Summary

In this lab, students will practice making and recording observations, analyzing data, and identifying chemical change. They will transfer dirt, germs, and bacteria from their hands onto a piece of white bread and observe the changes that occur during the following days. Students will analyze the results, make comparisons between clean and dirty samples of bread and learn about the importance of hand-cleaning.

Grade Level

Elementary and Middle School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• K-2-ETS1-3: Analyze data from tests of two objects designed to solve the same problem to compare the strengths and weaknesses of how each performs.
• 2-PS1-2: Analyze data obtained from testing different materials to determine which materials have the properties that are best suited for an intended purpose.
• 5-PS1-2: Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.
• 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

Objectives

By the end of this lab, students should be able to

• Make and record observations.
• Identify chemical changes.
• Analyze and interpret data.

Chemistry Topics

This lab supports students’ understanding of

• Chemical Reactions
• Chemical Change
• Observations

Time

Teacher Preparation: 20 minutes

Activity: 7-21 days (*See Teacher Notes)

Materials

• 4 Slices of organic or fresh white bread
• 4 Quart-sized Ziploc bags
• 1 roll of paper towel
• Spray bottle with water
• 1 bottle of hand sanitizer
• 1 bottle of liquid hand soap
• Disposable gloves
• Digital scientific scale
• Crayons/markers
• Pens/pencils
• Masking tape
• Timer

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Do not consume lab solutions, even if they’re otherwise edible products.
• Food in the lab should be considered a chemical not for consumption.

Teacher Notes

• It’s Alive! is designed to be used across multiple grade spans at any time of year, and can be interesting, enlightening, and gross all at the same time! Students will practice making and recording observations, analyzing data, and identifying reactions, while determining the “best” solution for a specific problem—cleaning their hands.

• *Note: The time frame for mold growth can vary greatly based on conditions; 7-21 days for the activity does not reflect total class time, but is an approximation for satisfactory growth and ample observation time.
• Mold can begin to grow within 48 hours and generally requires warm or humid conditions. Growth accelerates in dark, moist places.
• Background information:
  • The four major types of germs are bacteria, viruses, fungi, and protozoa.They can invade plants, animals, and people, sometimes making them sick. Germs, like any other living things, need food to live and grow.
  • All bacteria require energy (such as sugars, starch, protein, fats and other compounds that provide nutrients) to live and grow. Some bacteria require oxygen to grow (aerobes) while others can grow only in the absence of oxygen (anaerobes).
  • Bacteria spreads through direct contact: individuals touching infected bodily fluid; sharing beverages containing infectious bacteria; being bitten by an insect or other animal that is carrying the bacteria; or inhaling bacterial particles, often emitted by sneezing or coughing.
  • Not all bacteria are bad!
  • Human viruses don't grow on food, but food does serve as a transportation device to get viruses from one host to another. Once contaminated food is eaten, the virus can multiply in living cells and cause foodborne illness in humans.
  • Foods that are moldy may simultaneously be growing invisible bacteria. Some molds may cause allergic reactions or respiratory problems, but very few, with the right conditions, will produce mycotoxins (poisonous substances that cause illness).
  • Additional background information from the National Academies Press:
    • Chemical Reactions
    • Analyzing and Interpreting Data
    • Making and Recording Observations

• Certain chemical changes will happen in this activity. Mold, a living organism, is consuming the starch, sugar, water and minerals in the bread, and metabolizing it for energy and to create the structures of the mold. Certain other chemical reactions are changing the bread even without the action of the mold. These changes are irreversible, smelly gases will be released, and a small amount of heat will be produced.
  
  Classroom Procedures:

1. Introduce students to the concept of “germs” by viewing The Sneeze as a class. (Alternative video examples: Germs, Journey of a Germ, or Germ Wars. All videos will contribute to the activity however their selection may be based on grade level.)
2. Allow students to engage in talk moves by discussing thoughts, questions, and observations they may have about the video(s) in small groups before discussing with the entire class.
3. Divide the class into two groups (Group A= hand sanitizer; Group B=hand soap). Clearly label 4 Ziploc bags using masking tape and a marker, 2 labeled “dirty” and 2 labeled “clean”.
4. Wash or sanitize your hands and put on a pair of plastic gloves. Beginning with Group A, instruct students to pass around 1 slice of white bread. Be sure that every group member touches it on both sides and passes it without dropping or laying it on a table, counter, etc. The bread should be passed hand to hand only and the last member of the group should drop it into the bag labeled “dirty”. Spray the bread twice with water and seal the bag completely. Set it aside.
5. Next, get the bottle of sanitizer and give each member of Group A a single pump of sanitizer in their hands. Instruct them to thoroughly rub it around their hands until the liquid is absorbed (about 10 seconds). Instruct students not to touch anything until after they have handled the second slice of bread. Give them a second slice of white bread and instruct them to pass it in the same manner, only this time dropping it into the bag labeled “clean”. Spray the bread twice with water and seal the bag completely. Set it aside.
6. Repeat steps 4 and 5 with Group B, switching out the hand sanitizer for 1 pump of liquid hand soap in step 5 and allowing those group members to wash their hands at the sink for 20 seconds, then dry them with paper towels prior to handling the slice of bread.
7. Distribute the observation logs and allow students to complete Day 1. Choose a volunteer to weigh each of the four samples using a digital scale and instruct students to record their sample weights in their logs.
8. Decide where in the classroom you would like to display/store the bags and place them there. **Mold grows more rapidly in dark places Students will periodically observe what “grows” on their samples and compare the differences between the clean and dirty bags, while completing their observation logs. You may want to determine how often students will investigate the samples based on how quickly reactions become visible.
9. Upon the conclusion of the activity, students will be able to compare all samples from both groups and make a general determination of which substance was better suited for cleaning hands.

Helpful Tips:

• This is a wonderful activity to complete during flu season so students will develop a greater appreciation for hand washing and using hand sanitizer.
• The number of groups per class may vary but remember that the goal is for the bread to become as contaminated as possible, so the more hands the better!
• Mold grows best, and more rapidly in moist, dark places, so you may want to store the bags in a cabinet or drawer. However, it may also be quite impactful for the bags to be openly and prominently displayed in the classroom, where students can make general observations daily and curiosity will remain peaked. It may be beneficial to display them in the classroom during the school day and store them in a dark cabinet/drawer overnight.
• “Talk moves” is a great strategy to use to increase scientific discourse among your students. Until students have the process mastered, you may want have them complete a graphic organizer or take notes to share based on the conservation they had with their group.
• Divide Groups A and B into smaller groups (3-4 students) for observing, comparing, and discussing samples throughout the investigation. Creating an observation schedule may also be helpful, depending on the total number of groups and samples available.
• For more advanced students or higher grade levels, consider adding a research component to the activity: assign a specific topic, i.e. one of the four major types of germs; common viruses and how they spread; the effectiveness of sanitizer or liquid hand soap; etc. and have students present their findings to class.
• For lower grades/students, consider completing observation logs and discussions whole-group.
• By completing this activity, students should be able to better understand the necessity of keeping clean hands and how harmful dirty ones can be.
• An Answer Key is available for teacher download.
• Photographs of expected results have been included below: