Animal Kingdom Overview

Animal_Kingdom_Tree_-_good.gif Classification System



Animals are classified, put into groups, according to how they
are related to other animals. When biologists classify an
animal, they look at the structure of its body and the way it develops as an embryo at the very beginning of its life.
Biologists also examine the animal's DNA, which is a chemical
in cells that controls an organism's inherited characteristics.

What are animals?

Animals are many-celled organisms that must get
their food by eating other organisms. Most animals
reproduce sexually and can move from place to place.

How animal cells are organized.

All animals are multicellular. The cells of animals are grouped
together to form different kinds of tissue. A tissue is a group of
similar cells that perform the same job. Tissues might combine to form an organ, which is a group of similar tissues working
together to perform a job that is more complex than the tissue
itself. In most animals, different organs combine to form
organ systems.

How animals obtain food

Every animal is a heterotroph which means it must obtain food by eating other organisms. Most animals take food into a cavity inside their
bodies. Inside this cavity, the food is digested, or broken down into substances that the animal's body can absorb and use.

How animals reproduce

Animals typically reproduce sexually. Sexual reproduction is the process by which a new organism forms from the joining of two sex cells: the male sperm cell and female egg cell. The joining of egg and sperm is called fertilization. Sperm and egg cells carry information about the characteristics of the parent that produced them. When the sperm and egg cell unite, the resulting new individual has a combination of characteristics from both parents.
Some animals can reproduce asexually as well as sexually. Asexual reproduction is the process by which a single organism produces a new organism identical to itself. Asexual reproduction does not involve combining an egg and sperm cell from two individuals. Instead, the parent organism may divide, or produce an offspring from buds that grow on its body.

How animals move

Most of animal movement is relating to obtaining food, reproducing, and escaping danger. All animals move at some point in their lifetime, though it may not be at every stage. For example, and adult oyster does not move in it's adult stage, but for the first few weeks of its life, the oyster is a tiny swimmer.

How animals meet their needs

Water, food, and oxygen must come from an animal's environment, or surroundings. An animal needs to be able to respond to its environment, such as, escaping from predators. An adaptation is a characteristic that helps an organism survive in its environment or reproduce.

Important structural characteristics

One important structural characteristic is the presence or absence of a backbone. An animal that does not have a backbone is called an invertebrate. Most animal species are invertebrates.
In contrast, a vertebrate is an animal that has a backbone. Members of this group share three important characteristics: they have a notochord - a flexible rod that supports the animal's back, a nerve cord, and slits in their throat area.
In vertebrates, part or all of the notochord is replaced by a backbone. A few vertebrates have backbones made of cartilage, a connective tissue that is softer than bone, but flexible and strong. Most vertebrates have backbones made of hard bone.
Vertebrates also have a nerve cord that runs down their back. The nerve cord is the connection between the brain and the nerves, on which messages travel back and forth.
Finally, vertebrates have slits in their throat area called pharyngeal slits. In most vertebrates these gills disappear before birth.

Maintaining body temperature

One characteristic that distinguishes the major groups of vertebrates from each other is the way in which they control their body temperature. An ectotherm is an animal whose body does not produce much internal heat - its body temperature changes depending on the temperature of its environment. Ectotherms are sometimes called "coldblooded". An endotherm is an animal whose body controls and regulates its temperature by controlling the internal heat it produces. An endotherm's body temperature usually does not change much, even when the temperature of its environment changes.