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WHAT IS AN ANIMAL? Chapter 18 ALL ANIMALS ARE... Multicellular Eukaryotic Heterotrophic Obtain nutrients by ingestion Lack cell walls So, how are they different from plants? Fungi? ALL ANIMALS ARE... PLANTS Multicellular Eukaryotic Autotrophic Obtain nutrients by absorption Have cell walls (cellulose) ALL ANIMALS ARE... FUNGI Multicellular Eukaryotic Autotrophic Obtain nutrients by decomposition Have cell walls (chitin) ANIMAL LIFE CYCLE Adults are diploid and make haploid gametes via meiosis Egg (female) and sperm (male) fuse to make a zygote Zygote divides by mitosis producing a blastula (hollow ball of cells) Hollow blastula then folds inward (for most animals), forming gastrula. Internal sac becomes digestive tract After gastrulation,most animals develop into adults, some go through larva/metamorphosis Notice that later gastrulation produces internal layers EVOLUTIONARY HISTORY Animals most likely evolved from a “colonial” protist during the precambrian period over 575 million years ago Protists are eukaryotic, but normally single-celled organisms. However they can form loose associations with other cells...colonies. However, colonies of lack cellular specialization as would be found in true multicellular organisms (tissues). ALMOST ALL ANIMALS ARE INVERTEBRATES Some have radial symmetry (tend to be sedentary), others are bilateral (tend to be mobile...sense organ clustered to front) ANIMAL BODY PLANS Most animals (except sponges) have true tissues Most have three tissue layers that develop during gastrulation: endoderm (becomes digestive tract) , mesoderm (internal organs), ectoderm (outer covering) COMMON PHYLA: PORIFERA “Sponges” Lack true tissues, sedentary Suspension feeders Most are marine simplest of all animals COMMON PHYLA: CNIDARIAN “Jelly fish and sea anemones”...named for “stinging cells” radially symmetric carnivorous simple bodies with some tissues, one opening digestive tract marine COMMON PHYLA: NEMATODA “Round worms” Digestive tract with 2 openings tough outer covering some parasitic, decomposers, or free living most species look very similar COMMON PHYLA: ANNELIDA “Segmented worms” segmentation aids in movement closed circulatory system earthworms, leeches COMMON PHYLA: PLATYHELMINTHES “Flat worms”...like planarian (at left) simplest of bilaterally symmetrical animals most parasitic, some free living one-opening in gastrovascular cavity COMMON PHYLA: MOLLUSCA Name means “soft-bodied” Most protected by hard shell very varied body forms (octopus , squid, clams, oysters, snails) open circulatory system COMMON PHYLA: ARTHROPODA Name means “jointed feet” most successful of all animals in terms of sheer numbers of species have exoskeleton and open circulatory system includes: insects, crabs, lobsters, spiders, scorpions COMMON PHYLA: ECHINODERMATA Name means “spiny skin” have endoskeleton radially symmetric includes: starfish, urchins COMMON PHYLA: CHORDATA Have dorsal nerve chord notochord (supportive structure near nerve chord) pharyngeal slits and postanal tail includes: some invertebrates and all “familiar” animals (birds, reptiles amphibians, mammals, fish) Human embryo ~35-40 days pharyngeal slits post-anal tail ANIMAL FORM AND FUNCTION Chapter 20 BEING AN ANIMAL HAS ITS CHALLENGES Unlike unicellular, aquatic organisms, animals must: Obtain nutrients and oxygen from environment and distribute throughout body excrete wastes sense and respond to environment move and reproduce THE BIG IDEA... The relationship between form and function has repeated itself throughout the year... At many levels of biological hierarchy...from molecules, to cellular structures, to tissues, to organs and systems, to body shapes... the forms taken by structures have been shaped by natural selection for their function Animals solve their challenges, and reflect form/function relationships with specialization EPITHELIAL TISSUE Covers and lines surfaces, cavities and organs Varies in terms of layering (simple vs stratified) Varies in terms of cell shape (squamous vs columnar vs cuboidal) CONNECTIVE TISSUE sparse cells distributed in a matrix...primary function: support High degree of variation in forms Examples: bone, blood, adipose (fat), cartilage, fibrous, loose. MUSCLE TISSUE consists of long cells called fibers which aid in movement most abundant tissue (mass) in most animals Examples: cardiac, skeletal, smooth. NERVOUS TISSUE cells are called neurons senses stimuli and transmits information ORGANS ARE MADE OF TISSUES multiple tissues perform different roles which allow the organ to function For example the small intestine consists of epithelial, smooth muscle, and connective tissues ANIMALS MUST EXCHANGE MATTER WITH ENVIRONMENT Structural adaptations increase the efficiency of exchange • Wherever exchange is required (gills, lungs, digestive tract, urinary system, etc) linings tend to be thin with few layers of cells • Shapes (folds, sacs, elongated tubes) can maximize SA:Vol ratio...remember why cells themselves are small HOMEOSTASIS Maintenance of stable internal conditions A dynamic relationship between outside forces that tend to want to change the internal environment vs. internal controls that resist such change Mostly based on negative feedback