Problem 1 - Campbell Biology

Question

Vertebrates and tunicates share (A) jaws adapted for feeding. (B) a high degree of cephalization. (C) an endoskeleton that includes a skull. (D) a notochord and a dorsal, hollow nerve cord.

Step-by-Step Solution

Answer

Option (D) a notochord and a dorsal, hollow nerve cord.

Step 1: Identify the Common Characteristics

Vertebrates and tunicates are both part of the phylum Chordata. To find the correct answer, identify the characteristics that are shared by all chordates, including these two groups.

Step 2: Exclude Irrelevant Options

Option (A) mentions jaws adapted for feeding, which not all tunicates have. Options (B) and (C) refer to high degrees of cephalization and an endoskeleton with a skull, respectively, which are not common features among tunicates.

Step 3: Confirm the Correct Characteristic

Option (D) mentions a notochord and a dorsal, hollow nerve cord. These are characteristic features of all chordates, including vertebrates and tunicates.

Key Concepts

Notochord

The notochord is a vital structure in chordates. It is a flexible, rod-shaped support system found in all embryonic stages of chordates.
This rod runs along the length of the body and provides the main axial support.
Not all adult chordates keep the notochord, but they most definitely have one during the embryonic phase.

In vertebrates, the notochord is eventually replaced by the vertebral column (spine) during development.
In contrast, some chordates, like tunicates, retain the notochord throughout their life.
Key functions of the notochord include:

• Providing a scaffold for the development of the vertebral column in vertebrates
• Helping in the overall support and shape of the body
• Facilitating muscle attachment, enhancing movement

Understanding the role of the notochord is crucial because it ties into the evolution and structural mechanics of all chordates.

Dorsal Hollow Nerve Cord

Another defining feature of chordates is the dorsal hollow nerve cord.
This cord is a tube-like structure filled with fluid that runs along the back of chordates just above the notochord.
Unlike other animals that might have a solid nerve cord, the nerve cord in chordates stays hollow.

In vertebrates, this dorsal hollow nerve cord develops into the spinal cord and brain, forming the central nervous system.
Other chordates, like tunicates, also have a dorsal hollow nerve cord during their embryonic stage.

• It serves as a crucial component for transmitting neural signals
• It helps in coordination and control of various body functions
• It forms the foundation for complex nervous systems in higher chordates, including humans

Understanding this feature helps in grasping how nerve systems in various animals evolved and how they function in chordates.

Phylum Chordata

The phylum Chordata is a large and diverse group encompassing all chordates.
This phylum includes animals like vertebrates (mammals, birds, reptiles, amphibians, and fishes) and some invertebrates such as tunicates and lancelets.
A few key characteristics define this phylum, setting chordates apart from other animal groups.

• Notochord: Present at some stage of development
• Dorsal Hollow Nerve Cord: Located along the back
• Pharyngeal Slits: Present in the pharynx region sometimes involved in respiration or feeding
• Post-Anal Tail: A tail extending beyond the anus, seen in some form during the embryo stage

Whether focusing on the shared evolutionary traits or the specific developmental stages, the phylum Chordata provides a comprehensive view of how diverse and complex life forms can be. By studying chordates, we gain insights into the evolutionary history and anatomical structures that define much of the animal kingdom.