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parts of seed

the parts of a seed and their functions in seed and plant development

There are three basic parts of a seed in the angiosperms: (a) an embryo , (b) a food storage or nutritive tissue , and (c) seed covering .

Embryo

A mature seed has a diploid (2N) embryo which develops from a fertilized egg or zygote. It results from the union of a sperm (1N), from a germinated pollen, with a female egg (1N) in the embryo sac. It is the embryo that ultimately gives rise to a new plant.

The embryo can be distinguished from the other major parts of a seed based on component parts and function. It consists of the epicotyl, hypocotyl, radicle, and one or two cotyledons. It is the one which develops into a plant with an upward growing shoot and a downward growing root system.

The epicotyl is a tiny shoot from which the entire plant shoot system develops. The growing tip of the epicotyl is the plumule. The hypocotyl is the transition zone between the rudimentary root and shoot; the radicle is a small embryonic root. Cotyledons are specialized seed leaves which develop from the plumule and occur singly in most monocot seeds but two in dicot seeds. They are the most prominent parts of a fully developed embryo. Monocot means one cotyledon while dicot means two cotyledons. (Click here to read relevant update)

The stored food is present in most seeds in the form of carbohydrates , fats and proteins. This stored food may be found in the following parts of a seed: endosperm, cotyledons, or in the perisperm. The stored food is used to support the embryo during seed germination. But in orchid seeds, a functional storage tissue is lacking.

Storage Tissue or Nutritive Tissue

The endosperm differs from other parts of a seed by having a triploid chromosome complement (3N). It results from the union of one sperm nucleus (1N), from a germinating pollen, with the two polar nuclei (2N) in the embryo sac. In corn and other cereals it represents the major bulk of the seed. In other seeds (e.g. beans), the endosperm is absent because it is utilized in the development of the embryo. In this case the cotyledons, not the endosperm, serve as the food-storage tissue. This is an example that of the different parts of a seed, the endosperm may be wanting.

The endosperm can be described as either mealy, horny, continuous, or ruminated. It is mealy when granular, horny when hard and bone-like, continuous when smooth and uninterrupted, and ruminated when there are irregular depressions, as if chewed, as in betel nut ( Areca catechu ). Coconut water is a liquid endosperm .

When the plant food is stored outside of the embryo in a large endosperm, the seed is called albuminous . When the embryo stores its own food reserve, usually within the cotyledons, the seed is called exalbuminous . In the latter case the endosperm is absent, having been digested by the embryo during development, or it is reduced to a thin layer around the embryo.

The perisperm is a storage tissue that originates from the nucellus. Thus, just like other parts of a seed other than the endosperm, it has a diploid chromosomal content. But it occurs only in a few families, e.g. Amaranthaceae (amaranth family), Chenopodiaceae (goosefoot family) and Caryopyllaceae (pink (family). It is usually digested by the endosperm during seed development.

Seed Covering or Protective Coat

The seed covering is of maternal origin. This part of a seed consists of the seed coat or remnants of the nucellus and endosperm. Sometimes it consists of parts of the fruit. It covers and provides mechanical protection to the other parts of a seed.

The seed coat is usually hard, thickened, brownish or otherwise colored, and partly impermeable to water. It prevents excessive loss of water from within the seed and serves as a barrier against the entry of parasites. Hard seed coats cause dormancy, a condition which prevents germination when environmental conditions are not favorable for sustained growth of seedlings.

The seed coat is developed from the outer covering of the ovule, or integument. But it is not immediately apparent in the angiosperms because the seed is encased in a fruit wall or pericarp. The outermost, visible part of the corn kernel is in fact the exocarp, the outermost part of the pericarp.

There are usually two layers of the seed coat. The outer layer, known as the testa, is thicker. The inner one is more delicate, known as tegmen.

Externally, some parts of a seed are obvious. On some seed coats, the opening in the integuments of the ovule, called micropyle , is visible. The hilum is usually visible also, the scar left by the stalk which attached the seed to the placenta. The hilum is equivalent to the navel in humans to which the umbilical cord is attached. It appears dark in color when the seed becomes physiologically mature and is thus used as an indicator of seed maturity.

From the outside, seeds may be smooth, wrinkled, or hairy as in cotton, or winged. In the castor bean (Ricinus communis), there is wart-like growth at the hilum, called the caruncle. In mangosteen, the seeds are enveloped by a white fleshy aril which is edible.

Note: Do you know that some seeds used in propagating plants may not be entirely seeds? Click here to read .

REFERENCES

  1. AGROFORESTRY SEEDS CIRCULAR, March 1993. p. 30.
  2. FEININGER A. 1968. Trees. (1978 reprint). NY: The Viking Press. 116 p.
  3. FLORES HE, DAI Y, CUELLO JI, MALDONADO-MENDOZA IE, LOYOLA-VARGAS, VM. 1993. Green roots: photosynthesis and photoautotrophy in an underground plant organ. Plant Physiol. 101: 363-371. Retrieved November 27, 2010 from http://www.plantphysiol.org/content/101/2/363.full.pdf.
  4. FULLER HJ, RITCHIE DD. 1967. General Botany. 5th ed. NY: Barnes & Noble, Inc. 232 p.
  5. GOMEZ FP, PRADO CHBA. 2007. Ecophysiology of coconut palm under water stress. Brazilian Journal of Plant Physiology. Print version ISSN 1677-0420. Retrieved December 8, 2010 from http://www.scielo.br/scielo.php?pid=S1677-04202007000400008&script=sci_arttext.
  6. HARTMANN HT, KESTER DE. 1975. Plant Propagation: Principles and Practices. New Jersey: Prentice-Hall Inc. 662 p.
  7. http://www2.bioversityinternational.org/publications/Web_version/108/ch02.htm#TopOfPage, accessed Dec ember 7, 2010.
  8. JANICK J. 1972. Horticultural Science. 2nd ed. San Francisco: W. H. Freeman and Company. pp. 55-93.
  9. KESSELER R, STUPPY W. 2009. Seeds: Time Capsules of Life. P.O. Box 1338, Ellicott Station, Buffalo, NY: Firefly Books (U.S.) Inc. 264 p.
  10. KITAYA Y, YABUKI K, KIYOTA M, TANI A, HIRANO T, AIGA I. 2002. Gas exchange and oxygen concentration in pneumatophores and prop roots of four mangrove species. Retrieved December 7, 2010 from http://www.springerlink.com/content/0wtyb14gmpjc3qqu/.
  11. MADER SS. 1993. Biology Part 4: Plant Structure and Function. 4th ed. Dubuque, Iowa: Wm. C. Brown Publishers. pp. 474-493.
  12. MERRILL ED. 1912. A Flora of Manila. (1976 reprint), Manila: Bureau of Printing. 491 p.
  13. POINCELOT RP. 1980. Horticulture: Principles and Practical Applications. Englewood Ciffs, New Jersey: Prentice-Hall, Inc. 652 p.
  14. POSTLETHWAIT J, HOPSON JL. 1989. The Nature of Life. New York, NY: Random House, Inc. pp. 631-653.
  15. RYUGO K. 1988. Fruit Culture: Its Science and Art. NY: John Wiley & Sons. 344 p.
  16. UNIVERSITY OF ARIZONA. 1998. Botany: plant parts and functions. Retrieved November 27, 2010 from http://ag.arizona.edu/pubs/garden/mg/botany/plantparts.html.
  17. VERHEIJ EWM, CORONEL RE, eds. 1992. Edible fruits and nuts. Plant Resources of South-East Asia No. 2. Bogor, Indonesia: Prosea Foundation. 447 p.
  18. WENT FW, THE EDITORS OF LIFE. 1963. The Plants. NY: Time Incorporated. pp. 73-98.

(Ben G. Bareja 2010, edited Apr. 13, 2019)

Note: This page on parts of a seed is a component page of The Plant Structure in the Angiosperms . The references apply to the whole series of articles.

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The parts of a seed in the angiosperms and their role in seed and plant development are reviewed.

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.