Bacteria, why do they make me sick?/Science experiments
SCIENCE
EXPERIMENTS
Let's get started!
Learn by knowing and experimenting in the microworld of
bacteria. Helped by an adult, perform these activities.
Activity Nº1
“Growing microorganisms in Petri dishes”
Materials:
• 1 envelope of plain unflavored gelatin
• ½ liter of hot boiled water (2 ½ cups or 500 mL)
• 1 beef bouillon cube
• A 3 cups or 600 mL size bowl
• 2 cups
• Plastic or glass Petri dishes (You can also use short plastic
boxes with lids)
• 10 cm ruler
Dissolve the beef bouillon cube in 1/4 cup of water (50 mL). At
the same time, dissolve the envelope of plain unflavored gelatin in 3/4 cup of water (150 mL). Stir both mixtures, dissolve
and add 1 cup of water (200 mL).
Pour the resulting medium into the Petri dishes (or short plastic boxes with lids) until reaching 0.5 cm height (use the ruler to measure). Cover the Petri dishes and allow them to harden stored in a refrigerator. The content of the Petri dishes will be used in activities 2, 3, 4 and 5.
With the final mixture of this activity, you should be able to prepare around 20 Petri dishes of 90 mm in diameter.
Activity Nº2
“Growing environmental de microorganisms”
Materials:
• Cotton swabs
• 2 Petri dishes
• Permanent marker
Grab a cotton swab and swipe it over the surface of any object
around you, such as a table, chair, toilet, cell phone, etc. This
process is called sample collection or sampling.
Then, apply the sample to a petri dish from activity Nº1, rubbing the swab in a zigzag pattern. This process is called inoculate or plate.
Then, place the lid on the Petri dish and label it over the external side of the dish, writing down the place where the sample was collected, the name of the person collecting the sample and date. Do not label the lid. This process is called labeling. Repeat the steps of sampling, plate, and label for each place you want to analyze.
The incubation process consists in placing the inoculated plates in a place where bacteria can grow. Leave the plates upside down at room temperature for 48 hours and in a place with no direct light. Then, analyze the colonies present in the agar and compare color, texture, form, etc.
After two days, you can store the plates in a refrigerator (4 a 6ºC) for a couple of days.
Activity Nº3
“Growing microorganisms that live in our body”
Materials:
• Cotton swabs
• 2 Petri dishes
• Permanent marker
Using a swab, take a sample from inside the nose of a classmate. Plate the sample in a Petri dish following the instruction
in activity Nº2.
Do not forget to label the Petri dish! At the same time, use another swab to take a sample from inside the mouth (tongue or cheek) of another classmate and repeat the procedure.
Incubate the labeled plates in a warm place, with the agar facing upwards and with no direct light during 48 hours. Then, observe the microorganisms growing in each of the plates. Analyze the colonies comparing color, texture, form, etc. After two days, you can store the plates in a refrigerator (4 a 6ºC) for a couple of days.
Activity Nº4
“Optimal culture media for microorganisms”
Materials:
• Three 17 oz clean plastic bottles
• 3 cups of warm boiled water
• 1 beef bouillon cube
• Bowl to dissolve the bouillon cube
• 1 spoon (15 mL)
• Vinegar
• Salt
• Permanent marker
Dissolve the beef bouillon cube in 3 cups of water. Distribute
the content in the three bottles (1 cup per bottle). In the first
bottle, add 5 tablespoons of salt. In the second one, add 5
spoons of vinegar. And in the third one, do not add anything.
The third one will be the control bottle. Label each bottle to
easily distinguish them and place them in a warm place. Incubate for five days. After the incubation period, analyze the
bottles and compare their turbidity or lack of transparency.
Higher turbidity levels indicate greater growth of microorganisms.
Activity Nº5
“Microorganisms respiration”
Materials:
• One 17 oz bottle, ideally a plastic one
• 1 balloon
• 1 envelope of bread yeast (Saccharomyces cerevisiae)
• 2 tablespoons of sugar
• Warm water
• 1 pitcher (or similar)
• 1 spoon (15 mL)
• Tape
In the pitcher, pour 1 ½ cup of warm water and add the yeast
(1 envelope). Mix everything together. Then, add 2 tablespoons
of sugar. Stir until having a homogeneous mixture and pour
the content into the bottle.
At the same time, blow up the balloon to make it more elastic. Then, deflate it and put it in the mouth of the bottle. Fix it with tape. Finally, place the bottle with the balloon on a flat surface.
Incubate during some hours and observe and register the processes that happen with the balloon and the yeast dissolved inside the bottle.