Problem 10 - Biology

Question

During cleavage, an animal (a) undergoes metamorphosis (b) becomes a larva (c) undergoes a series of mitotic divisions and becomes a blastula (d) becomes diploid (e) reproduces sexually

Step-by-Step Solution

Answer

(c) Undergoes a series of mitotic divisions and becomes a blastula.

Step 1: Understanding the Question

We are asked to determine what happens to an animal during the cleavage stage.

Step 2: Identifying the Correct Process

During cleavage, the primary process is a series of rapid mitotic divisions. This leads to the formation of a blastula, which is a hollow sphere of cells.

Step 3: Conclusion

The correct answer is that during cleavage, an animal undergoes a series of mitotic divisions and becomes a blastula. This is option (c).

Key Concepts

Mitotic Divisions

Cleavage refers to the rapid series of mitotic divisions that take place after fertilization in early embryonic development. During these divisions, a single fertilized egg (zygote) divides into multiple smaller cells without increasing in total volume. This results in increased cell numbers and decreased size of individual cells, known as blastomeres. Cleavage divisions are characterized by:

• Being rapid and numerous, with minimal growth phases (G1 and G2) between them.
• Converting the large zygote into smaller cells without the embryo growing in size.
• Being synchronous at the beginning, which means all cells divide at the same time.

The purpose of mitotic divisions during cleavage is to create a large number of cells needed for the formation of the early embryo, eventually leading to the blastula stage.

Blastula Formation

As cleavage continues, the cells produced form a structure known as the blastula. This phase marks a crucial period in embryonic development, as the blastula is a spherical layer of cells surrounding a fluid-filled cavity called the blastocoel. The formation of the blastula includes several important aspects:

• The blastula is structured in such a way that it is hollow, which is essential for further embryonic processes.
• The arrangement of cells in the blastula prepares it for the subsequent stages of development, such as gastrulation.
• Its formation indicates the end of the cleavage process and the readiness for the next stages of embryogenesis.

This stage is vital for setting up the embryonic architecture and ensuring proper subsequent development.

Embryogenesis

Embryogenesis refers to the entire process of embryo development, starting right after fertilization and continuing until the embryo is a fully formed infant. This involves multiple stages beyond cleavage and blastula formation, including:

• Gastrulation, where the blastula reorganizes into a structure called the gastrula, establishing the primary germ layers.
• Neurulation, which is the formation of the neural tube, setting the basis for the central nervous system.
• Organogenesis, a process where individual organs and bodily structures start to take shape.

Throughout embryogenesis, cells differentiate and specialize, leading to the complex structures and functions necessary for life. Understanding embryogenesis highlights how a single fertilized cell can lead to a well-organized multicellular organism.