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Grade 3 Science: Hidden Germs

New Brunswick curriculum outcomes: Science 200-1, 202-7,203-1

Classrooms are contaminated Petri dishes ready to infect any person brave enough to enter. We begin each year giving the hygiene talk that will be repeated ad nauseam until the students leave the classroom.

“Wash your hands, cover your mouth when you cough, elephant trunks, stop picking your nose, and please don’t lick that!”

Do any of these sound familiar? Oftentimes our students will tune us out, especially at the height of cold and flu season, before our words have sunk in. That is what makes this lab so engaging. Why tell kids about germs when you can show them? 

Supply wise, this lab requires very little: 8-10 plastic Ziploc bags, a few potatoes cut into pieces, plastic gloves and a sharpie marker.

The classroom discussion starts first with listing the dirtiest spots in the classroom: let your students be creative and silly if they like. The dirtiest spots are not always the ones we first pick.

Next narrow your list down to 8-10 locations in the classroom, (outside in the hallway works well too). Then have the students vote for each location, creating a bar graph to show the results. 

Students observe the changes to potatoes after coming into contact with germs. | Grade 3 Science: Hidden Germs | FallsBrookCentre.ca

I try to break down the next tasks to get all the students involved:

  • First, ask a student to write the name of a location on the Ziploc bag, while another student puts on a glove and grabs a potato piece.
  • Next, they will rub the potato piece in the location, making sure to cover each side of the potato.
  • Once they have finished they will put the potato in the Ziploc bag and seal it up.
  • Finally, hang the bags with thumbtacks on a bulletin board, making sure not to puncture the bag itself.  

Be sure to have the students observe the potatoes every few days, noting changes in colour or texture. Magnifying glasses are a fun addition to help students examine the mould growing on the potatoes.

One week later, bring out the bags and examine them together as a class. If you need an additional week, it will only add to the growth of mould.

Create a chart on the board with each potato listed with its location. Next, describe each sample using colour, texture and size. Once the data is collected have the students decide which spot in your classroom is the dirtiest.

A writing prompt is another great way to expand this lesson: The dirtiest place in our classroom is __________ because _____________. 

Students observe the changes to potatoes after coming into contact with germs. | Grade 3 Science: Hidden Germs | FallsBrookCentre.ca

In an earlier lab, we discovered that under the teacher’s desk was full of the most germs. Why? She was often still working when the janitor arrived in the evening, so while the rest of the classroom was cleaned, under her desk rarely was.

We had another teacher give up on floor mats and switch to another type of seating after seeing the results of this experiment.

This lesson helps the students become more aware of the hidden germs around them and may keep you all a little healthier this year.

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