CASE 1 – OPTION 2: Deciding about Experimental Design
The objectives for this case are for students to learn:
 How to decide if their selected treatments are relevant to plants and, if not, how to turn
their ideas into investigations that are relevant to plants
 How to decide if their selected treatments are relevant to the gene they are studying (i.e.,
the one that has been altered in the mutant plants)
 How to support their decisions with evidence, either from scientific publications (e.g.,
textbooks, articles, websites) or through communication with their scientists partners
Part A
Seth and Jacob sat at their table wondering what in the world they were going to choose to
treat their wild-type and mutant plants. “I know,” Seth said, “Let’s use creatine phosphate –
that’s the stuff that body builders use to make their muscles huge.”
“Great idea!” Jacob exclaimed, “ I think my gym has some that I can buy. If not, I bet we
could pick some up at the vitamin store in the mall.”
“Alright,” Seth said, “So we’re set. Let’s get our plants…”
Creatine phosphate as a treatment fits one of the criteria for PREP investigations: it is safe to
apply to plants. Another criterion is that treatments have to be relevant to plants. In this case,
Seth and Jacob noted that creatine phosphate may be useful for people to build muscle as they
work out. Yet, humans and plants grow and develop in distinct ways.
1. What would be convincing evidence that creatine phosphate is relevant to plants?
2. Why would this evidence be convincing?
3. How could you find this evidence?
Part B
To get a sense of whether plants use creatine phosphate and what they use it for, Seth and
Jacob search several websites that are reliable sources of science information, including Science
Daily (http://www.sciencedaily.com/), LiveScience (http://www.livescience.com/), Google
Scholar (http://scholar.google.com/; which searches databases of peer-reviewed articles),
PubMed (http://www.ncbi.nlm.nih.gov/pubmed; which searches a database of biomedical
articles), and even Wikipedia. They find that almost all references to creatine phosphate are
about its role as a source of energy in animal muscles.
“What are we going to do now?” Jacob asks Seth.
“Wait,” Seth says, “I found some information about plants using phosphate.”
CASE 1 – OPTION 2: Deciding about Experimental Design
Jacob and Seth search a bit more and find that phosphate is part of the creatine
phosphate molecule, and is also a form of phosphorus, which is a key nutrient for plant growth
that is often used in fertilizer (http://www.ncagr.gov/cyber/kidswrld/plant/nutrient.htm;
http://www.ncbi.nlm.nih.gov/pubmed/20181569). They search Google Scholar with these
keywords: phosphate starvation in Arabidopsis. They find that phosphate starvation changes
which genes are active in plant leaves and roots.
1. What could Seth and Jacob do to study how their wild-type versus mutant plants
respond to changes in phosphate in the environment?
2. How should they treat their plants and why?
Part C
After thinking about it some more, Seth and Jacob realize that removing phosphate from the
soil is going to be a lot harder than adding extra phosphate. They approach Mr. Smithfield, a
chemistry teacher at their school, to ask whether there are any chemicals they can use that
contain phosphate. He says that the chemistry lab has calcium phosphate, potassium phosphate,
and sodium phosphate – they just need to let her know which one they want to use and how
much they need. They have no idea what amount of phosphate to use or which source would be
best, so they email their scientist partner, Dr. Roberts.
“Great idea” Dr. Roberts explains, “The mutants you are studying have a gene that is not
working – this gene may be important in the plant’s ability to sense phosphate in its
environment. If you treat your plants with extra phosphate, you may find that the mutant and
wild type grow differently.”
Dr. Roberts finds several articles that she shares with Seth and Jacob; in the articles, other
plant scientists have used 250 mM potassium phosphate as a phosphate source. The students go
back to Mr. Smithfield to get help making the right concentration of solution, which they then
use to water their experimental wild-type and mutant plants. They continue to water their control
plants with tap water.
1. Now that they have decided on their treatment, how could Seth and Jacob
examine the effects of the treatment on the plant?
2. What should they observe or measure and why?