Chapter Presentation Visual Concepts Transparencies Standardized Test Prep
Introduction to Animals Table of Contents Section 2 Animal Body Systems
Objectives Identify the features that animals have in common. Distinguish radial symmetry from bilateral symmetry. Summarize the importance of a body cavity. Identify how scientists determine evolutionary relationships among animals.
Characteristics of Animals
General Features of Animals Heterotrophy Animals are heterotrophs that is, they cannot 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.
Comparing Autotrophs and Heterotrophs
General Features of Animals, continued 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. Animals can swim, crawl, walk, run, and even fly. In fact, flight has evolved four times among animals, in insects, pterosaurs (extinct reptiles from the time of the dinosaurs), birds, and bats.
General Features of Animals, continued Multicellularity All animals are multicellular. In spite of differences in body size, there is little difference in the size of most of the cells that make up these 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 muscle of a hummingbird.
Comparing Organisms That Are Unicellular and Multicellular
General Features of Animals, continued 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. 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.
Comparing Haploid and Diploid Cells
General Features of Animals, continued 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, continued Absence of a Cell Wall Among the cells of multicellular organisms, only animal cells lack rigid cell walls. The absence of a cell wall has allowed animals mobility that other multicellular organisms do not have. You may not realize this, but there are cells moving about in your body all the time. Cells called macrophages, for example, act as mobile garbage collectors, crawling over tissues and removing debris.
General Features of Animals, continued Blastula Formation In all animals except sponges, the zygote (fertilized egg cell) undergoes cell divisions that form a hollow ball of cells called a blastula. 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
Cleavage and Blastula Formation
Cleavage and Blastula Formation
General Features of Animals, continued Tissues The cells of all animals except sponges are organized into structural and functional units called tissues. Tissues are groups of cells with a common structure that work together to perform a specific function.
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. Sponges have the simplest body plan of all animals. Sponges are asymmetrical, or irregular in shape, and sometimes their shape depends on where they are growing.
Body Symmetry, continued Radial Symmetry Animals with radial symmetry have body parts arranged around a central axis, somewhat like the spokes around a bicycle wheel. A plane passing through the central axis divides the organism into roughly equal halves. Today s radially symmetrical animals are aquatic. Most move slowly or drift in ocean currents.
Body Symmetry, continued Bilateral Symmetry The bodies of all other animals show bilateral symmetry, a body design in which there are distinct right and left halves. A plane passing through the animal s midline divides the animal into mirror image halves. Most bilaterally symmetrical animals have evolved an anterior concentration of sensory structures and nerves, a process called cephalization.
Radial and Bilateral Symmetries
Symmetry in Body Structure
Cephalization
Internal Body Cavity Bilaterally symmetrical animals have one of three basic kinds of internal body plans. The body plan may include a body cavity, or coelom, a fluid-filled space found between the body wall and the digestive tract (gut). This space is lined with cells that come from mesoderm. Animals with no body cavity are called acoelomates.
Internal Body Cavity, continued Animals called pseudocoelomates have a body cavity located between the mesoderm and endoderm. Coelomates have a true coelom, a body cavity located entirely within the mesoderm. A true coelom provides an internal space where mesoderm and endoderm can be in contact with each other during embryonic development.
Body Cavity
Three Body Plans of Symmetrical Animals
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 earthworms. In vertebrates, segments are not visible externally, but there is evidence of segmentation in a vertebrate embryo.
Segmentation
Kinds of Animals Kingdom Animalia contains about 35 major divisions called phyla (singular, phylum), depending on how certain organisms are classified. 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. The animal kingdom is often divided into two groups: invertebrates (animals without a backbone) and vertebrates (animals with a backbone).
Evolutionary Relationships in the Animal Kingdom
The Animal Body: An Evolutionary Journey
Animal Body Features and Phylogeny
Phylogenetic Tree
Section 2 Animal Body Systems Objectives Summarize the functions of the digestive, respiratory, circulatory, nervous, skeletal, and excretory systems. Compare a gastrovascular cavity with a one-way digestive system. Differentiate open from closed circulatory systems. Distinguish asexual from sexual reproduction.
Section 2 Animal Body Systems Tissues and Organs Digestion Single-celled organisms and sponges digest their food within their body cells. All other animals digest their food extracellularly (outside of their body cells) within a digestive cavity. Simple animals, such as the hydra and flatworms, have a gastrovascular cavity, a digestive cavity with only one opening. Other animals have a digestive tract (gut) with two openings, a mouth and an anus.
Section 2 Animal Body Systems Tissues and Organs, continued Digestion A hydra has a gastrovascular cavity, while a roundworm has a digestive tract in which food travels in one direction only.
Section 2 Animal Body Systems Tissues and Organs, continued Respiration In simple animals, oxygen gas and carbon dioxide gas are exchanged directly with the environment by diffusion. The uptake of oxygen and the release of carbon dioxide, called respiration, can take place only across a moist surface. Some aquatic (and a few terrestrial) animals respire with gills, very thin projections of tissue that are rich in blood vessels.
Section 2 Animal Body Systems Parts of the Human Respiratory System
Section 2 Animal Body Systems Fish Gills
Section 2 Animal Body Systems Tissues and Organs, continued Circulation In complex animals, oxygen and nutrients must be transported to these body cells by a circulatory system. In an open circulatory system, a heart pumps fluid containing oxygen and nutrients through a series of vessels out into the body cavity. In a closed circulatory system, a heart pumps blood through a system of blood vessels.
Section 2 Animal Body Systems Open and Closed Circulatory Systems
Section 2 Animal Body Systems Comparing Open and Closed Circulatory Systems
Section 2 Animal Body Systems Tissues and Organs, continued Conduction of Nerve Impulses Nerve cells (neurons) are specialized for carrying messages in the form of electrical impulses (conduction). Bilaterally symmetric animals have clusters of neurons called ganglia. More-complex invertebrates, such as the grasshopper, have brains with sensory structures, such as eyes, associated with them.
Section 2 Animal Body Systems Tissues and Organs, continued Conduction of Nerve Impulses The hydra has a simple nerve net, while the flatworm and the grasshopper have more-complex nervous systems.
Section 2 Animal Body Systems Tissues and Organs, continued Support Many soft-bodied invertebrates have a hydrostatic skeleton. A hydrostatic skeleton consists of water that is contained under pressure in a closed cavity, such as a gastrovascular cavity or a coelom. Other invertebrates, such as insects, have a type of skeleton known as an exoskeleton, which is a rigid external skeleton that encases the body of an animal. An endoskeleton is composed of a hard material, such as bone, embedded within an animal.
Section 2 Animal Body Systems Comparing Exoskeletons and Endoskeletons
Section 2 Animal Body Systems Tissues and Organs, continued Excretion The term excretion refers to the removal of wastes produced by cellular metabolism. Simple aquatic invertebrates and some fishes excrete ammonia into the water through their skin or gills by diffusion. Other animals, especially terrestrial animals, convert ammonia to nontoxic chemicals, like urea. As the excretory system eliminates these wastes, water and other useful substances are returned to the body.
Section 2 Animal Body Systems Reproductive Strategies Asexual Reproduction Reproduction that does not involve the fusion of two gametes is called asexual reproduction. An unusual method of asexual reproduction is parthenogenesis, in which a new individual develops from an unfertilized egg. Animals that reproduce asexually are usually able to also reproduce sexually.
Section 2 Animal Body Systems Reproductive Strategies, continued Sexual Reproduction In sexual reproduction, a new individual is formed by the union of a male and a female gamete. Gametes are produced in the sex organs. The testes produce the male gametes (sperm), and the ovaries produce the female gametes (eggs). Some species of animals, called hermaphrodites, have both testes and ovaries.
Section 2 Animal Body Systems Reproductive Strategies, continued Sexual Reproduction Most aquatic animals simply release the male and female gametes near one another in the water, where fertilization occurs. This method is called external fertilization because the egg is fertilized outside of the female s body. Most terrestrial animals reproduce sexually by means of internal fertilization. In internal fertilization, the union of the sperm and egg occurs within the female s body.
Section 2 Animal Body Systems Sexual Reproduction
Standardized Test Prep Multiple Choice The diagram on the right shows a phylogenetic tree of animal phyla. The letters A D on the diagram represent milestones in the evolution of animals. Use the diagram to answer questions 1 3.
Standardized Test Prep Multiple Choice, continued 1. Which letter on the phylogenetic tree represents the presence of tissues? A. A B. B C. C D. D
Standardized Test Prep Multiple Choice, continued 1. Which letter on the phylogenetic tree represents the presence of tissues? A. A B. B C. C D. D
Standardized Test Prep Multiple Choice, continued 2. Which phylum contains animals that lack body symmetry? F. Echinodermata G. Porifera H. Cnidaria J. Mollusca
Standardized Test Prep Multiple Choice, continued 2. Which phylum contains animals that lack body symmetry? F. Echinodermata G. Porifera H. Cnidaria J. Mollusca
Standardized Test Prep Multiple Choice, continued 3. Which phylum contains animals that have a pseudocoelom? A. Porifera B. Platyhelminthes C. Nematoda D. Annelida
Standardized Test Prep Multiple Choice, continued 3. Which phylum contains animals that have a pseudocoelom? A. Porifera B. Platyhelminthes C. Nematoda D. Annelida