Chapter 27: Introduction to Animals Section 1: Characteristics of 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.
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.
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. Thorax Head Abdomen
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: • Vertebrates – animals with backbones – humans, dogs, sharks • Invertebrates – animals without backbones – slugs, spiders, jellyfish