Question

Each group of questions consists of five lettered headings followed by a list of numbered phrases or sentences. For each numbered phrase or sentence, select the one heading that is most closely related to it and fill in the corresponding oval on the answer sheet. Each heading may be used once, more than once, or not at all in each group. Questions \(9-12\) (A) Zygote (B) Blastocoel (C) Morula (D) Blastula (E) Gamete A fluid-filled cavity that forms after several rounds of cell division.

Short answer

The most appropriate answer is (B) Blastocoel.

Step-by-step solution

Understanding the Terms

Familiarize yourself with the terms in the choices. Each term relates to a different stage or aspect of embryonic development.

Matching the Definition to the Term

The question states, 'A fluid-filled cavity that forms after several rounds of cell division.' This specifically refers to 'Blastocoel', which is a fluid-filled cavity that forms during the process of early embryonic development, characterized by rounds of cell division.

Key concepts

Zygote

The zygote is the initial stage of embryonic development. It forms immediately after the union of an egg and a sperm, a process known as fertilization. This single-celled entity contains a complete set of chromosomes, with half contributed by each parent.
In the zygote, the genetic material from both parents combines to form a unique organism. This is the starting point of all further development. As the zygote undergoes cell division, it remains within its initial cell membrane, dividing to form two cells, then four, and so forth.
Key features of the zygote include:

• Formation after fertilization
• Single-cell stage
• Contains full genetic material
• Initiates cell division processes

The significance of the zygote cannot be overstated; it marks the genesis of a new life in the reproductive cycle.

Blastocoel

As embryonic development progresses, the entity known as the blastocoel emerges. The blastocoel is a fluid-filled cavity that forms within the developing embryo. This occurs after the zygote has divided through repeated mitotic divisions.
The blastocoel plays a crucial role in cell differentiation and in setting the stage for the next phase of development. Its formation is marked within the blastula phase, where cells form a hollow sphere.
Characteristics of the blastocoel:

• Fluid-filled cavity
• Develops after multiple cell divisions
• Influences cellular arrangement
• An integral part of the blastula stage

Understanding the blastocoel is essential, as it aids in the spatial separation of cells, thus facilitating the next crucial stages of development.

Morula

Following the zygote stage, development progresses to the morula phase. This stage involves the embryo forming into a solid mass of cells resulting from the continuous division of the zygote. It resembles a mulberry, which is where its name is derived from.
During this stage, there is no increase in overall size since it is constrained within the original zygote membrane. Instead, cells become smaller and more compact as division continues.
Essential aspects of the morula include:

• Solid cluster of cells
• Typically around 16-32 cells
• No change in external size
• Precedes the blastula form

This tightly packed cluster signifies a crucial advancement in the transformation of the embryo, preparing it for cavitation and moral transition to blastula formation.

Blastula

The blastula stage follows the morula, characterizing a significant transition in embryonic development. In this phase, the cells arrange themselves into a hollow sphere, featuring the blastocoel inside.
The blastocoel further distinguishes the blastula from the solid morula. This hollow structure supports cell differentiation and paves the way for subsequent development stages like gastrulation.
Recognizable features of the blastula:

• Hollow ball of cells
• Presence of a central blastocoel
• Increased cellular organization
• Marks the beginning of increased cell specialization

The blastula phase is crucial as it sets the foundation for complex body structures to form, marking a milestone on the journey from zygote to fully developed organism.