Antibiotics in Action

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    Biology Activity
    Cell Membranes

    Major Biochemical Concept

    The cell membrane, as a complex molecular structure with several major subunits, controls the flow of chemicals into and out of the cell's interior. Several characteristics of these compounds, including molecular size, solubility, and presence or absence of electrical charge, affect the interaction between them and the membrane's structure. Antibiotics can penetrate the cell depending on their chemical interaction with the membrane.
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      General Safety Guidelines
      Microbiology Safety Guidelines
      Major Biochemical Concept
      Level and Expected Student Background
      Time
      Safety
      Materials and Apparatus
      Advance Preparation
      Relevant National Science Education
      Standards
      Relevant New Jersey State Science
      Education Standards

    Level and Expected Student Background

    This activity is appropriate for all student levels. Students should have the normal laboratory skills for following procedures, making good observations, and accurately recording data. Some chemistry vocabulary may have to be taught in conjunction with the lab exercise. Students must be familiar with using a microscope.

    Time

    These activities can be performed on consecutive days (3) or the first two activities can be done during a double period and the third activity done during a single class period, depending on the extent of teacher preparation before lab (heating and killing yeast cells; preparing live yeast cultures).

    Safety

    1. Wear safety goggles.

    2. Keep hands and writing tools out of the mouth when working with the various substances.

    3. Wipe up any chemical spills immediately.

    4. Caution students about hot water heaters and adding or removing test tubes.

      General Safety Guidelines
      Microbiology Safety Guidelines

    Materials and Apparatus

    You will need the following for each team participating in the activities:

    • 2 cellulose tubing, each 20 cm lengths (pre-soak)
    • Saturated GLUCOSE solution (for Activity #3)
    • Tes-tape or Clinitest tablets (from pharmacy) for Activity #3
    • Soluble starch solution (the easiest preparation is to spray commericial starch from an aerosol can into warm water). Test sample of solution with iodine to make sure the solution is concentrated enough. If starting with soluble starch powder, add 10 grams to about 100 ml of COLD water. Stir to create a fluid paste. Then transfer the liquid to 500 ml of warm water and bring the solution to near boiling. The solution will be hazy but not excessively cloudy if the starch is uniformly distributed. Whichever starch solution is prepared, test to make sure the solution does not pass through the cellulose membrane.
    • Ties for the tubing: dental flossing string is useful, particularly the waxed type that tends to be broader.
    • For the STOCK iodine solution, dissolve 15 grams of KI in 1 liter of water or equivalent ratio. To the liter of solution, add 3 grams of iodine. When using this stock solution, it needs to be diluted with water, 1:10. Place in dropper bottles for student use.
    • 20% sucose solution (20 grams sucrose, 80 ml or grams of water)
    • 5% salt (NaCl) solution (5 grams NaCl, 95 grams or ml of water)
    • 0.7% salt (NaCl) solution (physiologic saline solution): 0.70 g NaCl in 100 ml water
    • Egg albumin (fresh egg whites). Alternative: try different concentrations of albumin powder.
    • 600-ml beakers or equivalent size jars (2)
    • Yeast solution: prepare one day in advance. Combine Ŋ packet of yeast with 28 grams peptone in 500 ml of a 5-10% molasses solution (5-10 ml molasses in 495-490 ml distilled water). Culture at 25-30ēC for at least 12 hours.
    • Microscopes, glass slides, and coverslips
    • Droppers for salt and sucrose solutions
    • Small test tubes, 13 x 100 mm (2) and small jar as test tube holder
    • Test tube clamp (1)

    Advance Preparation

    1. Refer to list of materials above for advanced preparation of several solutions and the yeast culture.

    2. Cellulose tubing should be soaked in tap water in advance of the lab.

    3. Set up heating baths for group use.

    4. Tes-tape and Clinitest tablets are available from pharmacies; used to test the urine of diabetics for presence of glucose. An alternative test would be Benedict's or Fehling's solution. These test for glucose, not sucrose. You could modify Activity #2 by combining the starch and glucose solutions in the same cellulose tube, then using Benedict's or Fehling's to test for presence of glucose in the water ( iodine is still added to the water initially but does not interfere with the glucose test as it would if using the Tes-tape or Clinitest tablets).

    Relevant National Science Education Standards

      Unifying Concepts and Processes — The activity is concerned with evidence, models, and explanations and is also concerned with change, constancy, and measurement.

      Science as Inquiry — The activity is concerned with the abilities necessary to do scientific inquiryand is also concerned with scientific inquiry.

      Physical Science — The activity is concerned with the structure and properties of matter and is also concerned with chemical reactions.

      Life Science — The activity is concerned with the cell and also with matter, energy, and organization of living systems.

    Relevant New Jersey State Science Education Standards

      5.1 The activity involves conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results.
      5.5 The activity requires understanding of the basic characteristics of living organisms.
      5.6 The activity investigates the behavior of matter in biological systems.

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