Kingdom Plantae All plants are thought to have evolved from an ancestor of plant-like protists over 400 million years ago. Plant-like protists are also called phytoplankton or algae. They are not considered plants because: • Algae are mostly unicellular • May form colonies, but do not form tissues • Do not develop from an embryo Features which distinguish plants from protists • • • • • multicellular photosynthetic food storage molecule - amylose starch structural polysaccharide - cellulose life cycle - alternation of generations – diploid sporophyte – haploid gametophyte • produce multicellular embryo protected in multicellular haploid tissue which differs from green algae. Major adaptations of terrestrial plants • the development of a waxy cuticle (to prevent water loss or dessication) Major adaptations of terrestrial plants • The development of microscopic pores called stomata (to allow gases such as CO2 and O2 in and out through the cuticle) Major adaptations of terrestrial plants • differentiation of parts into distinct tissues such as leaves and stems (a feature of mosses and vascular plants but to a much lesser extent the liverworts and hornworts) Specialized Plant Tissues Tissue System and Its Functions Dermal Tissue System • protection • prevention of water loss Ground Tissue System • photosynthesis • food storage • regeneration • support • protection Vascular Tissue System • transport of water/minerals • transport of food Component Tissues Epidermis Periderm Parenchyma tissue Collenchyma tissue Sclerenchyma tissue Xylem tissue Phloem tissue Location of Tissue Systems Major adaptations of terrestrial plants • Development of vascular systems (to efficiently transport water and nutrients) Leaf structure • Specialization of above and below ground tissues (e.g., the development of leaves for efficient collection of sunlight energy or of roots specialized for nutrient transport as well as support) Root structure • Development of secondary growth (to allow the formation of thick structures as opposed to simply long, thin ones which grow only at either end) • Development of reproductive strategies which did not depend on the existence of standing water (e.g., pollen, seeds, flowers) Major adaptations of terrestrial plants • Decrease in the conspicuousness of the gametophyte and an increase in the conspicuousness of the sporophyte (i.e. alternation of generations) Alternation of Generations • Most plants display a life cycle that alternates between haploid and diploid phases • The haploid stage is generated by meiosis and is called the gametophyte (gamete-producing plant) • The diploid stage is generated by fertilization and is called the sporophyte (spore-producing plant) • A general pattern in plant evolution has been from early plants which had a dominant haploid stage to more recent plants which have a more dominant diploid stage.