of these plant groups in ancient times.

The chromosome numbers for the given plant structures are as follows: (I) Embryo of bryophyta is haploid (n), as bryophytes have a dominant gametophytic generation. (II) Embryo of Angiosperm is diploid (2n), as it develops from the zygote formed by the fusion of male and female gametes. (III) Endosperm of Angiosperm is triploid (3n), resulting from the fusion of one male gamete with two polar nuclei. (IV) Sporophyte of pteridophyta is diploid (2n), representing the dominant and spore-producing generation in pteridophytes. Thus, the correct option is (a) (I) n (II) 2n (III) 3n (IV) 2n.

The correct answer is d. Cycas. Pollination is not entomophilous in Cycas. Entomophilous pollination refers to pollination by insects. Hibiscus, Mangifera, and Chrysanthemum are all pollinated by insects and are therefore entomophilous. However, Cycas is a gymnosperm that is pollinated by wind, making it anemophilous rather than entomophilous. Wind pollination in Cycas involves the production of large quantities of pollen that are dispersed through the air to reach the female cones.

The correct answer is c: (I) True (II) True (III) False (IV) True. Statement (i) is true because Chara thallus is indeed encrusted with calcium carbonate, which gives it a characteristic gritty texture. Statement (ii) is true because diatoms have siliceous cell walls composed of silica, which forms their distinctive glass-like frustules. Statement (iii) is false because Fritschella is not a soil-inhabiting alga; it is actually an aquatic alga. Soil-inhabiting algae include forms like Chlorella and Scenedesmus. Statement (iv) is true because Cladophora crispata is a green alga that is currently growing and found in various aquatic environments.

The correct answer is a: (I) False (II) True (III) True (IV) False. Statement (i) is false because the prothallus or prothallium is the gametophyte stage in pteridophytes, and it develops into the sporophyte through fertilization, not the other way around. Statement (ii) is true because algae that grow on snow are indeed known as cryophytes or psychrophiles, adapted to cold environments. Statement (iii) is true because Postelsia palmaeformis is commonly known as sea palm, a brown alga found on rocky coasts. Statement (iv) is false because the endosperm in Pinus and other gymnosperms is haploid, not triploid. Triploid endosperm is characteristic of angiosperms, where it results from the fusion of two polar nuclei with one sperm nucleus.

The correct answer is d: (I) True (II) False (III) False (IV) True. Statement (i) is true because apogamy and apospory are indeed common phenomena in pteridophytes, representing deviations from the normal alternation of generations where the gametophyte can develop into a sporophyte without fertilization, or the sporophyte can produce a gametophyte without spore formation. Statement (ii) is false because spore-bearing leaves in pteridophytes are called sporophylls, and the clusters of sporangia on these leaves are called sori, not the leaves themselves. Statement (iii) is false because branches of limited and unlimited growth are not characteristic features that distinguish gymnosperms; these growth patterns are found in various plant groups. Statement (iv) is true because cambium does occur in gymnosperms in a manner similar to that in dicots, allowing for secondary growth and the formation of annual rings.

(i) False – Fungi do not play a direct role in soil conservation; rather, they are decomposers that break down organic matter. (ii) True – Vascular cryptogams (ferns and lycophytes) were indeed the predominant land plants during the Paleozoic era. (iii) False – Gymnosperms were dominant during the Mesozoic era, particularly the Jurassic and Cretaceous periods, not the early Cretaceous alone as the primary dominants. (iv) False – Angiosperms first appeared during the Cretaceous period, not the Jurassic period. They diversified and became dominant later in the Cretaceous and subsequent periods.

(i) False – Polyembryony is not typically traced in Pteridophyta; it is more commonly observed in gymnosperms and some angiosperms. (ii) True – Vessels are present in Gnetum and Ephedra, making them unique among gymnosperms as they possess this advanced vascular tissue. (iii) False – Heterospory is not seen in Lycopodium; Lycopodium is homosporous. Heterospory is found in some advanced pteridophytes like Selaginella. (iv) True – Corolloid roots (root-like structures) do occur in Cycas, serving as nitrogen-fixing symbiotic structures.