Question

Which of the following statements about common features of chordates is true? a. The dorsal hollow nerve cord is part of the chordate central nervous system. b. In vertebrate fishes, the pharyngeal slits become the gills. c. Humans are not chordates because humans do not have a tail. d. Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column.

Short answer

Both option a and option b are true statements about common features of chordates: a. The dorsal hollow nerve cord is part of the chordate central nervous system. b. In vertebrate fishes, the pharyngeal slits become the gills.

Step-by-step solution

Analyze each statement

: Let's break down and analyze each statement: a. The dorsal hollow nerve cord is part of the chordate central nervous system. b. In vertebrate fishes, the pharyngeal slits become the gills. c. Humans are not chordates because humans do not have a tail. d. Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column.

Determine the correct statement

: Now let's go through each statement and see if it is true or false: a. True. The dorsal hollow nerve cord is a unique component of the chordates' central nervous system. It is present in the ectoderm during the embryonic stage and develops into the spinal cord and brain in vertebrates. b. True. In vertebrate fishes, the pharyngeal slits do become the gills. This is part of the chordate's evolution and serves as an essential component for respiration in fish. c. False. Humans are indeed chordates. Even though humans do not have a tail as adults, they still possess a tail during their embryonic development. This means humans have all the characteristics of chordates during some stage in their life cycle. d. False. The vertebrate's notochord is a precursor to the vertebral column. During the development of vertebrates, the notochord is replaced by the vertebral column; this means that vertebrates do have a notochord at some point in their development.

Identify the correct answer

: Since both statements a and b are true, the correct answer is that both option a and option b hold true information about common features in chordates: a. The dorsal hollow nerve cord is part of the chordate central nervous system. b. In vertebrate fishes, the pharyngeal slits become the gills.

Key concepts

Dorsal Hollow Nerve Cord

The dorsal hollow nerve cord is a defining feature of chordates. Unlike other organisms whose nerve cords are solid and located on the ventral side, chordates have a nerve cord that is hollow and runs along the dorsal (or back) side of the body. This structure begins as a tube-shaped region in embryos. As development progresses, it becomes the central nervous system, comprising the brain and spinal cord. This transformation is crucial, as it facilitates complex nervous functions. The positioning and hollow nature of this nerve cord provide an adaptive advantage. It enables efficient signal transmission to control movements and process sensory information.

Pharyngeal Slits

Pharyngeal slits are another hallmark feature in chordates. In the early embryonic development of all vertebrates, these slits appear in the pharyngeal region, which is the area around the throat. While in terrestrial animals, these structures do not typically persist into adulthood, they play a significant evolutionary role.

• In aquatic vertebrates like fish, pharyngeal slits develop into gills, essential for breathing underwater.
• In humans and other mammals, although these slits do not form gills, they contribute to the formation of structures like the ear canals and parts of the neck.

This demonstrates the versatility in how ancestral features can adapt to different functions across species.

Human Embryonic Development

Human embryonic development exhibits key chordate features, affirming our place within this group. During early gestation, humans develop a tail, a notochord, a dorsal nerve cord, and pharyngeal slits, all characteristic of chordates. Although many of these features transform as development continues, their presence indicates shared ancestry with other chordates.
As humans develop further,

• The embryonic tail reduces, becoming the coccyx found at the base of the spine in adults.
• The notochord guides the formation of the spinal column.

This continuity underscores the remarkable process of evolution and development.

Notochord

The notochord is a flexible rod-shaped structure found in all chordate embryos from which the backbone, or vertebral column, develops. It serves two vital functions during development: it provides structural support and signals the position where the neural tube will form.
In vertebrates, the notochord is usually a temporary structure, replaced by vertebrae as the organism matures. Despite its transient nature, the notochord is crucial for organizing the body's layout. It ensures the proper alignment of tissues and organs, leading to a functioning anatomy.
The evolutionary role of the notochord underscores its importance, highlighting the link between early chordates and modern vertebrates.

Vertebrate Evolution

Vertebrate evolution is a fascinating chapter in the story of life on Earth. Over millions of years, vertebrates have evolved from simple chordates with mere notochords to complex organisms with a fully developed vertebral column. This evolutionary transition signifies the adaptation of structures allowing for greater flexibility and movement.
Key developments in vertebrate evolution include:

• The replacement of notochords by vertebrae, providing more protection for the spinal cord and better support for a larger body size.
• The diversification of pharyngeal slits into specialized structures like jaws and gills, enabling the exploitation of different environments.

Each evolutionary innovation allowed for new adaptive strategies, contributing to the incredible diversity of vertebrates today.