Seed Plants

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The three main organs in a plant are roots , stems, and leaves. Roots absorb water and dissolved nutrients from soil. They anchor plants to the ground. Roots are able to do all of these jobs because they grow , they develop complex branching networks that penetrate the soil and grow between soil particles. Stems hold a plants leaves up to the sun.

Leaves are the organ in which plants capture the suns energy. These tissues must be protected against water loss to dry air. That’s why most plants are covered in waxy coating called cuticle.

Plants have a well developed two way plumbing system consisting of xylem and phloem Xylem is primary responsible for carrying water and dissolved nutrients from the roots to stems and leaves. Phloem carries product of photosynthesis and certain other substances from one part of the plant to another. Seed plants do have alternation of generation. However life cycles of seed plants are well adapted to the rigors of life on land. Flowers and cones are specialized reproductive structures of seed plants. Because they developed within the sporophyte plant, neither the gametophyte nor the gametes need standing water to function The entire gametophye of seed plants is contained in a tiny structure called a pollen grain. The entire pollen grain is carried to the female gametophyte by wind, insects, birds, small animals, and sometimes even bats. The carrying of pollen to the female gamtophyte is called pollination. Seeds are structures that protect the zygote of seed plants. After fertilization the zygote grows into a tiny plant called an embryo. A seed coat surround the embryo and protects it and the food supply from drying out.

The first seed bearing plants appeared during the Devonian period. The most ancient surviving seed plants belong to the three classes: the Ginkgoae, the Coniferae, and the cicadae. In these plants leaves evolved into specialized male and female gametophyte called scales. Scales then are grouped into larger...
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