Growth
and Development. (Professor Joe Kunkel, Biology)
Growth
and development of plants and animals are a springboard to understanding
several
concepts in the state frameworks for biology.
In K-5 students "begin to use measuring devices to gather
quantitative data that they record, examine,
interpret, and communicate."
After reviewing these important skills we will proceed to use them to
pursue grade 6-8 level investigations of plants and animals.
"Middle
school students begin to study biology
at the microscopic level without delving
into the biochemistry of cells."
"At
the macroscopic level, students focus on the interactions that occur within
ecosystems. They explore the interdependence of living things,
specifically the
dependence of life on photosynthetic organisms such as plants, which in turn
depend upon the sun as their source of energy."
"Students
use mathematics to calculate rates of growth, derive
averages and ranges, and
represent data graphically to describe and interpret
ecological concepts."
"The
standards for grades 6-8 fall under the topics of Classification
of Organisms,
Structure and Function of Cells, Systems in Living Things, Reproduction and
Heredity, Evolution and Biodiversity, Living Things and Their Environment,
Energy and Living Things, and Changes in Ecosystems Over Time."
Several
Model Systems are available for developing a grade 6-8 student's
experimental
and analytical skills in the lab:
(1)
Growing pollen allows cellular level experiments to be pursued
with observations
and measurements taken through the microscope.
Lily pollen is available all year long from
florists.
The anatomy of the plant can be learned and the need for rapid
growth of
the pollen tubes understood based on the anatomy of the lily
flower.
Effects of environmental variables such as salt
levels (Ca++,
Na+, K+, Cl-) and pH (acidity) can be
observed
to work at the cellular level on pollen tube
growth rates.
Pollen tube growth can be followed using a microscope fitted with an
ocular micrometer or by taking digital images through the ocular.
(2)
Growing lima beans or corn allow several concepts of cellular responses to
the
environment to be examined quantitatively.
Environmental forces can be explored experimentally. Gravitropism
makes
roots grow down and stems grow up. Phototropism makes stems grow
toward light.
Not all wavelengths of light are effective; colored filters can
be used
to test a plants tropic response to the visible light spectrum.
During the early phase of germination the bean cotyledons shrivel
in size
as they provide nourishment to the growing roots and stems prior to plant
independence. True leaves
develop
and increase in area. If computers
are available, digital images of these structures can be taken and sizes of
cotyledons and leaves analyzed using free software (Image-J).
What are the effects of various environmental factors on these
hydroponically grown seedlings?
(3)
The meal worm, Tenebrio molitor, is a classical growing system which
allows students to experiment with the relation between populations and
resources. Population
size develops
over a period of months in an essentially closed environment which
requires some
student attention span. Evaluation
of the population structure at several points during the
semester satisfies the
framework objective of studying Changes in Ecosystems Over
Time.
Students can do experiments on effects of temperature on development
rate, effects of population density on birth
rate and cannibalism.
The simplicity of this closed system contrasts to the complexity of
doing
field studies.
(4)
Genetic plant mutants are available which allow experimentation with
remediation
of a genetic lesion. Dwarf pea
plants and normal pea plants are dramatically different in
size. Dwarfism in this particular plant is said to
be corrected by
providing a hormone, giberellin, which the dwarf plants are lacking.
Fieldwork
can involve a study of the diversity of life found in a measured area of
several
different environments.
(1)
A sample of forest floor litter.
(2)
A sample of meadow plants and turf.
(3)
A sample of stream bottom.
(4)
A sample of pond bottom.
Count
all the organisms and try to identify them
to order and perhaps family. Create a
diversity list for each environment chosen.
What would the list look like if the collection had been
done earlier or
later? How is
this fieldwork
different from the laboratory work on model systems?
K-5
students will have learned to use simple measuring devices such as
rulers and
calipers to gather data, which they can graph and evaluate with simple
graphing
skills to show differences. The
grade 6-8 student is expected to advance to observations that include more
complicated concepts such as environmental effects on
growth and the concept of
genetic effects on biological processes. The
use of mathematics to analyze the collected data go beyond the
simple graphical
differences used in earlier K-5 work.
I
maintain a website called “What Makes a Good Model System?”, URL: