Life Science & Biology Projects

Question: What is the Bacterial Content of Milk?

Summary: For this experiment we will use Methylene blue to study the presence of aerobic bacteria in milk. Methylene blue is a blue dye that reacts to the lack of dissolved oxygen by turning translucent if there is no dissolved oxygen in a sample. Methylene blue is a good indicator for the presence of aerobic bacteria in a sample because aerobic bacteria use up oxygen.

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Materials Needed:

(Any of The Materials Highlighted in Blue are Clickable Links for Purchasing)

Access to a stove and big pot for sterilizing equipment

5 Test Tubes

5 Test Tube Stoppers

Test tube rack

Paper towels

Calibrated pipette

50 ml graduated beaker

Pot and stove to use as a water bath

Refrigerated pasteurized milk

 Thermometer

 Kitchen tongs

 Methylene blue

Project Procedure:

1. Before starting, make sure you have sufficient temperature control with your stove. Fill a pot half-full with tepid water. Put it on the stove and raise the temperature to 98 degrees. Make sure you can keep it at this temperature for several hours.

2. Wash your hands. Cover the surfaces adjacent to your kitchen stove with paper towels. Place the test tube racks close to the stove on the paper towels.

3. Fill the pot with water and bring to a boil. Uncap your test tubes. Using your kitchen tongs, carefully drop your graduated beaker, test tubes and their caps in boiling water. Boil for one minute.

4. Remove your test tubes and graduated beaker from the water. Place the test tubes in the test tube rack.

5. Measure 9 ml of milk in the graduated beaker. Measure 9 ml milk into each test tube.

6. Using your measuring pipette, measure 1 ml methylene blue. Place the methylene blue in one of the test tubes

7. Using the kitchen tongs remove the test tube caps from the pot, and cap the test tubes. The test tube with the methylene blue is your test sample. The test tube without the methylene blue is your control. Label each test tube.

8. Pick up your test tube and gently shake it so that the methylene blue is dissolved.

9. Place each test tube in the water bath.

10. Examine the test tubes every 15 minutes for two hours and every hour afterwards. Record your observations. If it takes more than 8 hours for the milk to turn white again, the quality of the milk is excellent. If it takes 5.5 to 8 hours for the milk to turn white, then there are less than 0.5 million organisms/ml of milk. If it takes 2 to 5.5 hours for the milk to regain color, then there are 0.5 to 4 million organisms/ml of milk. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. If it takes less than 20 minutes, then there are over 20 million organisms/ml.

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Question: Are There Protozoa In My Pond—Or Fish Tank?

Summary: Protozoa are one-celled creatures that live in water or watery tissues. In a culture medium, they will be visible in about 24 hours, with the most variety of protozoa visible after about 3 days.

Materials Needed:

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Pond Water or Water from a Fish Tank

1 Egg

Pipet            

Microscope, Compound, up to 400x  

Microscope slides and cover slips    

Protozoa Calming Solution (Methyl Cellulose)            

Project Procedure:

1. Hard boil an egg and grind a pinch (1/4 gram) of the yolk in a bowl with a small amount of water to form a paste. Add the paste to 1 liter of boiled pond or fish tank water and let stand for two days.
2. Use the pipet to place one or two drops of the water on a microscope slide. Cover with the cover slips.
3. Place on a microscope stand and examine the slide with your microscope starting at 40x. Most protozoa have little color and are difficult to see in bright light, so turn your microscope diaphragm to the lowest light setting. It will take patience to adjust the lighting and focus the microscope.
4. Initially you will see very tiny dots moving around on the slide. Some move very rapidly, others more slowly. You can slow them down for observation by adding a drop of methyl cellulose.
5. Once you find an area of protozoa activity on the slide, turn the magnification up to 100x or even 400x to see them better.
6. If no animals are visible, try again each following day. Many conditions, such as water hardness, temperature, and water acidity, can affect the growth and development rate of these organisms. Each succeeding day you will typically find more and different varieties of protozoa in your culture. Initially, smaller species will be prevalent. As the days pass larger species will appear. You will also see different algae forms appear. Certain species will be more common from the top of the cup and others from near the bottom. Gradually, food and water conditions will change, affecting the growth and development rates of the different protozoa.