# Natural Selection Dandelion Lab

```Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
Lesson Plan: Natural Selection
Objectives:
● To investigate whether dandelions from a mowed vs unmowed area will have
different shoot-to-root ratios.
● To generate a hypothesis by making visual observations and critical thinking
● To conduct a scientific investigation using statistical skills in Google Sheets
● To evaluate results of the scientific investigation and form a valid conclusion
based on data and evidence from the investigation
● Communicate results on the findings of a scientific investigation in written form
● 1 A1: Natural selection is a major mechanism of evolution.
● 1 A2: Natural selection acts of phenotypic variations in populations.
● SP 1.5, 2.2: Student is able to convert a data set from a table of numbers that
reflect a change in the genetic makeup of a population over time and apply
mathematical methods and conceptual understandings to investigate the
cause(s) and effect(s) of this change.
● SP 2.2, 5.3: The student is able to evaluate evidence provided by data to
qualitatively and quantitatively investigate the role of natural selection in
evolution.
● SP 2.2: The student is able to apply mathematical methods to data from a real or
simulated population to predict what will happen to the population in the future.
● SP 5.3: The student is able to evaluate data-based evidence that describes
evolutionary changes in the genetic makeup of a population over time.
● SP 7.1: The student is able to connect evolutionary changes in a population over
time to a change in the environment.
Inquiry Level:
Level 2 – Directed Inquiry. Students are given the alternate hypotheses but are
expected to make the correct predictions for each alternate hypothesis. Students are
directed to examine the graphical results but are not expected to create the graphs
themselves. Students are expected to interpret the statistical results rather than
generate the results themselves.
Assessment Method:
Students will write a formal lab report, totalling 100 possible points. The lab report will
assess the students ability to compile necessary information in order to formally present
information for college-level publishing or to the class (AP Bio). The rubric and
Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
instructions for the formal lab report can be found here. Students have the option of
working together on the lab report or individually, although I encourage them to work
independently to improve their own writing skills.
Biol 8400: Experimental Lesson Plan- Natural Selection
Name:___________________________________________
Bridget Williams
Section:_______________
Natural Selection
Background
Natural selection discriminates against individuals with regards to their ability to produce
offspring. The individuals that survive and reproduce will pass on more of their alleles in a
population. These individuals would be considered to have a higher level of fitness than
individuals that do not survive long enough to reproduce and pass on their offspring.
In this experiment you will be examining the individuals of two different dandelion populations.
Dandelions are interesting because they reproduce asexually. Instead of sexual reproduction,
which typically occurs in most flowers, dandelions form seeds without fertilization. Because
dandelions asexually reproduce, they are essentially genetically identical to their parent plant.
One set of dandelions was grown from seeds collected from an area that experienced lawn
mowing for many years. The other set was collected from an area where the lawn was mowed
fairly infrequently.
This experiment test the prediction that dandelion populations grown for generations under
different mowing regimes will have different growth forms. What would you predict the
dandelions grown from a mowed vs unmowed area to look like?
Objectives
● Measure the shoot length to the nearest millimeter.
● Measure the root length to the nearest millimeter.
● Calculate the shoot-to-root ratio
● Calculate the total number of plants
● Average the shoot-to-root ratio
● Calculate the standard deviation and standard error for both plant types
● Graph the distribution of the shoot-to-root ratio of each plant type and the average shootto-root ratio of each plant type
● Analyze the differences in the shoot-to-root ratio of mowed vs unmowed areas
Hypothesis
H0: Dandelion populations will have different growth forms.
H1: Dandelion populations will have same growth forms.
Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
References
“Anatomy of A Lab Report.” Prezi.com, 24 Jan. 2014, prezi.com/ahx9d3v5xfoq/chromeextensionbpmcpldpdmajfigpchkicefoigmkfalcviewsap/.
Hilbish, Thomas & Goodwin, Minnie. University of South Carolina.
Starr, Cecie, et al. Biology: The Unity and Diversity of Life AP Biology Lab Manual. 14th ed., Cengage, 2019.
Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
Materials
Per student group (4):
● Flat of dandelion seedlings, labeled mowed or unmowed
● Trowel or large spoon
● Metric ruler
● Knife or single-edged razor blade
● Calculator
Per lab room:
● Several dishpans half filled with water
● Paper towels
● Soap
Procedure
1. Obtain a flat of dandelions. Observe the flat of the dandelion plants and note any
observable differences in appearance between those grown from mowed vs unmowed
areas.
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______
2. Create your own prediction on the different growth forms you think dandelions will have
based on the following question: What would you predict the dandelions grown from a
mowed vs unmowed area to look like? (include root length vs shoot length)
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
3. Remove the plants carefully from the flat with the
trowel or spoon. Be careful to remove the root
system but do not damage or lose the root
material. Wash each plant gently in the dish-pan
provided- not the sink- to remove residual soil.
Blot the plants dry with paper towel.
4. Cut each plant at the region separating the
root from the leafy shoot, keeping each root
portion with its corresponding shoot. See
Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
Figure 1-1.
5. Measure the shoot length to the nearest
millimeter as the length between the cut
surface and the tip of the longest leaf. Record
the measurements in Table 1-1 & Table 1-2
on the following Google Sheet. You will need
to save a copy for yourself.
File > Make a copy > (Rename) > OK
6. Measure the root length to the nearest
millimeter as the length between the cut
surface and the tip of the longest tap root (a
main root). Try to avoid measuring branch
roots (smaller roots). Record the
measurements in Table 1-1 & Table 1-2.
Figure 1-1: Root vs
Shoot Systems.
7. For each plant, divide the shoot length by the root length to calculate the shoot-to-root
ratio.
Record the ratio in Table 1-1 & Table 1-2.
8. Calculate the average shoot-to-root ratio of both mowed and unmowed dandelions.
Calculate the standard deviation for both plant types. Calculate the standard error for both
plant types. Directions for calculations can be found on the Google Sheet.
9. Graph the distribution of the shoot-to-root ratio of each plant on your flat & graph the
average shoot-to-root length of both types of dandelions.
Here are two sample graphs:
Lab
Repo
rt
Instr
uctio
ns
Instru
ction
s for
Biol 8400: Experimental Lesson Plan- Natural Selection
Bridget Williams
the formal lab report can be found here. Make sure to paste your tables and graphs in the
appropriate area.
Questions
Answer the following questions in the designated section on your formal lab report.
1. Are there any noticable differences in the distribution of shoot-to-root ratios between
dandelions from intensely mowed vs unmowed areas? If so, what are those
differences?
2. Was your hypothesis supported or rejected? Why? Provide evidence and explaination.
3. What did you learn from this lab and what additional question(s) would you like to
investigate further?
4. Describe how the main idea of this experiment applies to understanding other areas of
science or use other concepts in science to discuss the results of this experiment. You
will probably need to do some research here.
```