Movement and locomotion

Movement is one of the key signs of life. In Amoeba the cell's contents stream from place to place; cilia, flagella and tentacles move in many small animals; and we move our limbs, jaws, eyelids and tongue.

Some movements change an animal's place: walking, running, climbing, flying, swimming. These voluntary movements are called locomotion. So all locomotion is movement, but not all movement is locomotion: blinking moves your eyelid, but you stay where you are. Often the same structures do both jobs. The cilia of Paramoecium sweep food into its gullet and also move the whole animal. The tentacles of Hydra catch prey and also help it move.

Why do animals move from place to place? To find food, shelter, a mate, good breeding grounds or a better climate, and to escape from predators.

Cells in the human body show three kinds of movement:

• Amoeboid: some cells, like macrophages and white blood cells, crawl by pushing out false feet (pseudopodia), using the cell's tiny microfilaments.
• Ciliary: in tubes lined with ciliated epithelium, the beating cilia move things along. In the trachea they sweep out dust and germs trapped in mucus; in the female reproductive tract they help the ovum move along.
• Muscular: the movement of our limbs, jaws and tongue, by muscles.

Flagella help sperm swim, keep water flowing through the canals of sponges, and move Euglena. Locomotion in humans needs the muscular, skeletal and neural systems to work together.