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In sea urchins, the "fast block" and the longer lasting "slow block" to polyspermy, respectively, are


A) the acrosomal reaction and the formation of egg white.
B) the cortical reaction and the formation of yolk protein.
C) the jelly coat of the egg and the vitelline membrane.
D) membrane depolarization and the cortical reaction.
E) inactivation of the sperm acrosome.

F) A) and D)
G) D) and E)

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If gastrulation was blocked by an environmental toxin, then


A) cleavage would not occur in the zygote.
B) embryonic germ layers would not form.
C) fertilization would be blocked.
D) the blastula would not be formed.
E) the blastopore would form above the gray crescent in the animal pole.

F) A) and B)
G) A) and C)

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Which of the following correctly displays the sequence of developmental milestones?


A) cleavage → blastula → gastrula → morula
B) cleavage → gastrula → morula → blastula
C) cleavage → morula → blastula → gastrula
D) gastrula → morula → blastula → cleavage
E) morula → cleavage → gastrula → blastula

F) All of the above
G) A) and E)

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What structural adaptation in chickens allows them to lay their eggs in arid environments rather than in water?


A) extraembryonic membranes
B) yolk
C) cleavage
D) gastrulation
E) development of the brain from ectoderm

F) A) and B)
G) C) and D)

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In all vertebrate animals, development requires


A) a large supply of yolk.
B) an aqueous environment.
C) extraembryonic membranes.
D) an amnion.
E) a primitive streak.

F) A) and C)
G) A) and D)

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Contact of a sea urchin egg with signal molecules on sperm causes the egg to undergo a brief


A) mitosis.
B) membrane depolarization.
C) apoptosis.
D) vitellogenesis.
E) acrosomal reaction.

F) A) and E)
G) B) and D)

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In a developing frog embryo, most of the yolk is


A) located near the animal pole.
B) located near the vegetal pole.
C) found within the cleavage furrow.
D) found within the blastocoels.
E) distributed equally throughout the embryo.

F) A) and B)
G) All of the above

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In humans, identical twins are possible because


A) of the heterogeneous distribution of cytoplasmic determinants in unfertilized eggs.
B) of interactions between extraembryonic cells and the zygote nucleus.
C) of convergent extension.
D) early blastomeres can form a complete embryo if isolated.
E) the gray crescent divides the dorsal-ventral axis into new cells.

F) B) and D)
G) A) and B)

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The vertebrate ectoderm is the origin of the


A) nervous system.
B) liver.
C) pancreas.
D) heart.
E) kidneys.

F) A) and D)
G) A) and E)

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The cortical reaction functions directly in the


A) formation of a fertilization envelope.
B) production of a fast block to polyspermy.
C) release of hydrolytic enzymes from the sperm cell.
D) generation of a nerve-like impulse by the egg cell.
E) fusion of egg and sperm nuclei.

F) C) and D)
G) B) and E)

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A sea urchin zygote undergoes its first cell division


A) 5 seconds after fertilization.
B) 30 minutes after fertilization.
C) 90 minutes after fertilization.
D) 4 hours after fertilization.
E) 24 hours after fertilization.

F) All of the above
G) A) and E)

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A human blastomere is


A) an embryonic cell that is much smaller than the ovum.
B) an embryonic structure that includes a fluid-filled cavity.
C) that part of the acrosome that opens the egg's membrane.
D) a component of the zona pellucida.
E) a cell that contains a (degenerating) second polar body.

F) None of the above
G) All of the above

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Although it contributes no cells to the embryo, the formation of the primitive streak is guided by the structure known as the


A) endoderm.
B) mesoderm.
C) ectoderm.
D) neural crest.
E) hypoblast.

F) A) and B)
G) C) and D)

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During the early part of the cleavage stage in frog development, the rapidly developing cells


A) skip the mitosis phase of the cell cycle.
B) skip the S phase of the cell cycle.
C) skip the G₁ and G₂ phases of the cell cycle.
D) rapidly increase the volume and mass of the embryo.
E) skip the cytokinesis phase of the cell cycle.

F) A) and B)
G) A) and C)

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In a newly fertilized egg, the vitelline layer


A) opens the egg's nuclear membrane to allow haploid sperm DNA to enter.
B) hardens to form a protective cover.
C) secretes hormones that enhance steroidogenesis by the ovary.
D) reduces the loss of water from the egg and prevents desiccation.
E) provides most of the nutrients used by the zygote.

F) A) and C)
G) A) and E)

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Two primary factors in shaping the polarity of the body axes in chick embryos are


A) light and temperature.
B) salt gradients and membrane potentials.
C) gravity and pH.
D) moisture and mucus.
E) location of sperm penetration and cortical reaction.

F) A) and D)
G) B) and D)

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When you slice up a pie that contains a swirled mixture of chocolate and vanilla filling, you notice that some slices have more chocolate than vanilla and that other slices have more vanilla than chocolate. This uneven distribution of chocolate and vanilla is most like the uneven distribution of


A) nuclei in a zygote.
B) nuclei in an early embryo.
C) nuclei in an egg prior to fertilization.
D) cytoplasmic determinants in a newly formed zygote.
E) cytoplasmic determinants in a baby just prior to birth.

F) C) and D)
G) B) and E)

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The earliest developmental stage among these choices is


A) germ layers.
B) morula.
C) blastopore.
D) gastrulation.
E) invagination.

F) A) and D)
G) A) and C)

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The primitive streak in a bird is the functional equivalent of


A) the lip of the blastopore in the frog.
B) the archenteron in a frog.
C) polar bodies in a sea urchin.
D) the notochord in a mammal.
E) neural crest cells in a mammal.

F) None of the above
G) C) and D)

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As cleavage continues during frog development, the size of the blastomeres


A) increases as the number of the blastomeres decreases.
B) increases as the number of the blastomeres increases.
C) decreases as the number of the blastomeres increases.
D) decreases as the number of the blastomeres decreases.
E) increases as the number of the blastomeres stays the same.

F) A) and B)
G) All of the above

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