Question

Directions: Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case. Answers can be found here. Which of the following processes produces embryonic germ layers? (A) Gastrulation (B) Cleavage (C) Blastulation (D) Organogenesis (E) Fertilization

Short answer

(A) Gastrulation

Step-by-step solution

Understanding Embryonic Development

After a sperm fertilizes an egg, the resulting zygote begins to divide in a process called cleavage, forming a clump of cells. These cells then undergo a process of reorganization called blastulation, leaving a hollow sphere called a blastula. Further reorganization of cells within the blastula results in gastrulation, where the embryo folds inward to form three layers of cells, known as embryonic germ layers. The layers are the ectoderm, mesoderm and endoderm. Organogenesis is a process that follows, where organs develop from these germ layers.

Choosing the Correct Option

Knowing this, it is clear that the process that produces embryonic germ layers is gastrulation. Therefore, the correct answer is (A) Gastrulation.

Key concepts

Gastrulation

Gastrulation is a pivotal stage in embryonic development. It marks a significant reorganization of the blastula, transforming it into a multi-layered structure known as the gastrula. During this process, cells undergo complex movements, ultimately leading to the formation of three primary germ layers:

• Ectoderm: Forms the outermost layer, giving rise to the nervous system, skin, and hair.
• Mesoderm: Forms the middle layer, which develops into bones, muscles, and the circulatory system.
• Endoderm: Represents the innermost layer, producing the digestive tract, liver, and lungs.

The spatial reorganization during gastrulation is crucial as it sets the blueprint for the body's structure. Proper formation of these layers ensures that future steps in development occur without complications.

Germ Layers

Germ layers are fundamental aspects of the embryonic stage that indicate differentiated groups of cells. Their formation is essential because they serve as the building blocks for organ and tissue development.
The three germ layers formed during gastrulation are:

• Ectoderm: Develops into external structures, such as skin and the central nervous system.
• Mesoderm: Contributes to the formation of internal structures, including muscles, bones, and the circulatory system.
• Endoderm: Lines the internal cavities, eventually becoming the lungs and gastrointestinal tract.

Understanding these layers is crucial, as each layer has specific functions and destinies. Missteps in their development could lead to congenital anomalies.

Cleavage

Cleavage is the initial stage following fertilization, where the zygote divides into smaller cells. These cell divisions are rapid and consist of mitotic processes that increase cell number without growth, called morula. The process creates a solid ball-like mass of cells.
Characteristics of cleavage include:

• Increase in cell number without cell growth, leading to smaller cell sizes.
• Formation of blastomeres, which are the resulting cells from cleavage.
• Directed by cleavage furrows, a part of cell division.

Cleavage is an important early step, as it prepares the embryo for subsequent developmental stages like blastulation and gastrulation.

Blastulation

Blastulation follows cleavage and is a stage where the formation of a hollow, fluid-filled structure called the blastula occurs. This process transitions the solid ball of cells from cleavage into a cavity-filled sphere.

• The blastula consists of a layer of cells, known as the blastoderm, surrounding the blastocoel, a fluid-filled cavity.
• The arrangement facilitates nutrient transport and prepares cells for further differentiation.

Blastulation is crucial because it establishes the basic structure necessary for gastrulation. It determines the initial arrangement of cells that will later become distinct body layers.

Organogenesis

Organogenesis is the developmental stage where the three germ layers undergo extensive differentiation to form all internal organs of the body. This process depends on the organized interaction and signaling among the germ layers.

• Involves the formation of major organ systems from the ectoderm, mesoderm, and endoderm.
• Includes intricate processes like neurulation, where the nervous system begins to develop from the ectoderm.
• Relies on genetic and environmental factors for proper regulation and development.

Organogenesis is a complex stage requiring precise cellular communication to ensure that each organ forms correctly in its designated anatomical position. Errors during this stage can result in developmental disorders.