Animal Kingdom

All living things are divided into five kingdoms. Bacteria belong to the kingdom Monera, while the plantlike algae and animal-like protozoa are members of the Protista. The fungal kingdom includes molds, yeast, and mushrooms, and the kingdom Plantae includes all multicellular plants. The largest kingdom, however, is the Animalia. Its members range from very simple invertebrates, such as sponges, to highly complex mammals, such as whales, monkeys, and humans. Animals display some key differences that distinguish them from other living things. For example, what is the difference between a horse and grass? A horse moves around in the pasture eating grass. It trots toward you when you offer it a lump of sugar and shows pleasure when you stroke its head. The grass, however, is rooted to one place. It does not respond behaviorally to people or to the horse in any way

Most animals move freely from place to place and can sense their surroundings; that is, they can taste, smell, hear, see, and touch. Certain simple animals, such as the corals and barnacles, spend most of their lives fastened to one spot, but they are able to swim freely when they are young. Even these rooted animals have parts that move in order to capture food. Plants, however, cannot shift around at their own will. They react to heat, light, chemicals, and touch, but their responses are involuntary and automatic, quite different from those of animals.

All living things are made up of cells of protoplasm. They may consist of a single cell, as does an amoeba, or billions of cells, as do trees and horses. The cell wall of a plant is composed of a woody material called cellulose. No true animal contains cellulose. Animal cells are bounded by a membrane composed chiefly of fat and protein.

Дата добавления: 2015-07-11