Question 1

Events of Gastrulation and Organogenesis

Accepted Answer

• In chordates (during organogenesis) the notochord develops from the mesoderm followed by the formation of the neural tube from the ectoderm. • Two factors that influence cell differentiation are: 1. cytoplasmic factors-unequal distributions of cellular material during division. 2. cell-cell induction-certain cells signal the differentiation of totipotent cells through cell secretions and cell-cell contact. • Based upon a series of transplant experiments in the 1920s, Hans Spemann and Hilde Mangold determined that during gastrulation the cells at the dorsal lip of the blastopore are the primary inducers of cell differentiation.

Question 2

Review of the events following fertilization:

Accepted Answer

1. Cleavage: A zygote undergoes mitotic divisions forming a morula (solid ball of cells) that eventually changes into a blastula (hollow ball of cells.) 2. Gastrulation: The cells of the blastula rearrange to form three germ layers: ectoderm, mesoderm, and endoderm. 3. Organogenesis: Includes the processes of morphogenesis (change in appearance) and cell differentiation forming the beginnings of organs and tissues.

Question 3

note

Accepted Answer

- As a taxonomic group, the chordates share anatomical similarities including the presence of a notochord during embryological development. The notochord is a cartilaginous structure that establishes a dorsal axis in a developing embryo and may later take part in the formation of the vertebrae. - A subphylum of the chordates, the urochordates (also called tunicates, pictured to the left), displays the primitive chordate plan without other anatomical features displayed by vertebrate chordates. - During early organogenesis, formation of the notochord begins when neural ridges form on the ectoderm. Neural folds come together and fuse forming a hollow cylinder beneath the neural tube. The neural tube will eventually form the brain and the spinal cord. - A cross section of a frog embryo during early organogenesis shows the notochord, which is formed from the mesoderm layer. The two ridges (neural folds) comprise the lateral edges of the neural plate. The neural folds will come together and form the neural tube. - Some chordates, such as the tunicates, will lose their notochord, while others keep it for development of the vertebrae. - Somites, blocks of cells derived from mesoderm, develop along the notochord. These will later give rise to segmental structures, such as the vertebrae and spinal muscles.

Question 4

totipotency

Accepted Answer

- The term totipotency describes the ability for each cell of an embryo to have the potential to form all parts of an organism. During embryonic development, cells of a zygote are totipotent for a certain length of time, awaiting specific chemical instructions to enable cell differentiation into various tissues and organs. - Cytoplasmic factors and cell-cell induction are two controlling factors in cell differentiation. - Review: The presence of yolk, nutrients stored in the egg, affects the pattern of cleavage and establishes polarity in the zygote. - Cells may also concentrate different types of RNA and proteins at separate ends and establish polarity.

Question 5

note 2

Accepted Answer

- In the 1920s, German zoologist Hans Spemann and his student Hilde Mangold performed a series of experiments concerning induction during development. - Induction is the ability of a group of cells to initiate differentiation in other cells. - By performing a series of transplant experiments, Spemann and Mangold determined that the dorsal lip of the blastopore in the early gastrula has a key role in cell differentiation. - They transplanted cells from the dorsal lip of one gastrula to a different location on another embryo. - The transplanted cells induced the totipotent cells of the gastrula to form an entire second organism. Because of the results, Spemann and Mangold called the cells from the dorsal lip of the blastopore “the primary inducer.” The differentiation of totipotent cells as they reach the dorsal lip of the blastopore is a time-dependent phenomenon.

Question 6

The notochord establishes a dorsal axis in a developing embryo. What layer of germ cells form the notochord?

Accepted Answer

- mesoderm

Question 7

Organogenesis includes which two processes?

Accepted Answer

- morphogenesis and cell differentiation

Question 8

The work of Spelmann and Mangold found that the dorsal lip of the blastopore serves what role in embryological development?

Accepted Answer

- Primary inducer

Question 9

Identify the structures indicated by numbered blanks in the figure.

Accepted Answer

- 1. notochord; 2. somite; 3. neural plate

Question 10

Which of the following statements is a conclusion drawn from the experiments of Spemann and Mangold?

Accepted Answer

- The dorsal blastopore lip is involved in the initiation of gastrulation.

Question 11

During embryological development, what is the hollow ball of cells formed after cleavage called?

Accepted Answer

- blastula

Question 12

Gastrulation results in the formation of three primary tissue layers that will give rise to all of the organs and tissues of the body. Which of the following statements is correct?

Accepted Answer

- Ectoderm gives rise to nerve tissues.

Question 13

__________ includes the process of __________ and cell differentiation forming the beginnings of organs and tissues.

Accepted Answer

- Organogenesis, morphogenesis

Question 14

True or false? The formation of the notochord in chordates causes a dorsal anterior-posterior axis in the embryo.

Accepted Answer

- true

Question 15

Which of the following describes a chordate?

Accepted Answer

- An organism that has a notochord at some point in its embryological development.

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11.12.3 Events of Gastrulation and Organogenesis Flashcards

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