How Clean is the Water in Your Town?

Bacteria are everywhere in our environment, especially in our water. Because they are so small, it is difficult for us to see them with our naked eyes. In this investigation, students will be able see bacteria by streaking samples on plates and incubating them.

II. Performance or learner outcomes

1. Explain the quality of our water by seeing how much bacteria is in water.

2. Demonstrate how to streak agar plates in order to find distinct colonies of bacteria.

III. Resources, materials and supplies needed

For each student:

Phenol Red

Sodium Hydroxide

Plastic Cups

Pipettes

Eye Droppers

Gloves

Goggles

For each group:

5 LB plates

Cotton swabs or inoculating loops

Water samples

IV. Safety Considerations

Sodium hydroxide can be caustic, students should be supervised when use these chemicals. If any spill is detected, clean with soap and water and wipe with paper towels and notify teacher as soon as possible. Soap will neutralize the dilute sodium hydroxide solution. Phenolphthalein is an indicator that can also be dangerous when swallowed. Make sure there is no spill.

V. Supplementary materials, handouts

None

Five-E Organization

Teacher Does Probing Questions Student Does

Engage: Learning Experience(s) Time: 10 minutes	Critical questions that will establish prior knowledge and create a need to know	Expected Student Responses/Misconceptions
Teacher will have clear cups with water on the resource desk. He/she will also have another cup with dilute sodium hydroxide solution that is identical in character to the other cups. Each student will be informed to take a cup and a plastic transfer pipette. STUDENTS MUST WEAR GLOVES AND GOOGLES	While working with chemical, it is important to be really careful.
Students will be instructed to carefully walk around with their cup in their hand and transfer some “water” to another student’s cup. The class will do this for about 3 minutes; they will be informed that one cup contains a chemical that’s harmful if swallowed or spilled on the skin. Afterward teacher will stop the class and tell them to go back to their seats.	One of the cups has sodium hydroxide; does anyone know what sodium hydroxide is? Is it basic or acidic? Is there any caution we need to take before using sodium hydroxide? What does this activity tell you?	Sodium hydroxide is a chemical made from Na and O and H. The formula is NaOH (aq). It is basic and caustic can causes irritation upon skin contact. We should be careful of spill. It tells us that we are in contact with people everyday and we also exchange germs.
Teacher will say: “what if I tell you that one of the cups, the cup with NaOH, represents a model of how viruses can spread and cause diseases like the following.”	How does a bacterium transmit?	As you can see, bacteria can be transmitted through fluid exchange.

Explore:

Learning Experience(s)

Time: 15 minutes

Critical questions that will allow you to decide whether students understand or are able to carry out the assigned task (formative)

Expected Student

Responses/Misconceptions

Teacher will then asks students form groups of three. Each group should dispose of their cups in the trash. Any fluid should go into the sink. He then asks a material manager to get 5 LB plates from the material desk and inoculating loops or cotton swabs. He will also get five different samples from the front of the class.

Students will actively take materials and work on them.

Teacher tells students to dip the cotton swab into the sample and apply a thin layer on the LB plate. Each group should have five samples and streak 5 plates. Teacher will educate students on how to streak plates with sterile techniques to obtain good result. The teacher will tell students to put the plates into a provided incubator at 37 degrees C. Two or three days later, the teacher will ask students to count the colonies on their plates.

1. What do you think are the white dots on your plates?

2. Why do you think pond water gets more colonies than home water?

1. Colonies.

2. Because the pond water is dirtier.

Explain:

Learning Experience(s)

Time: 10 minutes

Critical questions that will allow you to help students clarify their understanding and introduce information related to concepts to be learned

Expected Student

Responses/Misconceptions

Teacher will explain the reason why sterile techniques are useful in labs. He will also tell students some incidents where people can infect other people in daily activities.

Extend / Elaborate:

Learning Experience(s)

Time: 5 minutes

Critical questions that will allow you to decide whether students can extend conceptual connections in new situations

Expected Student

Responses/Misconceptions

Evaluate:

Lesson Objective(s)

Learned (WRAP –UP at end) -> Summarize

Time: 5 minutes

Critical questions that will allow you to decide whether students understood main lesson objectives

Expected Student

Responses/Misconceptions

Teacher will evaluate students’ work as he circulates around the room. He will ask students why they are doing what they are doing.

Name: ________________

Date: __________________

Teacher: ________________

Bacteria in Water

Bacteria in Different Water Source
	Water Sample	Number of Colonies
Plate 1	Pond Water
Plate 2	Water from Faucet
Plate 3	Water from Mouth
Plate 4	Water from River
Plate 5	Water from Pool

What water source has the most colonies?

What does the number of bacterial colonies tell us about the quality of the water source?

Does the water from your mouth have any bacteria? If yes, why do you think your saliva have bacteria?

Why is it important to practice sterile techniques when you streak your plates?

A very small percent of bacteria are harmful to human, while the rest are harmless or even beneficial. What do you think is a benefit of these harmless bacteria in our body?