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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.

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.

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.

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.

Waste-watching: Sewage can help track pandemic virus trends

Across the U.S. and in Europe, researchers and health officials say they can track the course of a community outbreak of the new coronavirus by studying the waste flushed from its bathrooms. And that can provide a valuable addition to public health tools, they say.

Evaluating Science in the News

In this activity, students evaluate a science news article to determine whether it is a trustworthy source of information.