Problem 12 - Biology

Question

Which of the following is an example of a deuterostome? (a) a lophotrochozoan (b) coral (c) chordate (d) planarian (e) a pseudocoelomate

Step-by-Step Solution

Answer

The correct example of a deuterostome is (c) a chordate.

Step 1 - Define Deuterostome

Deuterostomes are a group of animals distinguished by their embryonic development. In these animals, the blastopore (the first opening that forms during early embryonic development) becomes the anus. This is in contrast to protostomes, where the blastopore becomes the mouth. Common examples of deuterostomes include echinoderms (such as starfish) and chordates (such as vertebrates, which include humans).

Step 2 - Evaluate Each Option

Examine each given option to determine whether it is a deuterostome: - (a) A lophotrochozoan is part of protostomes. - (b) Coral is a cnidarian, which is not a deuterostome. - (c) A chordate is a deuterostome, as it includes vertebrates. - (d) A planarian is a flatworm, belonging to the protostomes. - (e) A pseudocoelomate refers to the type of body cavity, not specifically related to deuterostomes or protostomes.

Step 3 - Identify the Correct Option

From the evaluation, the only option that is an example of a deuterostome is (c) a chordate. Chordates are part of the deuterostome clade, which includes animals like vertebrates.

Key Concepts

Chordates

Chordates are a fascinating and diverse group of animals recognized by specific anatomical features. One of the key characteristics of chordates is the presence of a notochord at some stage of their life. The notochord is a flexible rod-shaped structure that provides support. While in some chordates, like humans, this structure is only present during the embryonic stage, in others, it persists throughout their life.
Other defining traits of chordates include a dorsal nerve cord, pharyngeal slits, and a post-anal tail. The dorsal nerve cord is a hollow tube that in many chordates forms the central nervous system components such as the brain and spinal cord.

Types of Chordates

Chordates can be broadly divided into three groups:

• Urochordata (Tunicates): Often referred to as sea squirts, these organisms are mainly sessile as adults.
• Cephalochordata (Lancelets): These small, fish-like marine animals retain the notochord throughout life.
• Vertebrata: This includes a massive variety of species, including mammals, birds, reptiles, amphibians, and fish. Vertebrates have a more complex structure including a well-defined skeleton and skull.

Overall, chordates play essential roles in various ecosystems, demonstrating a wide array of adaptations to different environments.

Blastopore

The blastopore is an essential feature in the early stages of embryonic development in animals. During the process called gastrulation, where the single-layered blastula reorganizes into a multilayered structure, the blastopore forms as the first opening. In deuterostomes, which include chordates, this opening becomes the anus.
In contrast, in protostomes, which encompass groups like lophotrochozoans and arthropods, the blastopore forms the mouth. This difference is one of the primary distinctions between these two fundamental evolutionary lines of animals.

Significance of the Blastopore

The formation of the blastopore and its subsequent development is crucial for the organization of the body plan and the digestive system. It marks the beginning of the development of the gut. Understanding the role of the blastopore helps in comprehending how complex organisms establish their basic body structures during early development.

Embryonic Development

Embryonic development is a complex process that transforms a fertilized egg into a fully formed organism. This journey begins with fertilization, followed by several key stages that involve extensive cell division and differentiation.
One of the first milestones in embryonic development is cleavage, a series of rapid cell divisions that create a multi-cellular embryo from the single-celled zygote. This leads to the formation of the blastula, a hollow ball of cells. Gastrulation follows, where the blastula reorganizes into a structure with multiple layers, setting the stage for all subsequent development.

Stages of Embryonic Development

• Cleavage: Cell divisions that transform the zygote into the blastula.
• Gastrulation: Critical process in which the blastula infolds to form different germ layers, eventually leading to the formation of the blastopore.
• Organogenesis: The process where the germ layers develop into organs and tissues.

Throughout embryonic development, the coordinated actions of genes guide each step, ensuring the organism develops correctly. This intricate process underscores the beauty and complexity of life.