Kids Research Express

The major parts of a tree The major parts of a tree are its roots, trunk, leaves, flowers, and seeds. These components play vital roles in a tree’s growth, development, and reproduction. A. Roots Trees are held in place by anchoring organs called roots . In addition to anchoring the tree, roots also absorb water and minerals through tiny structures called root hairs. From the roots the water and mineral nutrients are carried upward through the wood cells to the leaves. Although the internal structure of most kinds of roots is similar, there are often external differences. Pines, for example, have a strongly developed taproot, or main root, in addition to branching side roots. In maples, on the other hand, there is little or no central taproot, and the other roots are produced in great numbers near the surface of the soil. Roots grow constantly, and at the growing tip of each root is a region called the meristem, which is composed of special rapidly dividing cells. Just behind the meris

Seed, term applied to the ripened ovule of a seed plant before germination. Seeds of the angiosperm , or flowering plant, differ from those of the gymnosperm , or conifer and related plants, in being enclosed in the ovary that later forms a fruit ; gymnosperm seeds lie exposed on the scales of the cones. During the process of fertilization the pollen tube enters the ovule through a small opening known as the micropyle. One of the two sperm nuclei in the pollen tube unites with the egg cell in the ovule to form a zygote, which develops into the embryo. In flowering plants the other sperm nucleus unites with two polar nuclei present in the embryo sac to form an endosperm nucleus, which later produces the nutritive endosperm tissue surrounding the embryo in the seed. In gymnosperms, the endosperm is formed from the tissue of the embryo sac itself. The nucellus, or megasporangium, is the tissue composing the main part of the ovule; it is partially digested during the development of the em

Monocotyledons (monocots) and dicotyledons (dicots) make up the two large groups of flowering plants, differentiated by their seed structures. Monocot seeds contain one cotyledon, or embryonic leaf. When these seeds germinate, the cotyledon remains below ground, absorbing nutrients from the endosperm, the starchy food supply in the seed. The coytledon transports these nutrients to the developing seedling. Dicot seeds contain two coytledons, which absorb and store the nutrients from the endosperm before the seed germinates. The cotyledons, thick with stored nutrients, emerge above ground during germination, and then transport the stored nutrients to the developing seedling. For a brief time, the cotyledons also serve as the first photosynthesizing leaves, but they wither and die when the true leaves emerge. related articles: flower flower variations in structure flower sexual reproduction flower pollination and fertilization flowering and the life cycle evolution of flowers angios

The term gymnosperm is derived from two Greek words: gymnos, meaning naked, and sperma, meaning seed. The term refers to plants, such as pine and spruce , in which seeds mature on the surface of cone scales. In contrast, the term angiosperm means a seed contained in a vessel and refers to flowering plants, in which seeds mature within a fruit. The seeds of angiosperms develop in an ovary, a part of the carpel that surrounds and protects the egg-containing ovules . Seeds develop from the ovules after pollination and fertilization of the eggs. Ovules and seeds are not exclusive to angiosperms. The “naked-seed” plants (see Gymnosperm ), which include the conifers , cycads , and ginkgo , have ovules that lie exposed on the surface of specialized, scalelike leaves arranged into cones. The development of seeds from ovules enclosed in an ovary, which enlarges into a fruit as the fertilized seeds grow, is a feature unique to the angiosperms. See also: angiosperms parts of a flower evolution o