LECTURE BIO NOTES (2/18/09)
Key Concepts: o Animals are particularly species-rich and morphologically diverse lineage of multicelluar organisms o Major groups of animals are recognized by their basic body plan, which differs in the number of tissues observed in embryos, symmetry, the presence or absence of a body cavity, and the way in which early events in embryonic development proceed o Recent phylogenetic analyses of animals have shown that there were three fundamental splits as animals diversified, resulting in two protostome groups (Lophotrochozoa and Ecdysozoa) and the deuterstomes o Within major groups of animals, evolutionary diversification was based on innovative ways of feeding and moving. Most animals ... intro o Animals are a monophyletic group that can be recognized by three traits: (1) They are multicellular (2) They are heterotrophs -- they ingest their food (3) They move under their own power at some point in their life cycle o Over 1.2 million animal species have been described and named to date, and biologists predict that tens of millions more have yet to be discovered Characteristics of Animals o In addition to multicellularity, eating and moving, several other traits are shared by animals (1) Animal cells have no cell walls but do have an extensive extracellular matrix (2) Animals are the only lineage wit muscle and nerve tissue (3) No animals undergo alternation of generations (4) Adults of most species are diploid; only gametes are haploids o Beyond these characteristics, animals are incredibly diverse, particularly in morphology o About 34 major animal phyla are recognized The Evolution of Tissues o All animals have tissues -- tightly integrated structural and functional units of cells o All animals have epithelium, a layer of tightly joined cells that covers the boy surface o Diploblasts are animals whose embryos have two types of tissues or germ layers: the ectoderm (outer skin) and endoderm (inside skin) o Triploblasts are animals whose embryos have three types of tissues: the ectoderm, endoderm, and mesoderm (middle skin). These germ layers develop into distinct adult tissues and organs Symmetry and cephalization
o A basic feature of a multicellular body is the presence or absence of a plane of symmetry o Most sponges are asymmetrical o Animals with radial symmetry have at least two planes of symmetry. Organisms with bilateral symmetry have a single plane of symmetry and face their environment in one direction (ex: starfish and sea urchins) o Bilateral symmetry allowed cephalization (organization of an animal to become a head with mouth parts and sensory organs to feed and etc), the development of a ahead region where structures for feeding, sensing the environment, and processing information are concentrated There are three types of body symmetry in animals o Asymmetry no plane of symmetry ( sponge) o Radial symmetry multiple planes of symmetry (jellyfish) o Bilateral symmetry single plane of symmetry (lizard) Why was the evolution of a body cavity important? o Animals may or may not hae an enclosed, fluid-filled body cavity called a coelom o Triploblasts that do not have coelom are called coelomates; those that possess a coelom are celomates o The coelom forms from within the mesoderm and thus is lined in both sides with cells from the mesoderm o The coelom creates a container for circulation of oxygen and nutrients, and also acts as an efficient hydrostatic skeleton that allos soft-bodied animals to move even without fins or limbs Animals may or may not have a body cavity o Acelomates have no enclosed body (endoderm, mesoderm, ectoderm but no coelom) o Pseudocoelomates have an enclosed body cavity partially lined with mesoderm (ectoderm, endoderm, and mesoderm only lines one side of the cavity) o Coelomates have an enclosed cavity completely lined with mesoderm (ectoderm, endoderm, and mesoderm lines both sides of cavity)
o hydrostatic skeletons allow limbless animals to move
o coordinated muscle contractions result in when locomotion the muscles on one side contract, the fluid-filled chamber changes shape and the animal bends protostome and deuterostome patterns of development o except for adult echinoderms, all coelomates (including juvenile echinoderms) are bilaterally symmetric and have three embryonic tissue layers o this group, called bilateral, can be divided into protostomes (arthropods (crabs), mollusks (clams), and segmented worms (earth worms)) and deuterostomes (starfish), chordates and enchinoderms) o three events in embryonic development cleavage, gastrulation, and coelom formation differ in protostomes and deuterostomes and give them their names o cleavage is a rapid series of mitotic divisions that occurs in the absence of growth o gastrulation is a series of cell movements that results in the embryonic tissue layers; as gastrulation proceeds, the colem forms o protostomes vs. deuterostomes cleavage (zygote undergoes rapid divisions, eventually forming a mass of cells) gastrulation (mass of cells formed by cleavage is rearranged to form gut and embryonic tissue layers) colem (body cavity covered with mesoderms) see figure 2 major groups within the protostoma and deuterostoma o after the split between the protosomes and the deuterosteomes, the protostomes split to form two major subgroups, the ecdysozoa (grow by shedding exterior skeleton in a series of stages (bug)) and lophotrochozoa (grow by simply standing their external skeleton (clam)) o segmentation evolved independently in annelids and arthropods, as well as in vertebrates Vertebrates (have skulls and usually backbones), those animals with skulls and usually backbones, are a monophyletic lineage. Invertebrates (have everything else), all animals that are not vertebrates, are a paraphyletic group feeding o the feeding tactics observed in animals can be broken into four general types: suspension feeders (whales drink in water and filter out crustaceans), deposit feeders (eat organic matter in soil deposits) , fluid feeders (organisms that feed on nutritious fluid such as sap), and mass feeders (takes chunks of plants/animals) the three general sources of food for animals are plants or algae, other animals, or detritus (general term for organic matter) What animals eat: three general sources o carnivores, omnivores, herbivores; those that feed on dead organic matter are detrivores o typically carnivores can be subslassified as either predators or parasites
o predators o parasites take nutrients from living animals endoparasites live inside their hosts ectoparasites live outside their hosts (ticks) o
o figure 2 Movement o Many animals are sit-and-wait predators, and some are sessile (permanently attached to a surface) throughout their adult lives. But the vast majority of animals move under their own power either as juveniles or as adults o movement has three functions in adult animals find food find mates escaping from predators o the major innovation of limbs made highly controlled, rapid movement possible reproduction and life cycles o eggs or embryos may be retained in the females body during development (viviparous), or eggs may be laid outside to develop independently of mother (oviparous) o Some species are ovoviviparous. In such species, the female retains eggs inside her body during early development, but the growing embryos are nourished by yolk inside the egg and not by nutrients transferred directly from the mother o Animals life cycles vary widely, and may include metamorphosis o Metamorphosis is the change from juvenile to adult body type o In holometabolous metamorphosis, the juvenile individual is called a larva and looks quite different from the adult form. When the larva has grown
enough, it encases itself and becomes a pupa; in this stage it is remodeled into an adult. This process is also known as complete metamorphosis o In hemimetabolous metamorphosis, the juvenile from is called a nymph and looks like a miniature adult (may get wings as they get older but dont undergo radical change)