Mouldy bread: A science experiment
I just bought a loaf of fresh-baked bread (without preservatives!) from the bakery. I placed a slice of bread in a ziploc bag, and left it out on the kitchen counter. I placed a second slice of bread in a separate ziploc bag and placed it in the refrigerator. I placed a third slice of bread in a different ziploc bag and placed it in the freezer. I left the slices of bread in each of the three places for 2 weeks. I observed the slices of bread for mould growth every other day.
Why do you think I placed the bread in ziploc bags and made sure they were sealed?

Explanation

### Step-by-Step Solution:

1. **Purpose of Using Ziploc Bags**: The primary reason for placing the slices of bread in Ziploc bags is to create a controlled environment for the bread samples. This helps to minimize external contamination from airborne microorganisms, dust, and other potential sources of mold.

2. **Sealing the Bags**: By sealing the Ziploc bags, the experimenter ensures that the bread is protected from exposure to the surrounding environment. This is crucial because it allows for a more accurate observation of mold growth that is solely due to the conditions in which each slice is kept (room temperature, refrigeration, and freezing).

3. **Controlled Variables**: The use of sealed bags helps in controlling variables in the experiment. It allows the experimenter to isolate the effects of temperature on mold growth without interference from other environmental factors.

...