Ch 47 HW

Part D An ectodermal thickening above the frog's notochord forms a _____.

neural plate

Part E The _____ is(are) formed when the neural folds join and a portion of the neural plate sinks beneath the embryo's surface.

neural tube

Part A During gastrulation in frogs, a rod of mesoderm under the dorsal surface forms the _____.

notochord

Part H In vertebrates, the ectoderm gives rise to the _____.

outer layer of skin

Part C As cleavage continues, a zygote forms into a solid multicellular ball called a(n) _____.

morula

Part B During gastrulation in frogs, cells from the animal pole spread over the embryo and form the _____.

ectoderm

Part D Which of the following stages of development is defined by the three embryonic tissue layers (ectoderm, mesoderm, and endoderm)?

gastrula

Part E The three-layered embryo is the _____.

gastrula

Part G True or false? Early animal development progresses through distinct stages: first the production of the zygote through fertilization, then cleavage, then the formation of the gastrula, and then the formation of the blastula.

False

Part A In animal development, which of the following best describes the process of cleavage?

Mitosis

Part D Time point 5 corresponds to the 12th cell division, except in the presence of the toxin, which blocks cell division. Do the data support the hypothesis that the timing of the end of cleavage depends on counting cell divisions?

No, because the toxin's blockage of cell division does not affect the timing of the end of cleavage.

Part E - Drawing conclusions In a separate experiment, researchers disrupted the block to polyspermy, generating embryos with 7 to 10 sperm nuclei. At the end of cleavage, these embryos had the same nucleus-to-cytoplasm ratio as the wild-type embryos, but cleavage ended at the 10th cell division rather than the 12th cell division. What do these results indicate about the timing of the end of cleavage?

The end of cleavage depends on the nucleus-to-cytoplasm ratio.

Part B What are the cells created by cleavage called?

Blastomeres

Part A - Differentiating between cleavage, gastrulation, and organogenesis Determine which terms, phrases, and images describe each phase of development. Drag each item to the appropriate bin.

Cleavage: blastula, cytoplasm partitioned into many cells, (yellow ball of cells) Gastrulation: embryonic germ layers form, gastrula, blastopore, (ball of cells with three layers yellow, red and blue) organogenesis: organs begin to develop from germ layers, neural tube, somites

Part C Which of the following are the three germ layers contained in the gastrula?

Ectoderm, mesoderm, endoderm

Part F A child is born without a fully developed pancreas. He is normal in all other respects, and thus doctors believe that the problem most likely began early in development. During which of the following processes did the original error most likely occur?

Endoderm formation

Part E What happens to a cell during the process of differentiation?

It undergoes a change toward a more specialized form or function.

Part C - Organogenesis in a frog embryo Tissue and organ formation begins during the process of organogenesis. Which five of the following statements are true about organogenesis in a frog embryo?

The endoderm gives rise to the lining of the frog's digestive tract. The neural tube forms from ectoderm and develops into the central nervous system. The notochord does not persist in adult frogs. Somites form along the length of the notochord and neural tube. Some somite cells migrate to other locations in the developing embryo.

Part B - Interpreting the graph Select Figure 2 from the dropdown menu at left (Figure 2) . The graph shows DNA synthesis and RNA synthesis with and without the toxin that prevents cell division. For the DNA data, one straight line represents the general trend for time points 1-5, and another straight line for time points 5-11. What changes in synthesis occur at the end of cleavage, at time point 5?

The rate of DNA synthesis decreases, and RNA synthesis begins.

Part C The researchers hypothesized that the toxin increases diffusion of thymidine into the embryos. What was their reasoning?

The rates of DNA synthesis are the same with and without the toxin, so the likely explanation is that the DNA is labeled more extensively due to a greater uptake of the labeled thymidine.

Part A - Understanding the experimental design How were the researchers able to independently measure DNA synthesis and RNA synthesis?

Thymidine is a nucleoside building block for DNA, but not RNA, whereas uridine is a nucleoside building block for RNA, but not DNA.

Part B - Gastrulation in a frog embryo Gastrulation is the stage of embryonic development following cleavage. During gastrulation, cell division slows dramatically, and cells are rearranged in a precise way, forming three germ layers. The diagram below illustrates gastrulation in a frog embryo, represented in cross section. Drag the labels to their appropriate locations on the diagram. Use only pink labels for pink targets. Not all labels will be used.

a. blastocoel b. primitive gut (archenteron) c. ectoderm d. mesoderm e. endoderm f. blastopore g. yolk plug h. blastopore forms i. primitive gut begins to form j. three germ layers inplace

Part F The _____ eventually develops into the sea urchin's digestive tract.

archenteron

Part C The notochord functions as a core around which mesodermal cells form the frog's _____.

backbone

Part G During gastrulation, invagination occurs at the _____.

blastopore

Part D Several hours after fertilization, cleavage results in the formation of a hollow ball of cells called a _____.

blastula

Part F The enlarged anterior portion of the neural tube will develop into a frog's _____.

brain

Part A An embryonic cell that is "totipotent" is one that can _____.

by itself, give rise to the entire embryo, as cleavage proceeds

Part A The first stage of embryonic development is _____. This process produces _____.

cleavage ... a cluster of cells

Part A The mesoderm gives rise to _____.

skeletal and muscular systems

Part G The posterior portion of the neural tube will develop into the frog's _____.

spinal cord

Part B What is the cortical reaction?

the formation of a fertilization envelope that bars additional sperm from entry into the egg

Part A Embryonic cells especially active in assuring nutritional exchange between a pregnant woman and her embryo are found in the _____.

trophoblast

Part A In sea urchins, the process of fertilization produces a(n) _____.

zygote