Biology 2nd period McFall

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Biology 2nd periodMcFall
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Chapter Contents page xi
Chapter 25 What is an animal? 25.1 Typical
Animal Characteristics 25.2 Body Plans and
Adaptations
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25.1 Section Objectives page 673
Section Objectives

• Identify the characteristics of animals.

• Identify cell differentiation in the development
  of a typical animal.

• Sequence the development of a typical animal.

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Section 25.1 Summary pages 673 - 679
Characteristics of Animals

• Animals are eukaryotic, multicellular organisms
  with ways of moving that help them reproduce,
  obtain food, and protect themselves.

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Section 25.1 Summary pages 673 - 679
Characteristics of Animals

• Most animals have specialized cells that form
  tissues and organssuch as nerves and muscles.

• Animals are composed of cells that do not have
  cell walls.

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Section 25.1 Summary pages 673 - 679
Animals obtain food

• One characteristic common to all animals is that
  they are heterotrophic, meaning they must consume
  food to obtain energy and nutrients.

• All animals depend either directly or indirectly
  on autotrophs for food.

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Section 25.1 Summary pages 673 - 679
Animals obtain food

• Scientists hypothesize that animals first evolved
  in water.

• In water, some animals, such as barnacles and
  oysters, do not move from place to place and have
  adaptations that allow them to capture food from
  their water environment.

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Section 25.1 Summary pages 673 - 679
Animals obtain food

• Organisms that are permanently attached to a
  surface are called sessile.

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Section 25.1 Summary pages 673 - 679
Animals obtain food

• Some aquatic animals, such as corals and sponges
  move about only during the early stages of their
  lives.

• Most adults are sessile and attach themselves to
  rocks or other objects.

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Section 25.1 Summary pages 673 - 679
Animals obtain food

• There is little suspended food in the air.

• Land animals use more oxygen and expend more
  energy to find food.

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Section 25.1 Summary pages 673 - 679
Animals digest food

• In some animals, digestion is carried out within
  individual cells in other animals, digestion
  takes place in an internal cavity.

• Some of the food that an animal consumes and
  digests is stored as fat or glycogen, a
  polysaccharide, and used when other food is not
  available.

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Section 25.1 Summary pages 673 - 679
Animals digest food

• In animals such as planarians and earthworms,
  food is digested in a digestive tract.

Mouth
Digestive tract
Digestive tract
Extended pharynx
Anus
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Section 25.1 Summary pages 673 - 679
Animal cell adaptations

• Most animal cells are differentiated and carry
  out different functions.

• Animals have specialized cells that enable them
  to sense and seek out food and mates, and allow
  them to identify and protect themselves from
  predators.

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Section 25.1 Summary pages 673 - 679
Development of Animals

• Most animals develop from a fertilized egg cell
  called a zygote.

• After fertilization, the zygote of different
  animal species all have similar, genetically
  determined stages of development.

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Section 25.1 Summary pages 673 - 679
Fertilization

• Most animals reproduce sexually.

• Male animals produce sperm cells and female
  animals produce egg cells.

• Fertilization occurs when a sperm cell penetrates
  the egg cell, forming a new cell called a zygote.

• In animals, fertilization may be internal or
  external.

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Section 25.1 Summary pages 673 - 679
Cell division

• The zygote divides by mitosis and cell division
  to form two cells in a process called cleavage.

cleavage
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Section 25.1 Summary pages 673 - 679
Cell division

• Once cell division has begun, the organism is
  known as an embryo.

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Section 25.1 Summary pages 673 - 679
Cell division

• The two cells that result from cleavage then
  divide to form four cells and so on, until a
  cell-covered, fluid-filled ball called a blastula
  is formed.

• The blastula is formed early in the development
  of an animal embryo.

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Section 25.1 Summary pages 673 - 679
Gastrulation

• After blastula formation, cell division continues.

• The cells on one side of the blastula then move
  inward to form a gastrulaa structure made up of
  two layers of cells with an opening at one end.

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Section 25.1 Summary pages 673 - 679
Gastrulation

• The cells at one end of the blastula move inward,
  forming a cavity lined with a second layer of
  cells.

• The layer of cells on the outer surface of the
  gastrula is called the ectoderm.

• The layer of cells lining the inner surface is
  called the endoderm.

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Section 25.1 Summary pages 673 - 679
Gastrulation
Ectoderm

• The ectoderm cells of the gastrula continue to
  grow and divide, and eventually they develop into
  the skin and nervous tissue of the animal.

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Section 25.1 Summary pages 673 - 679
Gastrulation

• The endoderm cells develop into the lining of the
  animals digestive tract and into organs
  associated with digestion.

Endoderm
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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• Mesoderm is found in the middle of the embryo
  the term meso means middle.

Mesoderm

• The mesoderm is the third cell layer found in the
  developing embryo between the ectoderm and the
  endoderm.

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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• The mesoderm cells develop into the muscles,
  circulatory system, excretory system, and, in
  some animals, the respiratory system.

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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• When the opening in the gastrula develops into
  the mouth, the animal is called a protostome.

• Snails, earthworms, and insects are examples of
  protostomes.

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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• In other animals, such as sea stars, fishes,
  toads, snakes, birds, and humans, the mouth does
  not develop from the gastrulas opening.

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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• An animal whose mouth developed not from the
  opening, but from cells elsewhere on the gastrula
  is called a deuterostome.

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Section 25.1 Summary pages 673 - 679
Formation of mesoderm

• Scientists hypothesize that protostome animals
  were the first to appear in evolutionary history,
  and that deuterostomes followed at a later time.

• Determining whether an animal is a protostome or
  deuterostome can help biologists identify its
  group.

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Section 25.1 Summary pages 673 - 679
Cell differentiation in Animal Development

• The fertilized eggs of most animals follow a
  similar pattern of development. From one
  fertilized egg cell, many divisions occur until a
  fluid-filled ball of cells forms.

• The ball folds inward and continues to develop.

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Section 25.1 Summary pages 673 - 679
Sperm cells
Cell Differentiation in Animal Development
Fertilization
Egg cell
Formation of mesoderm
First cell division
Endoderm
Mesoderm
Ectoderm
Gastrulation
Additional cell divisions
Formation of a blastula
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Section 25.1 Summary pages 673 - 679
Growth and development

• Most animal embryos continue to develop over
  time, becoming juveniles that look like smaller
  versions of the adult animal.

• In some animals, such as insects and echinoderms,
  the embryo develops inside an egg into an
  intermediate stage called a larva (plural larvae).

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Section 25.1 Summary pages 673 - 679
Growth and development
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Section 25.1 Summary pages 673 - 679
Growth and development

• A larva often bears little resemblance to the
  adult animal.

• Inside the egg, the larva is surrounded by a
  membrane formed right after fertilization.

• When the egg hatches, the larva breaks through
  this fertilization membrane.

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Section 25.1 Summary pages 673 - 679
Adult animals

• Once the juvenile or larval stage has passed,
  most animals continue to grow and develop into
  adults.

• This growth and development may take just a few
  days in some insects, or up to fourteen years in
  some mammals.

• Eventually the adult animals reach sexual
  maturity, mate, and the cycle begins again.

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25.2 Section Objectives page 680
Section Objectives

• Compare and contrast radial and bilateral
  symmetry with asymmetry.

• Trace the phylogeny of animal body plans.

• Distinguish among the body plans of acoelomate,
  pseudocoelomate, and coelomate animals.

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Section 25.2 Summary pages 680 - 685
What is symmetry

• Symmetry is a term that describes the arrangement
  of body structures.

• Different kinds of symmetry enable animals to
  move about in different ways.

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Section 25.2 Summary pages 680 - 685
Asymmetry

• An animal that is irregular in shape has no
  symmetry or an asymmetrical body plan.

• Animals with no symmetry often are sessile
  organisms that do not move from place to place.

• Most adult sponges do not move about.

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Section 25.2 Summary pages 680 - 685
Asymmetry

• The bodies of most sponges consist of two layers
  of cells.

• Unlike all other animals, a sponges embryonic
  development does not include the formation of an
  endoderm and mesoderm, or a gastrula stage.

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Section 25.2 Summary pages 680 - 685
Radial symmetry

• Animals with radial symmetry can be divided along
  any plane, through a central axis, into roughly
  equal halves.

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Section 25.2 Summary pages 680 - 685
Radial symmetry

• Radial symmetry is an adaptation that enables an
  animal to detect and capture prey coming toward
  it from any direction.

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Section 25.2 Summary pages 680 - 685
Radial symmetry

• The body plan of a hydra can be compared to a
  sack within a sack.

• These sacks are cell layers organized into
  tissues with distinct functions.

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Section 25.2 Summary pages 680 - 685
Radial symmetry

• A hydra develops from just two embryonic cell
  layersectoderm and endoderm.

Inner cell layer
Outer cell layer
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Section 25.2 Summary pages 680 - 685
Bilateral symmetry

• An organism with bilateral symmetry can be
  divided down its length into similar right and
  left halves.

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Section 25.2 Summary pages 680 - 685
Bilateral symmetry

• Bilaterally symmetrical animals can be divided in
  half only along one plane.

• In bilateral animals, the anterior, or head end,
  often has sensory organs.

• The posterior of these animals is the tail end.

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Section 25.2 Summary pages 680 - 685
Bilateral symmetry

• The dorsal, or upper surface, also looks
  different from the ventral, or lower surface.

• Animals with bilateral symmetry can find food and
  mates and avoid predators because they have
  sensory organs and good muscular control.

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Section 25.2 Summary pages 680 - 685
Bilateral Symmetry and Body Plans

• All bilaterally symmetrical animals developed
  from three embryonic cell layersectoderm,
  endoderm, and mesoderm.

• Some bilaterally symmetrical animals also have
  fluid-filled spaces inside their bodies called
  body cavities in which internal organs are found.

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Section 25.2 Summary pages 680 - 685
Acoelomates

• Animals that develop from three cell
  layersectoderm, endoderm, and mesodermbut have
  no body cavities are called acoelomate animals.

• They have a digestive tract that extends
  throughout the body.

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Section 25.2 Summary pages 680 - 685
Acoelomates
Acoelomate Flatworm

• Flatworms are bilaterally symmetrical animals
  with solid, compact bodies. Like other
  acoelomate animals, the organs of flatworms are
  embedded in the solid tissues of their bodies.

Ectoderm
Mesoderm
Endoderm
Body cavity
Digestive tract
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Section 25.2 Summary pages 680 - 685
Acoelomates
Acoelomate Flatworm

• A flattened body and branched digestive tract
  allow for the diffusion of nutrients, water, and
  oxygen to supply all body cells and to eliminate
  wastes.

Ectoderm
Mesoderm
Endoderm
Body cavity
Digestive tract
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Section 25.2 Summary pages 680 - 685
Pseudocoelomates
Pseudocoelomate Roundworm

• A roundworm is an animal with bilateral symmetry.

Ectoderm
Mesoderm
Endoderm

• The body of a roundworm has a space that develops
  between the endoderm and mesoderm.

Body cavity
Digestive tract
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Section 25.2 Summary pages 680 - 685
Pseudocoelomates
Pseudocoelomate Roundworm

• It is called a pseudocoeloma fluid-filled body
  cavity partly lined with mesoderm.

Ectoderm
Mesoderm
Endoderm
Body cavity
Digestive tract
Pseudocoelom
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Section 25.2 Summary pages 680 - 685
Pseudocoelomates

• Pseudocoelomates can move quickly.

• Although the roundworm has no bones, it does have
  a rigid, fluid-filled space, the pseudocoelom.

• Its muscles attach to the mesoderm and brace
  against the pseudocoelom.

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Section 25.2 Summary pages 680 - 685
Pseudocoelomates

• Pseudocoelomates have a one-way digestive tract
  that has regions with specific functions.

• The mouth takes in food, the breakdown and
  absorption of food occurs in the middle section,
  and the anus expels waste.

Intestine
Anus
Mouth
Round body shape
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Section 25.2 Summary pages 680 - 685
Coelomates
Coelomate Segmented Worm

• The body cavity of an earthworm develops from a
  coelom, a fluid-filled space that is completely
  surrounded by mesoderm.

Ectoderm
Mesoderm
Endoderm
Body cavity
Digestive tract

• The greatest diversity of animals is found among
  the coelomates.

Coelom
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Section 25.2 Summary pages 680 - 685
Coelomates

• In coelomate animals, the digestive tract and
  other internal organs are attached by double
  layers of mesoderm and are suspended within the
  coelom.

• The coelom cushions and protects the internal
  organs. It provides room for them to grow and
  move independently within an animals body.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• Over time, the development of body cavities
  resulted in a greater diversity of animal species.

• Some animals, such as mollusks, evolved hard
  shells that protected their soft bodies.

• Other animals, such as sponges, evolved hardened
  spicules between their cells that provided
  support.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• Some animals developed exoskeletons. An
  exoskeleton is a hard covering on the outside of
  the body that provides a framework for support.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• Exoskeletons also protect soft body tissues,
  prevent water loss, and provide protection from
  predators.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• As an animal grows, it secretes a new exoskeleton
  and sheds the old one.

• Exoskeletons are often found in invertebrates.
  An invertebrate is an animal that does not have a
  backbone.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• Invertebrates, such as sea urchins and sea stars,
  have an internal skeleton called an endoskeleton.
  It is covered by layers of cells and provides
  support for an animals body.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• The endoskeleton protects internal organs and
  provides an internal brace for muscles to pull
  against.

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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• An endoskeleton may be made of calcium carbonate,
  as in sea stars cartilage, as in sharks or
  bone.

Calcium carbonate
cartilage
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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• Bony fishes, amphibians, reptiles, birds, and
  mammals all have endoskeletons made of bone.

bone
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Section 25.2 Summary pages 680 - 685
Animal Protection and Support

• A vertebrate is an animal with an endoskeleton
  and a backbone. All vertebrates are bilaterally
  symmetrical.

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Section 25.2 Summary pages 680 - 685
Origin of Animals

• Most biologists agree that animals probably
  evolved from aquatic, colonial protists.

• Scientists trace this evolution back in time to
  late in the Precambrian.

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Section 25.2 Summary pages 680 - 685
Origin of Animals
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Section 25.2 Summary pages 680 - 685
Origin of Animals

• Many scientists agree that all the major animal
  body plans that exist today were already in
  existence at the beginning of the Cambrian
  Period, 543 million years ago.

• All known species have variations of the animal
  body plans developed during the Cambrian Period.