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Consortium for Educational Communication Consortium for Educational Communication Frequently asked questions (FAQS) 1. What are gymnosperms? Name some important gymnosperms that are found in India. Ans. Gymnosperms are group of plants with naked seeds. The word gymnosperm has been derived from Greek words where gymnos means naked and sperma means seeds. The word gymnosperm was first used by Theophrastus in 300 B.C. Gymnosperms act as bridge between pteridophytes and angiosperms. Gymnosperms flourished well during Mesozoic era. Hence the Mesozoic era is called the age of gymnosperms. However, most of the members of this group have now become extinct and only few living forms are known today. Some gymnosperms like Ginkgo biloba, Cycas, Metasequoia are called living fossils, as these plants are found both in living and fossil forms, and the number of fossil forms is much more than the living forms. In India there are about 16 genera and 53 species of gymnosperms. They are Cycas from Cycadales, Abies, Cedrus, Cephalotaxus, Cupressus, Juniperus, Larix, Picea, Pinus, Podocarpus, Taxus, Tsuga from Coniferales, Ephedra from Ephedrales and Gnetum from Gnetales. In addition Ginkgo biloba is also growing in certain parts of India. 2. Discuss briefly the distribution of gymnosperms. Ans. Gymnosperms are found both in tropical and temperate regions. Some are found in arctic regions. The living gymnosperms comprise 70 genera and 725 species. Of these, majority belong to conifers or cone-bearing plants. The conifers are mostly distributed in the cooler regions of Europe, Asia and North America. They are dominant in upper timberline zone of mountain ranges including the Himalayas. The living gymnosperms are widely distributed in the cold climates where snow, rather than rain, is the source of water. The only native gymnosperms which thrive in warm areas are the cycads. In India, mostly the conifers thrive well in hilly areas. Very few gymnosperms, except some cycads, grows in plains. Cycas circinalis grow wild in some southern States. Some are grown as ornamental plants in gardens, e.g. Araucaria. 3. Write a short note on the morphology of gymnosperms. Ans. Gymnosperms are tall, evergreen trees or shrubs. There are no herbs. Certain species of Gnetum are twiners. The plant body is a sporophyte and differentiated into root, stem and leaves. Plants possess well-developed tap root system. Roots often show symbiotic association with algae e.g. Cycas, or with fungi e.g. Pinus. In Cycas coralloid roots are present in addition to normal roots. The stem is aerial, erect, woody, unbranched as in Cycas, or branched as in Pinus, Cedrus etc. In some genera like Pinus, the branches are of two types, long shoots or branches of unlimited growth and dwarf shoots or branches of limited growth. The leaves are mostly xerophytic, evergreen, and simple or compound, and vary in size from small scaly leaf to more than six feet long leaves as in Cycas. The leaves of Pinus are of two types; scale leaves and foliage leaves. Scale leaves are minute, membranous, brown and deciduous. Foliage leaves are present on dwarf shoots only, and they are known as foliage spurs. They are green, simple, needle-like or pinnately compound. The leaves of Cycas exhibit circinate vernation, a characteristic feature of ferns. The arrangement of leaves may be opposite and decussate as in Gnetum, whorled as in Cedrus or spirally arranged as in Taxus. 4. Name the tallest and the smallest gymnosperm. Ans. Gymnosperms vary in their size from small herbs to large gigantic trees. Sequoia sempervirens, a gymnosperm, is the tallest living plant in the world, reaching a height of about 125 meters, and girth of about 30 meters. It is also known as coast red-wood of California. Taxodium mucronatum and Sequoiadendron giganticum with a girth of 125feet and 80feet respectively, are the other gigantic gymnosperms. On the contrary Zamia pygmaea, with the underground tuberous Consortium for Educational Communication stem, is the smallest gymnosperm, about 25cm in height. 5. Discuss the internal structure of a gymnosperm stem. Ans. Anatomically the stem of gymnosperms shows an epidermis, cortex and stele. The epidermis is singlelayered and is very soon replaced by periderm. Cortex is parenchymatous. Based on the relative quantity of soft tissue and mechanical tissue, gymnosperms are classified into manoxylic and pycnoxylic types. In manoxylic forms, as in Cycads, the wood is not compact, and has parenchyma. In pycnoxylic forms wood is compact, and relatively less amount of soft tissue is present. The stele is surrounded by a typical epidermis followed by a layer of pericycle. The vascular system consists of a number of vascular bundles arranged in the form of a ring surrounded by central pith. The bundles are collateral, endarch and open. Phloem consists of only sieve tubes and phloem parenchyma. Companion cells are absent. Xylem consists of trachieds and xylem parenchyma only. Vessels are absent except in Gnetales. The xylem is either endarch or mesarch. Secondary growth is seen in all the members. It is usually normal. However, anomalous secondary growth may be found in Cycas and Gnetum. Normal secondary growth takes place due to the activity of fascicular cambium, which produces the typical annual rings. Parenchymatous pith is present in the central region of the stem. In some cases mucilage ducts or resin canals are found both in the pith and cortex. 6. Discuss briefly the general structure of a gymnospermic leaf. Ans. Gymnosperm leaves exhibit xerophytic characters. Anatomically gymnospermic leaves consist of epidermis which is always covered by a cuticle. The stomata are sunken and often present on pits. The mesophyll may be differentiated into palisade and spongy parenchyma as in Cycas or undifferentiated with arm parenchyma as in Pinus. In some members, as in Cycas with a single veined leaf, a transfusion tissue is present to help in lateral conduction, necessitated by the absence of side veins. The stomata are Consortium for Educational Communication either syndetocheilic or haplocheilic. In syndetocheilic type, guard cell and subsidary cells originate from same mother cell. For haplocheilic type, the guard cells and subsidiary cells originate from the different mother cells. Haplocheilic stomata are considered to be primitive compared to syndetocheilic. In Gnetum both types of stomata can be seen. Stomata may be distributed on both sides of leaf as in Pinus, Ginkgo or confined to lower side as in Cycas. 7. Give the general organisation of a gymnospermic ovule. Ans. In gymnosperms, ovules are naked and born on megasporophylls. The ovule consists of central mass of parenchymatous tissue called nucellus. The nucellus is surrounded by integument, which covers the whole nucellus except at the top, where it leaves a small passage called microphyle. The integument is differentiated into an outer fleshy layer, middle stony layer and the inner fleshy layer. The apex of the nucellus develops into pollen chamber, where pollen grains undergo period of rest after pollination. The development of female gametophyte begins with the differentiation of megaspore mother cell in the nucellus. Its development is either monosporic or tetrasporic. Megaspore mother cell undergoes meiosis to form linear tetrad of four megaspores, out of which, upper three cells degenerate, and the lower most remains as functional megaspore. The functional megaspore then develops into female gametophyte. Archegonia are formed towards the micropylar end of the female gametophyte. In Gnetum archegonia are not formed. A few nuclei at the microphylar end, of the female gametophyte act as egg, which is an angiospermic character. The archegonia of gymnosperms do not have neck canal cells and Venter canal cells. 8. Discuss briefly the germination of microspores in gymnosperms. Ans In gymnosperms, pollen grains or microspores are unicellular. In Pinus pollen grains are winged. Microspores develop into male gametophyte. During the germination of microspores, one or two prothalial cells are cut off at one end, leaving large antheridial cell, which divides into Consortium for Educational Communication generative cell and larger tube cell. The generative cell divides into stalk cell and body cell. Body cell produces two male sperms. The tube cell forms the pollen tube, which acts as carrier of sperms. 9. How does pollination occur in gymnosperms? Ans. In gymnosperms pollination is anemophilous. The ovule secretes mucilaginous substance, which oozes out from the micropyle of the ovule and forms pollination drop, which traps pollen grains. The pollen grains are drawn on due to drying of pollination drop. Further changes take place in the pollen chamber. The pollen tube grows through the tissue of the nucellus, until it reaches the neck of the archegonia. 10. What is the difference between simple and cleavage polyembryony? Ans. Polyembryony is the characteristic feature of gymnosperms. In cycads, more than one archegonia are fertilized, resulting in the formation of more than one embryo. This phenomenon is known as simple polyembryony. In conifers, polyembryony is due to the separation of four embryonal cells, and each of them develops into an embryo. This phenomenon is called cleavage polyembryony. It occurs in Pinus, but only one embryo attains maturity and rest degenerate. In gymnosperms, embryo is differentiated into root, stem and leaf. 11. Discuss briefly the formation of seed in gymnosperms after fertilization Ans. In gymnosperms, after fertilization, the ovule develops into seed. The inner fleshy layer of ovule turns into tegmen and middle stony layer forms testa of the seed coat, which protect inner embryo. Embryo is developed at the end of long suspensor which is pushed down into the food laden endosperm that develops before fertilization. Female gametophyte, soon after it has absorbed the food from the nucellus, becomes endosperm. As there is no double fertilization or triple fusion, the endosperm is a haploid tissue. The whole of the nucellus except a small portion is crushed. The remaining small part of the nucellus persists in the seed in the form a narrow film, or cap, known as Consortium for Educational Communication perisperm. Since there is no closed ovary, true fruits, like that of angiosperms are not found in the gymnosperms. The developed ovules remain naked. Middle stony layer of the integument becomes extremely hard and protects the female gametophyte and embryo. Cotyledons may be one or two as in Cycas or a whorl of many as in Pinus. They become green while still enclosed within the seeds. The seed generally undergo a period of dormancy. However, the seed of Ginkgo and Cycas germinate without undergoing period of rest. 12. Point out the similarities between gymnosperms and pteridophytes. Ans. Gymnosperms form a heterogeneous plant group with several evolutionary trends which have been operating since past to present day. Evolutionary trends reveal that gymnosperms form a bridge between pteridophytes and angiosperms. Gymnosperms resemble with pteridophytes in the following features. i). Both the plant groups show heterologous alternation of generation. Sporophytic generation is dominant, independent and large at maturity while the gametophytic generation shows progressive reduction and dependence. ii).Sporophytes of both the plant groups is distinguished into root, stem and leave, and possess well marked vascular system. iii) Many cycads resemble ferns in having large compound leaves and circinate venation. iv).Both heterosporous pteridophytes and gymnosperms possess endosporic gametophytes. v).Male gametes of cycads (Cycas) and Ginkgo are motile like that of pteridophytes. vi).Female sex organs are archegonia in both pteridophytes and gymnosperms. vii).Male gametophytes of heterosporous pteridophytes and majority of gymnosperms are highly reduced and posses only two prothalial cells. Consortium for Educational Communication viii).Endosperm develops before fertilization, as a result of free nuclear division in the tissue of female gametophyte in both gymnosperms and pteridophytes. Consortium for Educational Communication following features. 1. Plants of both the groups are woody and perennial. ix).Embryogeny is endoscopic in many pteridophytes, and majority of gymnosperms 2. The stele is eustelic both in gymnosperms and angiosperms. 13. Enumerate the differences between gymnosperms and pteridophytes. 3. Both show secondary growth except monocots. 4. Both are heterosporic and endosporic. Ans. Gymnosperms differ from pteridophytes in the following features. 5. Megaspore is retained in megasporangium resulting in the formation of seed. I). Gymnosperms are commonly large sized trees, shrubs or climbers. Pteridophytes on the other hand, are smaller in size. 6. The male gametophytes are highly reduced. II). Gymnosperms posses tap roots; where as roots of pteridophytes are adventitious. 8. The sperms are non-motile except in Cycas. III). Gymnosperms have eustelic organisation, whereas in pteridophytes eustele is not found. 15. Enumerate the main differences between gymnosperms and angiosperms. IV). Gymnosperms undergo secondary growth, whereas pteridophytes lack secondary growth. V). In gymnosperms male and female gametophytes are simple, non-green and dependent on sporophytes. They are very much reduced in comparison to gametophytes of pteridophytes. VI). In gymnosperms megaspore remains in megasporangium, whereas in pteridophytes they shed from the sporangia and develop into independent female prothallus. VII). In gymnosperms, neck canal cells and venter canal cells are absent, whereas archegonia of pteridophytes, are provided with neck canal cells and venter canal cells. VIII). Seed formation is not common in pteridophytes except in Selaginella, whereas in gymnosperms seeds are produced. 14. Point out the similarities between gymnosperms and angiosperms. Ans. Gymnosperms resemble with angiosperms in the 7. Pollen tube acts as carrier of sperms. 9. The plants show distinct alternation of generation Ans. Gymnosperms differ from angiosperms in the following features. 1.Majority of angiosperms are herbaceous, whereas gymnosperms are mostly woody. 2.Angiosperms may be annuals, biannual or perennials whereas gymnosperms are mostly perennials. 3.In angiosperms, xylem possesses vessels and phloem bears companion cells, whereas in gymnosperms (except in Gnetales) xylem in devoid of vessels and phloem lacks companion cells. 4.In gymnosperms cones are unisexual, whereas in angiosperms the flowers are usually bisexual. 5.In gymnosperms ovules are naked, whereas in angiosperms they are enclosed by the carpels. 6.Gymnosperms do not show double fertilization or triple fusion, whereas in angiosperms it very common phenomenon. Consortium for Educational Communication 7.Angiospermic seeds are enclosed within the ovaries that develop fruit, whereas in gymnosperms seeds are exposed. Consortium for Educational Communication