GRADE 10LESSON: 1BIODIVERSITY OF ANIMALS( UNDERSTANDING LIFE SCIENCES, CHAPTER 12, P342)
The animal kingdom extends far beyondhumans and other animals we may encounter 1.3 million living species of animals have beenidentified Invertebrates (animals that lack a backbone)account for 95% of known animal species.
Most animals reproduce sexually, with thediploid stage usually dominating the life cycle After a sperm fertilizes an egg, the zygoteundergoes rapid cell division called cleavage Cleavage leads to formation of a blastula The blastula undergoes gastrulation, forming agastrula with different layers of embryonictissues.
Animal body plans also vary according to theorganization of the animal’s tissues Tissues are collections of specialized cells During development, three germ layers giverise to the tissues and organs of the animalembryo
Ectoderm is the germ layer covering theembryo’s surface Endoderm is the innermost germ layer andlines the developing digestive tube, called thearchenteron Mesoderm: middle layer of some body plans
Diploblastic animals have ectoderm andendoderm Triploblastic animals have an ectoderm,endoderm and intervening mesoderm layer.
Most triploblastic animals possess a body cavity A true body cavity is called a coelom and isderived from mesoderm Coelomates are animals that possess a true coelom A pseudocoelom is a body cavity derived from themesoderm and endoderm Triploblastic animals that possess a pseudocoelomare called pseudocoelomates Triploblastic animals that lack a body cavity arecalled acoelomates
Based on early development, many animals canbe categorized as having protostomedevelopment or deuterostome development
These two types of developments differ inregard to: Different cleavage Different coelom formation Fate of the blastop
In protostome development, cleavage is spiraland determinate In deuterostome development, cleavage isradial and indeterminate With indeterminate cleavage, each cell in theearly stages of cleavage retains the capacity todevelop into a complete embryo
In protostome development, the splitting ofsolid masses of mesoderm forms the coelom. In deuterostome development, the mesodermbuds from the wall of the archenteron to formthe coelom.
The blastopore forms during gastrulation andconnects the archenteron to the exterior of thegastrula In protostome development, the blastoporebecomes the mouth In deuterostome development, the blastoporebecomes the anus
Sedentary animals (fixed in one position) They live in both fresh and marine waters Cellular level of development Lack true tissues and organs Asymmetrical
True tissue – Eumetazoa Both sessile and motile forms including jellies,corals, and hydras Diploblastic body plan Radial symmetry The basic body plan of a cnidarian is a sac witha central digestive compartment, thegastrovascular cavity A single opening functions as mouth and anus
Carnivores that use tentacles to capture prey The tentacles are armed with cnidocytes,unique cells that function in defense andcapture of prey Nematocysts are specialized organelles withincnidocytes that eject a stinging thread.
Live in marine, freshwater, and dampterrestrial habitats. Triploblastic development Acoelomates Flattened dorsoventrally and have agastrovascular cavity Gas exchange takes place across the surface Protonephridia regulate the osmotic balance
Found in most aquatic habitats, in the soil, inmoist tissues of plants, and in body fluids andtissues of animals They have an alimentary canal, but lack acirculatory system Sexual Reproduction Internal fertilization Some species are parasites of plants andanimals.
Bodies composed of a series of fused rings orcompartments - Metamerism
Found in nearly all habitats of the biosphere The arthropod body plan consists of a segmented body, hard exoskeleton (made of layers of proteinand the polysaccharide chitin jointed appendages The body is completely covered by the cuticle When it grows, it molts its exoskeleton. Includes: insects, crabs, spiders, millipedes,centipedes, mites
Phylum Chordata consists of two subphyla ofinvertebrates as well as hagfishes andvertebrates Vertebrates are a subphylum within thephylum Chordata Chordates are bilaterian animals that belong tothe Deuterostomia. All chordates share a set of derived characters Some species have some of these traits onlyduring embryonic development