→ Plant kingdom includes algae, bryophytes, pteridophytes gymnosperms, and angiosperms.
→ Algae are chlorophyll-bearing simple, thalloid, autotrophic, and largely aquatic organisms. Depending on the type of pigment possessed and the type of stored food, algae are classified into three classes, namely Chlorophyceae, Phaeophyceae, and Rhodophyceae.
→ Bryophytes are plants that can live on soil but are dependent on water for sexual reproduction. Their plant body is more differentiated than that of algae. It is thallus-like and prostrate or erect, attached to the substratum by rhizoids. They possess root-like, leaf-like, and stem-like structures.
→ The bryophytes are divided into liverworts and mosses.
→ In pteridophytes, the main plant is a sporophyte that is differentiated into true root, stem, and leaves. These organs possess well-differentiated vascular tissues.
→ The gymnosperms are the plants in which ovules are not enclosed by any ovary wall. After fertilization, the seeds remain exposed and therefore these plants are called naked seeded plants.
→ The gymnosperms produce microspores and megaspores which are produced in microsporophylls and megasporophylls- are arranged spirally on axis to form male and female cone respectively.
→ In angiosperms the male sex organs (stamen) and female sex organs (pistil are borne in a flower. Each stamen consists of a filament and an anther. The anther produces pollen grains (male gametophyte) after meiosis.
→ The pistol consists of an ovary enclosing one to many ovules. Within, the ovule is. the female gametophyte or embryo sac which contains the egg cell.
→ The pollen tube enters the embryo sac where two male gametes are discharged. One male gamete fuses with egg cell (syngamy) and the other fuses with diploid secondary nucleus (triple fusion).
→ However different plant groups, as well as individuals, may show different patterns of life cycle haplontic, diplontic er intermediate.
Table 3.1 Divisions of algae and their main characteristics:
→ Phylogenetic classification System: A system based on evolutionary relationships between the various organisms.
→ Antheridium: Male sex organ in bryophytes.
→ Archegonium: Female sex orgen in bryophtes.
→ Homosporous: Ptendophytes plants having similar kinds of spores.
→ Heterosporous: Plants that produce two kinds of spores, macro, and microspores.