The Arizona STEM Acceleration Project

Water Analysis for Microorganisms

Water Analysis for Microorganisms

An 11th and 12th Grade STEM Lesson

Miranda Thornton

April 2023

Notes for Teachers

• Context: This lesson takes place in a classroom for one 55-minute period to perform the plating of the water sources and a block day to analyze the results and come up with a plan for sterilization, run plan and maybe another class period to analyze those results and write up lab.

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• Students will work in their lab groups of 3-4 students.

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List of Materials:

• Petri dishes( 2 per group)
• Water sources: pond water, distilled water, tap water, and drinking water
• P100 pipette, and tips
• Sterile cotton swab
• Sharpie to label petri dish
• Incubator

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AZ Standards

Life Science

Essential HS.L2U3.18

Obtain, evaluate, and communicate about the positive and negative ethical, social, economic, and political implications of human activity on the biodiversity of an ecosystem.

Plus HS+B.L4U1.2

Engage in argument from evidence that changes in environmental conditions or human interventions may change species diversity in an ecosystem.

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Math

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QR.SPR.2: Analyze statistical information and identify limitations, strengths, or lack of information in studies including data collection methods (e.g. sampling, experimental, observational) and possible sources of bias. Identify errors or misuses of statistics to justify particular conclusions. Encompasses P.S-IC.B.3

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QR.CR.3: Identify, create, and use appropriate models for bivariate data sets (i.e. linear, exponential) to estimate solutions for contextual questions, identify patterns and identify how changing parameters affect the models.

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English

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11-12.W.1 Write arguments to support claims in an analysis of substantive topics or texts, using valid reasoning and relevant and sufficient evidence. a. Introduce precise, knowledgeable claim(s), establish the significance of the claim(s), distinguish the claim(s) from alternate or opposing claims, and create an organization that logically sequences claim(s), counterclaims, reasons, and evidence.

Objective(s):

The students will…

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1. use bacterial culturing procedures to test for microorganisms in water.
2. distinguish between harmful bacteria and non-harmful bacteria.
3. Analyze bacteria data and develop a procedure to sterilize water.

Agenda (about 4 days)

Total activity takes about 4 days.

1st day - plate water sources then incubate overnight.

2nd day - analyze bacteria growth and make plan to sterilize water, replate with technique.

3rd day - look at results, log data.

4th day - draw graphs and finish lab report.

Driving Question

Water is important, not only for living organisms, but for biological studies. As a biologist, you need to know what is in your water, so that your investigations are not contaminated with substance in your water that does not belong. Think about different sources of water. Do you think there is non-visible matter in that water? What do you think could be in the water? How would you purify the water of this non-visible matter?

Hands-on Activity Instructions

Before the activity: the teacher can have the petri dishes made already or order them pre-made.

1. Collect one Nutrient agar petri dish. Nutrient agar is a nutrient source for bacteria on a solid medium. A single cell of bacteria will grow into a single colony overnight.
2. Divide each plate into four quadrants and label each sector with the water source you will be adding to the plate, your name, and today’s date.
3. Pipet 100 ml of each water source to the appropriately labeled quadrant of the plate and carefully spread the liquid with a sterile loop or spreader over the quadrant. Take care to not jab the agar and stay within the quadrant.
4. Let water absorb into agar then place your petri dish into the 37°C incubator, agar side up. Tomorrow you will analyze and quantitate any growth. Predict which water sample will have growth, speculate as to why or why not.

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Hands-on Activity

Instructions

Day 2: Look at each petri dish and determine if there was any growth. What did the growth look like? Does the growth all look the same or are there different things growing?

2. If you can count the number of colonies, how many colonies are on each plate? Which water has the most growth and which has the least? Is this what you expected?

3. The number of colonies can be extrapolated to determine the number of bacteria colonies in a cup of water (8 oz = 250 ml, this is 2500 X the amount of liquid you added to the plates). How many bacteria are in a cup of water for each of the water sources you tested? Fill out the table.

4. If you cannot count the number of colonies, what could you do to so that you could count the number of colonies?

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Hands on Activity

Instructions

Sterilization of water:

1. Work with your group to develop a technique to sterilize your water samples with what there is in the lab.
2. Plate that water and then incubate.
3. Next day analyze data.
4. Make data table #2.
5. Create graphs.
6. Write-up lab.

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Data Tables for experiment

Assessment

The students will be assessed when they present their findings to the class.

The students will also do a full lab write-up and be assessed that way.

Differentiation

Place students in groups that will help them, but still enable them to do the lab.

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Provide key vocabulary with images.

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Provide step-by-step directions for students to reference for the lab.

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Allow students to verbally explain the lab to replace a full lab write-up.

Remediation

Extension/Enrichment

Determine the species of bacteria present in your contaminated water. There are a variety of ways of analyzing the microorganism growth you see on the plates. First would be general morphological determination includes characterization of the bacterial under the microscope and determination of the size and shape. Gram staining will allow categorization of the bacteria as gram positive or gram negative. This can be confirmed with antibiotic selection, as some antibiotics will affect only gram positive and others are broad spectrum. In addition there are a plethora of physical test utilized in categorizing bacteria, such as catalase activity. More recently sequencing of the 16S rRNA gene has replaced the phenotypic methods of bacterial identification as a faster less expensive alternative. 16S rRNA offers highly conserved regions between species for primer binding sites, yet hypervariable regions between species for bacterial identification.