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Seed plants have leaves, stems,roots, and vascular tissue. Seed plants reproduce by forming seeds. The seed contain a plant embryo and stored food which provides energy for the embryoso it can grow into a plant. Seed plants are classified into two groups; Angiosperm and Gymnosperm.
Study with Quizlet and memorize flashcards containing terms like A plant that grows from a seed, The part of a plant that contains a plant embryo and stored food, Scientists classify seed plants into these two groups and more.
Study with Quizlet and memorize flashcards containing terms like Seed, Seed Birth, Gymnosperms Production and more.
Jan 18, 2024 · Seed plants are composed of two major lineages: gymnosperms (meaning naked seed) and angiosperms (meaning covered seed). These two lineages represent major differences in life history traits connected to the evolutionary conditions during which each evolved.
- Overview
- Angiosperm seeds
seed, the characteristic reproductive body of both angiosperms (flowering plants) and gymnosperms (e.g., conifers, cycads, and ginkgos). Essentially, a seed consists of a miniature undeveloped plant (the embryo), which, alone or in the company of stored food for its early development after germination, is surrounded by a protective coat (the testa). Frequently small in size and making negligible demands upon their environment, seeds are eminently suited to perform a wide variety of functions the relationships of which are not always obvious: multiplication, perennation (surviving seasons of stress such as winter), dormancy (a state of arrested development), and dispersal. Pollination and the “seed habit” are considered the most important factors responsible for the overwhelming evolutionary success of the flowering plants, which number more than 300,000 species.
The superiority of dispersal by means of seeds over the more primitive method involving single-celled spores, lies mainly in two factors: the stored reserve of nutrient material that gives the new generation an excellent growing start and the seed’s multicellular structure. The latter factor provides ample opportunity for the development of adaptations for dispersal, such as plumes for wind dispersal, barbs, and others.
In the typical flowering plant, or angiosperm, seeds are formed from bodies called ovules contained in the ovary, or basal part of the female plant structure, the pistil. The mature ovule contains in its central part a region called the nucellus that in turn contains an embryo sac with eight nuclei, each with one set of chromosomes (i.e., they are haploid nuclei). The two nuclei near the centre are referred to as polar nuclei; the egg cell, or oosphere, is situated near the micropylar (“open”) end of the ovule.
With very few exceptions (e.g., the dandelion), development of the ovule into a seed is dependent upon fertilization, which in turn follows pollination. Pollen grains that land on the receptive upper surface (stigma) of the pistil will germinate, if they are of the same species, and produce pollen tubes, each of which grows down within the style (the upper part of the pistil) toward an ovule. The pollen tube has three haploid nuclei, one of them, the so-called vegetative, or tube, nucleus seems to direct the operations of the growing structure. The other two, the generative nuclei, can be thought of as nonmotile sperm cells. After reaching an ovule and breaking out of the pollen tube tip, one generative nucleus unites with the egg cell to form a diploid zygote (i.e., a fertilized egg with two complete sets of chromosomes, one from each parent). The zygote undergoes a limited number of divisions and gives rise to an embryo. The other generative nucleus fuses with the two polar nuclei to produce a triploid (three sets of chromosomes) nucleus, which divides repeatedly before cell-wall formation occurs. This process gives rise to the triploid endosperm, a nutrient tissue that contains a variety of storage materials—such as starch, sugars, fats, proteins, hemicelluloses, and phytate (a phosphate reserve).
The events just described constitute what is called the double-fertilization process, one of the characteristic features of all flowering plants. In the orchids and in some other plants with minute seeds that contain no reserve materials, endosperm formation is completely suppressed. In other cases it is greatly reduced, but the reserve materials are present elsewhere—e.g., in the cotyledons, or seed leaves, of the embryo, as in beans, lettuce, and peanuts, or in a tissue derived from the nucellus, the perisperm, as in coffee. Other seeds, such as those of beets, contain both perisperm and endosperm. The seed coat, or testa, is derived from the one or two protective integuments of the ovule. The ovary, in the simplest case, develops into a fruit. In many plants, such as grasses and lettuce, the outer integument and ovary wall are completely fused, so seed and fruit form one entity; such seeds and fruits can logically be described together as “dispersal units,” or diaspores. More often, however, the seeds are discrete units attached to the placenta on the inside of the fruit wall through a stalk, or funiculus.
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The hilum of a liberated seed is a small scar marking its former place of attachment. The short ridge (raphe) that sometimes leads away from the hilum is formed by the fusion of seed stalk and testa. In many seeds, the micropyle of the ovule also persists as a small opening in the seed coat. The embryo, variously located in the seed, may be very small (as in buttercups) or may fill the seed almost completely (as in roses and plants of the mustard family). It consists of a root part, or radicle, a prospective shoot (plumule or epicotyl), one or more cotyledons (one or two in flowering plants, several in Pinus and other gymnosperms), and a hypocotyl, which is a region that connects radicle and plumule. A classification of seeds can be based on size and position of the embryo and on the proportion of embryo to storage tissue; the possession of either one or two cotyledons is considered crucial in recognizing two main groups of flowering plants, the monocotyledons and the eudicotyledons.
- Hans Lambers
A seed is a mature ovule that comprises an embryo or a miniature undeveloped plant and food reserves, all enclosed within a protective seed coat. Seeds are a way of reproduction for all flowering plants.
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Seed Plants. Seed plants are called spermatophytes. The evolution of seeds by vascular plants was a very big deal. In fact, it was arguably as important as the evolution of vascular tissues. Seeds solved the problem of releasing offspring into a dry world.
