Summer Research Program for
Baruch College Campus HS
The Effects of Ultra-Violet Light on
Unit: Genetics, Immunology, or Cancer
- Students (Ss) will understand the basics of yeast as a
- Ss will use scientific inquiry to design and conduct
- Ss will understand how to conduct an experiment,
formulate hypotheses, set up controls and variables, and collect and analyze
- Ss will draw upon their understanding of genetics and
- Ss will make connections to UV light and Cancer in
- Ss will see that while yeast are simple single celled
organisms, they share genes in common with other higher level eukaryotes.
(Unity of life)
- Ss will learn culturing techniques to grow yeast in a
- Ss will work cooperatively to design and conduct their
- Ss will present/defend their results to their peers
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.
- YPD/YEPD agarose plates (you will need to determine how
many you will need depending on how you want your students to conduct this
experiment). YPD plates contain a nutrient rich agar that provides everything
yeast need to grow. They can be ordered through Carolina Biological as well as
other biological supply companies.
- Strains of yeast. You can use ordinary bakerís yeast
from the super market (Saccharomyces cerevisiae) or you can order yeast
strains from a biological supply company. If you have access to a college or
university microbiology lab you could probably borrow a couple of plates and
streak out your own colonies. If you use bakerís yeast you should dissolve it
in warm water and a bit of sugar or a YPD medium, prepare serial dilutions,
and plate the appropriate dilutions from which students can collect colonies.
- A UV light source: a goggle sterilizer, an
electrophoresis gel box, a portable UV light, and the sun are suitable
sources. If you use a source other than the sun, call the manufacturer to
determine if UV-C rays are also emitted. Most sunscreens do not protect
against UV-C light.
- An incubator set at 30 oC (optional)
- Glass spreaders
- Bunsen burners
- Materials to protect against UV-light such as: a variety
of sunscreens, different pieces of fabric, and sunglasses (have the students
generate ideas about these materials)
- Test tubes (sterile)
- 1ml pipettes (sterile. These can sterilized by
autoclaving, using brand new pipettes, microwaving, boiling in water for 20-30
minutes, or at the very least cleaning the tip surface with alcohol)
- Sterile water (you can purchase this or prepare your own
by boiling-or autoclaving- the water for at least 30 minutes)
Students learn and practice culturing techniques
- 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.
- Teacher demonstrates to students how to transfer a
colony of yeast from an existing plate and prepare serial dilutions.
- 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
- 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.
- Once you have demonstrated this technique have students
Students Design their experiments
- 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
- Provide necessary rubrics and guidelines for assessment.
Students conduct experiments
- 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
- 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.
- The following are some modifications on this experiment
using different variables;
- Comparing yeast cells that are Wild type versus those
that have a necessary DNA repair gene knocked out. Such UV sensitive strains
can be ordered through Carolina Biological.
- UV exposure time
- Different SPFís of sunscreen (if sunscreen is used,
the plates should be covered with plastic wrap and sunscreen should be
spread on the plastic wrap. After exposure to UV light, the plastic should
- Different brands of SPF
- Oils, Lotions (non-SPF)
- Different types and colors of fabric (e.g. denim v.
something light and sheer or black v. white fabric)
- Direct v. indirect UV light
- Different sources of UV light (sun v. portable UV
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.
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
(Science Exhibition style or in front of whole class)
This project aligns with the
following New York State and National Science Standards:
- New York State Living Environment Standards
- Standard 1: Students will use mathematical
analysis, scientific inquiry, and engineering design, as appropriate, to
pose questions, seek answers, and develop solutions.
-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
- Standard 4: Students will understand and
apply scientific concepts, principles, and theories pertaining to the
physical setting and living environment and recognize historical
development of ideas in science.
-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.
- National Science Education Standards
- Content Standard A: As a result of activities
in grades 9-12, all students should develop:
a). abilities necessary to do
b). understandings about
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