DEVELOPMENT QUESTION 1988:				L. PETERSON/AP BIOLOGY
	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 internally from blastopore.
    	(chordamesoderm, primary mesoderm)
__Forward movement of mesodermal wings internally from blastopore.
    	(lateral plate mesoderm, somitic mesoderm)
    					    				(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/AP BIOLOGY

	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 
      (deuterostomes) 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