AP Bio 2012 Q1

Topics: Developmental biology, Stem cell, Cellular differentiation Pages: 11 (1445 words) Published: May 4, 2014
Question 1
Note: At least 1 point must be earned from each of parts (a), (b), (c), and (d) in order to earn a maximum score of 10.
The ability to reproduce is a characteristic of life.
(a) Describe the process of embryological development in a typical vertebrate embryo, beginning with a fertilized egg and ending with the development of three tissue layers. (4 points maximum)
Embryological process

(can occur in other stages)



Description of embryological process (1 point per box)
• Egg is fertilized by sperm.
• Zygote is formed.
• Polyspermy is blocked.
• Diploid number of chromosomes is restored.
• Nuclei of egg and sperm fuse.
• Sex of offspring is determined.
• Polarity is determined.
• Rapid cell divisions.
• Cell divisions without cell growth.
• Cleavage divisions form a small, solid ball of cells (morula). • Rapid DNA replications and mitotic divisions occur.
• Cells get smaller in early cleavage with each division.
• Cleavage divisions form a hollow ball of cells surrounding a fluidfilled cavity. • Room for germ layers is developed.
• Germ cell layers (ectoderm, endoderm, and mesoderm) are
• Opening called a blastopore forms.
• Cells near the surface of the blastula reorganize and move to an interior location.
• Primitive digestive gut (archenteron) forms.

(b) Identify the developmental origin of TWO of the following tissues in vertebrates: • central nervous system
• digestive system
• muscle
(2 points maximum)
Central nervous system
Digestive system

Identification of developmental origin (1 point per box)
• Ectoderm / outer germ layer
• Endoderm / inner germ layer (lining)
• Mesoderm / middle germ layer (other layers of digestive tract) • Mesoderm / middle germ layer

© 2012 The College Board.
Visit the College Board on the Web: www.collegeboard.org

Question 1 (continued)
(c) Identify and explain THREE differences between the embryological development of protostomes and the embryological development of deuterostomes.
(3 points maximum)
Developmental differences:
protostomes vs. deuterostomes
Pattern of cleavage

Determination of cell fate

Blastopore fate

Coelom formation

Explanation (1 point per box)
• Patterns of cleavage occur along different planes.
• Spiral (diagonal planes in protostomes).
• Radial (parallel/perpendicular in deuterostomes).
• Determination of cell fate occurs in different developmental stages.
• Early determination in protostomes (determinate).
• Late determination in deuterostomes (indeterminate).
• Blastopore fate differs.
• Mouth forms first; anus forms second in protostomes.
• Anus forms first; mouth forms second in deuterostomes.
• Coelom formation from mesoderm occurs by different
• Coelom forms from splitting of mesoderm in protostomes.
• Coelom forms from outpocketing of mesoderm in

(d) Explain TWO unique properties of human embryonic stem cells that distinguish them from other human cell types. Describe a current medical application of human stem cell research. (3 points maximum)

Unique properties

Explanation (1 point per box; 2 points maximum)
• Totipotent: can become any type of cell, tissue, organ, or entire organism.
• Pluripotent: can become many types of cells, tissues, or organs. • Undifferentiated: has the ability to follow any differentiation pathway.
• Unspecialized: can give rise to specialized cell types.
• Infinite reproduction: no restriction on cell types.

© 2012 The College Board.
Visit the College Board on the Web: www.collegeboard.org

Question 1 (continued)
Description of a current medical application (1 point maximum) Acceptable responses include, but are not limited to, the following: • Repair of brain and spinal tissues.
• Treatment of diseases...
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