Question

Protostomes and deuterostomes can be classified based on a. cleavage pattern. b. destiny of the blastopore. c. whether the fate of the embryonic cells is fixed early during development. d. all of the above.

Short answer

The correct answer is option d. 'all of the above'. Protostomes and deuterostomes can be classified based on cleavage pattern, destiny of the blastopore, and whether the fate of the embryonic cells is fixed early during development.

Step-by-step solution

Understanding Cleavage Pattern

The cleavage pattern refers to the way cells divide during early animal development. In protostomes, the cleavage is spiral and determinate, meaning the fate of cells is determined early. In deuterostomes, it's radial and indeterminate, allowing each cell to develop into a complete organism. Thus, it's a point of differentiation.

Determining Destiny of the Blastopore

The fate of the blastopore can also serve as a distinguishing factor. In protostomes, the blastopore (first opening in development) becomes the mouth while in deuterostomes, it develops into the anus and the second opening becomes the mouth.

Considering Legacy of Embryonic Cells

The fate of embryonic cells is indeed fixed early in the development of protostomes. This happens during the 'spiral and determinate' cleavage. However, in deuterostomes, it is 'radial and indeterminate', the opposite situation. Thus, it is also a potential classification point.

Combining the Criteria

By examining each criterion individually, it is clear that all apply as unique characteristics that distinguish between protostomes and deuterostomes. Therefore, the correct classification basis would be 'all of the above'.

Key concepts

Cleavage Patterns

Cleavage patterns define the initial phase of animal development and are crucial in classifying protostomes and deuterostomes. During cleavage, the fertilized egg divides to form multiple cells, known as blastomeres. In protostomes, cleavage is spiral and determinate. This means that cells divide in a spiral pattern and the fate of each cell is predetermined early. This early determination restricts the potential of these cells to develop only specific tissues. On the other hand, deuterostomes exhibit radial and indeterminate cleavage. Here, cells divide parallel or perpendicular to one another, allowing each cell to retain the potential to form any tissue type until much later in development. This indeterminacy gives deuterostomes an edge in flexibility during early development.

Blastopore Fate

The fate of the blastopore is a pivotal aspect distinguishing protostomes from deuterostomes. The blastopore is the first opening that forms in an embryo during gastrulation, a phase where the embryo transforms from a blastula into a multilayered structure. In protostomes, this first opening becomes the mouth, with the opposite end eventually developing into the anus. In contrast, deuterostomes exhibit an opposite developmental pathway. The blastopore in deuterostomes forms the anus first and the mouth develops afterwards, making this a crucial differentiator between the two groups. Understanding the destiny of the blastopore helps in comprehending the basic body plan and orientation of these organisms.

Embryonic Cell Fate

The fate of embryonic cells during early development is another key characteristic separating protostomes and deuterostomes. In protostomes, embryonic cells are determinate. This means their fate is set very early, as each cell already knows what tissues it will become, often right after the first few divisions. This can limit their ability to compensate for lost or damaged cells during early development. Meanwhile, deuterostomes have indeterminate embryonic cells, allowing each cell the potential to develop into a complete organism on its own. This flexibility is a significant evolutionary advantage as it permits greater adaptability in varying environmental conditions.

Animal Development

Animal development is a complex process beginning right after fertilization and involving several crucial stages. The early divisions, known as cleavage, lead to the formation of a blastula. This stage is succeeded by gastrulation, during which the primary gut is formed and the blastopore's fate is set. Following these initial distinctions, organisms develop intricate body plans.

• Protostomes and deuterostomes diverge early in these processes.
• Their varied cleavage patterns and blastopore fate result in vastly different morphologies and developmental strategies.
• These differences highlight the evolutionary pathways both groups have taken.

Understanding animal development provides insight into the inherent diversity and complexity of the animal kingdom, illustrating the remarkable adaptations these creatures undergo during evolution.