Question

Arrange the following phases of pattern formation in animals in the correct sequence: 1\. Tissues, organs, and other body structures in each segment are formed. 2\. Axes of the entire animal are determined. 3\. Cells become differentiated. 4\. The entire animal is divided into segments. a. 2, 3, 4, 1 b. 1, 2, 4, 3 c. 2, 4, 3, 1 d. 3, 2, 4, 1 e. 2, 4, 1, 3

Short answer

The correct answer is 'c' which is the sequence: 2, 4, 3, 1.

Step-by-step solution

Identify the Steps

In biological terms, pattern formation refers to the developmental process by which cells in early development form the structures of a mature organism. During pattern formation, cells go through a series of transformations. This includes the determination of axes, segmentation, cell differentiation, and formation of tissues, organs, and structures.

Arrange the steps

The correct chronological sequence would be as follows. \n\n- First, the axes of the entire animal are determined. This lays out the basic body plan, forming the head-tail, left-right, and dorsal-ventral axes. \n\n- Next, the entire animal is divided into segments. Segmentation creates repeating units, building on the original body plan. The segments will eventually form different body parts. \n\n- After segmentation, cells within each segment become differentiated. Differentiation is the process by which a cell becomes specialized in order to perform a specific function. \n\n- Finally, within each segment, the tissues, organs, and other body structures are formed. Each segment will develop structures appropriate to its function, as determined by the original body plan and the process of cell differentiation.

Identify the correct answer

Looking at the answer choices provided, the sequence of phases that matches the correct chronological order that was previously determined is 2, 4, 3, 1. Therefore, the correct answer to this exercise is choice 'c'.

Key concepts

Axes Determination

In the fascinating process of pattern formation, determining the axes of an animal is the first crucial step. This stage sets up the fundamental blueprint of the organism. There are three key axes:

• Head-to-tail (anterior-posterior) axis
• Left-to-right (lateral) axis
• Back-to-belly (dorsal-ventral) axis

These axes are determined very early in development, often even before cellular divisions get underway.
They provide a spatial reference framework that dictates where different body parts will form. Think of them as the imaginary lines that allow an artist to sketch out a symmetrical and proportional drawing.
This stage is critical, as any irregularities here can manifest as structural or functional anomalies in the organism.

Segmentation

Segmentation follows axes determination and adds another layer of organization to the animal's body plan. Imagine taking a long train and dividing it into individual cars connected to one another.
Each "car" or segment represents a basic repeated unit of the body layout, often seen in species such as insects, worms, and vertebrates.
This step is essential because it sets the stage for further specialization and division of labor among cells and tissues.
Segmentation allows for the efficient allocation of different functions to each unit, and it enables flexibility and adaptability in the body structure.

Cell Differentiation

Once segmentation is in place, the individual cells begin to specialize. This process, known as cell differentiation, involves cells taking on unique identities and roles based on the segments they are part of.
They may become skin cells, muscle cells, nerve cells, or others, depending on their specific location and the chemical signals they receive.
This transformation is guided by gene expression, which is meticulously regulated to ensure that the right genes are turned on or off in each cell.
Differentiation is vital as it leads to the multiplicity of functions that tissues and organs collectively perform, allowing the organism to thrive and adapt to its environment.

Tissue and Organ Formation

The final stage involves the mature formation of tissues, organs, and body structures within each segment. Here, the differentiated cells come together to form sophisticated structures like hearts, lungs, and livers, among others.
During tissue formation, cells organize themselves into units that perform specific functions and support the structure of the organ.
This precise arrangement is influenced by the predetermined axes and previously segmental differentiation.
Integration of tissues into functional organs marks the completion of the developmental journey described by pattern formation, ensuring the organism's survival and functionality in its ecosystem.