Type of Entry:
Type of Activity:
- inquiry lab
- group/cooperative learning
- Advanced/ AP Biology
- Integrated science - levels 3 or 4
In this open-ended multicultural lab activity, students investigate the effectiveness of herbal remedies. Students prepare extracts from plants that are used in a variety of herbal medicines; they test the antibiotic effects of the herbs on gram positive and gram negative bacteria, and look for antifungal effects using common molds. The effectiveness of the herbal extracts is compared with traditional antibiotic and antifungal preparations. Each student group is in charge of their experimental design; variables include types of herbs chosen, methods of preparing extracts, microbes tested, and type of exposure of microorganisms to the extract (applied to agar surface, on sensitivity disks, in agar itself, heated, cooled, etc.).
The activity presented here helps students to become critical thinkers about substances that are called medicines and it guides them into an inquiry process of carrying out their own investigations of the attributes of some common herbal remedies.
Our everyday world is full of reminders that medicines are part of society: TV commercials, newspaper and magazine advertisements surround us with suggestions about what medicines are best for us. The unit begins with an introductory brainstorming session that involves a discussion of the term "medicine". This is followed by students examining a collection of materials I have assembled that include some traditional samples of substances from Western medicine, Chinese medicine, Native American, Ayurvedic, and homeopathic therapies. Students are asked to identify those items that fit their paradigm of "medicine". The difficulties in agreeing on the collective idea of medicine soon surface. Students are broken into research groups to find out more about the systems of medicine that are represented; an alternate activity at this point is to ask student to interview various people to get their definition of medicine (pharmacist, customer buying over-the-counter medicine, worker in a health food store, school nurse, lawyer, parents, grandparents, etc.). Research groups sometimes share their findings with the class in a formal way or more creatively in scripting medicine "commercials" that highlight the active principles of the system of medicine investigated.
This introduction is followed by the following activity. Dandelion, garlic, ginger, goldenseal, and ginseng are easy to obtain and study in the laboratory as well. Ginseng is the only costly herb and its effects are much harder to evaluate (given the description of its effects) so you may wish to omit this one. Students can make separate extracts from leaves, flowers, and roots of dandelions, as well as extracts from ground ginger and garlic and apply these to petri dishes that are inoculated with various bacteria and molds. You might also ask students to add these extracts to the agar itself before pouring the plates.
Studies can be done with paramecium to see what effect dilute solutions of extracts have on these protists. Another possibility is the use of nematodes and planaria since some of the herbs are used to combat worm infections. Dilute solutions of extracts should be used on readily obtainable worm cultures.
TEACHERS should be able to prepare materials for this lab in about an hour once the agar, bacteria and molds, and various herbs are obtained. All students would be required to do this lab.
STUDENTS can perform this activity in a single class period and then spend about 30 minutes the following day recording the results.
For thousands of years, man has sought healing powers from the natural world. In this lab exercise and research activity, you will examine some herbs that are used as in western and Chinese medicines and investigate the claims that some of them are effective in killing bacteria and fungi.
The beginning of traditional Chinese medicine can be traced back more than 5,000 years. The Yellow Emperor's Canon of Medicine, the earliest and most comprehensive medical classic, was compiled around the third century B.C. Early in the third century A.D., Zhang Zhongjing wrote the Treatise on the Febrile (those with fever) Diseases, and in the Ming Dynasty medical scientist Li Shizhen completed Compendium materia Medica. The contributions of these two men did much for the development of medicine and the systematization of medical theory. In diagnoses, traditional Chinese physicians apply the four methods of observation: auscultation (listening to chest sounds), smelling, interrogation, and pulse feeling. Unique treatments and ways to keep one strong are embodied in acupuncture, massage, qigong, and bone-setting. With the knowledge of the function, effect and usage of over 3,000 plants, animals, and minerals, Chinese pharmacy provides not only decoction (boiling a substance in water to extract its useful components) but also ready-prepared medicine in the form of pills, powder, pellets and electuaries (medicine composed of powders incorporated with some conserve, honey or syrup).
The following is a list of herbs that have been used as medicines. After reading the descriptions of biological effects attributed to the herbs, choose one to use for your investigation. (Please note that the stated biological effects of some of these herbs are not uniformly accepted by the scientific community.)
Aloe: used as an antiseptic, taken internally as laxative and as a treatment for liver inflammation and intestinal parasites; aloe gel is best known for its use in healing burns, skin rashes, insect bites, acne, herpes and wounds. The powder of aloe is a very strong purgative and it stimulates strong blood circulation.
Dandelion: leaves and roots are used for infections, inflammations, boils, abscesses, swellings, red, swollen and painful eyes, fever, and other heat-related conditions. Externally, its juice is applied to snake bites. It has a diuretic effect - cleansing the kidneys and lowering blood pressure; it reduces cysts in the breasts, stimulates the production of breast milk, and is used in treating tumors and clots in the lungs.
Garlic: cleans arteries, aids digestion, and eases skin problems; a powerful rejunvenative herb, strengthening along with detoxifying; antibiotic for staphylococcus and streptococcus resistant to standard antibiotic drugs; good for treating roundworms, tuberculosis, ringworm.
Ginger: although this root is used as a spice in cooking, it is used in many Chinese multi-herb formulas because its warming and stimulating energy aids stomach upset, nausea, motion sickness, poor digestion, gas and excessive mucus accumulation. External application of juice relieves muscle pain; ginger oil on scalp is used for dandruff and placed in the ear treats earaches. Ginger tea or tincture can be used as a gargle for sore throats.
Ginkgo: these trees are native to China but now grow around the world; fruits and seeds are believed to benefit the circulation and have anti-asthma properties; the ginkgo nut expels mucus from the lungs, stops wheezing and cough, regulates urination, adds heat to the body, increases sexual energy and stops bedwetting. The leaf is used to improve peripheral blood circulation, possibly improving memory, mental efficiency, concentration and decreases headaches, vertigo, ringing in the ears. It is a powerful anti-oxidant, and has antifungal and antibacterial properties.
Ginseng: this root comes from a perennial herb that grows in Asia and North America. There are many types but they all strengthen the body and its energy. Anemia, diabetes, insomnia, gastritis, sexual impotence, and other disorders are treated with it. Ginseng promotes weight and tissue growth in the body, increases resistance to disease, wisdom and longevity.
Goldenseal: this root is used an anti-inflammatory herb with antibiotic and antiseptic properties; it cleanses the mucous membranes and lymph glands throughout the body. It kills yeast and bacteria in the gastrointestinal tract.
Joint fir (Ma huang): this small shrub is also known as ephedra; it is useful for asthma and bronchitis, because it widens the airways; this decongestant is considered to be the world's oldest medicine. The laboratory analog of ephedra is pseudoephedrine, widely used in cold formulas today; it is a strong stimulant with an action like adrenaline; it also has a diuretic effect.
- Collections of common herbs: ginger, garlic, ginseng, aloe, dandelion, goldenseal
- Sterile nutrient agar in petri dishes; other nutrient agar to which herbs may be added
- Gram + (Staph epidermis, M. luteus, B.cereus) and gram - bacteria (E coli, Ps. fluorescens )
- Molds (collected from old refrigerator foods) or order Rhizopus, Sordaria
- Alcohol lamps or Bunsen burner
- Inoculating loops
- Petri dishes
- Mortars and pestles for grinding herbs
- Distilled water
- Filter paper
Note: Use accepted safety guidelines whenever using and disposing of potentially biohazardous products.
1. After reading the description of the herbs and observing the herbal medicines on display in the lab, obtain a sample of a common herb (garlic, dandelion, ginger, goldenseal, ginseng or aloe) , some distilled water, and a mortar and pestle.
2. Grind a sample of the herb (in the case of dandelion, make separate mixtures of leaves, flowers, and roots) and add enough water so an extract of this herb can be drawn into a medicine dropper.
3. Soak several filter paper disks in your herbal extract (or add varying amounts of the herbal extract to melted agar which has not already been poured into petri dishes.)
4. Inoculate the sterile agar with Staph epidermis or other bacteria (using either a streak technique or a spread from a dilution), and/or a selected type of mold and then add the filter paper disks to the inoculated plate. Cover, label and incubate at 37oC (if possible) until the next class period.
5. Set up a control for this experiment, applying only distilled water to the filter paper disks in each petri dish; the alternative method "control" is to inoculate an agar plate without the herbal extract.
6. Incubate overnight at 37oC. Bacterial plates should be turned upside down.
7. After incubation, look at the microbial growth on the plates you have prepared. Look for any indication that the herbal extract inhibits growth on these plates and compare your results with growth on the control plate.
Method of Assessment/Evaluation
1. Make a sketch of the results you obtained in your experimental and control dish.
2. Prepare a data table summarizing the class results for this experiment.
3. Present the finding from your lab tests in a well organized paragraph.
4. Observe the samples of herbal medicines on display in the lab. How do they differ from your idea of a traditional medicine? List as many observations as possible about these herbs.
5. What differences do you notice in the plants that are used as herbal medicines?
6. Which of the herbs are more likely to inhibit the growth of bacteria? of molds?
7. What further tests should be done before you draw any conclusions from your lab results?
- collect and/or research other herbal medicines; information about these could be put on a student-developed HyperCard stack. The chemistry (pharmacognosy) of these herbs can be researched using Kee Chang Huang's Pharmacology of Chinese Herbs and this information added to the data base.
- invite an herbalist to speak to the class.
- watch the PBS video "Healing and the Mind" for a first-hand glimpse of Chinese herbal medicine vs. western medicine in mainland China today.
- watch Nova video on "Hidden Power of Plants" to extend discussion of herbal medicines to the rain forest.
- participate in a debate on the merits of western medicines vs. herbal medicines.
- do further research on ethnobotanicals; a great way for students to exchange regional and cultural information using the Internet.
- investigate the scientific research that has been done on such herbs as ginseng.