Summer Research Program for Science Teachers

August 2004

 

Uzma Shah

Baruch College Campus HS

Manhattan

 

 

The Effects of Ultra-Violet Light on Yeast

 

Unit: Genetics, Immunology, or Cancer

Objectives:

 

Introduction: My summer research has focused on DNA repair mechanisms in yeast. Yeast, like other eukaryotes have a number of genes and proteins necessary to repair DNA damage (e.g. double strand breaks caused by Ionizing radiation or Ultra Violet radiation). This project brings pieces of my summer research into my own classroom making it accessible to my students.  Prior to conducting these experiments, students should spend some time learning about the basics of yeast (e.g. What is it? How does it compare to other microbes? What does it look like? What is its life cycle like? Why is it a model organism for scientific research?)  The lesson plan that I designed last summer is an internet activity that offers this basic introduction. Once students have a grasp of these basics and have a solid foundation in genetics they can easily design and conduct these experiments to examine the effects of UV light on yeast growth.

This lesson plan is a two-three week inquiry based lab project in which students will work cooperatively to learn culturing techniques (how to grow yeast), design and conduct an experiment using yeast and UV light, and present their results to their peers. While I will provide overall guidelines on how to conduct the experiment and a rubric for assessment, the students will generate their own questions and hypotheses, collect data, analyze that data and make connections to how it relates to other topics studied in class. Ideally, each group of students will have a unique experiment that their peers can learn from and assess.

            Students will also need to use communication and group work skills to work cooperatively. Some of the data collection and work may be divided. It will be imperative for them to discuss how they will efficiently work together.

 

Materials:

 

Outline:

I.                   Students learn and practice culturing techniques

  1. Create a sterile work environment by cleaning all tabletops with a mild bleach solution (10% bleach, 90% water), washing hands thoroughly and having a Bunsen burner on throughout the procedure.
  2. Teacher demonstrates to students how to transfer a colony of yeast from an existing plate and prepare serial dilutions.
  3. Using a sterile loop (flame sterilized) or a sterile wooden stick, collect a single yeast colony and transfer into 1ml of sterile water. Shake the loop or stick vigorously to distribute cells throughout the water.
  4. Transfer .1ml (100Ķl) of the yeast culture (using a sterile pipette) into another test tube with .9ml (900 Ķl) of water. This creates your 10-1 dilution. Pipette up and down to mix thoroughly. Transfer .1ml to another test tube with .9ml of water, mix. This creates your 10-2 dilution. Continue in this manner until you have prepared 10-4 and 10-5 dilutions. Take .1ml of the 10-4  solution and place on a YPD plate. Spread using a sterile spreader or glass beads). Let the agar absorb the cells for about 5 minutes then turn the Petri dish upside down. Let the yeast grow for about a week at room temperature or for 3 days at 30oC. Repeat for the 10-5 dilution. You will need to determine which dilution works best for you. If you use one of the more concentration dilutions, it is highly probable that you will have far too many colonies growing to be able to count them. 10-4 and 10-5 dilutions generally work best.
  5. Once you have demonstrated this technique have students practice themselves.

 

II.                Students Design their experiments

  1. Explain to students that they will be designing experiments to test the effects of UV light on yeast. Prior to this they should already know what UV light is and how it affects DNA. You may wish to briefly review this. Ask students to come up with questions, hypotheses and design their own experiments. You may also wish to have the class brainstorm items that are supposed to protect against UV light. They should also try to come up with UV light sources, exposure times, what data they will need to collect, etc. I would have students work in groups of three or four on this project. Provide what guidelines you feel comfortable with. You may want to provide more or less guidance depending on the abilities of your students. I would ask students to submit a preliminary plan to me for approval before they could begin. Also they should be told that they will need to bring their own sunscreens, etc.
  2. Provide necessary rubrics and guidelines for assessment.

 

III.             Students conduct experiments

  1. Students should transfer one colony from the plate they grew the previous week, prepare serial dilutions and use the 10-4 or 10-5 dilutions replate on a new YPD plate. Depending on how many plates you have ordered you may want the students to divide the plates in half, using one side as a control and one as an experimental. You may also divide the plate into three or four sections, using one as a control and the others as experimentals. However you choose to distribute plates, all groups should do their experiment in triplicate (3 experimentals). If you are low on supplies, you could have three groups do the same experiment and then pool their data.
  2. After spreading, the experimental plates should be left in the sun for at least five minutes and then left to grow in a non-sunny location (alongside the control) at room temp (for one week) or in a 30 degree Celsius incubator for three days.
  3. The following are some modifications on this experiment using different variables;

 

IV.              Students collect and analyze data

After three days to one week, students should count the number of colonies on each plate and determine if those yeast exposed to the sun had fewer colonies than those that were not exposed to the UV light. Students should document (in written and pictorial form) this data. You may ask the students to write formal lab reports, answer a series of questions, do presentations or some other form of assessment.

 

V.                 Student Presentations (optional)-Whatever option is chosen it is important for other students to review the research and ask their peers questions about content, techniques, errors, data, etc.

        Students present power point presentations to the whole class

Poster Session (Science Exhibition style or in front of whole class)

 

This project aligns with the following New York State and National Science Standards:

 

-Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing and creative process

-Key Idea 2: Beyond the use of reasoning and consensus, scientific inquiry involves testing of proposed explanations involving the use of conventional techniques and procedures and usually requiring considerable ingenuity

-Key Idea 3: The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into natural phenomena

-Key Idea 1: Living things are both similar to and different from each other and from non-living things.

-Key Idea 2:  Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.

-Key Idea 5:  Organisms maintain a dynamic equilibrium that sustains life.

 

a). abilities necessary to do scientific inquiry

b). understandings about scientific inquiry

 

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