lesson 1 reading guide - kc what characteristics do all animals have? how are animals classified?...

• What characteristics do all animals have?

• How are animals classified?

What defines an animal?

• vertebrate

• invertebrate

• radial symmetry

• bilateral symmetry

• asymmetry

What defines an animal?

Although animals have many traits that make them unique, all animals have certain characteristics in common.

Animal Characteristics

The McGraw-Hill Companies, Inc./Barry Barker, photographer Dynamic Graphics Value/SuperStock

Animals are multicellular and eukaryotic.

Animal Characteristics (cont.)

Animal cells are specialized for different functions, such as digestion, reproduction, vision, or taste.

Animal Characteristics (cont.)

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Animals have a protein, called collagen, that surrounds the cells and helps them keep their shape.

Animal Characteristics (cont.)

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Animals get energy for life processes by eating other organisms.

Animal Characteristics (cont.)

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Animals digest their food.

Animal Characteristics (cont.)

Most animals reproduce sexually and are capable of movement at some point in their lives.

Animal Characteristics (cont.)

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• Scientists have described and named more than 1.5 million species of animals.

• Many scientists estimate that Earth is home to millions of animal species that no one has discovered.

Animal Classification

• Animals can be grouped into two large categories: vertebrates and invertebrates.

Animal Classification (cont.)

A vertebrate is an animal with a backbone.

Animal Classification (cont.)

The McGraw-Hill Companies, Inc./Barry Barker, photographer

An invertebrate is an animal that does not have a backbone.

Invertebrates make up most of the animal kingdom—about 95 percent.

Animal Classification (cont.)

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Symmetry describes an organism’s body plan and can help identify the phylum to which an animal belongs.

Animal Classification (cont.)

An animal with radial symmetry can be divided into two parts anywhere through its central axis. Parts are arranged in a circle around the center of its body.

Animal Classification (cont.)

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An animal with bilateral symmetry has body parts arranged the same way on both sides of its body.

Animal Classification (cont.)

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Animal Classification (cont.)

bilateral

from Latin bi–, means “two” and latus, means “side”

An animal with asymmetry has body parts arranged in a way that cannot be divided into matching parts.

Animal Classification (cont.)

(c) Ian Cartwright/Getty Images

Body Plans

• Bilateral Symmetry—can be divided into two mirror image halves

• Radial Symmetry—has parts arranged around a central point

• Asymmetry—no symmetry

• Molecules such as DNA, RNA, and proteins in an animal’s cells can be used for classification.

• The more similar the DNA of two animals, the more closely the animals are related.

Animal Classification (cont.)

Scientists classify the members of the animal kingdom into as many as 35 phyla.

The nine major phyla contain 95–99 percent of all animal species.

Animals belonging to the same phylum have similar body structures and other characteristics.

Only one animal phylum, chordata, contains vertebrates.

• All animals share a series of characteristics.

• Animals can be classified in several ways.

• Animal classifications are always changing based on advanced technology.