Question

All chordates have (a)__________ as embryos. a. backbone b. jaws c. notochord d. both \(b\) and \(c\)

Short answer

All chordates have a notochord as embryos (Option c).

Step-by-step solution

Understand the Question

The question is asking for a feature that all chordates possess during their embryonic development. Chordates are a group of animals that include vertebrates, and it's important to recall what distinguishes them from other animals in their early development.

Recall Key Chordate Characteristics

In studying chordates, a notochord is one of the fundamental structures that defines this group. A notochord is a flexible rod-like structure that provides support in the embryo stage of all chordates.

Evaluate the Options

Option (a) 'backbone' (or vertebrate column) is a feature of more developed chordates like vertebrates but not all chordates. Option (b) 'jaws' describes a feature found in some vertebrates, not in all chordates. Option (c) 'notochord' is indeed present in all chordate embryos, even if lost or replaced by other structures later in life. Option (d) suggests both (b) and (c), but since not all chordates have jaws, this option is incorrect.

Choose the Correct Answer

The notochord is the defining and unifying feature found in all chordate embryos. Thus, the correct answer according to our evaluations is option (c).

Key concepts

Notochord

The notochord is a key feature of chordates, marking its importance during the embryonic development of these animals. It is a flexible, rod-like structure composed mainly of cells filled with fluid. This structure acts as a primary support mechanism for the embryo. It runs along the body in a dorsal (back) position and provides a scaffold that helps in the elongation and shaping of the developing body.

In early chordates, the notochord remains throughout their life as their main axial support, but in most vertebrates, it is present only during the embryonic stage. As the embryo develops into an adult, the notochord is typically replaced by a vertebral column, also known as a backbone. However, it plays a crucial role during the initial phase of development by guiding the cells that will form the backbone in vertebrates.

• The notochord induces the formation of surrounding structures like the neural tube, which later becomes the central nervous system consisting of the brain and spinal cord.
• It marks the embryological path that sets apart chordates from other phyla.
• Despite its replacement or reduction in the adult stages of many species, its presence in the embryonic form is a consistent characteristic of all chordates.

Embryonic Development

Embryonic development is a pivotal phase in the life cycle of chordates, where key structures are formed and organized. This stage begins soon after fertilization and is characterized by a series of complex and precisely timed changes that transform a single cell into a more complex organism.

During this process, the fertilized egg undergoes multiple cell divisions and follows a series of stages including cleavage, blastula, gastrula, and neurulation. Each stage marks a specific transformation and the differentiation of cells into various tissues and organs. The notochord forms early in this sequence, signaling the development of the central nervous system and the axial skeleton.

• The steps of embryonic development include: fertilization, cleavage (cell division), formation of the blastula, gastrulation (cell movement to form layers), and neurulation (formation of the neural tube).
• Notochord facilitates the differentiation of the mesoderm into the somites, which eventually form the vertebrae and muscles.
• The close coordination of development ensures that the embryo grows into a functionally sound organism.

Understanding these processes is crucial because any disruptions can lead to developmental anomalies or malformations.

Vertebrates

Vertebrates are a subgroup within the chordates distinguished by the development of a vertebral column, or backbone. Even though all chordates start with a notochord, in vertebrates, this structure gets replaced by a more rigid and complex series of bones or cartilage in adulthood.

The backbone serves two main functions: it protects the spinal cord and provides structural support for the body, allowing vertebrates to have diverse sizes and forms. The emergence of such a structure is pivotal for their capability to thrive in various environments and engage in complex movements.

• Vertebrates include familiar animals like mammals, birds, reptiles, amphibians, and fish.
• They exhibit a high level of complexity, with closed circulatory systems, a well-developed nervous system, and advanced organ systems.
• The backbone not only provides structural integrity but also contributes to the body's ability to leverage muscles for movement.

In essence, vertebrates represent an evolutionary advancement that showcases the incredible diversity and adaptability of life forms within the chordate family.