Section 1: Characteristics of Animals

Chapter 27: Introduction to Animals

General Features of Animals Heterotrophy

Animals are heterotrophs – that is, they can not make their own food.

Most animals move from place to place searching for food.

Once food is located, it is eaten and then digested in a cavity inside the animal’s body.

General Features of Animals

Mobility Animals are unique

among living things in being able to perform rapid, complex movements.

Animals move by means of muscle cells, specialized cells that are able to contract with considerable force.

General Features of Animals

Animals can swim, crawl, walk, run, and even fly. In fact, flight has

evolved four times among animals , in insects, pterosaurs, birds and

bats.

General features of Animals

• Multicellularity• All animals are

multicellular.• In spite of

differences in body size, there is little difference in the size of most cells that make up these animals

General Features of Animals The cells on the

skin of your hand are roughly the same size as the cells in the heart of a whale or in the wing of a hummingbird.

General Features of Animals Diploidy

With few exceptions, animals are diploid, meaning adults have two copies of each chromosome, one inherited from their father and one from their mother.

General Features of Animals Only their gametes

(egg and sperm) are haploid.

A great advantage of diploidy is that it permits an animal to exchange genes between the two copies of a set of chromosomes, creating new combinations of genes.

General Features of Animals

Sexual Reproduction Almost all animals reproduce

sexually by producing gametes, as do many plants, fungi, and protists.

The females’ egg cells are much larger than the males’ sperm cells.

Unlike the egg cells, the sperm cells of animals have a flagella and are highly mobile.

General Features of Animals

Absence of a Cell Wall Among the cells of

multicellular organisms, only animal cell lack rigid cell walls.

General Features of Animals The absence of a rigid cell wall has

allowed animals mobility that other multicellular organisms do not have.

You may not realize this, but there are cells moving in your body at all time.

Cells called macrophages, for example, act as mobile garbage collectors, crawling over tissues and removing debris.

General Features of Animals

Blastula Formation In all animals

except sponges, the zygote (fertilized egg cell) undergoes cell division that form a hollow ball of cells called a blastula.

General Features of Animals Cells within the blastula

eventually develop into three distinct layers of cells – ectoderm, endoderm, and mesoderm.

These layers are called the primary tissue layers because they give rise to all of the tissues and organs of the adult body.

Origin of Animal Tissues and Organs

Primary Tissue

Gives rise to:

EctodermOuter layer of skin; nervous system; sense organs, such as eyes

EndodermLining of the digestive tract; respiratory system; urinary bladder; digestive organs; liver; many glands

MesodermMost of the skeleton; muscles; circulatory system; reproductive organs; excretory organs

Gastrulation

General Features of Animals Tissues

The cells of all animals except sponges are organized into structural and functional units called tissues.

Tissues are group of cells with a common structure that works together to perform a specific function

NO tissues

Body Symmetry

All animals have their own particular body plan, a term used to describe an animal’s shape, symmetry, and internal organization.

An animal’s body plan results from a pattern of development programmed into the animal’s genes by natural selection

Body Symmetry

Sponges have the simplest body plan of all animals.

Sponges are asymmetrical – irregular in shape and sometimes their shape depends on where they are growing.

Body Symmetry

Animals with radial symmetry have body parts arranged around a central axis – like the spokes on a wheel.

Most are aquatic organisms.

Body Symmetry

The bodies of all other animals show bilateral symmetry – body design with distinct right and left halves that are mirror images.

Body Symmetry

Most bilaterally symmetrical animals have evolved an anterior concentration of sensory structures and nerves, a process called cephalization.

Anterior

Internal Body Cavity Bilaterally

symmetrical animals have one of three basic kinds of internal body plans: Coelomates: body plan

that includes a body cavity – a fluid filled space found between the body wall and the digestive tract.

Internal Body Cavity

Acoelomates – animals with no body cavity.

Internal Body Cavity

Pseudocoelomates – Animals that have a body cavity located between the mesoderm and endoderm.

3 Types of Body Plans

Body Segmentation

Segmented animals are composed of a series of repeating, similar units called segments.

Segmentation underlies the organization of all advanced animals and is easy to observe in some animals, such as ants and earthworms.

ABDOMEN

THORAX

HEAD

Body Segmentation

In vertebrates, segments are not visible externally, but there is evidence of segmentation in a vertebrate embryo.

HEAD

THORAX

ABDOMEN

Kinds of Animals

Kingdom Animalia contains about 35 major divisions called phyla depending on how certain organisms are classified.

Kinds of Animals

To visually represent the relationships among various groups of animals, scientists often use a type of branching diagram called a phylogenetic tree. A phylogenetic tree

shows how animals are related through evolution.

Two Groups of Animals

The animal kingdom is divided into two groups of organisms:1. Vertebrates – animals

with backbones – humans, dogs, sharks

2. Invertebrates – animals without backbones – slugs, spiders, jellyfish