All life forms are composed of cells. The number may vary from a single cell in Bacteria to trillions of cells in a human body. Many of the basic activities of life such as protein synthesis, extraction of energy from nutrients and replication are carried out in cells. In multi-cellular organisms some cells perform special functions. Gland cells secrete hormones, muscle cells contract and nerve cells conduct electrical signals.

A closer look at the sun flower reveals the highly ordered structure that characterizes life. Sunflowers grow well in full Sun by converting solar energy into chemical energy of food and in the bud stage exhibit heliotropism by tracking the Sun from east to west, while at night they return to an eastward orientation.

This motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud.