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Citric Acid Cycle

This animation shows the reactions of the citric acid cycle, which splits off carbon atoms and generates energy-rich reduced forms of cofactor molecules. It is the first of three animations about cellular respiration.

ATP Synthesis

This animation shows how the proton gradient across the mitochondrial membrane powers the ATP synthase enzyme to make ATP. It is the third of three animations about cellular respiration.

Electron Transport Chain

This animation shows how the enzyme complexes of the electron transport chain harvest energy from cofactor molecules to pump protons across the mitochondrial membrane and establish a chemical gradient. It is the second of three animations about cellular respiration.

Mystery of the Missing Tusks

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.

Evolution of Ant-Mimicking Beetles

This activity guides the analysis of a published scientific figure from a study that explored the evolutionary origins of parasitic beetles that mimic army ants.

Sodium Channel Evolution in Electric Fish

This activity guides the analysis of a published scientific figure from a study that investigated how gene duplication contributed to the evolution of electric fish.

Developing an Explanation for Tuskless Elephants

This activity builds on information presented in the video Selection for Tuskless Elephants. Students use scientific evidence and reasoning to construct an explanation of and develop an argument for tusklessness in elephant populations.

Understanding Global Change

This interactive module allows students and educators to build models that explain how the Earth system works. The Click & Learn can be used to show how Earth is affected by human activities and natural phenomena.

Cougars and Trees in a Trophic Cascade

This activity guides the analysis of a published scientific figure from a study that investigated the effects of tourism on cougars and cottonwood trees in a national park.