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2:18 Human embryonic development depends on stem cells. During the course of development, cells divide, migrate, and specialize. Early in development, a group of cells called the inner cell mass (ICM) forms. These cells are able to produce all the tissues of the body. Later in development, during gastrulation, the three germ layers form, and most cells become more restricted in the types of cells that they can produce.

The worst cancer cells don't sit still. Instead they metastasize-migrate from their original sites and establish new tumors in other parts of the body. Once a cancer spreads, it is harder to eliminate. A study by developmental biologists offers a fresh clue to how cancer cells acquire the ability to invade other tissues-a prerequisite for metastasis. It reveals that invasion requires cells to stop dividing. Therefore, the two processes- invasion and proliferation-are mutually exclusive. The finding could inform cancer therapies, which typically target rapidly proliferating cancer cells.

The physical connection between mother and fetus is provided by the placenta, an organ, built of cells from both the mother and fetus, which serves as a conduit for the exchange of nutrients, gasses, and wastes. Cells may migrate through the placenta between the mother and the fetus, taking up residence in many organs of the body including the lung, thyroid, muscle, liver, heart, kidney and skin. These may have a broad range of impacts, from tissue repair and cancer prevention to sparking immune disorders.

From single-celled organisms to giant redwoods, Life Science explores all of Earth's life forms. Use interactive, animated activities to identify the living and nonliving components of an ecosystem, design a Venn diagram to compare the migrations of monarch butterflies and red knot shorebirds, and take a virtual field trip to a solar farm. Resources in Life Science gives you a wide range of topics, including the cell cycle, genetic disorders, and bioethics.

Neutrophils are our body's first line of defense against bacterial infections. After leaving nearby blood vessels, these cells recognize chemicals produced by bacteria in a cut or scratch and migrate "toward the smell". The above neutrophils were placed in a gradient of fMLP (n formyl methionine- leucine- phenylalanine), a peptide chain produced by some bacteria. The cells charge out like a "posse" after the bad guys.