Science and Our Food Supply: Investigating Food Safety from Farm to Table

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MIDDLE LEVEL

CROSSED UP! 

2

LAB:

 DEVELOP, HYPOTHESIZE, AND CONDUCT LAB    

1. 

Ask each student to label his/her storage bags by the type 

of item (e.g., sponge, can opener, etc.). Students’ names 

should not be put on the bags.  

2. 

Have each team develop a hypothesis and design a lab to 

test the hypothesis. 

3. 

Pose these questions to guide students through their labs: 

• 

Which type of kitchen items might have the most/least 

bacteria? Why? 

• 

How can you find out which items have the most/

least bacteria? (Swab the items and inoculate the Petri 

dishes.) 

• 

What’s a good way to get a sample of the bacteria in 

these items? (Swab the item directly, or add water to 

the bags and sample the water.) 

• 

What kind of water would be best to use? (Sterile or 

distilled water) 

• 

How can you transfer bacteria from the kitchen item to 

the water? (Squeeze/massage the item in the bag.) 

• 

What does the water look like after you squeeze/ 

massage the item? (The water in some bags will  

appear very dirty. Water in other bags will appear 

clean.) 

• 

Is the appearance of the water an indication that 

bacteria are present? (Not necessarily.) 

• 

How can you be sure you’re not introducing new 

bacteria to the test samples? (Use sterile dishes and 

swabs. Use a control bag with distilled or sterile water.)