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What plant classification do you follow? Why do we need scientific classification of plants? Plant Classification Review 1. What are the main cellular features of the beings of the plant kingdom? The typical plant cells are eukaryotic (have nucleus), autotrophic (produce their own food) and photosynthetic (use light to make food). Plant cells also have chloroplasts and a cell wall (a structure exterior to the plasma membrane) made of cellulose. 2. How different are animal cells from plant cells? While plant cells are eukaryotic, autotrophic, photosynthetic and have chloroplasts and cell wall, the animal cells are eukaryotic, heterotroph and do not present chloroplasts nor cell wall. 3. Do plants have tissue organization and specialized organs? Plants have specialized organs (like reproductive organs, roots, limbs, leaves) and differentiated tissues (vascular tissue in tracheophytes, support tissue, parenchyma, etc.) 4. What are the subkingdoms into which the plant kingdom is divided? The kingdom Plantae is divided into two big subkingdoms: the bryophytes and the tracheophytes (pteridophytes, gymnosperms and angiosperms). The criterion for the division is the presence or not of conductive (vascular) tissue. Plant Classification - Image Diversity: bryophytes pteridophytes gymnosperms angiosperms 5. What is the difference between bryophytes and tracheophytes? Bryophytes are nonvascular plants (mosses, liverworts, hornworts), i.e., they do not have a conductive system for transport of sugar, water and nutrients. Tracheophyte plants are vascular plants, they have conductive structures. 6. What are the four main groups into which the study of the plants is divided? In Botany the plant kingdom is divided into bryophytes, pteridophytes, gymnosperms and angiosperms. 7. What is the difference between cryptogamic and phanerogamic plants? Cryptogamic (hidden sex organs) plants are those that do not present flowers or seeds. They comprise the bryophytes and the pteridophytes. Phanerogamic plants are those having seeds. They comprise the gymnosperms and the angiosperms. Plant Classification - Image Diversity: seeds 8. What are the two divisions of the angiosperms? The angiosperms are divided into monocotyledonous and dicotyledonous. (These categories are explained later in this text.) Plant Classification - Image Diversity: monocots dicots 9. What are the three basic sexual life cycles studied in Biology? Which of them corresponds to metagenesis? Which of them is the human life cycle? Sexual reproduction may take place through three different types of life cycles: the haplontic (the being is haploid) haplobiontic (a single type of being) cycle; the diplontic (the being is haploid) haplobiontic (a single type of being) cycle; and the diplobiontic cycle (two types of beings, one haploid and the other diploid). The diblobiontic cycle is known as alternation of generations, or metagenesis. In humans the cycle is diplontic haplobiotic (a single diploid being). 10. What respectively are zygotic meiosis, gametic meiosis and sporic meiosis? Zygotic meiosis is the one that occurs in the haplontic haplobiontic life cycle. Gametes from adult haploid individuals unite forming the diploid zygote. The zygote undergoes meiosis and generates four haploid cells that by mitosis develop into adult individuals. Therefore in the zygotic meiosis the cell that undergoes meiosis is the zygote and the gametes are formed by mitosis. Gametic meiosis is that in which meiosis produces gametes, i.e., haploid cells that each of which can unite with another gamete forming the zygote. It occurs in the diplontic haplobiontic life cycle (e.g., in humans) in which the individual is diploid and meiosis forms gametes. Sporic meiosis happens in metagenesis (alternation of generations, or diplobiontic life cycle). In this life cycle cells from the diploid individual (called sporophyte) undergo meiosis producing haploid spores that do not unite with others but instead develop by mitosis into haploid individuals (called gametophytes). In this life cycle the gametes are made by mitosis from cells of the gametophyte. 11. Are gametes always made by meiosis? In the plant life cycle (diplobiontic life cycle) and in the haplontic haplobiontic life cycle gametes are made by mitosis and not by meiosis. Obviously in some stage of these sexual life cycles meiosis must occur. 12. Why is the plant life cycle known as alternation of generations? The plant life cycle is known as alternation of generations because in this cycle there are two different forms of living beings that alternate each other, one haploid and the other diploid. Alternation of generations is also called the diplobiontic cycle, or metagenesis, and it does not occur only in plants, other living beings, like cnidarians, present the cycle. 13. For each of the three types of life cycles what is the respective ploidy of the individual that represents the adult or lasting form? In the haplontic haplobiontic life cycle the single and lasting form is haploid. In the diplontic haplobiontic life cycle it is diploid. In the diplobiontic life cycle the lasting individual that alternates with the intermediate form may be the haploid gametophyte (as in bryophytes) or the diploid sporophyte (as in pteridophytes). Plant Classification - Image Diversity: haplontic haplobiontic life cycle diplontic haplobiontic life cycle diplobiontic life cycle 14. Do plants present only sexual reproduction? There are asexual forms of reproduction in plants. Some naturally detached pieces of root, limbs or leaves develop into another complete individual. Artificial asexual reproduction of plants can be obtained by means of grafting or cutting. |