BZYCT-133 Solved Assignment
-
a) Explain keratinization in terrestrial vertebrates.
b) Give five features that you can use to distinguish between the skulls of frog and rabbit.
-
a) Explain the major differences between reptilian and avian digestive systems.
b) Describe the structure of the respiratory system of cartilaginous fishes and state how does it differ from that of bony fishes.
-
a) Discuss lymphatic system in different vertebrates.
b) Write short notes on:
i) Blood filteration in kidney
ii) Types of mammalian uteri
-
a) Which part of the brain is well developed in all vertebrates and why?
b) What are pit organs in reptiles? How do vipers and boas locate prey?
-
Briefly write the functions of the following hormones secreted in mammals.
a) Adrenocorticotropic hormone
b) Parathormone
c) Aldosterone
d) Testosterone
e) Progesterone
-
List at least three stages in gene expression that can be regulated to result in differentiated cell types? Explain any one of them with the help of an example.
-
Describe the mechanisms evolved by eggs to prevent polyspermy.
-
Make a flow chart to show the events in metamorphosis.
-
Discuss the process of development of extra embryonic membranes in chick.
-
a) Draw a flow chart to show how the three germinal layers are derived from the zygote.
b) How do genetic and environmental defects cause problems in embryonic development?
Answer:
Question:-1
1. a) Explain keratinization in terrestrial vertebrates.
Answer:
1. Introduction to Keratinization in Terrestrial Vertebrates
Keratinization is a crucial biological process that occurs in terrestrial vertebrates as part of the development of their outermost protective layer. It involves the formation of keratin, a tough, fibrous protein that provides strength, water resistance, and protection to epithelial cells. This process is particularly important for terrestrial vertebrates as it helps them adapt to life on land by preventing desiccation and offering protection against physical damage and pathogens.
In this process, keratinocytes, the predominant cell type in the epidermis, undergo a series of stages in which they gradually become keratinized, eventually forming the skin, scales, feathers, and hair that serve as protective barriers. This transformation occurs through a process of cell differentiation and accumulation of keratin, which ultimately provides durability and resistance to environmental stresses.
2. The Structure and Function of Keratin
Keratin is a structural protein made up of long, thin strands of polypeptides that are twisted into coils or sheets. These polypeptides form a helix, which is a key feature of the protein’s structure. The two major types of keratin are soft keratin (found in hair and skin) and hard keratin (found in nails, claws, and horns). These types differ in their arrangement of amino acids, the degree of cross-linking, and their structural properties.
The primary function of keratin is to provide mechanical strength and protection to cells and tissues. By forming tough, insoluble fibers, keratin shields the underlying cells from mechanical stress, abrasion, and dehydration. It is a critical component of epidermal cells, hair follicles, and other epithelial structures in vertebrates, helping to protect them from harmful environmental factors such as UV radiation and pathogens.
3. The Stages of Keratinization
Keratinization involves a series of well-coordinated stages, during which the keratinocytes in the epidermis undergo significant changes. These stages are typically divided into four phases: basal, spinous, granular, and corneal. Each phase has specific characteristics that contribute to the final keratinized structure of the skin or other epidermal tissues.
-
Basal Stage: In the basal layer of the epidermis, keratinocytes divide and differentiate. These stem cells are actively involved in cell division to replace older cells that migrate toward the surface. This stage is crucial for the generation of new keratinocytes.
-
Spinous Stage: As cells move upward, they begin to synthesize keratin and other proteins such as filaggrin, which play a role in cell-cell adhesion. The keratinocytes become more flattened and start forming connections with each other through desmosomes, which are intercellular junctions.
-
Granular Stage: In the granular layer, keratinocytes accumulate more keratin and other specialized proteins like keratohyalin, which helps in the aggregation of keratin filaments. These cells begin to lose their nuclei and other organelles, becoming more keratin-rich.
-
Corneal Stage: In the outermost layer, the keratinocytes are fully keratinized, dead cells that form a tough, impermeable layer known as the stratum corneum. These cells are essentially flattened sacs filled with keratin fibers. The cells are no longer living and serve as the primary protective barrier.
4. The Role of Keratinization in Terrestrial Adaptation
Keratinization is essential for the survival of terrestrial vertebrates in a land-based environment. Aquatic vertebrates do not need this extensive keratinized covering, as their outer skin remains moist due to the surrounding water. However, as vertebrates transitioned to land, they faced challenges such as:
-
Desiccation (drying out): The skin of terrestrial vertebrates must prevent excessive water loss, which is where keratinization comes in. The keratinized layers, particularly the stratum corneum, act as an effective water-resistant barrier, reducing evaporation and preventing desiccation.
-
Protection from physical damage: The hard, keratinized structures such as nails, claws, and scales provide mechanical protection. They protect the underlying tissues from abrasions, physical injuries, and punctures.
-
Protection from pathogens: The keratinized skin layer serves as a physical barrier against invading microorganisms. Additionally, keratin itself has antimicrobial properties, further helping in defending against pathogens.
-
Temperature regulation: In some vertebrates, keratinized structures like feathers or hair serve not only as protective barriers but also play a role in temperature regulation. Feathers, for example, trap air close to the body, providing insulation and helping to regulate body temperature.
5. Keratinization in Different Terrestrial Vertebrates
The process of keratinization is highly varied among different terrestrial vertebrates, depending on their ecological niche, evolutionary adaptations, and physiological needs. For example:
-
Mammals: In mammals, keratinization is seen in the formation of skin, hair, and nails. The skin of mammals undergoes extensive keratinization, forming a tough, protective layer. Hair and nails are also composed of keratin, providing both structural support and protection.
-
Reptiles: In reptiles, keratin is primarily found in the formation of scales, which provide protection from dehydration and mechanical damage. These keratinized scales help reptiles conserve water and regulate their body temperature.
-
Birds: Birds have feathers and beaks made of keratin. Feathers are essential for flight, temperature regulation, and mating displays, while beaks, composed of hard keratin, are used for feeding and other activities.
While keratinization plays a critical role in protecting terrestrial vertebrates, abnormalities in the process can lead to several skin disorders. Some common conditions include:
- Ichthyosis: This is a genetic disorder where keratinization is impaired, leading to the buildup of thick, scaly skin.
- Epidermolysis bullosa: This condition involves defective keratin production, making the skin highly fragile and prone to blisters.
Conclusion
Keratinization is a crucial physiological process that provides protective barriers for terrestrial vertebrates, helping them survive in challenging land-based environments. The formation of keratin-rich structures such as skin, hair, feathers, and nails not only prevents desiccation and physical damage but also plays important roles in temperature regulation and pathogen defense. Despite the diverse ways in which keratinization occurs across species, the central theme remains the same: it is an adaptation to life on land that has allowed terrestrial vertebrates to thrive in various ecosystems.
1. b) Give five features that you can use to distinguish between the skulls of frog and rabbit.
Answer:
1. Introduction
The skulls of different species, such as frogs and rabbits, exhibit a variety of distinguishing features that reflect their distinct evolutionary adaptations, feeding habits, and ecological niches. While frogs and rabbits are both vertebrates, their skull structures vary greatly due to their different lifestyles. Frogs are amphibians, typically adapted for jumping and a carnivorous diet, while rabbits are mammals with adaptations for herbivory and continuous movement. By analyzing these skulls, we can identify various features that help differentiate between them.
2. Shape and Size of the Skull
The overall shape and size of the skull are one of the most striking differences between frogs and rabbits. The frog skull is generally smaller and flatter, suited for its amphibious lifestyle. It has a relatively broad, short shape with fewer bones than the rabbit skull. The frog’s skull is adapted to its jumping and swimming capabilities, providing a compact structure that supports the frog’s large mouth, which is essential for catching prey.
In contrast, the rabbit skull is larger, more elongated, and more robust. The rabbit’s skull is adapted for chewing and digesting plant material, which requires a more complex and larger jaw structure. The shape of the rabbit’s skull is more specialized for its herbivorous diet, with more developed teeth and a stronger jaw to grind plant matter.
3. Structure of the Jaw
One of the most notable differences between the skulls of frogs and rabbits is the structure of the jaw. Frogs have a simplified jaw structure, with fewer teeth and a wide mouth that allows for capturing prey in one swift motion. The lower jaw of the frog is usually not fused in the center and can move independently, allowing the frog to open its mouth quickly and catch insects or small prey. Additionally, frogs do not have cheek teeth but may have vomerine teeth on the roof of their mouth for holding prey.
On the other hand, rabbits possess a complex jaw structure with incisors and molars that are specialized for grinding plant material. Their incisors are sharp for cutting plants, while their molars are designed for chewing and breaking down fibrous plant matter. The rabbit’s jaw is also stronger and more robust than that of a frog, reflecting its need to chew and grind food thoroughly. The lower jaw of the rabbit is fused in the midline and works in a rotary motion for grinding food.
4. Presence of Teeth
The number and type of teeth present in the skull of frogs and rabbits provide another distinguishing feature. Frogs typically have few teeth, mainly vomerine teeth that help hold onto prey once captured. These teeth are located on the roof of the mouth and are not used for chewing. Most frogs lack cheek teeth, and their teeth are not specialized for grinding or tearing food, as their diet mostly consists of insects and small invertebrates that can be swallowed whole.
In contrast, rabbits have a complete set of teeth suited for herbivory. They have four incisors in the upper and lower jaws and cheek teeth (molars and premolars) that are used to grind and chew plant material. The rabbit’s incisors continuously grow throughout its life, and this helps in cutting plant material. The cheek teeth are flat and designed for grinding. This large set of specialized teeth indicates the herbivorous diet of rabbits, in contrast to the more simplified teeth of frogs.
5. Foramen Magnum and Neck Vertebrae
The position of the foramen magnum, which is the hole in the skull through which the spinal cord passes, is another feature that distinguishes the skulls of frogs and rabbits. In frogs, the foramen magnum is located at the posterior part of the skull, facing downwards, due to the frog’s horizontal posture. This placement reflects the frog’s adapted body structure for swimming and jumping.
In rabbits, the foramen magnum is positioned more centrally and vertically, which aligns with their upright posture. The vertical position of the foramen magnum is indicative of the rabbit’s bipedal locomotion and herbivorous stance, with the head held upright for grazing. Additionally, rabbits have a more developed neck region with multiple cervical vertebrae, which provide the mobility necessary for their lifestyle.
6. Temporal Region and Jaw Musculature
The temporal region of the skull, which houses the muscles responsible for jaw movement, also differs significantly between frogs and rabbits. Frogs have a reduced temporal region and relatively weak jaw muscles because they do not need a strong biting force. Their jaw is designed more for holding prey than for chewing.
Rabbits, in contrast, have a larger temporal region with well-developed jaw muscles. These muscles are responsible for the grinding motion of their teeth, essential for processing plant material. The increased size and development of the temporal region in rabbits support their herbivorous diet, requiring strong, efficient jaw movement to break down fibrous plant matter.
Conclusion
In summary, the skulls of frogs and rabbits exhibit several distinguishing features, including differences in the shape and size of the skull, jaw structure, teeth type and arrangement, the position of the foramen magnum, and the development of the temporal region and jaw musculature. These differences reflect the distinct ecological adaptations of each species, with frogs being more specialized for insectivory and jumping, while rabbits are adapted for herbivory and grinding plant material. Understanding these features provides valuable insights into the evolutionary differences between amphibians and mammals, highlighting the diversity in vertebrate morphology that supports their varied lifestyles.
Question:-2
2. a) Explain the major differences between reptilian and avian digestive systems.
Answer:
1. Introduction to Digestive Systems of Reptiles and Birds
The digestive systems of reptiles and birds are adapted to their specific dietary requirements, environments, and evolutionary history. While both groups belong to the class Tetrapoda and share certain physiological features, their digestive systems differ significantly due to their different ecological niches, feeding habits, and metabolic needs. Understanding these differences helps to highlight the evolutionary adaptations that these animals have developed for their survival.
2. General Structure of Reptilian Digestive System
The reptilian digestive system is relatively simpler than that of birds, with some variation depending on the species. However, it typically consists of the following main components:
-
Mouth and Teeth: Reptiles generally have teeth that are adapted to their specific diet. For example, carnivorous reptiles like snakes have sharp, curved teeth to hold and tear prey, while herbivores like tortoises have flat teeth for grinding plants. The mouth is used primarily for ingestion and initial processing of food.
-
Esophagus: The food passes through the esophagus, which is a simple muscular tube. In some reptiles, the esophagus can be very elongated, as seen in snakes, which swallow large prey whole.
-
Stomach: Reptiles typically have a simple stomach where the majority of chemical digestion occurs. Some reptiles have a gizzard (like birds), but it is less developed and less important for mechanical digestion. The stomach of reptiles secretes gastric juices containing hydrochloric acid and digestive enzymes for breaking down proteins.
-
Intestines: The small intestine in reptiles is where most of the nutrient absorption occurs. It is shorter compared to birds, reflecting the relatively low metabolic rate of reptiles. The large intestine absorbs water and salts, and the cloaca serves as the common exit for digestive, urinary, and reproductive products.
-
Cloaca: In reptiles, the cloaca is the final chamber that serves multiple functions, including the elimination of waste and the expulsion of eggs or sperm.
3. General Structure of Avian Digestive System
The avian digestive system is much more complex and highly specialized to meet the needs of flight and high-energy metabolism. The main components include:
-
Beak: Birds do not have teeth. Instead, they use their beak to break down food mechanically. The shape of the beak is adapted to their feeding habits, whether they are seed eaters, insectivores, or carnivores.
-
Esophagus and Crop: The esophagus in birds is similar to reptiles, but many birds have a specialized pouch called the crop. The crop stores food temporarily, allowing birds to regurgitate food when necessary or digest it in a controlled manner.
-
Stomach: The avian stomach is divided into two parts: the proventriculus and the gizzard. The proventriculus is the glandular stomach that secretes digestive enzymes and hydrochloric acid to begin breaking down food. The gizzard, a muscular organ, serves as a mechanical digestive tool, grinding up food, especially in species that consume hard foods like seeds.
-
Small Intestine: Like reptiles, the small intestine in birds is responsible for most of the nutrient absorption. It is longer than that of reptiles and has more surface area due to the presence of villi and microvilli. Birds have a more efficient absorption system, which is necessary to support their high metabolic rate.
-
Ceca: Birds possess two ceca, which are blind pouches located at the junction of the small and large intestines. These structures are involved in the fermentation and breakdown of cellulose, which is particularly important for herbivorous birds. The ceca help to digest plant material that is otherwise difficult to break down.
-
Large Intestine and Cloaca: The large intestine in birds is relatively short and primarily absorbs water and salts. The cloaca in birds functions similarly to reptiles, serving as the exit for waste, eggs, or sperm.
4. Major Differences Between Reptilian and Avian Digestive Systems
Several significant differences exist between the digestive systems of reptiles and birds, primarily due to their dietary needs, metabolic demands, and physical structures.
-
Beak vs. Teeth: One of the most obvious differences is that birds lack teeth, relying on their beak for mechanical digestion, while reptiles have teeth suited to their specific diets. For example, carnivorous reptiles have sharp teeth for tearing prey, while herbivores have flat teeth for grinding plant matter.
-
Crop and Gizzard: Birds possess a crop, which acts as a storage organ for food, and a gizzard, which is a specialized muscular organ used for grinding food, especially in birds that consume hard materials like seeds. In contrast, reptiles generally do not have a crop or gizzard, and their digestive processes are simpler.
-
Stomach Structure: Birds have a two-chambered stomach (proventriculus and gizzard), with the proventriculus secreting digestive enzymes and acid, and the gizzard physically grinding food. Reptiles have a simpler, single-chambered stomach that performs both enzymatic digestion and some mechanical breakdown.
-
Ceca: Birds have two ceca that play a role in the fermentation of plant material, especially in herbivorous species. Reptiles, on the other hand, usually do not have a functional cecum or have a less developed one. This difference is related to the fact that birds often consume fibrous plant material and need additional digestive processing for it.
-
Digestive Efficiency: The avian digestive system is more efficient in terms of nutrient absorption, given the high metabolic rate required for flight. In contrast, the reptilian digestive system is slower and less complex due to the generally lower metabolic rate of reptiles.
5. Conclusion
In summary, the digestive systems of reptiles and birds exhibit clear differences due to their distinct dietary requirements and metabolic demands. Birds have a more specialized and efficient digestive system, including the presence of a crop, gizzard, and ceca, which allow them to digest food more efficiently and support their high metabolic rate. In contrast, reptiles have a simpler digestive system with fewer specialized organs, such as lacking a crop and gizzard, and typically possess slower digestion processes. These differences reflect the evolutionary adaptations of both groups to their environments and lifestyles, with birds evolving for high-energy activities like flight, while reptiles are more adapted to a slower, energy-efficient lifestyle.
2. b) Describe the structure of the respiratory system of cartilaginous fishes and state how does it differ from that of bony fishes.
Answer:
1. Introduction to the Respiratory System of Fishes
The respiratory system of fishes is essential for their survival, as it enables the extraction of oxygen from water, which is crucial for their metabolic needs. There are two main types of fish: cartilaginous fishes (Chondrichthyes) such as sharks, rays, and skates, and bony fishes (Osteichthyes) such as goldfish, salmon, and trout. While both types of fishes perform gas exchange in water, their respiratory systems differ in terms of anatomical structures, mechanisms, and efficiency. This variation is largely due to their evolutionary adaptations to different environments and lifestyles.
2. Structure of the Respiratory System in Cartilaginous Fishes
The respiratory system of cartilaginous fishes is adapted to their active, predatory lifestyles, and these fishes rely on efficient oxygen extraction. The key components of their respiratory system include the gills, spiracles, and pharyngeal slits.
-
Gills: Cartilaginous fishes typically have five to seven pairs of gill slits located on the side of their head. These gills are responsible for the exchange of oxygen and carbon dioxide. Unlike bony fishes, cartilaginous fishes do not have gill covers (operculum); the gill slits are exposed, which makes them more vulnerable to physical damage but provides greater access to water for respiration.
-
Spiracles: A distinctive feature of many cartilaginous fishes is the spiracle, which is a small opening located behind the eyes. The spiracle allows water to enter the gills even when the fish’s mouth is closed. This adaptation is particularly useful when the fish is feeding or resting on the seafloor, as it enables continuous water flow over the gills for respiration.
-
Gill Rakers: The gills of cartilaginous fishes are often equipped with gill rakers, which filter out particulate matter from the water before it passes over the gill filaments. This ensures that debris and larger particles do not clog the delicate gill structures.
-
Pharyngeal Slits: Water enters the fish’s mouth and flows over the gills, and the exchange of gases (oxygen and carbon dioxide) occurs through the gill filaments. As water exits the gill slits, it helps maintain the continuous flow of water necessary for gas exchange.
-
Water Flow: Cartilaginous fishes do not rely on a suction pump mechanism for water intake, as many bony fishes do. Instead, they utilize ram ventilation, a process where water is forced over the gills by the fish’s forward movement through the water. As a result, many cartilaginous fishes must keep swimming to ensure a constant flow of water through their gills, although some species (like rays and skates) can also use spiracles to actively pump water when stationary.
3. Structure of the Respiratory System in Bony Fishes
Bony fishes, as the name suggests, have a bony skeleton, and their respiratory system is highly adapted to their environment and lifestyle. The major components of their respiratory system include gills, gill arches, operculum, and gill filaments.
-
Gills and Gill Arches: Like cartilaginous fishes, bony fishes also have gills for respiration, typically organized into four pairs of gill arches. The gill arches support the gill filaments, which are lined with gill lamellae that facilitate the gas exchange process.
-
Operculum: One of the key differences between bony fishes and cartilaginous fishes is the presence of the operculum, a bony flap that covers the gill slits. The operculum helps to regulate the flow of water over the gills by creating a pressure differential, allowing water to pass over the gill filaments even when the fish is not swimming. This is especially beneficial for fish that are less active or stationary in their environment.
-
Mouth and Buccal Cavity: Water enters the mouth and is forced across the gills by the fish’s buccal pump mechanism. When the fish opens its mouth, the pressure in the buccal cavity drops, and water flows in. The operculum is then lifted to create a pressure difference, which forces the water out over the gills, facilitating gas exchange.
-
Gill Filaments and Lamellae: Bony fishes have highly efficient gill structures that allow them to extract oxygen from water even when it has low oxygen content. The gill filaments are lined with gill lamellae, which increase the surface area for gas exchange. This structure is highly efficient in extracting oxygen and expelling carbon dioxide.
-
Water Flow: Unlike cartilaginous fishes, bony fishes rely on a buccal-pump mechanism for water intake. This allows them to actively control water flow over their gills without needing to swim continuously, although many bony fishes also swim to enhance this process.
4. Key Differences Between the Respiratory Systems of Cartilaginous and Bony Fishes
Several structural and functional differences exist between the respiratory systems of cartilaginous and bony fishes:
-
Gill Slits vs. Operculum: Cartilaginous fishes have exposed gill slits that are not covered by an operculum, while bony fishes possess an operculum that covers the gill slits, providing a more protected and regulated water flow.
-
Spiracles: Cartilaginous fishes often possess spiracles, which allow water to enter the gills even when the fish’s mouth is closed. This is particularly useful for species like rays and skates, which feed on the seafloor. Bony fishes do not have spiracles, and water is typically taken in through the mouth.
-
Water Flow Mechanism: Cartilaginous fishes rely on ram ventilation, where water is continuously pushed over the gills through the fish’s forward motion. In contrast, bony fishes use a buccal-pump mechanism, actively drawing water in through their mouths and forcing it out over the gills using the operculum.
-
Gill Filaments and Efficiency: Bony fishes tend to have more efficient gill filaments and lamellae, which are more finely adapted to extract oxygen from water. Cartilaginous fishes, although having similar gill structures, often require continuous movement to maintain an efficient oxygen supply due to the lack of a buccal pump.
-
Number of Gill Slits: Cartilaginous fishes typically have five to seven pairs of gill slits, whereas bony fishes usually have four pairs of gill slits.
5. Conclusion
The respiratory systems of cartilaginous fishes and bony fishes show significant differences in structure and function, reflecting their adaptations to different lifestyles and environments. Cartilaginous fishes rely on ram ventilation and have exposed gill slits and spiracles, while bony fishes use an efficient buccal-pump mechanism with a protective operculum and a more sophisticated gill structure. Despite these differences, both systems are highly effective at extracting oxygen from water, ensuring the survival of these diverse groups of fish in their respective habitats.