Describe an example of endosymbiosis that has been observed and documented.

In 1987, Professor Kwang Jeon of the University of Tennessee observed a number of amoebas (single-celled eukaryotes) that had ingested bacteria cells. The bacteria were killing off most of the amoebas, but a small number of the amoeba survived and returned to their normal modes. However, the invading bacteria were still present within surviving amoebas. Jeon continued to experiment with the amoebas and discovered that these surviving amoebas, and their offspring, could not survive without the bacteria. Jeon's discovery and experimentation proves it is possible for a cell to become dependent on an invading organism.

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

brain development. a child's brain undergoes an amazing period of development from birth to three—producing more than a million neural connections each second. the development of the brain is influenced by many factors, including a child's relationships, experiences and environment.

explanation: