Daily Junction: Motorola MotoMing PDA Phone

Daily Junction: Motorola MotoMing PDA Phone

PLANT VARIETY

THERE ARE MORE THAN 300,000 SPECIES of plants. They show a wide diversity of forms and life-style, ranging, for example, from delicate liverworts, adapted for life in a damp habitat, to cacti, capable of surviving in the desert and from herbaceous plants, such as corn, which completes it s life-cycle in one year, to the giant redwood tree, which can live for thousand of years. This diversity reflects the adaptations of plants to survive in a wide range of habitats. This is seen most clearly in the flowering plants (phylum Angiospermophyta), which are the most numerous, with over 250,000 species, and the most widespread, being found from the tropics to the poles. Despite their diversity, plants share certain characteristics: typically, plants are green, and make their food by photosynthesis; and most plants live in or on a substrate, such as soil, and do not actively move. Algae (kingdom Protista) and fungi (kingdom Fungi) have some plant-like characteristics and are often studied alongside plants, although they are not true plants.

ROOTS

ROOTS are the underground parts of plants. They have three main functions. First, they anchor the plant in the soil. Second, they absorb water and minerals from the spaces between soil particles; the roots’s absorptive properties are increased by root hairs, which grow behind the root tip, allowing maximum uptake of vital substances. Third, the root is part of the plant’s transport system: xylem carries water and minerals from the roots to the stem and leaves, and phloem carries nutrients from the leaves to all parts of the root systems. In addition, some roots (e.g. carrots) are food stored.

STEMS

THE STEM IS THE MAIN SUPPORTIVE PART OF A PLANT that grows above ground. Stems bear leaves (organs of photosynthesis), which grow at nodes; buds (shoots covered by protective scales), which grow at the stem (axillary or lateral buds); and flowers (reproductive structures). The stem forms parts of the plant’s transport system: xylem tissue in the stem transports water and minerals from the roots to the aerial parts of the plant, and phloem tissue transport nutrients manufactured in the leaves to other parts of the plant. Stem tissues are also used for sorting water and food.

LEAVES

LEAVES are the main sites of photosynthesis and transpiration (water loss by evaporation) in plants. A typical leaf consists of a thin, flat lamina supported by a network of veins; a petiole (leaf stalk); and a leaf base, where the petiole joins the stem. Leaves can be classified as simple, in which the lamina is a single unit, or compound, in which the lamina is divided into separate leaflets. Compound leaves may be pinnate, with pinnae (leaflets) on both sides of a rachis (main axis), or palmate, with leaflets arising from a single point at the tip of the petiole. Leaves can be classified further by the overall shape of the lamina and by apex, margin and base.