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Chapter 27: Introduction to Animals
Section 1 Characteristics of Animals
Objectives:

Identify the features that animals have in common.

Distinguish radial symmetry from bilateral symmetry.
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Summarize the importance of a body cavity.

Identify how scientists determine evolutionary relationships among animals.
Characteristics of Animals (Video clip)
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Multicellular

Lack cell walls

Cannot make their own food

Must seek out food sources.

Movement in many different ways to seek: o Food o Shelter o Mate

Sexual Reproduction

Differentiation of cells
Heterotrophy
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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 (Video Clip)
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Autotophs obtain energy by making their own food. o Most autotrophs, such as plants, use sunlight as their source of energy. o Other autotrophs use chemicals in their environment as their source of energy.

Hetertrophs must take in food to meet their energy needs.
Mobility

Animals are unique among living things in being able to perform rapid, complex movements.
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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.
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 (Video clip)
Unicellular Organism Multicellular Organism
# of cells
Example & Number of cells
1
Bacteria: 1
More than 1
Human: over 100 trillion
Can individual cell live on its own? Yes No
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 (Video Clip)
Examples of organisms
# of sets of chromosomes
# of chromosomes in humans
Diploid
Humans & many other eukaryotes
2
23 pairs or 46
Haploid
Prokaryotes & gametes
(sperm & eggs) of many eukaryotes
1
23
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.
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.
Blastula Formation
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In all animals except sponges, the zygote (fertilized egg cell) undergoes cell divisions that form a hollow ball of cells called a blastula.
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Cells within the blastula eventually develop into three distinct layers of cells—ectoderm, endoderm, and mesoderm.
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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 (Video clip)

After fertilization, a zygote undergoes cleavage, a series of rapid mitotic divisions.

The fertilized cell first divides into 2 cells each of which is roughly half the size of the original.
 Each of these daughter cells divides again. The resulting cells are roughly ¼ the size of the fertilized egg.

This process continues until the zygote is a mass of cells. While the size of the cells has decreased, the total size of the zygote has remained roughly the same as that of the fertilized egg.

The zygote has become a hollow ball of cells called a blastula. The hollow space in the center of the blastula is called a blastocoel.
Cleavage and Blastula Formation
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.

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.

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.
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 (Video clip)

The symmetry of an animal describes the overall pattern or structure of its body.

Sponges are irregular in shape; they are called asymmetrical.

In an animal with radial symmetry, the body parts are arranged in a circle around a central point.

Sea anemones have radial symmetry. You can cut through the center of a sea anemone in any direction and both halves would look the same.

Most animals have bilateral symmetry

Two sides of their bodies mirror each other. There is only one way you could cut through the center of a bilaterally symmetrical organism for both halves to look the same.


Animals with bilateral symmetry usually have a head and a tail.
Cephalization (Video clip)

Cephalization is the concentration of sensory organs and nerves in the anterior end of an animal. Cephalized animals have a head.
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Animals that are bilaterally symmetric have an anterior and a posterior and are therefore usually cephalized.
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Cephalization is a major evolutionary change because it allows animals to seek out mates, sense food and avoid prey as they move in the forward direction through their environment.

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.
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Animals with no body cavity are called acoelomates.
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Animals called pseudocoelomates have a body cavity located between the mesoderm and endoderm.
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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 (Video clip)

Many animals that are bilaterally symmetric have a body cavity of coelem, a fluid filled space that forms between the digestive tract and the outer wall of the body during development. o Earth worms are coelomates, animals that have a true coelom that is completely surrounded by mesoderm. o The true coelom wraps around the digestive tract suspending and protecting digestive organs. o It also provides a firm base for the animal’s muscles to push against. o The fluid in the coelom also serves as a reservoir for nutrients and waste that diffuse into and out of the animal’s cells.

Some bilaterally symmetric animals like nematode worms are pseudocoelomates. o Their body cavity is surrounded by mesoderm on one side and endoderm on the other side.

A few animals that are bilaterally symmetric do not have a coelom at all. o For example, flatworms have bodies that are completely filled with tissue. These animals are called acoelomates.
Three Body Plans of Symmetrical Animals


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 (Video clip)

In animals, segmentation refers to a body composed of a series of repeating similar units that can move independently permitting great flexibility and mobility.

Within the phylum Arthropoda, segments may look different and have different functions. A small change in a segment can modify it for eating, defense or reproduction.

In some arthropod species, like this butterfly, the larva exhibit segmentation, but many segments are fused in the adult.
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 (Video clip)

A phylogenic tree is a visual representation of the evolutionary relationships among different animals. o Animals that are more closely related are shown on the same branch of the tree. o Animals that are more distantly related are shown on different parts of the tree.

These relationships are based on the presence or absence of various traits. o For example all of the animals on the bracketed portion of the tree share the trait of being multicellular. Only the protists at the base are unicellular. o All animals except the sponges have true tissues. They are grouped together in the part of the tree in the red bracket.

o Animals that have body cavities are grouped together in the region of the tree indicated by the green bracket. o Animals that have jointed appendages, such as crabs, shrimp & lobsters, are all grouped together on the branch circled in purple.

Each of these groupings - multicellularity, tissues, body cavities and jointed appendages - represent key evolutionary innovations found in animals that are alive today.
Phylogenetic Tree (Video clip)

A phylogenetic tree is a family tree that shows the evolutionary relationships thought to exist between groups of animals. This phylogenetic tree shows the relationship thought to exist between vertebrates.

The branch points on phylogenetic trees represent common ancestors. o For example, reptiles and birds are believed to share a relatively recent common ancestor. o Therefore reptiles and birds lie relatively close to a branch point. o The common ancestor for reptiles and mammals lived sometime before the common ancestor for reptiles and birds. o Therefore the branch point or reptiles and mammals is further down the phylogenetic tree. o Lampreys and hagfishes shared a common ancestor with reptiles back in time. o Therefore the branch point for reptiles and lampreys is even further down the 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.
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.
Digestion

A hydra has a gastrovascular cavity, while a roundworm has a digestive tract in which food travels in one direction only.
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.

Parts of the Human Respiratory System (Roll over) Label!
10 3
Fish Gills (Video clip)

Fishes breathe with gills.

Gills are supported by 4 sets of curved bone on each side of the fish’s head called gill arches.

Each gill has a double row of tiny tissue projections called gill filaments.

These are rich in blood vessels and have a large surface area for rapid gas exchange.
 Water flows from the fish’s mouth over its gills through the gill filaments.

As the water flows over the gill filaments and away from the head, blood travels toward the fish’s head.

Deoxygenated blood moves against the water and absorbs oxygen from the water.

The blood releases carbon dioxide back into the water.
This pattern of flow is called countercurrent exchange.

It allows for more efficient gas exchange than if the blood and water flowed in the same direction.

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.
Comparing Open and Closed Circulatory Systems (Video clip)

Both transport nutrients and oxygen to cells and wastes away from cells.

Open circulatory system: o A blood like circulatory fluid called hemolymph is pumped from vessels into a body cavity and then is returned to vessels. o Ex: arthropods and most mollusks

Closed circulatory system o A heart circulates blood through a network of blood vessels that form a closed loop. o Materials pass into and out of the blood by diffusing through the blood vessels. o Ex: cephalopods and vertebrates
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.

The hydra has a simple nerve net, while the flatworm and the grasshopper have morecomplex nervous systems.
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.
Comparing Exoskeletons and Endoskeletons (video clip)
Check the appropriate box.
Rigid external skeleton that encases the body of an animal
Rigid internal skeleton embedded within an animal
Act as frames that support and protect the animal’s internal organs
Provides surfaces against which the muscles can pull
Arthropods and mollusks are examples
Vertebrates and echinoderms are examples
Some vertebrates such as a turtle
Does not grow with the animal; must be shed and grown again as the animal gets bigger
Grows w/ an animal & is able to support a large heavy body
Exoskeleton
√
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√
√
√
√
Endoskeleton
√
√
√
√
√
√

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.
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.
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.

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.
Sexual Reproduction (Video clip)

Reproduction is the process by which new offspring are produced.

In sexual reproduction, the genetic material from more than 1 parent combines to produce offspring.

This makes these offspring unique.

Sexual reproduction enables species to adapt rapidly to new conditions.

Chapter 37: Introduction to Body Structure
Section 1 Body Organization
Objectives:

Identify four levels of structural organization within the human body.

Analyze the four kinds of body tissues.

List the body’s major organ systems.

Evaluate the importance of endothermy in maintaining homeostasis.
Levels of Structural Organization

The body is organized into four levels: cells, tissues, organs, and organ systems.

A tissue is a group of similar cells that work together to perform a common function.

The body has four basic kinds of tissues: epithelial, nervous, connective, and muscle tissues.
Tissue Organ Organ System (Video clip)

In most multicellular organisms, cells are organized into tissues.

A tissue is a group of similar cells that perform a common function. o The function of the spongy tissue in the lung is to take in oxygen and release carbon dioxide.

An organ is a collection of tissues that carry on a particular function of the body or specialized task. o The function of the lungs is to take oxygen from the air and deliver it to the blood and take carbon dioxide from the blood and transfer it to the air.

An organ system is a set of organs that work together to perform a set of related tasks. o The lungs are part of the respiratory system, a group of organs that work together to help you breathe.
Four Kinds of Tissues

Epithelial tissue lines most body surfaces and protects other tissues from damage and dehydration.


Nervous tissue consists of nerve cells, which carry information throughout the body.

Various kinds of connective tissue support, protect, and insulate the body.

Muscle tissue enables the movement of body structures by muscle contraction.
Human Body Tissues
Body Tissues (Thumbnails)

The human body has 4 main types of tissue: nervous, connective, muscle and epithelial.

Nervous tissue contains special cells called neurons that receive and transmit messages in the form of electrical impulses.

Connective tissue (CT) binds, supports and protects structures in the body. o Bone is a mineralized CT with blood vessels for nourishment. o Blood and lymph are also types of CT o Adipose CT is composed of fat cells and lies under the top layers of skin to help insulate the body and store energy. o Tendons are CT that attaches skeletal muscle to bone. o Ligaments are CT that attaches bone to other bone.


Muscle tissue is composed of cells that can contract.

Cardiac muscle, found in your heart, pumps blood through the body.

Skeletal muscles are attached to your bones and contract to help you move.
 Smooth muscle handles body functions that you don’t have to think about such as the movement of food through your digestive system.
Stem Cells

Embryonic stem cells are early, undifferentiated cells that give rise to all of the types of cells in the developing body.

Embryonic stem cells will divide indefinitely.

Adult stem cells are not as versatile and do not divide indefinitely.
Organ Systems

Body organs are made of combinations of two or more types of tissues working together to perform a specific function.

An organ system is a group of organs that work together to carry out major activities or processes. Some organs function in more than one organ system.
Major Organ Systems of the Human Body

Overview of Organ Systems (Video clip)
Body Cavities

The human body contains four large fluid-filled spaces, or body cavities, that house and protect the major internal organs.

These body cavities are the thoracic cavity (heart and lungs), cranial cavity (brain), abdominal cavity (digestive organs), and spinal cavity (spinal cord).
Cavities of the Human Body Inside the Human Coelom

Endothermy

Like all mammals, humans are endotherms. Humans maintain a fairly constant internal temperature of about 37°C (98.6 °F).

The human body uses a great deal of energy to maintain a constant body temperature.
Advantage of Endothermy (video clip)

Unlike exotherms that vary their body temperatures along with the changing outside temperature, endothermic animals such as mammals and birds generate body heat internally.

Most endotherms, like humans, are also homeotherms meaning they maintain a fairly constant internal temperature regardless of environmental conditions.

To maintain our body temperature, we shiver when cold and sweat when hot.

Endotherms have the advantage to live in a wide range of habitats.

The ability to migrate between vastly different habitats is another advantage of endothermy.