OBJECTIVE QUESTIONS

Here are the correct options for each question:

(a) Heart in vertebrates is-
(ii) Ventral

(b) Chordates with a backbone are called?
(iv) Vertebrates

(c) Pipe fish is the common name of-
(i) Syngnathus

(d) Era of Age of reptiles was-
(i) Mesozoic

(e) The body of lung fishes is covered with-
(ii) Cycloid scales

SUBJECTIVE QUESTIONS

Answer ay two questions only in paper.

2. Describe the vertebral column of Frog.

The vertebral column of a frog, classified within the order Anura, is a fundamental skeletal structure that plays a crucial role in supporting the animal’s body and protecting the spinal cord. This structure exhibits several notable features:

• Structure: The vertebral column is composed of a series of vertebrae arranged in a linear sequence. It can be divided into three main regions:
• Cervical Vertebrae: Frogs typically possess one cervical vertebra, which articulates with the skull and facilitates limited head movement. This vertebra is crucial for adjusting the frog’s line of sight, especially while hunting for prey.
• Trunk Vertebrae: This region consists of several vertebrae (usually ranging from 8 to 10) that connect to the ribs and form the thoracic cavity. These trunk vertebrae provide structural support to the body and are responsible for protecting vital organs located in the chest area, such as the heart and lungs.
• Sacral Vertebrae: The sacral region comprises a single sacral vertebra, which is fused to the pelvic girdle. This fusion is vital for providing stability and strength during locomotion, especially when frogs leap or swim. The integration of the sacral vertebra into the pelvic structure is a key adaptation for supporting the weight of the body during jumping activities.
• Function: The vertebral column serves multiple essential functions:
• Support: It provides structural integrity to the body, allowing frogs to maintain their shape and posture while transitioning between aquatic and terrestrial environments. The vertebral column also serves as an anchor for muscle attachment, enabling movement.
• Flexibility: The intervertebral joints between adjacent vertebrae allow for a degree of flexibility, which is critical for activities such as jumping, swimming, and navigating through their environments. The vertebral column’s flexibility enhances the frog’s ability to perform powerful jumps and rapid directional changes while swimming.
• Protection: The vertebral column encases and protects the spinal cord, a vital component of the central nervous system. The spinal cord transmits signals between the brain and the body, coordinating motor and sensory functions essential for survival.
• Adaptations: The structure of the vertebral column in frogs reflects their unique adaptations for a dual lifestyle—living both on land and in water. The ability to transition between these environments requires a well-developed vertebral column that can provide both strength and flexibility. Furthermore, the reduction in the number of vertebrae compared to other vertebrates allows frogs to maintain a lightweight body, which is beneficial for jumping and swimming.

3. Describe the forelimbs of Frog.

The forelimbs of frogs are critical for various functions, including locomotion, grasping, and swimming. Their unique structure is adapted to meet the demands of both terrestrial and aquatic environments. Here’s a detailed description:

• Structure: The forelimbs of frogs consist of several segments:
• Humerus: The humerus is the primary bone of the upper arm, which connects to the shoulder girdle. This bone is relatively short and robust, providing the necessary strength for limb movements. The proximal end of the humerus articulates with the scapula, allowing for a degree of rotation and movement.
• Radius and Ulna: The forearm comprises two bones, the radius and ulna, which are slightly fused in frogs. This fusion enhances stability during movement. The radius is located on the thumb side of the forearm, while the ulna is on the opposite side.
• Carpals, Metacarpals, and Phalanges: The wrist area (carpals) consists of several small bones that allow flexibility. The hand is composed of elongated metacarpals and digits (phalanges). Frogs typically have four fingers on each forelimb, with the third finger often being the longest. The structure of the digits enables frogs to grasp and manipulate objects, especially in climbing species.
• Function: The forelimbs serve several critical functions:
• Locomotion: While frogs are primarily recognized for their powerful hindlimbs used in jumping, the forelimbs also contribute to locomotion. During a jump, the forelimbs play a role in stabilizing the body upon landing. They help to absorb the impact and guide the frog’s body position to avoid injury.
• Swimming: In aquatic environments, the forelimbs serve as paddles, assisting in swimming. Frogs can spread their forelimbs outwards and use them to navigate through the water. The webbed structure of the digits in some species enhances their swimming efficiency.
• Climbing and Grasping: Frogs that inhabit arboreal (tree-dwelling) environments have forelimbs adapted for climbing. The presence of webbing between the fingers aids in grasping branches and maintaining stability while navigating through foliage. Some species have evolved adhesive pads on their fingertips, which allow them to cling to vertical surfaces.
• Adaptations: The forelimbs of frogs are highly adaptable, with their length and structure varying among species depending on their habitat and lifestyle. For example:
• Aquatic Frogs: In species that primarily live in water, the forelimbs may be more elongated and equipped with greater webbing to facilitate swimming.
• Terrestrial and Arboreal Frogs: Species that live on land or in trees may exhibit shorter, sturdier forelimbs for climbing and jumping, reflecting their need to navigate diverse environments.

4. Nerve Cord (Spinal Cord)

The nerve cord, specifically the spinal cord, is a critical component of the central nervous system in vertebrates, including frogs. It serves as a major pathway for information traveling between the brain and the rest of the body. Here’s an in-depth description:

• Structure: The spinal cord is a cylindrical structure that extends from the base of the brain and runs through the vertebral column. It is composed of nerve tissue and is segmented into distinct regions corresponding to the vertebrae:
• Cervical Region: The cervical region contains the first few segments of the spinal cord and is associated with the nerves that control the head, neck, and forelimbs.
• Thoracic Region: This section includes the spinal segments that connect to the trunk and ribs, facilitating movements and sensations in these areas.
• Lumbar and Sacral Regions: These regions control the hindlimbs and pelvic organs. The sacral region is particularly important for movements related to locomotion and balance. The spinal cord comprises both white matter and gray matter. The outer layer of white matter consists of myelinated axons, which facilitate rapid communication between different parts of the nervous system. The inner layer of gray matter contains neuronal cell bodies and is responsible for processing sensory information and coordinating motor commands.
• Function: The spinal cord performs several essential functions:
• Conduction: It acts as a conduit for transmitting nerve signals between the brain and the body. Sensory neurons convey information from the skin and muscles to the spinal cord, which then relays this information to the brain for processing. Conversely, motor signals generated in the brain are transmitted through the spinal cord to control muscle contractions.
• Reflex Actions: The spinal cord is integral to reflex actions that occur independently of the brain. For instance, when a frog’s foot comes into contact with a hot surface, sensory neurons transmit signals to the spinal cord, which processes this information and activates motor neurons to withdraw the foot rapidly. This reflex arc allows for immediate responses to potentially harmful stimuli, enhancing survival.
• Protection: The spinal cord is protected by the vertebral column, which encases it and prevents physical damage. Additionally, three protective membranes known as the meninges surround the spinal cord, providing further protection and stability. Cerebrospinal fluid, which circulates within the meninges, serves to cushion the spinal cord and supply essential nutrients while removing waste products.
• Clinical Significance: Understanding the structure and function of the spinal cord is vital in the context of health and disease. Injuries to the spinal cord can lead to significant impairments, including paralysis or loss of sensation below the injury site. Research into spinal cord injuries and diseases aims to develop therapeutic approaches that could enhance recovery and improve the quality of life for affected individuals.

5. Write a short note on hypothetical vertebrate ancestor.

The concept of a hypothetical vertebrate ancestor represents a significant point in the evolutionary history of vertebrates, theorized to have existed approximately 500 to 600 million years ago during the Cambrian period. This ancestor is believed to have given rise to all modern vertebrate groups, including fish, amphibians, reptiles, birds, and mammals. Here’s an expanded overview of its characteristics and significance:

• Physical Characteristics: The hypothetical vertebrate ancestor likely exhibited several key features common to early chordates:
• Notochord: A flexible, rod-like structure that provided support and defined the body plan. In later vertebrates, this structure evolved into the vertebral column, allowing for increased strength and flexibility in the skeleton.
• Dorsal Nerve Cord: This tubular structure is located above the notochord and is a defining characteristic of chordates. It would eventually develop into the spinal cord and brain in more advanced vertebrates, facilitating complex neural functions.
• Pharyngeal Slits: These structures were present in the ancestor and are believed to have evolved into gills in aquatic vertebrates. In terrestrial vertebrates, they contributed to various anatomical features, including parts of the ear and throat.
• Segmentation: The body of the hypothetical ancestor may have been segmented, a characteristic seen in many vertebrates. This segmentation allowed for specialized regions, facilitating movement and organ differentiation.
• Habitat and Lifestyle: This ancestral organism likely inhabited shallow marine environments, where it would have thrived among various aquatic organisms. It is presumed to have been a free-swimming creature that used a form of lateral undulation for movement. Feeding might have involved filter-feeding or scavenging, using the pharyngeal slits to filter small particles and plankton from the water.
• Evolutionary Significance: The hypothetical vertebrate ancestor is crucial for understanding vertebrate evolution as it represents a pivotal transition in the evolutionary tree. Its characteristics laid the foundation for the development of key vertebrate traits, including:
• Backbone Evolution: The transition from a notochord to a bony or cartilaginous vertebral column marked a significant evolutionary advancement, allowing for greater flexibility, mobility, and structural support.
• Complex Nervous System: The evolution of a dorsal nerve cord into a more sophisticated spinal cord and brain allowed for improved sensory processing and motor control, enabling vertebrates to adapt to a variety of environments.
• Modern Implications: Research into the hypothetical vertebrate ancestor has important implications for modern biology. By studying the genetic and developmental pathways of contemporary vertebrates, scientists can gain insights into the evolutionary processes that shaped vertebrate diversity. Comparative studies with extant species, such as lancelets and tunicates, help to reconstruct the evolutionary relationships among vertebrates and understand the genetic underpinnings of major developmental innovations.