Biology 5B Midterm 1 Study Guide
Biology 5B Midterm 1 Study Guide Bio5B
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This 16 page Study Guide was uploaded by Akash Patel on Wednesday June 15, 2016. The Study Guide belongs to Bio5B at University of California Riverside taught by Redak in Spring 2015. Since its upload, it has received 11 views. For similar materials see Biology 5B: Organismal Biology in Biology at University of California Riverside.
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Date Created: 06/15/16
Phylogeny and the Tree of Life ● Kind People Can Only Find Good Sex ● Kingdom, Phylum, Class, Order, Family, Genus, and Species ● Homologies: similarities due to shared ancestry ○ morphological: similarities in structure (like bones) ○ molecular: similarities in genes and DNA sequences ● Analogy: similarities due to convergent evolution ○ occurs when environmental pressures and natural selection gave similar adaptations in organisms from different evolutionary lineage ○ Homoplasies: analogous structures that arose independently ● monophyletic ● paraphyletic ● polyphyletic ● Shared ancestral character: character that originated in an ancestor of the taxon ● shared derived character: evolutionary novelty unique to a clade ● Outgroup: species or group of species from an evolutionary lineage that is known to have diverged before ● Ingroup: species that includes ours/ species being studied ○ by comparing members of the ingroup to members of the outgroup, you can see which characters were derived at various branch points of vertebrate evolution il ● In the beginning, organisms were classified as either plants or animals ○ bacteria, eukaryotic unicellular organisms, and fungi were placed in plants ○ unicellular eukaryotes that move and ingest food (protozoans) were classified as animals ○ Euglena: move and photosynthetic was in both kingdoms ● 1960s biologists recognized 5 different kingdoms: Monera (prokaryotes), Protista (unicellular organisms), Plantae, Fungi, and Animalia ● Because the prokaryotes were so diverse in their own kingdom, developed 3 domain system: Bacteria, Archaea, and Eukarya ○ Bacteria: has most of the currently known prokaryotes ■ includes bacteria close to chloroplasts and mitochondria ○ Archaea: diverse group of prokaryotic organisms that inhabit a wide variety of environments ○ Eukarya: organisms that have cells containing true nuclei ■ includes many singlecelled organisms and multicellular plants, fungi, and animals ○ 3 domain system highlights that fact that the history of life has been about singlecelled organisms ■ only a small portion of branches are multicellular organisms ■ biologists don’t really recognize Monera and Protista ● Monera: members in 2 different domains ● Protista: polyphletic; includes members that are more closely related to plants, fungi, or animals than to other protists ● the tree of life compares the rRNA genes because they evolve slowly that homologies between distantly related organisms can still be detected ○ useful for determining evolutionary relationships between deep branches in the history of life ● horizontal gene transfer: process where genes are transferred from one genome to another through mechanisms like exchange of transposable elements and plasmids, viral infection, and fusions of organisms Bacteria and Archaea ● Prokaryotes: most are unicellular, but the cells of some species remain attached to each other after cell division ○ 0.55 micrometers ○ well organized , achieves all of an organisms life functions within a single cell ○ 3 common shapes: spherical, rodshaped, spiral ● Cell wall maintains shape, protects cell, and prevents from bursting in a hypotonic environment ○ bacterial cell wall contains peptidogylcan: polymer made of modified sugars crossed linked by short polypeptides ■ anchors other molecules that extend from its surface ○ Archaeal cell walls have polysaccharides and proteins by no peptidoglycan ● Gram positive: bacteria that have simpler walls with a large amount of peptidoglycan ● Gram negative: bacteria that have less peptidoglycan and are structurally more complex, with outer membrane containing lipopolysacchrides ○ outer membrane protects from body defenses ○ tend to be more resistant than gram positive to antibiotics ● Capsule: sticky layer of polysaccharide or protein that surrounds the cell wall of prokaryotes ● Fimbriae: prokaryotes use these hairlike appendages to stick to substrates or one another ○ usually shorter and more numerous than pili (pilus) ● Pilus: appendages that pull 2 cells together before DNA transfer from one cell to the other ● Half of prokaryotes are capable of taxis ○ Taxis: directed movement toward or away from a stimulus ● Flagella/Flagellum: most common structure that let prokaryotes move ○ can be scattered over the surface of the cell or concentrated at one or both ends ○ Prokaryotic flagella: 1/10 the width of a eukaryotic flagella , different in molecular composition, mechanism of propulsion ■ bacterial and archaeal flagella are the same in size and rotation mechanism but are made from different proteins ● Exaptation: process where existing structures take on new functions through descent with modification ● Prokaryotic cells lack complex compartment found in Eukaryotes. ○ has specialized membranes that perform metabolic functions ○ prokaryote genome is structurally different than the eukaryotic genome and has less DNA ■ in a circular chromosome with few proteins than found in the linear chromosomes of eukaryotes ○ lacks a membrane bounded nucleus so the chromosome is found in the nucleiod ○ typical cells have smaller rings of independently replicating DNA molecules (plasmids) that carry only a few genes ● Prokaryotes are highly successful because they can reproduce quickly in the right environment ○ reproduce through binary fission where a single prokaryotic cell splits into 2, then 4, then 8… ○ can divide every 13 hours and produce a new generation in 20 minutes ○ prokaryotes are small, reproduce by binary fission, and have short generation times ■ population can have trilllions of individuals ○ can withstand harsh living conditions ■ some develop resistant cells called endospores when lacking an essential nutrient ● Because of their short generation times, prokaryotic populations can evolve in a short amount of time ○ the ability of the cells to adapt rapidly shows that prokaryotes are not primitive or inferior ● Prokaryotes are genetically diverse due to rapid reproduction, mutation, and genetic recombination ○ After repeated rounds of binary fission/division, most of the offspring cells are identical to the parent cell ○ if there are errors in replication, some cells are different ○ the mutations can increase genetic diversity fast with short generations and large populations ■ leads to rapid evolution: individuals that are better equipped for the environment survive and reproduce better ○ genetic recombination: combining of DNA from 2 sources ■ transformation, transduction, and conjugation can bring prokaryotic DNA from different cells ■ cells from different species, genes move from one organism to another (horizontal gene transfer) ○ transformation: genotype and phenotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings ■ nonpathogenic cell takes up DNA that has an allele for the pathogen and replaces their normal allele with the pathogen allele; becomes a recombinant: DNA from 2 different cells ○ transduction: phages (viruses that infect bacteria) have prokaryotic genes from one host cell to another ■ results from accidents when replicating phages ■ virus that has prokaryotic DNA can’t replication because it lacks its own genetic material ■ virus can attach to another prokaryotic cell and inject prokaryotic DNA from the first cell (recombinant is formed) ○ conjugation: DNA is transferred between 2 prokaryotic cells that are temporarily joined ■ In bacteria: one cell donates the DNA and another receives it ● Prokaryotes are categorized by how the obtain energy and the carbon used in making organic molecules that make up cells ○ Phototrophs: organisms that get energy from light ○ Chemotrophs: organisms that get energy from chemicals ○ Autotrophs: organisms that only need 2as a carbon source ○ Heterotophs: need at least one organic nutrient to make other organic compounds ○ can be combined to make 4 major modes of nutrients ■ Photoautotrophs: photosynthetic prokaryotes ■ Chemoautotrophs: certain prokaryotes ■ Photoheterotroph: certain aquatic and saltloving prokaryotes ■ Chemoheterotroph: prokaryotes, protists, fungi, animals, some plants ● Cooperation between prokaryotic cells lets them use environmental resources they couldn’t use as individual cells ○ Heterocysts: cells that only carry out nitrogen fixation ■ surrounded by thickened cell wall that restricts entry of oxygen ■ intercell connections let them transport fixed nitrogen and get carbohydrates ○ Biofilms: surfacecoating colonies where metabolic cooperation between different prokaryotic species ■ secrete signal molecules to recruit nearby cells making colonies grow ■ also makes polysaccharides and proteins ● Prokaryotes play a major role in recycling chemical elements between the living and nonliving components of the environment ○ chemoheterotrophic prokaryotes function as decomposers ■ unlocks supply of carbon, nitrogen, and other elements ○ convert some molecules to forms that can be taken up by other organisms ■ CO2s used to make organic compounds like sugars which passes through the food chain ○ can increase/decrease availability of nutrients that plants need for growth ● Symbiosis: ecological relationship where 2 species live in close contact with each other ○ larger organism in the relationship is the host and the smaller is known as the symbiont (usually a prokaryote) ○ Mutualism: both organisms benefit ○ Commensalism: one species benefits, the other is neither harmed nor helped ○ Parasitism: parasite eats the cell contents, tissues, or body fluids of its hosts ■ harm but do not kill host (not immediately) ■ Pathogens: parasites that cause disease ■ Exotoxins: proteins secreted by certain bacteria and their organisms ■ Endotoxins: lipopolysaccharide components of the outer membrane of gram negative bacteria Protists ● classified as eukaryotes and are in the domain Eukarya ● Eukaryotic cells have a nucleus and other membranebounded organelles ● Organisms in most eukaryotic lineages are protists and most protists are unicellular ● Most protists are unicellular but there are some colonial and multicellular species ○ In multicellular organisms, functions are carried out by organs ○ In unicellular organisms, protists use subcellular organelles ○ mainly use nucleus, endoplasmic reticulum, golgi apparatus, and lysosomes ○ certain ones use contractile vacuoles that pump water from the cell ● Some are photoautotrophs (containing chloroplasts), heterotrophs (absorbs or ingests large food particles), or mixotrophs (combines both) ● Reproduce both asexually and sexually ● Endosymbiosis: process where certain unicellular organisms engulf other cells, becoming endosymbionts and organelles in the host cell ○ gave diversity to protists ○ In history, lineage of heterotrophic eukaryotes acquired an additional endosymbiont (photosynthetic cyanobacterium) and evolved into plastids ■ gave rise to 2 lineages of photosynthetic protists or algae: red and green algae ○ Secondary Symbiosis: red and green algae were ingested in the food vacuoles of heterotrophic eukaryotes and became endosymbionts ● Clade Excavata proposed based on morphological studies of the cytoskeleton ○ some members have an excavated feeding groove on one side of the cell body ○ lack plastids and have modified mitochondria ○ Diplomonads: modified mitochondria called mitosomes ■ lack functional electron transport chains and cannot use oxygen to help extract energy from carbohydrates and other organic molecules ■ anaerobic biochemical pathway ■ 2 equal sized nuclei and multiple flagella (extensions of the cytoplasm, consisting of bundles of microtubules covered by the cell’s plasma membrane ■ most are parasites ● Giardia: inhabits the intestines of mammals ○ Parabasalids: have reduced mitochondria called hydrogenosomes ■ generate energy anaerobically, releasing hydrogen gas as a byproduct ■ Trichomonas vaginalis: sexually transmitted parasite that infects 5 million people a year ● travels along mucuscoated lining of the human reproductive and urinary tracts by moving its flagella and by undulating part of its membrane ● females: vagina’s normal acidity is disturned ● feeds on the vaginal lining, promoting infection ○ Euglenozoans: ● Clade Chromalveolates: ○ a large, diverse clade that has either come about from a monophyletic group or a common ancestor of the group engulfed a singlecelled, photosynthetic red alga (secondary symbiosis) ○ Alveolates: have membrane bound sacs just under the plasma membrane ■ 3 subgroups: dinoflagellates, apicomplexans, ciliates ■ Dinoflagellates: characterized by cells that are reinforced by cellulose plates ● 2 flagella located in grooves in the armor spin as they move through water ● components of marine and freshwater plankton ■ Apicomplexans: parasites of animals and some cause human diseases ● spreads through their host as tiny infectious cells called sporozoites ● one end (apex) has a complex of organelles used to penetrate host cells and tissues ● Plasmodium: parasite that causes malaria, lives in both mosquitoes and humans ○ lives inside cells, hidden from the host’s immune system ○ changes its surface proteins ■ Ciliates: named for their use of cilia to move and feed ● cilia can completely cover the cell surface or may be clustered in few rows or tufts ● certain species use the rows of tightly packed cilia in locomotion ● 2 nuclei: tiney micronuclei and large macronuclei ● genetic variation comes from conjugation: sexual process where 2 individuals exchange haploid micronuclei but don’t reproduce ● asexual ● Macronucleus has multiple copies of the genome and controls everyday functions of the cell, such as feeding, waste removal, and maintaining water balance ○ Stramenopiles: refers to their characteristic flagellum: numerous hairlike projections that are paired with smooth (nonhairy) flagellum ■ Diatoms: unicelluar algae that have unique glasslike wall made of hydrated silica embedded in an organic matrix ● walls provide protection from the pedator’s jaws ● major component of phytoplankton ● because they are so abundant, their photosynthetic activity affects global carbon dioxide levels ■ Brown Algae: multicellular and most are marine (known as seaweeds) ● most complex multicellular anatomy of all algae ● some have specialized tissues and organs that are like plants ● analogous to plants ● Clade Rhizarians: ○ monophyletic group ○ Amoebas: use pseudopodia to move and feed ■ pseudopodia: extensions that may bulge from almost anywhere on the cell surface ■ extends a pseudopodium and anchoring the tip and more cytoplasm streams into the pseudopodium ○ Radiolarians: delicate, intricately symmetrical internal skeletons that are made of silica ■ pseudopodia radiate from the central body and are reinforced by bundles of microtubules covered by a thin layer of cytoplasm to engulf smaller microorganisms that attach to the pseudopodia ■ foraminiferans/forams: named for their porous shells, called tests ● consists of a single piece of organis material hardened with calcium carbonate ● pseudopodia that extend through the pores function in swimming, test formation, and feeding ● also get nourishment from photosynthesis of symbiotic algae ● found in ocean and fresh water or live in sand/ attach themselves to rocks or algae ○ Cercozoans: large group that has most of the amoeboid and flagellated protists that feed with threadlike pseudopodia ■ common in marine, freshwater, and soil ecosystems ■ most are heterotrophs and parasites of plants, animals, or protists; many others are predators ■ does not have tests ● Clade Archaeplastida: ○ monophyletic group that descended from the ancient protist that engulfed a cyanobacterium ■ Red algae: red from phycoerythrin ● multicellular (seaweeds) ● diverse life cycles and alternation of generations is common ● no flagellated stages in life cycle and depends on water currents to bring gametes together for fertilization ■ Green algae: structure and pigment composition like the chloroplasts of land plants ● Charophytes: algae most closely related to land plants ● Chlorophytes: most are fresh water and are unicellular ○ complex life cycles with sexual and asexual reproductive stages ● Clade Unikonta: ○ includes animals, fungi, and some protists ○ 2 major clades: Amoebozoans and opisthokonts ○ supported by molecular systematics ○ Amoebozoans: lobe or tube shaped rather than thread like pseudopodia Animal Kingdom Nutrition: ● Animals can’t make their own organic molecules so they ingest them by eating other living organisms or eating nonliving organic material ○ use enzymes to digest within their bodies Cell Structure and Specialization ● lack a cell wall and instead have a variety of proteins external to the membrane that give structural support to the cell and connects them to one another ● 2 specialized cells not found in other multicellular organisms: muscle and nerve cells ○ most animals, these cells are organized into tissues (groups of cells with common structure, function, or both) ○ Muscle and nervous tissue are responsible for moving the body and conducting nerve impulses (respectively) Reproduction and Development ● Animals reproduce sexually: small flagellated sperm fertilizes a larger, non motile egg forming a diploid zygote ○ Zygote undergoes cleavage (meiosis/mitosis) ○ cleavage leads to the formation of the blastula (multicellular hallow ball) ○ gastrulation occurs: layers of embryonic tissue develop into adult body parts ■ result of this stage is the gastrula ● life cycles of most animals include at least one larval stage ○ larva: sexually immature form of an animal that is morphologically distinct from the adult ○ undergoes metamorphosis: developmental transformation that turns the animal into a juvenile that resembles an adult but is not yet sexually mature ● Homeoboxes: sets of DNA sequences found in developmental genes that regulate the expression of other genes ○ Hox genes: unique homeobox containing family of genes ■ important in embryonic development: controls the expression of dozens or hundreds of other genes that influence animal morphology Paleozoic Era: 542251 Million Years Ago ● Cambrian explosion: 535525 million years ago ○ before only a few phyla have been observed but after, they found the oldest fossils of phyla that have been extinct (arthropods, chordates, and echinoderms) ○ found the first animals with hard, mineralized skeletons ○ decline in the diversity of Ediacaran lifeforms ○ hypotheses of the Cambrian Explosion: ■ new predatorprey: predators had new adaptations to help catch prey (like locomotion) and prey had new defenses (protective shells) ■ Increase in atmospheric oxygen: more oxygen would have let animals with higher metabolic rates and larger body size to thrive and harm others ■ origin of Hox genes and other genetic changes affecting the regulation of developmental genes helped the evolution of new body forms Mesozoic Era: ● Oceans: coral reefs formed giving marine animals new habitats ● Some reptiles returned to water leaving, large aquatic predators as descendants ● descent with modification in some tetrapods led to the origin of wings in pterosaurs and birds ● dinosaurs emerged ● first mammals appeared (tiny nocturnal insecteaters) Cenozoic Era: ● mass extinction of both terrestrial and marine animals started the Cenozoic Era ● large nonflying dinosaurs and marine reptiles disappeared ● Rise of large mammalian herbivores and predators as mammals began to exploit the vacated ecological niches Body Plans: ● set of morphological and developmental traits, integrated into a functional whole, the living animal ● Radial symmetry: can be cut any way and is symmetrical on both sides ○ has top side (where mouth is) and bottom side ● Bilateral symmetry: two sided symmetry ○ 2 axis of orientation: front to back and top to bottom ○ Dorsal side (top) and ventral side (bottom) ○ left and right side ○ anterior (front) end and posterior (back) end ○ most animals with bilateral symmetry have sensory equipment concentrated at the anterior end ○ cephalization: central nervous system (brain) in the head ● Tissues: specialised cells isolated from other tissues by membranous layers ○ Ectoderm: germ layer covering the surface of the embryo, gives rise to the outer covering of the animal and, in some phyla, to the central nervous system ○ Endoderm: innermost germ layer, lines the pouch that forms during gastrulation, gives rise to the lining of the digestive tract (or cavity) and organs such as the liver and lungs of vertebrates ○ Diploblastic: animals that have only these 2 germ layers ■ include cnidarians, comb jellies ○ All bilaterally symmetrical animals have a third germ layer (mesoderm) ○ Mesoderm: fills much of the space between the ectoderm and endoderm ○ Animals with bilateral symmetry are triploblastic (3 germ layers) ■ mesoderm forms the muscles and most other organs between the digestive tract and outer covering of the animal Body Cavities: ● Body cavity: fluid or air filled space between the digestive tract and outer body wall ○ also called a coelom ○ True coelom: derived from mesoderm, inner and outer layers of tissue that surround the cavity connect and form structures that suspend the internal organs ■ triploblastic animals with true coelom are known as coelomates ○ Pseudocoelom: body cavity formed from the mesoderm and endoderm ■ triploblastic animals with pseudocoelom called pseudocoelomates ■ fully functional body cavity ○ Acoelomates: triploblastic animals that lack a body cavity altogether ● Fluid in body cavity cushions the suspended organs, preventing internal injury ● Softbody coelomates: coelom contains noncompressible fluid that acts like a skeleton where muscles can work ○ lets internal organs group and move independently Protostome and Deuterostome Development: ● Protostome development: ○ undergo spiral cleavage where the planes of cell division are diagonal to the vertical axis of the embryo ○ smaller cells are centered over the grooves between larger, underlying cells ○ determinate cleavage: determines the developmental fate of each embryonic cell early; each cell cannot develop into a whole animal ● Deuterostome development: ○ radial cleavage where the planes are either parallel or perpendicular to the vertical axis of the embryo ( one directly above another) ○ indeterminate cleavage: each cell produced by early divisions keeps the capacity to develop into a complete embryo ■ makes it possible for identical twins ● During gastrulation, developing digestive tube forms as a blind pouch, the archenteron, becoming the gut ○ forms in protostome development, solid masses of mesoderm split and form the coelom ○ in deuterostome, mesoderm buds from the wall of the archenteron and cavity becomes the coelom ● Blastopore: indentation that during gastrulation leads to the formation of the archenteron ○ after archenteron develops, most animals have a second opening that forms at the opposite end of the gastrula ○ blastropore and the second opening become the mouth and anus ■ protostome: mouth is the blastropore ■ deuterostome: mouth is from second opening, anus is blastropore Invertebrates: Clade Bilateria includes Lophotrochozoa, Ecdysozoa, and Deuterostomia Invertebrates: animals that lack a backbone ● 95% of known animal species Phylum Porifera: ● Porifera: called sponges ○ Sessile animals that lack true tissue, groups of similar cells that act as a functional unit, and are isolated from other tissues by membranous layers ○ different cell types: ■ choanocytes: collar cells ● lining interior of the spongocoel ● engulf bacteria and other food particles by phagocytosis ● similar to choanoflagellates (suggests that animals evolved from a choanoflagellatelike ancestor) ■ Amoebocytes: use of pseudopodia ● move through mesohyl ● take up food from the surrounding water and from choanocytes, digest it, and carry nutrients to other cells ● make tough skeletal fibers in the mesohyl ● capable of becoming other types of sponge cells ○ can adjust shape in response to changes of physical environment ○ most are hermaphrodites: both male and female in sexual reprodution ○ Gametes are from choanocytes or amoebocytes ■ eggs in mesohyl; sperm carried out of the sponge by water current ○ body has 2 layers of cells separated by the mesohyl ■ both layers are in water; gas exchange and waste removal occur by diffusion across the membranes ○ most are marine but some live in fresh water ○ Suspension feeders: traps particles that pass through internal channels of their body ■ water is drawn through the pores into a central cavity (spongocoel) ■ flows out of the sponge through a larger opening (osculum) ■ more complex sponges have folded body walls, and can contain branched water canals and several oscula Phylum Cnidarians: ● all animals except sponges and a few other groups belong to the clade Eumetazoa: animals with true tissues ● forms that are both sessile and motile ● includes hydras, corals, and jellies ● simple diploblastic, radial body plan ○ basic body plan is a sac with a central digestive compartment, gastrovascular cavity (GVC) ○ single opening that is both the mouth and anus ○ Sessile polyp: cylindrical dorms that adhere to the substrate by the end opposite of the mouth and extend tentacles, waiting for prey (sea anemones) ○ Motile medusa: flattened mouthdown version of the polyp; moves freely in water by passive drifting and contractions of its bellshaped body (jellyfish) ● 4 different classes: Hydrozoans (hydras), Scyphozoans (jellies), Cubozoans, Anthozoans (anemones) Lophotrochozoans: ● Phylum Platyhelminthes (flatworms): ○ live in marine, freshwater, and damp terrestrial habitats ○ include parasitic species (flukes and tapeworms) ○ thin bodies that are flattened dorsoventrally (between dorsal and ventral surfaces) ○ Triploblastic development but are acoelomates ■ flat shape places their cells close to water in surrounding environment or in their gut ■ because of closeness to water, gas exchange and elimination of nitrogenous waste diffuse across the body surface ■ no organs for gas exchange and excretory apparatus functions to maintain osmotic balance with surroundings ● apparatus has protonephridia: networks of tubles with ciliated structures called flame bulbs that pull fluid through branched ducts opening to the outside ○ most have a GVC with one opening ○ lacks circulatory system but branches of the GVC bring food to the cells ○ 4 classes: Turbellaria (free living flatworms), monogenea, trematoda (flukes), cestoda (tapeworms) ○ Turbellaria: predators and scavengers in freshwater and marine ■ most common: planarian ■ prey on smaller animals or feed on dead animals ■ use cilia to move on ventral surface ■ can modify responses to stimuli; has light sensitive eyespots and centralized nerve nets ■ Hermaphrodites ○ Monogenea & Trematoda: ■ parasites in or on other animals ■ require an intermediate host where larvae develop before infecting the final host, where the adult worms live ■ complex life cycles with sexual and asexual stages ■ spend part of their lives in snail hosts before infecting humans ■ releases molecules to manipulate the hosts’ immune system into tolerating the parasites’ exisistence ■ Monogenea infect fish ○ Cestoda (tapeworms): ■ adults live in vertebrates like humans ■ scolex/anterior end had suckers and hooks that lets the worm attach itself to the intestinal lining of its host ■ lack a mouth and GVC ● absorb nutrients released by digestion in the host’s intestine ■ after sexual reproduction, thousands of fertilized eggs are released from the posterior end of the tapeworm and leaves the host’s body in feces ● Phylum Molluscs: ○ majority are marine, partial are in freshwater and land ○ softbodied and most secret a hard protective shell made of calcium carbonate ○ Slugs, squids, and octopuses have a reduced internal shell or lost it during evolution ○ coelomates ○ have 3 main parts: muscular foot used for movement, visceral mass that has most of the internal organs, and a mantle that is a fold of tissue that drapes over the visceral mass and secrets a shell ■ mantle produces a waterfilled chamber: mantle cavity that has the gills, anus, and excretory pores ○ feed by using a straplike organ called radula to scrape up food ○ most have separate sexes and gonads are in the visceral mass ○ Chitons: ■ oval shaped body and shell composed of eight dorsal plates ■ unsegmented body ■ clings to rocks along the shore ■ foot is used as a suction cup and to creep slowly over rock surface ○ Gastropods: ■ ¾ of living species of molluscs ■ most are marine but there are freshwater species, some adapted to land ■ undergo torsion: as embryo develops, visceral mass rotates up 180 degrees causing the anus and mantle cavity above its head ● after, organs that were bilateral may be reduced in size or may be lost on one side of the body ■ single spiraled shell where they can retreat ■ moves slowing by ripling motion of foot or by cilia ○ Bivalves: ■ aquatic and include clams, oysters, mussels, and scallops ■ shell divided into 2 halves ● hinged and powerful muscles draw them closer together to protect the animal’s soft body ■ no distinct head ■ some have eyes and sensory tentacles on the outer edge of their mantle ■ mantle cavity has gills that are used for gas exchange and feeding in most species ■ most are suspension feeders ○ Cephalopods: ■ active marine predators that catch prey when they bite wit beaklike jaws and immobilize with a poison present in saliva ■ foot is modified into a muscular excurrent siphon and part of the tentacles ■ shell is reduced and internal or missing altogether ■ only molluscs with a closed circulatory system: blood remains separate from fluid in the body cavity ■ well developed sense organs and complex brain ■ Ammonites: shelled cephalopods but became extinct at the end of the cretaceous period ● Phylum Annelids: ○ body resembles a series of fused rings ○ segmented worms that live in the dea in most freshwater habitats and in damp soil ○ coelomates and are from 1 mm to more than 3m ○ Polychaetes: ■ each segment has a pair of paddlelike or ridgelike structure called parapodia that function in locomotion ■ each parapodium has numerous chaetae (bristles made of chitin) ■ parapodia are supplied with blood vessels and function as gills ■ marine ■ live in burrows or build tubes to live in with sand and broken shells ○ Oligochaetes: ■ named for relatively sparse chaetae ■ includes earthworms and their aquatic relatives, and leeches ■ Earthworms: eat their way through soil, extracting nutrients though the alimentary canal ■ hermaphrodites but they crossfertilize ○ Class Hirudinea: ■ marine and terrestrial leeches ■ some feed on other invertebrates, but some are parasites that suck blood by attaching temporarily to other animals, like humans ■ secretes another chemical, hirudin, that keeps the blood of the host from coagulating near the incision Ecdysozoans: animals that shed a tough external coat (cuticle) as the grow ● process is called ecdysis or molting ● 8 animal phyla and has more species than all other animal, protist, fungus, and plant group combined ● Nematodes: roundworms ○ found in most aquatic habitats, soil, moist tissues of plants, and in body fluids of tissue of animals ○ do not have segmented bodies ○ cylindrical bodies range from less than 1mm to more than 1m long; fine tip at the posterior end and a blunter tip at the anterior end ○ body is covered in a tough cuticle and periodically sheds and creates a new one as it grows ○ have alimentary canal, but lacks a circulatory system ○ nutrients is transported by fluid in the pseudoceolem ○ body wall muscles are longitudinal, contraction is a thrashing motion ○ reproduce sexually, by internal fertilization; female has 100,000 fertilized eggs ○ play an important role in decomposition and nutrient cycling ○ includes parasitic plants and can parasitize animals ● Arthropods: ○ segmented body, hard exoskeleton, and joined appendages ○ Appendages used in walking, feeding, sensory reception, reproduction, and defense ■ jointed and come in pairs ○ body is covered by the cuticle made of protein and polysaccharide chitin ■ sheds and makes a larger one during growth ○ have welldeveloped sensory organs (eyes, olfactory receptors, antennae for touch and smell) ■ most are concentrated at the anterior end of the animal ○ have an open circulatory system: fluid called hemolymph is propelled by a heart through short arteries and into spaces called sinuses surrounding tissue and organs ■ hemolymph reenters the heart through pores equipped with valves ○ coelom forms in the embryo and becomes much reduced as development progresses and hemocoel become main body cavity ■ hemocoel: hemolymph filled body sinuses ○ gas exchange organs allow the diffusion of respiratory gases in spite of the exoskeleton ■ most aquatic have ills with feathery extensions to increase surface area ■ terrestrials have internal surfaces specialized for gas exchange ○ Chelicerates: claw like feeding appendages that serve as pincers or fangs ■ have anterior cephalothorax and posterior abdomen ■ lack antennae and have simple eyes (eyes with single lens) ■ Arachnids: group that includes scorpions, spiders, ticks, and mites ● Ticks and mites are parasitic; ticks are bloodsucking parasites that live on the body of reptiles or mammals ● Arachnids have a cephalothorax that has 6 pairs of appendages: chelicerae
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