1. An intrepid visitor to the perpetually frozen Antarctic could stand at the coastline, raise binoculars, and witness a dramatic sight just a few hundred meters offshore: a spout as tall and straight as a telephone pole fountaining upward from the blowhole of a blue whale, then condensing into massive cloud of water vapor in the frigid air. The gigantic animal beneath the water jet would be expelling stale air from its 1-ton lungs after a dive in search of food. Then, resting at the surface only long enough to take four deep breaths of fresh air, the streamlined animal would raise its broad tail, thrust mightily, and plunge into the ocean again. The observer on shore might see such a sequence only twice per hour, since the blue whale can hold its breath for 30 minutes as it glides along like a submarine, swallowing trillions of tiny shrimp-like animals called krill.
2. It is difficult to comprehend the immense proportions of the blue whale, the largest animal ever to inhabit our planet. At 25 to 30 m (80-100 feet) in length, this marine mammal is longer than three railroad boxcars and bigger than any dinosaur that ever lumbered on land. It weighs more than 25 elephants or 1600 fans at a basketball game. Its heart is the size of a beetle - a Volkswagen beetle. And that organ pumps 7200 kg (8 tons) of blood through nearly 2 million kilometers (1.25 million miles) of blood vessels, the largest of which could accommodate an adult person crawling on hands and knees. The animal has a tongue the size of a grown elephant. It has 45,500 kg (50 tons) of muscles to move its 54,500 kg (60 tons) of skin, bones, and organs. And this living mountain can still swim at speeds up to 48 km (30 mi) per hour!
3. Leviathan proportions aside, it is difficult to grasp the enormous problems that so large an organism must overcome simply to stay alive. For starters, a blue whale is a warm-blooded animal with a relatively high metabolic rate; to stay warm and active in an icy ocean environment, it must consume and burn 1 million kilocalories a day. This it does by straining 3600 kg (8000lb) of krill from the ocean water each day on special food-gathering sieve plates. In addition, each of the trillions of cells in the whale's organs must exchange oxygen and carbon dioxide, take in nutrients, and rid itself of organic waste, just as single-cell protozoan living freely in seawater must do. Yet a given whale cell - a liver cell, let's say - can lie deep in the body, separated from the environment by nearly 2 m (6 ft) of blubber, muscle, bone, and other tissues. For this reason, the whale needs elaborate transport systems to deliver oxygen and nutrients and to carry away carbon dioxide and other wastes. Finally, the galaxy of living cells inside a whale must be coordinated and controlled by a brain, a nervous system, and chemical regulators (hormones) so that the organism can function as a single unit.
4. Although the blue whales are the largest animals that have ever lived, they share with all other animals the same fundamental physical problems of day-to-day survival: how to extract energy from the environment; how to exchange nutrients, wastes, and gases; how to distribute materials to all cells in the body; how to maintain a constant internal environment despite fluctuations in the external environment, how to support the body; and how to protect it from attackers or from damaging environmental conditions. Blue whales have evolved with unique adaptations of form and function that meet such challenges and leave the animals suited to their way of life.

Source: Joe Cortina and Janet Elder. Opening Doors: Understanding College Reading. (New York: The McGraw-Hill Companies, Inc., 1998.