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DEVELOPMENT QUESTION 1988: L. PETERSON/ECHS Discuss the processes of cleavage, gastrulation, and neurulation in the frog embryo; tell what each process accomplishes. Describe an experiment that illustrates the importance of induction in development. STANDARDS: 1 point for each major item under each major heading CLEAVAGE (max. 3 points) Mitotic or cell division, or increase in cell number No cellular growth Holoblastic (complete division) Unequal Radial (Indeterminant) Involves use of maternal RNA 1st vertical [1 point for directionality of early cleavage divisions] 2nd vertical, perpendicular to 1st 3rd horizontal, perpendicular to 1st and 2nd, unequal Grey crescent establishes planes of cleavage Divisions more rapid at animal pole (max. 2 points) Accomplishes Forms blastula or hollow ball of cells Forms blastocoel Forms blastomeres (micromeres, macromeres) Forms or increases DNA in embryo Produces unequal distribution of cytoplasmic contents in blastomeres (max. 2 points) NEURULATION (max. 3 points) Epidermal thickening, flattening in dorsal midline (neural plate formation) Plate develops longitudinal depression (neural groove, neural folds) Neural folds fuse Neural tube pinches free of epidermis, sinks inward Notochord (chordamesoderm) required for neurulation (max. 2 points) Accomplishes Forms neural tube (CNS, nerve cord, spinal cord, brain, nervous system) Forms neurula Forms neural crests (max. 2 points) GASTRULATION (max. 3 points) Formation of yolk plug Formation of blastopore Invagination ("folds in", "pushes in") Involution Epiboly/cell migration Proliferation/movement forward of notochordal tissue (chordamesoderm, primary mesoderm) internally from blastopore. Forward movement of mesodermal wings (lateral plate mesoderm, somitic mesoderm) internally from blastopore. (max. 2 points) Accomplishes Establishes germ layers or triploblastic embryo; ecto-, meso-, endo- (or ento-)derm (must mention 2) Forms gastrula Establishes embryonic axes Forms gastrocoel (archenteron, gut or digestive system) Internalizes yolk Obliterates blastocoel Moves cells to sites where poised for organogenesis (max. 2 points) INDUCTION EXPERIMENT (max. 3 points) In the context of an experiment, description of: What induction is: Cells [or products] influence neighboring cells What induction does: Changes gene expression Induces differentiation Alters subsequent development Inducing Tissue (organizer) Induced Tissue and what it forms Examples: Dorsal lip of blastopore --- induces gastrulation or neurulation of "belly" ectoderm Optic vesicle --- induces lens formation in epidermal ectoderm Notochord --- induces neurulation of neural ectoderm
DEVELOPMENT QUESTION 1990 (EVOLUTION): L. PETERSON a. Describe the differences between the terms in each of the following pairs. (1) Coelomate versus acoelomate body plan (2) Protostome versus deuterostome development (3) Radial versus bilateral symmetry b. Explain how each of these pairs of features was important in constructing the phylogenetic tree shown below. Use specific examples from the tree in your discussion. Chordata Arthropoda Annelida Echinodermata Mollusca Nematoda Rotifera Platyhelminthes Cnidaria Porifera STANDARDS: a. (1) COELOMATE VS. ACOELOMATE: Max. = 2 points [Must define both for full credit] __ Coelomate: internal body cavity lined with mesoderm (not sufficient to say: "true body cavity") __ Acoelomate: lacking internal cavities altogether or having: a pseudocoelom (Nematoda and Rotifera) a spongocoel (Porifera) mesoglea (Cnidaria) a solid layer of mesoderm (Platyhelminthes) (2) PROTOSTOME VS. DEUTEROSTOME DEVELOPMENT: Max. = 2 points [Must define both for full credit] __ Protostome: mouth develops near/at the blastopore or anus forms secondarily (later), or featuring: --spiral cleavage (micromeres between macromeres) --determinate/mosaic development (blastomere fate is established at very early stages of development) --mesoderm from cells that migrate into the blastocoel near blastopore --schizocoelous coelomation (internal split in solid wedge of mesoderm that is independent of gut) --trochophore larva __ Deuterostome: anus develops near/at the blastopore or the mouth forms secondarily (later), or featuring: --radial cleavage (micromeres directly above macromeres) --indeterminate/regulative development (blastomere fate is variable and not established until late in development) --mesoderm arises from outpocketings of the gut --enterocoelous coelomation (outpocketing of gut) --dipleurula larva (3) RADIAL VS BILATERAL SYMMETRY: Max. = 2 points __ Radial: several planes passing through the long or central axis can divide the organism into similar parts. __ Bilateral: (only) one plane passing through the long axis divides the organism into similar right and left sides - exhibits cephalization. __ Echinoderms: bilaterally symmetrical larvae, but appear to have radially symmetrical adult forms. b. Max. = 6 points One point for each for examples of contrasting pairs (phyla or organisms) using terms from a.; (answer here or in a) One point each for using a. terms in explanation of why phyla are in separate groups (on separate branches) of tree. __ Body symmetry (cephalization) permits separation of Porifera and Cnidaria (radially symmetrical) from other phyla (bilaterally symmetrical). __ Coelomation permits separation of Platyhelminthese, Nematoda, and Rotifera from other phyla above Cnidaria: flatworms are acoelomate, whereas those other than nematodes and rotifers are coelomate. __ Origin of mouth and anus permit separation of Echinodermata and Chordata (deutero stomes) from Arthropoda, Annelids, and Molluscs (Protostomes) [Some include Platyhelminthese, Nematodes, and Rotifera as protostomes] __ Nematodes and rotifers are grouped separately because both are pseudocoelomate. __ Phylogenetic trees base taxonomic relationships on homologous structures, patterns of embryonic development, and common ancestry