Life Cycle - Human Biology (2B)
Post Lab 

   
OBJECTIVES:
  • Exploring the largest organ of the human body. 
  • Analyzing fingerprints.
VOCABULARY:
  • fingerprint
  • organ
  • skin
MATERIALS:

Students make fingerprints and look under the microscope.

 

BACKGROUND:

The skin is the largest organ of the body and with the exception of the brain, probably the most complex.  It wraps the adult body in about 20 square feet of tissue, weighing some seven pounds.  The skin can be very sensitive or very tough.  Human skin is furrowed by ridges and valleys, pitted with tunnels from which hair tips project, moistened by salt water and lubricated by an invisible moving film of oils.  

The skin is a layered organ.  The outer skin or epidermis, has several anatomical layers.  The topmost horny layer is composed of dead cells that are always being worn off.  We shed our skins continuously, not all at once as reptiles do.  Beneath the epidermis is the dermis.  It contains connective tissue, is strong and elastic, and is the part of animal skin that makes leather when tanned.  It is laced with blood vessels, nerve fibers, receptor organs for sensations of touch, pain, heat and cold. Beneath the dermis is a layer of tissue with fatty elements that help cushion the skin above it.

Our skin is equipped with upward of two million tiny glands which excrete fluids well known as sweat or more generally as perspiration.   We have about as many oil secreting glands in the skin as we have sweat glands.  Most of these occur in or near hair follicles.

Hair is a modified form of skin cells and so are fingernails and toenails.  Hairs grow in almost the entire skin, though in many areas they are so inconspicuous that they are never noticed.

PROCEDURE:
  1. Students should complete the worksheet on the skin so they can see all the different layers. You may want to tell students that the color pigments of our skin are only on the first layer. The pigment melanin, is responsible for the darkening. The pigments are there as an evolutionary reaction to being out in the sun for a long time. The darker the skin the more that person's ancestry was exposed to the sun (this is a simple explanation.)

Answers: 1=fat cells; 2=papilla; 3=nerve ending; 4=sweat glands; 5=oil secreting glands; 6=shaft; 7=epidermis; and 8=dermis.

  1. Making fingerprints is relatively easy. Using an ink pad, have the students roll the tip of their fingers on the pad. Then have them roll it on the sticky part of tape. Then put the tape (sticky side down) a paper, so you can easily view it with your microscope or hand lense. Instruct students to compare their fingerprints with a partner's and have them determine how they differ.

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