What is an Animal? Chapter 25

Characteristics of Animals Animals obtain food  Sessile – Organisms that are permanently attached to a surface  Sessile animals filter feed  Sessile animals are aquatic

Characteristics of Animals Animals digest food  Multicellular organisms digest food in a digestive tract

Characteristics of Animals Animal cell adaptations  Animal cells are differentiated and carry out different functions

Development of Animals Fertilization  The fusing of a sperm cell to an egg cell  Zygote – a fertilized egg

(n) (2n)

Cell Division Zygotes divide by mitosis Once cell division had begun, the organism is known as an embryo Blastula – a fluid-filled ball covered with cells (2n)

Gastrulation Gastrula – the cells on one side of the blastula move inward

Gastrulation Layers of gastrula  Ectoderm – the outer layer; becomes skin and nervous tissues  Mesoderm – the middle layer; becomes muscles, circulatory system, excretory system, (and for some animals, the respiratory system)  Endoderm – the inner layer; becomes the lining of the digestive tract

Gastrulation

Protostome – the opening in the gastrula develops into the mouth  Examples: Snails, earthworms, and insects Deuterostome – an animal whose mouth developed from other cells on the gastrula  Examples: Fishes

Animal Reproduction Asexual reproduction – requires only one parent  Ex. – bacteria Sexual reproduction – requires two parents Reproduction AsexualSexual External fertilization Internal fertilization

Animal Reproduction Internal fertilization – sperm and egg unite inside the body External fertilization – sperm and egg unite outside the body Reproduction AsexualSexual External fertilization Internal fertilization

Animal Reproduction External fertilization occurs in water Pro: Many offsprings can be produced Con: Parental protection is reduced

Animal Reproduction Internal fertilization occurs inside animals Pro: Increased parental protection Con: Low number of offsprings produced

Directional Terms Superior – Toward the head; above Inferior – Away from the head; below Anterior (or ventral) – Toward the front Posterior (or dorsal) – Toward the backside

Directional Terms Medial – Toward the midline of the body Lateral – Away from the midline; the outer side of the body Proximal – Close to Distal – Far from

Directional Terms Superior Inferior Anterior (Ventral) Posterior (Dorsal) Medial Lateral Proximal Distal

Symmetry Asymmetry – an animal that has no symmetry  Example: sponge

Symmetry Radial symmetry – divided along a plane, through a central axis, into roughly equal halves Bilateral symmetry – divided down its length into similar right and left halves

Symmetry

Body Cavities Coelom - cavity Cavity – an empty space Body cavities make it possible for animals to grow larger

 Three body cavities  1. Acoelomates – animals that develop from three cell layers but have no body cavities

Body Cavities  2. Pseudocoelomates – a fluid-filled body cavity partly lined with mesoderm  Pseudocoelomate animals are larger and thicker than acelomate animals

Body Cavities 3. Coelomates – a fluid-filled space that is completely surrounded by mesoderm  More complex animals are coelomates

Animal Protection and Support Exoskeleton – a hard covering on the outside of the body that provides a framework for support Crayfish

Animal Protection and Support Endoskeleton – an internal skeleton within animals

Animal Protection and Support Invertebrate – an animal without a backbone Vertebrate – an animal with a backbone

Animal Classification Animals Invertebrates Vertebrates Sponges Cnidarians Worms Mollusks Arthropods Enchinoderms Ectotherms (cold-blooded) Endotherms (warm-blooded) Fishes Amphibians Reptiles Birds Mammals