Work Sample & Commentary: DNA Models
The task
Student groups were asked to design and build models representing DNA molecules. The models were to include details such as base pairs and nucleotide components, and to illustrate the overall double-stranded and helical nature of DNA.

Circumstances of performance
This sample of student work was produced under the following conditions:
alone in a group
in class as homework
with teacher feedback with peer feedback
timed opportunity for revision

This work sample illustrates a standard-setting performance for the following parts of the standards:
b Life Sciences Concepts: Molecular basis of heredity.
a Scientific Connections and Applications: Big ideas and unifying concepts.
c Scientific Investigation: Design.
What the work shows

b Life Sciences Concepts: The student produces evidence that demonstrates the molecular basis of heredity, such as DNA….
The students illustrate complementary base pairs; alternate sugar-phosphate side chains, and appropriate placement of the nucleotide components. The model also shows the double stranded and helical nature of DNA. It includes an illustrated key [not shown]. The students attempted to illustrate the dynamic nature of the molecule with a crank handle that turns the model that is not visible in the photo.
The students had an opportunity to revise their initial submission . They more accurately depict the sugars and they added the phosphates. An attempt was made to illustrate more clearly the spatial relationship between these nucleotide components. In further revising the model, the hydrogen bonds between the nucleotide base pairs could be illustrated along with a more accurate depiction of accurate base pair size.
The students illustrate complementary base pairs, hydrogen bonding, alternate sugar phosphate side chains, and appropriate placement of the nucleotide components. The model also shows the double stranded nature of DNA and the process of the unzipping and formation of replicated strands. However, this model does not illustrate the helical nature of DNA, an omission that should be corrected in a revision.

a Scientific Connections and Applications: The student produces evidence that demonstrates understanding of big ideas and unifying concepts, such as order and organization….
The students demonstrated in model form the organization of the DNA molecule.
c Scientific Investigation: The student demonstrates scientific competence by completing [a] design.
The students developed and executed designs that, while requiring revision, were creative and largely accurate.