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parts of a plant seed

Parts of a plant seed

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  • University of California Museum of Paleontology – Seed plants: Fossil Record
  • UNESCO World Heritage Centre – Bordeaux, France
  • seed – Children’s Encyclopedia (Ages 8-11)
  • seed – Student Encyclopedia (Ages 11 and up)

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.

Economically, seeds are important primarily because they are sources of a variety of foods—for example, the cereal grains, such as wheat, rice, and corn (maize); the seeds of beans, peas, peanuts, soybeans, almonds, sunflowers, hazelnuts, walnuts, pecans, and Brazil nuts. Other useful products provided by seeds are abundant. Oils for cooking, margarine production, painting, and lubrication are available from the seeds of flax, rape, cotton, soybean, poppy, castor bean, coconut, sesame, safflower, sunflower, and various cereal grains. Essential oils are obtained from such sources as juniper “berries,” used in gin manufacture. Stimulants are obtained from such sources as the seeds of coffee, kola, guarana, and cocoa. Spices—from mustard and nutmeg seeds; from the aril (“mace”) covering the nutmeg seed; from the seeds and fruits of anise, cumin, caraway, dill, vanilla, black pepper, allspice, and others—form a large group of economic products.

The nature of seeds

Angiosperm seeds

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.

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.

Seed, the characteristic reproductive body of both angiosperms and gymnosperms. Essentially, a seed consists of a miniature undeveloped plant (the embryo), which, alone or in the company of stored food, is surrounded by a protective coat. Learn more about seed characteristics, dispersal, and germination.

Parts of a Seed

Target Grade Level / Age Range:

Purpose:

Students will learn about two types of plants and the parts of their seeds, using Iowa corn and soybeans as examples.

Materials:

  • Corn seeds
  • Soybean seeds
  • Variety of edible seeds
  • Pencils
  • Crayons

Suggested Companion Resources (books and websites)

  • How A Seed Grows by Helene J. Jordan

Vocabulary (with definitions)

  • seed coat – covers and protects the seed
  • embryo – forms the new plant
  • endosperm – acts as food for the seed, and nourishes the embryo
  • germinate – when a seed begins to grow, or puts out shoots
  • cotyledon – the first “leaves” of a plant
  • monocot – a plant with one cotyledon
  • dicot – a plant with two cotyledons

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content):

This lesson dives into the anatomy of seeds, as well as how seeds differ between monocot and dicot.

  • Monocot:
    • The term monocot is short for monocotyledonous. This simply means that the plant has one cotyledon. A cotyledon is the plant’s first leaf.
      • Cotyledon is pronounced like cot-ill-E-don.
    • Monocots are grasses. They have long, thin leaves instead of broad, or palmate leaves. The veins in the leaves are usually parallel. There are also differences in roots, stem, and flower development between monocots and dicots.
    • An example of a monocot would be corn. When corn germinates, the roots emerge from the bottom of the kernel, and the cotyledon emerges from the top. This is called epicotyl emergence.
  • Dicot:
    • The term dicot is short for dicotyledonous. This means that the plant has two cotyledons.
    • Dicots are broadleaf plants. Their leaves can be interesting shapes, and will have more webbed veins in the leaves. Dicots tend to have taproots instead of fibrous roots.
    • An example of a dicot would be soybeans. When soybeans germinate, the seed actually ends up above ground. The root shoots from the seed, the hypocotyl elongates and forms an arc, which projects the seed and the cotyledons above the ground. This is called hypocotyl emergence.
      • Soybeans are a non-endospermic dicot. This means that its cotyledons act in the same way as the endosperm does in other seeds (food storage for the embryo). Cotton would be an example of a dicot seed that contains an endosperm.
  • The student worksheet takes a relatively simple version of all of this information. The main goal of the worksheet is to help students understand that there are two types of plants, and that there are parts within the seed that help it to grow.
    • The students will need to know:
      • Common Iowa crop representatives of monocots and dicots (corn and soybeans)
      • How to identify three main parts of each seed
        • In corn:
          • Endosperm, cotyledon, and embryo
        • In soybeans:
          • Seed coat, cotyledon, and embryo
    • When working through the worksheet, talk with students about the function of each part of the plant. Students may not remember what a cotyledon is, but if they remember that some plants start with one leaf and others start with two, that is good.
      • After students label the parts of the seed on page 2, it could be possible to go through as a class and write a short description of what that part does.
  • Seed germination requires only moisture and heat.
    • Though this lesson doesn’t directly include a germination lab, one could easily follow. Students could use one corn seed and one soybean seed and watch as the parts of the seed they once identified germinated and began to grow.
      • Water beads or orbeez and a jewelry sized Ziploc bag create a good environment for seeds. Ensure that the seeds are placed in a warm place, and they should germinate. After about a week, the seed will need to be planted in soil in order for it to continue to grow.
  • Corn and soybeans have a variety of uses.
    • Most of these crops go to feeding livestock, like hogs and cattle. However, corn can also be made into ethanol, sweeteners, or even fibers in yarn and carpet, or biodegradable packing peanuts and plastic! Soybeans can be made into soy biodiesel, tofu, vegetable oil, or the foam in car seats!
    • Both corn and soybeans are planted in the spring and harvested in the fall. For the most part, the same equipment can be used for both crops. However, the header, or front attachment on the combine, must be changed if a farmer needs to harvest these two crops.
    • The animals that the corn and soybeans feed help give back to the farmland though the nutrients in their manure. This can be used as a cheap and valuable fertilizer for crop ground.
      • Manure isn’t applied carelessly, however. There are regulations dictating times, temperatures, and amounts allowed for applying certain types of manure.
      • Farmers can also test their soils for the amount of nutrients in them, as well as the manure they plan to apply. This way, farmers can calculate exactly the needs of the field, and not over apply nutrients.

Interest Approach or Motivator:

Ask students what they think are inside of seeds. Do seeds hatch like eggs? What do they need to grow?

Students will learn about two types of plants and the parts of their seeds, using Iowa corn and soybeans as examples.