Activity 1: Measuring antibacterial properties of honey

1. Using the paragraph on page one of the handout, introduce how bees gather their food from flowers during the spring, summer, and fall, but must protect this food for use during dearth periods.
2. Have students predict and write down which preservation methods they think bees might use.
3. Listen online to the audio clip “Why Honey Doesn’t Spoil.” Discuss if their predicted answers matched those in the audio clip. (Bees use dehydration by removing water from nectar. This could also be described as highly concentrating the sugars in honey. Students will not be introduced to it yet, but bees also keep out water by sealing honey in honeycomb cells with a wax capping and by adding an enzyme that produces hydrogen peroxide).
4. Review how to grow a colony of bacteria on agar in petri dishes (use slides 4-6 of the PowerPoint for visual support). Point out how antibiotic discs can be applied to a petri dish to inhibit bacterial growth (if the bacteria are susceptible to the antibiotic in the disc). Facilitate student discussion of how antibiotics might be tested in the lab for their efficacy against bacteria. (Measuring and comparing the zones of inhibition for different antibiotics is one way.)
5. Show students how to measure the zone of inhibition (slide 7 of PowerPoint). (Use a ruler; measure area with no bacterial growth including the disc.)
6. Divide students into pairs to complete "Part 1" of the worksheet. Students will measure zones of inhibition for each antibacterial disc and use their data to determine the relationship between concentration of honey and the size of the zone of inhibition.
7. Facilitate a whole class discussion of what students observed from the experiment. (The higher the honey concentration on the disc, the larger the zone of inhibition, and therefore the fewer bacteria were able to grow.)
8. Listen online to the audio clip “Honey: Food for Yeast or a Natural Preservative.”
9. Guide discussion on why bacteria doesn’t thrive in honey. (By the process of osmosis, the high concentration of sugar in honey forces the water out of any yeast or bacteria cells, drying them out and destroying them.)
10. Have students work in pairs again to predict if a concentrated sugar solution could be used as a more cost effective preservative. (Based on what they have observed and listened to so far, students will likely predict that sugar is a good substitute for honey as a preservative.) Have students provide evidence for their prediction.

Activity 2: Comparing sugar to honey

1. Ask students to read the information found on page three of their handout to familiarize themselves with the sugar experiment setup explained in "Part 2" of the worksheet.
2. Divide students into pairs to measure zones of inhibition for each antibacterial disc and use their data to determine the relationship between concentration of sugar and the size of the zone of inhibition. (There is no effect of the concentration of sugar on the growth of bacteria.)
3. Ask students to compare the effectiveness of honey to a concentrated solution of table sugar and provide evidence to support their choice. (Honey was an effective antibacterial, however, concentrated sugar was not effective at inhibiting bacterial growth.)
4. Discuss if students thought this would be the case. Why or why not? (Based on information presented so far, this should be surprising to students. Honey must be more than simply a source of concentrated sugar.)
5. Read and discuss as a class how nectar is ripened into honey from the student worksheet and have students predict if there is anything special about honey.
6. Have students discuss why honey and concentrated sugar might have had different effects on bacterial growth. Examine the honey ripening diagram. Have students note that hydrogen peroxide and acid are produced by the addition of an enzyme, glucose oxidase.
   • What do we use hydrogen peroxide for? (Cleaning bacteria from wounds)
   • How have we used acid in food preservation? (Vinegar is used to pickle foods to prevent bacterial growth.)
7. Have students predict which components found in honey may have inhibited bacterial growth on their worksheet.

Activity 3: Can honey inhibit the growth of bacteria in food products?

1. Lead a discussion to review what has been learned about honey and how we might use what we have learned about the antibacterial properties of honey to benefit society (slide 8 of the PPT). (Answers may vary. Honey could be used as a wound dressing in hospitals or as a food preservative in areas without access to other means of food preservation such as refrigeration.)
2. Have students read part 3 of the student worksheet about an experiment testing honey as a preservative for milk. Discuss the following (slide 9 of PowerPoint):
   • What is turbidity? (Turbidity is a measure of how clear a liquid is.)
   • How does measuring turbidity help us to determine bacteria growth in milk? (Turbidity is an indicator of bacterial presence; the cloudier a liquid is, the higher the turbidity, the more bacterial is assumed to be present.)
3. Instruct students to calculate the percent difference in turbidity of milk with honey compared to milk without honey as a sign of inhibition of bacterial growth. Use this data as evidence when answering the two follow-up questions.
4. Facilitate class discussion about the feasibility of using honey as an effective preservative for milk. Have students make a list of benefits and challenges. (Potential benefits include availability of an inexpensive, protein-rich food source in areas with no refrigeration, better bone and teeth health, access to calories in areas dealing with malnutrition; potential challenges include cost of adding honey, change in flavor of milk, consumer acceptance of this new method for preservation.)
5. Using the class discussion as a starting point, have students complete the final question on the worksheet on their own. Encourage students to think critically about this issue.