12. The primitive streak results from a. lateral epiboly of epiblast cells b. la
ID: 201544 • Letter: 1
Question
12. The primitive streak results from a. lateral epiboly of epiblast cells b. lateral epiboly of hypoblast cells c. evagination of epiblast cells d. evagination of hypoblast cells 13. In the avian egg cleavage occur in the germinal disk Yolk b. cmbryonie aiak a. d. blastocyst 14. A11 of the following are derived from the lateral mesoderm EXCEPT a. axial skeleton c. somatic b. heart d. peritoneal linings 15. The human egg is classified as a. telolecithal b. holoblastic c d. mesolecithal e Spira 16. The neural plate a. develops from lateral epiboly endodermal cells. b. results from constriction & elongation of epiblast cells. c. develops similarly in birds and mammals. d. a,b& c e. a & b 17. In mammals the embryonic mesoderm arises by 1. epiboly of hypoblast toward the primitive streak. 2. epiboly of epiblast toward the primitive streak. 3. ingression of epiblast cells through the primitive groove. 4. evagination from the epiblast laterally. a. 1&2 b.2&3 c.3&4 d. 1,2&3 e.1&4 13. In mammals the blastocyst consists of the a. embryonic disk b. trophoblast c. blastocoelExplanation / Answer
ANS 12) The primitive streak results from:
c) evagination of epiblast cells
The primitive streak begins to form on the surface of the epiblast at the beginning of the third week. It is at the primitive streak that epiblast cells invaginate to form the mesoderm, through the process of gastrulation.
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ANS 13) In the avian egg cleavage occur in the
d) blastocyte
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ANS 14) All of the following are derived from the lateral mesoderm except:
b) heart
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ANS 15) The human egg is classified as:
b) holoblastic
Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic that is total or entire cleavage.
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ANS 16) The neural plate:
d) a, b & c i.e develops from lateral epiboly endodermal cells, results from constriction & elongation of epiblast cells, and develops similarly in birds and mammals.
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ANS 17) In mammals the embryonic mesoderm arises by:
b) 2 & 3 i.e epiboy of epiblast toward the primitive streak and ingression of epiblast cells through the primitive groove.
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ANS 18) In mamals the blastocyst consists of the:
e) b & c i.e trophoblast and blastocoel.
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