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Laetoli Footprints

This activity explores an image of fossil footprints at Laetoli, which serves as a phenomenon for learning about fossil evidence and human evolution.

Beetle keeps rivals off scent of food buried for offspring

Some beetles roll the flesh of dead animals into a ball and cover it in goop — all to feed their future offspring. Now scientists think that goo might do more than just slow decay. It also appears to hide the scent of the decomposing bounty and boosts another odor that repels competitors.

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.

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.

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.