Plant Kingdom

The One Thing

Plant evolution shows increasing complexity in body structure, vascular tissues, reproduction, and seed formation, progressing from thalloid, non-vascular, spore-producing forms to vascular plants with seeds, flowers, and fruits. Despite these differences, all major plant groups show alternation of generations between a haploid gametophyte and a diploid sporophyte.

Reactions, Processes and Experiments

Key Terms

• Plant Kingdom: A group of multicellular, generally non-motile, eukaryotic organisms that usually contain chlorophyll and make food by photosynthesis.
• Algae: Simple, mostly aquatic, photosynthetic organisms with a thalloid body that lacks true roots, stems, and leaves.
• Bryophytes: Small, non-vascular plants such as liverworts and mosses that require water for sexual reproduction and have a dominant gametophyte.
• Pteridophytes: Seedless vascular plants such as ferns that possess true roots, stems, and leaves, with a dominant and independent sporophyte.
• Gymnosperms: Vascular seed-producing plants in which the ovules and seeds are not enclosed within an ovary or fruit.
• Angiosperms: Flowering plants whose ovules are enclosed in an ovary and whose seeds develop inside fruits.
• Thallus: A simple plant body that is not differentiated into true roots, stems, and leaves.
• Vascular tissue: Specialized conducting tissue: xylem transports water and minerals, while phloem transports food.
• Cryptogams: Plants that do not produce visible seeds; algae, bryophytes, and pteridophytes are commonly included in this group.
• Phanerogams: Seed-producing plants, including gymnosperms and angiosperms.
• Homosporous: Producing only one type of spore, as seen in most pteridophytes.
• Heterosporous: Producing two types of spores: microspores and megaspores; this condition occurs in some pteridophytes and all seed plants.
• Alternation of generations: The regular alternation between a haploid gametophyte generation that produces gametes and a diploid sporophyte generation that produces spores.
• Gametophyte: The haploid phase of the life cycle that forms gametes by mitosis.
• Sporophyte: The diploid phase of the life cycle that forms haploid spores by meiosis.
• Oogamy: A type of sexual reproduction involving a large, non-motile female gamete and a small, usually motile male gamete.
• Double fertilisation: A characteristic feature of angiosperms in which one male gamete fuses with the egg to form the zygote and the other fuses with the polar nuclei to form the primary endosperm nucleus.
• Dominant generation: The generation that is larger, longer-lived, and nutritionally independent in a plant life cycle.

Easily Confused

• Cryptogams and phanerogams: Cryptogams do not produce visible seeds and include algae, bryophytes, and pteridophytes; phanerogams produce seeds and include gymnosperms and angiosperms.
• Homosporous and heterosporous: Homosporous plants produce one type of spore; heterosporous plants produce microspores and megaspores.
• Bryophyte and pteridophyte dominance: Bryophytes have a dominant, nutritionally independent gametophyte, whereas pteridophytes have a dominant, independent sporophyte.
• Gymnosperms and angiosperms: Gymnosperms have naked ovules and seeds and generally lack fruits; angiosperms have ovules enclosed in ovaries and produce fruits.
• Gametophyte and sporophyte: The haploid gametophyte produces gametes by mitosis, whereas the diploid sporophyte produces haploid spores by meiosis.
• Monocotyledons and dicotyledons: Monocotyledons generally have one cotyledon, parallel venation, fibrous roots, and scattered vascular bundles; dicotyledons generally have two cotyledons, reticulate venation, tap roots, and ring-arranged vascular bundles.
• Algae and bryophytes: Algae generally have a simple aquatic thallus, whereas bryophytes are small land plants that lack vascular tissues and require water for fertilisation.
• Seeds and spores: Spores are reproductive units produced by spore-producing plants, whereas seeds protect and nourish a developing embryo.

What Gets Asked

• Classification questions: Identify algae, bryophytes, pteridophytes, gymnosperms, and angiosperms from body organisation, vascular tissues, seeds, flowers, fruits, and ovule position. The common mark-losing error is confusing naked seeds of gymnosperms with enclosed seeds of angiosperms.
• Comparison questions: Compare monocotyledons and dicotyledons using cotyledon number, leaf venation, root system, and vascular bundle arrangement. Omitting one of these specified features can lose marks.
• Life-cycle questions: Explain alternation of generations and distinguish the haploid gametophyte from the diploid sporophyte. The key error is reversing the generation that produces gametes and the generation that produces spores.
• Reproductive questions: Define homospory, heterospory, oogamy, and double fertilisation. The specific error in double fertilisation is failing to state that the second male gamete fuses with the polar nuclei to form the primary endosperm nucleus.
• Evolutionary questions: Describe the progression from thalloid, non-vascular, spore-producing forms to differentiated, vascular plants with seeds, flowers, and fruits. The mark-losing error is presenting the sequence without explaining the increasing independence from water for reproduction.
• Dominant-generation questions: State which generation is dominant in bryophytes, pteridophytes, and seed plants. The common error is describing the bryophyte sporophyte as independent or the pteridophyte gametophyte as dominant.