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In this phenomenon-driven activity, students investigate how cells are signaled to make melanin and explain how mutations in melanin pathway proteins affect the coat color of various organisms.

This activity explores images of elephants with and without tusks, which serve as phenomena for learning about selection and human impacts on the frequency of traits within populations.

This activity explores an image of tattoo ink particles inside cells, which serves as a phenomenon for learning about the structure and color of human skin.

This activity explores images of planarians regenerating missing body parts, which serve as phenomena for learning about cell division and differentiation.

This activity supports the film Popped Secret: The Mysterious Origin of Corn. Students analyze data on the expression of the tb1 gene to explain how variations in this gene played a role in the evolution of corn.

This activity complements the video Virus Hunter: Monitoring Nipah Virus in Bat Populations. Students explore cases of Nipah virus infection, analyze evidence, and make calculations and predictions based on data.

This activity explores images of plant cells and structures, which serve as phenomena for learning about how plants respond to stimuli.

This activity outlines two demonstrations that model how enveloped and nonenveloped viruses are released from infected cells.

This demonstration models the first step of the HIV life cycle: the binding of HIV envelope proteins to receptors on human helper T cells.

This activity allows students to model how the anti-HIV drug AZT (azidothymidine) interferes with the process of viral replication.

This demonstration models how the HIV protease enzyme functions and how its activity is blocked by a class of anti-HIV drugs.

In this hands-on activity, students model how a double-stranded DNA copy of the HIV genome is integrated into the host cell DNA.