Download 4-1 HOW CAN YOU TEST FOR BACTERIA IN FOOD

Microorganisms
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State Standard: H.3S.5 -- Explain how technological problems and
advances create a demand for new scientific knowledge and how new
knowledge enables the creation of new technologies
Score
10
Response
Exceeds
(excellent)
Meets
(proficient)
Nearly
Meets
Scoring Rubric
Explain how the relationship between scientific knowledge and new technologies is used by current
scientists to advance science and technology
Explain how technological problems and advances create a demand for new scientific knowledge and how
new knowledge enables the creation of new technologies
Recognizes that new scientific knowledge enables the creation of new technologies
4
Does Not
Meet
1
Incomplete
Assignment and its explanations are not accurate. Group did not demonstrate understanding or authentic
knowledge
Fails to complete
8
6
Score
HOW CAN YOU TEST FOR BACTERIA IN FOOD?
Bacteria are living things too small to be seen without a microscope. Bacteria are said to be
microscopic. Often a test can be done to show the presence of microscopic living things. The test can be
done with a chemical indicator.
As its name says, a chemical indicator is a chemical that “indicates” something. One type of chemical
indicator will tell you if carbon dioxide is present. The chemical turns from blue to yellow or green if carbon
dioxide is present.
Respiration in bacteria and other living things produced carbon dioxide. Thus, this chemical can tell
if bacteria or other living things are present in a sample being treated.
Bacteria are used to make many dairy products. The samples you will be testing in this exercise are
different dairy products.
OBJECTIVES:
In this exercise, you will:
a. Lean how to do a chemical test foe the presence of carbon dioxide.
b. Test diary products to determine of they contain bacteria.
KEYWORDS: Define the following keywords:
Control:
Microscopic:
Respiration:
Variable:
MATERIALS:
6 test tubes , wax paper, 6 cork stoppers, 2 droppers, Test tube rack , 3 wooden splints,150ml bromythymol,
blue solution, dairy products---Milk, buttermilk, yogurt, cottage cheese, sour milk
PROCEDURE:
1. Label 6 test tubes 1 through 6.
2. Fill each test tube with the blue chemical solution.
3. Use a clean dropper to add one drop of the following to each tube. (Do not let the dairy product go
down the sides of the test tubes)Figure 1 shows you how.
Tube 1-nothing
Tube 2- milk
Tube 3-buttermilk
4. Using a wooden splint, add an amount about the size of a
green pea of the following to each tube.
Tube 4-plain yogurt Tube 5-cottage cheese
Tube 6-sour cream
5. Stopper each tube with a crock. Record in Table 1 the
color of the tube contents. Leave the tubes undisturbed.
Do not shake.
6. Observe and record the color of tube contents at the
bottom of each tube, both at the end of the class period
and the next day.
Table 1. Test for Bacteria in Food.
Tubes
Contents
1
2
3
4
5
6
Nothing
Milk
Butter
Yogurt
Cheese
Cream
Color at
Start
Color at
class end
Colors 1
day later
Carbon
dioxide gas
present?
QUESTIONS:
1. Was there a color change on the contents of Tube 1 one day later?
What was the purpose of Tube 1?
What name is given to this part of the experiment?
2. In which tube was a color change detected one day later?
3.
What foods were added to these test tubes?
Do these foods contain bacteria?
What is your proof?
4. What is the variable in this experiment?
5. Why are Bacteria important to the dairy industry?
6. Are bacteria in dairy products helpful or harmful?
Bacteria
present?