General Biology II - Complete Text PDF

GENERAL BIOLOGY II PART 1(AEB) 2 CREDITS 1  COURSE CONTENT/OUTLINE S/N Course Contents Allocation Coordinator 1 The characteristics, methods of identification Dr. Suleman O. and classification of...

GENERAL BIOLOGY II PART 1(AEB) 2 CREDITS 1  COURSE CONTENT/OUTLINE S/N Course Contents Allocation Coordinator 1 The characteristics, methods of identification Dr. Suleman O. and classification of viruses Ikhuoriah 2 The unique characteristics of animal kingdoms Dr. Suleman O. Dr. Suleman O. (the study of similarities and differences in the Ikhuoriah Ikhuoriah external features of plants and animals) 3 Ecological adaptations in the animal kingdoms Mr. Olowo Cyril 4 Nutrition, respiration, circulatory systems, Mr. Alari excretion and reproduction in animals (Briefs on physiology) 5 Growth and development in animals (Briefs Mr. Olowo Cyril on physiology) 2  CHAPTER 1 CHARACTERISTICS, METHODS OF IDENTIFICATION, AND CLASSIFICATION OF VIRUSES Introduction Viruses are microscopic infectious agents that play significant roles in the fields of medicine, biology, and ecology. Viruses are noncellular parasitic entities that cannot be classified within any kingdom. They are unique among pathogens because they exist at the boundary between living and non-living things. They can infect organisms as diverse as bacteria, plants, and animals. Unlike bacteria, fungi, or protozoa, viruses cannot reproduce on their own. Instead, they must invade a host cell and hijack its machinery to create more viruses. Living things grow, metabolize, and reproduce. In contrast, viruses are not cellular, do not have a metabolism or grow, and cannot divide by cell division. Viruses can copy, or replicate themselves; however, they are entirely dependent on resources derived from their host cells to produce progeny viruses—which are assembled in their mature form. This chapter will explore the characteristics of viruses, how they are identified, and how scientists classify them. Section 1: Characteristics of Viruses 1.1. Size and Structure Viruses are exceptionally small, ranging from 20 to 300 nanometers in size, far smaller than most bacteria and other cellular organisms. They are often so tiny that they can only be visualized using an electron microscope. Structurally, a virus consists of two or three main components: 1. Genetic Material (Genome): The viral genome can be composed of either DNA or RNA, which can be single-stranded (ss) or double-stranded (ds). This genome carries the 3  instructions necessary for the virus to replicate and produce viral proteins inside the host cell. 2. Capsid: The genetic material is encased within a protein coat called a capsid, which protects the viral genome and helps the virus attach to host cells. The capsid is composed of repeating protein subunits known as capsomeres, and its shape can be helical, icosahedral, or complex. 3. Envelope (optional): Some viruses have an outer lipid envelope derived from the host cell membrane. This envelope may contain viral proteins (glycoproteins) that help the virus attach to and enter host cells. Non-enveloped viruses are known as "naked" viruses. 1.2. Obligate Intracellular Parasites Viruses are obligate intracellular parasites, meaning they cannot replicate outside a host cell. Once inside the host cell, they rely on the host's cellular machinery to synthesize viral components and produce new virions (virus particles). This dependency on a host cell sets them apart from other microorganisms, such as bacteria, which can reproduce independently. 1.3. Lack of Cellular Structure Viruses do not have a cellular structure, which means they lack organelles such as mitochondria, ribosomes, and a nucleus. They are essentially nucleic acid wrapped in protein, with some viruses possessing an additional lipid envelope. This minimalistic design makes them distinct from even the simplest prokaryotic cells. 1.4. High Mutation Rates Many viruses, particularly RNA viruses, exhibit high mutation rates due to the lack of proofreading mechanisms during replication. This rapid evolution allows them to adapt to new environments and evade host immune responses, making viral infections challenging to treat and control. 4 Section 2: Methods of Virus Identification Viruses are too small to be seen with a light microscope, and their unique characteristics make them difficult to study using conventional microbiological techniques. As a result, specialized methods have been developed for virus identification. These include: 2.1. Electron Microscopy Since viruses are smaller than most cellular organisms, electron microscopy (EM) is often used to visualize them. This technique uses a beam of electrons instead of light to create high-resolution images of viral particles. While EM is valuable for observing the morphology of viruses, it is time- consuming and requires expensive equipment. 2.2. Cell Culture A common method for identifying and studying viruses is through cell culture. In this method, the virus is introduced into a monolayer of living cells. If the virus successfully infects the cells, it will cause visible changes known as cytopathic effects (CPEs). These changes can include cell lysis, the formation of syncytia (fused cells), or changes in cell shape and size. Cell culture remains a cornerstone technique for virus isolation and identification. 2.3. Serology Serological methods involve detecting the presence of viral antigens (proteins) or antibodies produced by the host in response to viral infection. Common serological tests include the enzyme- linked immunosorbent assay (ELISA) and immunofluorescence assays. These tests can help identify a specific virus based on its unique antigenic properties. 2.4. Polymerase Chain Reaction (PCR) 5 PCR is a molecular technique that amplifies specific segments of viral DNA or RNA, making it easier to detect even minute quantities of virus in a sample. Reverse transcriptase PCR (RT-PCR) is particularly useful for RNA viruses. This method is highly sensitive, specific, and widely used for the rapid detection of viral infections, including those caused by HIV, influenza, and coronaviruses. 2.5. Hemagglutination Some viruses, such as influenza and measles, cause the clumping (agglutination) of red blood cells when mixed with them. This characteristic is exploited in hemagglutination assays, which can indicate the presence of a virus based on its ability to bind to and agglutinate red blood cells. Section 3: Classification of Viruses Viruses are classified based on a variety of factors, including their genome type, replication strategy, morphology, and host range. The International Committee on Taxonomy of Viruses (ICTV) is the primary body responsible for the classification of viruses. The ICTV organizes viruses into a hierarchical classification system that includes orders, families, genera, and species. 3.1. Baltimore Classification The Baltimore classification system, named after Nobel laureate David Baltimore, classifies viruses based on their genome type and replication strategy. There are seven classes in this system: 1. Class I: Double-stranded DNA viruses (e.g., Herpesviruses) 2. Class II: Single-stranded DNA viruses (e.g., Parvoviruses) 3. Class III: Double-stranded RNA viruses (e.g., Reoviruses) 4. Class IV: Positive-sense single-stranded RNA viruses (e.g., Coronaviruses) 5. Class V: Negative-sense single-stranded RNA viruses (e.g., Influenza viruses) 6  6. Class VI: Retroviruses (e.g., HIV), which have single-stranded RNA genomes and use reverse transcriptase to integrate into the host genome. 7. Class VII: Double-stranded DNA viruses that replicate through an RNA intermediate (e.g., Hepatitis B virus). 3.2. ICTV Classification The ICTV classification scheme categorizes viruses based on: 1. Nucleic Acid Type: DNA or RNA, and whether it is single-stranded or double-stranded. 2. Capsid Symmetry: Icosahedral, helical, or complex. 3. Presence of an Envelope: Enveloped or non-enveloped. 4. Size of Virion: The physical dimensions of the virus particle. 5. Host Range: The types of organisms the virus can infect (e.g., animals, plants, fungi, bacteria). An example of this classification: Order: Caudovirales Family: Herpesviridae Genus: Simplexvirus Species: Human herpesvirus 1 (HSV-1) 3.3. Host-Based Classification Viruses can also be classified according to their preferred host: 1. Animal Viruses: Infect animals (e.g., Rabies virus). 2. Plant Viruses: Infect plants (e.g., Tobacco mosaic virus). 3. Bacteriophages: Infect bacteria (e.g., T4 phage). 4. Fungal Viruses: Infect fungi (e.g., Mycoviruses). 7 Section 4: Emerging Concepts in Virology As new viruses are discovered, and viral behaviors are better understood, the field of virology continues to evolve. Advances in molecular biology, genomics, and bioinformatics have introduced new ways to study viruses, expanding our knowledge about viral evolution, zoonotic spillover (how viruses jump from animals to humans), and their role in ecosystems. The COVID- 19 pandemic, caused by the SARS-CoV-2 virus, underscored the global importance of studying and classifying viruses to develop effective treatments and vaccines. Conclusion Viruses are fascinating and complex entities that occupy a unique position in the biological world. Their characteristics, such as small size, simple structure, and dependence on host cells, make them distinct from other life forms. Identification methods, from cell culture to molecular techniques like PCR, are essential for studying and diagnosing viral infections. Virus classification, whether through the ICTV system or the Baltimore scheme, helps organize our understanding of viral diversity and evolution. Understanding viruses is not only important for the control of infectious diseases but also for appreciating their role in the biosphere. Key Takeaways: Viruses are small, acellular, and obligate intracellular parasites. They can be identified through techniques like electron microscopy, PCR, and serological tests. 8  Virus classification is based on genome type, replication strategy, and other factors, with ICTV and Baltimore systems being the most widely used. This foundational knowledge in virology will be critical for future studies in microbiology, immunology, and medical sciences. References Viral Evolution, Morphology, and Classification: In Introductory Biology: Evolutionary and Ecological Perspectives Copyright © by Various Authors 9  CHAPTER 2 THE UNIQUE CHARACTERISTICS OF THE ANIMAL KINGDOM (SIMILARITIES AND DIFFERENCES IN THE EXTERNAL FEATURES OF PLANTS AND ANIMALS) Introduction The biological world is broadly divided into two primary kingdoms: plants and animals. Although both belong to the larger domain of life and share some fundamental biological processes, their external features and characteristics set them apart in remarkable ways. These differences in external morphology reflect their distinct evolutionary pathways, environmental adaptations, and functional roles in ecosystems. This chapter will examine the unique characteristics of the animal kingdom, comparing and contrasting the external features of plants and animals to better understand their distinct adaptations and functions in nature. Section 1: Fundamental Differences Between Plants and Animals Before delving into the specific external characteristics of the animal kingdom, it's important to highlight the foundational differences between plants and animals, as these shape the way their external features have evolved. 1.1. Autotrophy vs. Heterotrophy Plants are autotrophs, meaning they produce their own food through photosynthesis. Their primary external features, like broad leaves and root systems, are adapted to harness light and water for this process. Animals, on the other hand, are heterotrophs, meaning they must consume other organisms for energy. Their external features are adapted for mobility, predation, or foraging. 10 1.2. Cell Structure and External Composition Plants possess cell walls made of cellulose, giving them a rigid structure. This structural feature leads to less mobility but supports vertical growth in response to sunlight. Animals lack cell walls and instead have more flexible membranes, allowing for greater mobility, flexibility, and a variety of external forms. 1.3. Movement Plants are generally immobile, rooted to a specific location, and their external features reflect adaptations to their immediate environment. Animals are capable of movement, often equipped with specialized external features like limbs, fins, or wings that allow them to seek food, mates, or escape predators. Table 1. Difference between plant and animal Basis for comparison Plants Animal Meaning Green-coloured living things Living organisms that feed capable of preparing their own on organic material and food through photosynthesis. contain an organ system Movement Cannot move as they are rooted Can move freely from one in the ground. Exceptions- place to the other. Volvox and Chlamydomonas. Exception- Sponges and Corals. Digestive System Absent Present Food Storage Store food in the form of starch Store food in the form of glycogen Structure of Cell Contains cell wall, chloroplast, Do not have cell walls, have plasmodesmata, plastids and other organelles like tight other organelles junction and cilia. 11  Respiration Take in Carbon Dioxide and Take in oxygen and release release Oxygen carbon dioxide Respiration through Occurs through stomata Occurs through lungs, gills, skin and more. Growth The meristematic system in the Organs and organ system tip of roots and stems supports support the growth growth Reproduction Method Asexual reproduction by Animals reproduce budding, vegetative methods, sexually whereas some wind, spores, insects. lower animals like algae have asexual reproduction Response Show response through touch The proper nervous system and light allows responding quickly Sensitive Less sensitive Highly sensitive Section 2: External Features of Animals Animals are incredibly diverse in their external morphology. These differences are driven by their habitat, mode of locomotion, feeding strategies, and reproductive methods. Below are the major types of external characteristics that define members of the animal kingdom. 2.1. Body Symmetry Body symmetry is a fundamental characteristic that distinguishes different groups of animals. There are three primary types of symmetry found in animals: Radial Symmetry: Animals with radial symmetry, like jellyfish or starfish, have body parts arranged around a central axis. This symmetry is common in animals that are sessile (fixed in one place) or move slowly, allowing them to interact with their environment from all directions. 12  Bilateral Symmetry: Most animals, including humans, exhibit bilateral symmetry, where the body has a distinct left and right side that are mirror images. This symmetry is associated with directional movement and the development of a head (cephalization) where sensory organs and the brain are located. Asymmetry: Some animals, like sponges, have no defined symmetry, and their external form is irregular. These animals are often sessile and rely on other mechanisms, like water flow, for feeding and respiration. 2.2. Body Covering The external covering of animals is critical for protection, temperature regulation, and sometimes camouflage. The type of body covering varies widely across the animal kingdom: Skin: Mammals, icluding humans, have skin that may be covered with fur or hair to regulate body temperature and provide protection. Skin in amphibians is moist and permeable to allow for gas exchange, while reptiles have scales that protect them from dehydration. Feathers: Birds are characterized by feathers, which are unique to their class. Feathers serve multiple functions, including flight, insulation, and courtship displays. The lightweight structure of feathers is a key adaptation for avian flight. Scales and Exoskeletons: Fish have scales that provide a protective barrier and reduce water resistance. Insects, crustaceans, and many other invertebrates possess an exoskeleton, a hard, external covering made of chitin that provides support and protection. Exoskeletons also play a role in preventing water loss in terrestrial arthropods. 13 2.3. Limbs and Locomotion Animal locomotion is facilitated by a wide range of limb adaptations, each suited to different environments and modes of movement. Legs: Most terrestrial animals, including mammals, reptiles, and insects, use legs for movement. Bipedalism, as seen in humans, involves walking on two legs, while most animals, such as dogs and horses, are quadrupeds, walking on all fours. Wings: Birds, bats, and many insects have developed wings for flight. Wings are specialized limbs that allow animals to move through the air. In birds, wings are modified forelimbs with feathers, while in bats, wings consist of a membrane stretched between elongated finger bones. Fins and Flippers: Aquatic animals like fish and marine mammals use fins or flippers for swimming. Fins help fish maintain balance and navigate through water, while marine mammals like dolphins have modified limbs called flippers for efficient swimming. 2.4. Mouthparts and Feeding Structures The external features of animals are often closely related to their feeding strategies. The diversity of mouthparts and feeding structures reflects the variety of diets in the animal kingdom. Herbivores like cows and horses have flat, grinding teeth designed for chewing plant material. In contrast, carnivores like lions and wolves possess sharp teeth for tearing flesh. Insects exhibit a remarkable variety of mouthparts, including sucking (as in butterflies), chewing (as in beetles), and piercing-sucking (as in mosquitoes). These specialized mouthparts allow them to exploit different food sources. 14  Beaks: Birds have beaks, which vary in shape and size depending on their diet. For example, eagles have sharp, hooked beaks for tearing meat, while hummingbirds have long, slender beaks for feeding on nectar. 2.5. Sensory Organs The external sensory organs of animals are highly specialized to their environment and survival strategies. Eyes: Vision is a primary sense for many animals, and the size, placement, and type of eyes can vary. For example, predators like hawks have forward-facing eyes that provide depth perception for hunting, while prey animals like rabbits have eyes on the sides of their heads to maximize their field of view. Ears: In mammals, ears are prominent external structures that detect sound. Bats, for example, have large, sensitive ears for echolocation, while owls have asymmetrically placed ears to detect prey in the dark. Antennae: Insects and other arthropods possess antennae, which are external sensory structures used for detecting environmental cues such as chemical signals, vibrations, or air currents. Section 3: Similarities Between Plants and Animals Despite their differences, plants and animals share several external features that highlight their common ancestry and the evolutionary pressures that shaped their adaptations to the environment. 3.1. Protective Structures Both plants and animals have developed protective external features that help them survive in their environments. 15  Thorns and Spines: Some plants, such as cacti, have evolved thorns and spines to deter herbivores. Similarly, many animals, like hedgehogs or porcupines, possess quills or spines that provide physical defense against predators. Camouflage: Both plants and animals use camouflage to blend into their surroundings. For example, the color and texture of tree bark help certain plants merge with their environment, while many animals, like chameleons and certain insects, can change their external appearance to avoid predators. 3.2. Reproductive Structures Reproduction is a fundamental process in both plants and animals, and both have external structures dedicated to this purpose. Flowers: In plants, flowers are external reproductive structures that attract pollinators and facilitate the transfer of pollen. Similarly, many animals have external reproductive organs that play a role in mating and the transfer of genetic material. Fruits and Seeds: Plants produce fruits and seeds as reproductive structures, often with mechanisms to disperse them via wind, water, or animals. Animals, on the other hand, may lay eggs externally (as in birds and reptiles) or carry their offspring internally and give birth (as in mammals). Section 4: Differences in External Features of Plants and Animals While there are some similarities between plants and animals, their external features often reflect their fundamentally different ways of life. 4.1. Locomotion 16  Plants: Plants are sessile organisms, meaning they do not move from place to place. Their external features, such as roots, stems, and leaves, are adapted to remain anchored in one location while maximizing access to resources like sunlight, water, and nutrients. Animals: Animals are mobile and possess external features like legs, wings, or fins that enable them to move, escape predators, find food, and reproduce. The need for movement has resulted in the development of highly specialized external structures. 4.2. Growth Patterns Plants: Plant growth is typically indeterminate, meaning that they continue to grow throughout their lives. Their external features, such as branches and leaves, grow in response to environmental stimuli like light and gravity. Animals: Animal growth is generally determinate, meaning they stop growing after reaching a certain size. The external features of animals, such as bones and limbs, are usually fixed in size once they reach maturity. Conclusion The study of the similarities and differences in the external features of plants and animals reveals the diversity and complexity of life. While both kingdoms share some fundamental characteristics that help them survive and reproduce, their external forms reflect their unique evolutionary paths. Animals, with their specialized sensory organs, diverse locomotion structures, and protective coverings, are highly adapted for active, mobile lifestyles. In contrast, plants have evolved external features like leaves, stems, and roots that allow them to thrive in a fixed location, making efficient use of sunlight and water. Understanding these external features provides insight into the adaptive strategies that enable plants and animals to occupy almost every ecological niche on Earth. 17 Key Takeaways: Animals are characterized by bilateral or radial symmetry, body coverings such as skin, fur, or scales, and limbs adapted for locomotion. Plants are sessile, with external features like leaves, roots, and stems designed for photosynthesis and nutrient absorption. Both plants and animals share protective structures like thorns or spines and have specialized reproductive organs. Differences in locomotion, growth patterns, and energy acquisition reflect the distinct life strategies of plants and animals. References Features of the Animal Kingdom: In Introductory Biology: Evolutionary and Ecological Perspectives Copyright © by Various Authors 18  CHAPTER 3 EOLOGICAL ADAPTATIONS IN THE ANIMAL KINGDOMS An ecological adaptation is any morphological (structural), physiological, or behavioural trait of an organism that allows it to survive and reproduce in a habitat or ecosystem. In the animal kingdom, these adaptations are diverse and fascinating, reflecting the incredible variety of ecosystems and environmental challenges that animals face. Ecological adaptations can be broadly categorized into three main types: i. Morphological (Structural) Adaptations ii. Physiological Adaptations iii. Behavioral Adaptations 1. Morphological (Structural) Adaptations: it involves changes in an animal's physical structure that enhance its survival in a particular environment. These adaptations can involve changes in body shape, size, colouration, or the development of specialized structures. a) Camouflage and Colouration: are among the most widespread and diverse structural adaptations in the animal kingdom. They serve multiple purposes, including predator avoidance, prey capture, and thermoregulation. a) Background matching: this refers to the ability of animals to blend with their surroundings. For example, the peppered moth's wing patterns evolved to match tree bark colour during the Industrial Revolution, shifting from light to dark as pollution darkened tree trunks. b) Disruptive Colouration: these are patterns that break up the body's outline. Such as the stripes in Zebras that make it difficult for predators to isolate individual animals in a herd. 19  c) Countershading: the is the ability of animals to have darker colouration on top and lighter underneath, which can be found in many fish species with dark backs and light bellies, making them less visible from above and below. d) Mimicry: it involves resembling another species for protection. i. Batesian Mimicry: in this kind of mimicry a harmless species mimics a harmful one. Such as the non-venomous scarlet king snake which mimics the venomous coral snake. ii. Müllerian Mimicry: here multiple harmful species share similar warning colouration. As can be found in various species of the poison dart frogs with bright, warning colours. e) Masquerading: it involves resembling an inanimate object. Such as the walking stick insect which looks like a twig or small branch. b) Body Shape and Size: they involve the body dimensions and general size, which can significantly impact an animal's survival and ecological niche. Aerodynamic Shapes: birds have streamlined bodies, hollow bones, and specialized feathers for efficient flight. Flying squirrels have flaps of skin between their limbs, allowing them to glide between trees. Aquadynamic Shapes: penguins have torpedo-shaped bodies and flipper-like wings for efficient swimming. Manta rays have flat, wide bodies for effortless gliding through water. Size Adaptations: shrews have a high surface area to volume ratio, allowing rapid heat loss and necessitating frequent feeding. Elephants have a low surface area to volume ratio, helping them maintain body temperature in hot climates. 20 c) Specialized Appendages: many animals have evolved specialized limbs or body parts to suit their lifestyle and habitat. Locomotion Adaptations: kangaroos have powerful hind legs for hopping, an energy- efficient mode of travel in open areas. Sloths have long, curved claws for hanging upside- down from tree branches. Feeding Adaptations: anteaters have long, sticky tongues to reach into ant nests and termite mounds. Woodpeckers have strong, chisel-like beaks and shock-absorbing skulls for drilling into wood. Sensory Adaptations: star-nosed moles have a specialized snout with 22 fleshy appendages, providing an exceptional sense of touch for foraging underground. Barn owls have asymmetrical ear openings, allowing for precise sound localization when hunting in the dark. d) Protective Structures: some animals have evolved structures specifically for defense against predators or harsh environmental conditions. Armour and Shells: these occur as bony plates or keratinized overlapping scales found in turtles, tortoise, armadillos and pangolins which provide protection against predators. Spines and Quills: the sharp quills of porcupines and long movable spines of sea urchins are good examples for these structure usage for defense and protection. Each squill or spine is coated in a thick, hardened layer of keratin. 2. Physiological Adaptations: it involves internal systems and processes that help animals cope and survive in their environment. 21 a) Thermoregulation: is the ability of an organism to maintain its body temperature within certain boundaries, even when the surrounding temperature is different. Desert animals: many desert creatures, like camels, have adaptations to conserve water and regulate body temperature in extreme heat. Arctic animals: polar bears have a thick layer of blubber and dense fur for insulation in cold climates. b) Osmoregulation: is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body's water content. Salt glands: in marine birds and reptiles helps to excrete excess salt. Specialized kidneys: in kangaroo rats to conserve water in desert environments. Marine fishes: have special rectal gland to excrete excess salt in sharks and rays Teleost fish: drink seawater and excrete excess salt through specialized chloride cells in gills and produce very concentrated urine to conserve water. Freshwater fishes: produce dilute urine and can absorb ions through gills to maintain proper salt balance. c) Respiration: which is the movement of oxygen from the outside environment to the cells within tissues, and the removal of carbon dioxide in the opposite direction to the surrounding environment, allows animals to efficiently extract oxygen from their environment, whether it's air or water. Aquatic mammals: Whales and dolphins have evolved to hold their breath for extended periods, dive to great depths and have higher concentration of myoglobin in muscles to store oxygen. Fish make use of gills for underwater breathing. Cutaneous respiration: in amphibians for supplemental oxygen absorption through skin. 22  Book lungs: in spiders for terrestrial gas exchange. High-altitude animals: Tibetan antelopes have hemoglobin that binds oxygen more efficiently and increased lung capacity and density of capillaries in lung tissue, which allows them to thrive in low-oxygen environments. d) Metabolism: is the set of life-sustaining chemical reactions in organisms, and involve changes in an animal's biochemical processes to suit their environment or lifestyle. Fast metabolism: in hummingbirds to support high energy demands. Hibernation: bears and ground squirrels can lower their metabolic rate during winter to conserve energy. Aestivation: some desert snails enter a state of dormancy during hot, dry periods by sealing their shell openings with a layer of mucus to prevent water loss, which drastically reduce metabolic rate and conserves energy. lungfish can survive in a cocoon of dried mucus for years without food or water to survive dry periods. e) Venom and Toxins: these are lethal chemical secretions produced by animals for protection, defense or capture of prey. Venomous snakes: produce toxic compounds for defence and prey capture. Poison dart frogs: synthesizing toxins from their diet for protection. f) Digestive adaptations: allow animals to efficiently extract nutrients from their specific diets. ▪ Ruminants (cow, sheep and goats): have four-chambered stomach for fermenting plant material. Process of rumination (chewing cud) to further break down plant matter. ▪ Carnivores (predators): short, simple digestive tract optimized for processing protein-rich diets. Strong stomach acid (pH around 1) to kill pathogens and break down proteins. 23 3. Behavioural Adaptations: are actions animals perform to increase their chances of survival and reproduction. These can be innate (instinctive) or learned behaviours. a) Migratory Behaviours: it involves animals undertaking long-distance movements to exploit seasonal resources or breeding grounds. ▪ Seasonal Migrations: monarch butterflies travel up to 3,000 miles between North America and Mexico, while humpback whales migrate between polar feeding grounds and tropical breeding areas. ▪ Altitudinal Migrations: mountain goats move to higher elevations in summer and lower in winter. ▪ Diel Vertical Migrations: many marine plankton species move up towards the surface at night and down to deeper waters during the day. b) Foraging Strategies: these are the various strategies evolved by animals to efficiently obtain food in their environments. Specialized Feeding Behaviours: trap-building in spiders, were they construct intricate webs to catch flying insects. Ambush predation in the Anglerfish, which use a bioluminescent lure to attract prey in the deep sea. Social Foraging: cooperative hunting of the African wild dog, which hunt in packs, allowing them to take down larger prey. Information Sharing, observed in many bird species form mixed-species flocks, which benefit by sharing vigilance and foraging information. c) Anti-Predator Behaviours: these are evolved by animals to avoid becoming prey. 24  Vigilance and Alarm Systems: meerkats take turns acting as sentinels, watching for predators while the group forages, while vervet monkeys have distinct alarm calls for different predators (e.g., eagles, leopards, snakes), allowing appropriate responses. Defensive Behaviours: Opossums exhibit thanatosis (playing dead) when threatened, while the horned lizards can squirt blood from their eyes to deter predators. Mobbing: many bird species collectively harass predators to drive them away from nesting areas. d) Thermoregulatory Behaviours: these are evolved to maintain optimal body temperature. ▪ Basking: marine iguanas in the Galápagos Islands bask in the sun to warm up after foraging in cold waters. ▪ Huddling: emperor penguins form dense huddles to conserve heat during Antarctic winters. ▪ Mud Wallowing: hippopotamuses spend time in water or mud to stay cool and protect their skin from the sun. e) Communication and Social Behaviours: responsible for complex social structures and communication systems. Courtship Displays: Male frigate-birds inflate a bright red throat pouch to attract females, while male bower birds construct and decorate elaborate structures to attract mates. Territorial Behaviours: many bird species sing to establish and defend territories. Wolves use scent marking to delineate pack territories. 25  Eusocial Behaviours: honey bees have a complex social structure with division of labour and intricate communication through dance language. Naked mole rats live in colonies with a queen and workers, more similar to social insects than to other mammals. Circadian rhythms: nocturnal activity in owls and bats to avoid competition and predation. Crepuscular behaviour in rabbits and deer to balance predator avoidance and foraging. Importance of Ecological Adaptations I. Survival: they allow animals to survive and thrive in their specific environments, overcoming challenges such as extreme temperatures, limited resources, and predation. II. Resource utilization: these adaptations enable animals to efficiently exploit available resources, reducing competition and allowing for niche specialization. III. Reproductive success: many adaptations directly or indirectly enhance an animal's ability to find mates, reproduce, and care for offspring. IV. Ecosystem balance: these adaptations contribute to the complex interactions between species, helping maintain ecosystem stability and biodiversity. 26  CHAPTER 4 NUTRITION INTRODUCTION The processes by which an animal consumes, breaks down, absorbs, stores, and utilises food (nutrients) to meet its needs for energy are collectively referred to as nutrition. Digestion is the process by which food is broken down chemically or mechanically into small enough pieces for individual animal cells to absorb (L. digestio, from dis, apart gerere, to carry). This chapter covers animal nutrition, diverse animal digestive systems, and the ways in which animals use and consume food. An animal needs nutrients in its diet to produce energy and to provide the chemicals needed for growth and maintenance. Overall, an animal's capacity to synthesise molecules necessary for life is inversely correlated with its nutritional needs. Animals that possess fewer biosynthetic abilities are required to obtain a greater variety of nutrients from their surroundings. Autotrophs, Herbivores, Omnivores and Carnivores Because they are autotrophs—meaning they can synthesise all of their complex molecules from simpler inorganic substances—green plants and photosynthetic protists have the fewest nutritional requirements of any kind (Gr. auto, self trophe, nourishing). Heterotrophs are organisms (Greek: heteros, another or different + trophe, nourishing) that are unable to synthesise many of their own organic molecules and must instead obtain them by consuming other organisms or their products. This includes bacteria, fungi, and animals. Herbivores (L. herba, plant vorare, to eat) are animals, like rabbits, that only eat plant material. Carnivores (L. caro, flesh), such as hawks, are animals that eat only meat. 27 Omnivores (L. omnius, all), such as humans, bears, raccoons, and pigs, eat both plant and animal matter. Insectivores, such as bats, eat primarily arthropods. Fig. 1: Autotrophs Plate 1: Caterpillar feeding (herbivore) Plate 2: Lion (a carnivore) Plate 3: Bear (an omnivore) Invertebrate Digestive Systems Animal digestive systems have evolved to facilitate the digestion of the various foods they eat. The most basic illustration is the gastrovascular cavity (Fig. 2a), which is present in organisms that have a single digestive opening. This kind of digestion is used by comb jellies, sea anemones, coral, and jellyfish, as well as flatworms called Platyhelminthes and Ctenophora. Typically, a gastrointestinal cavity is a blind tube or cavity with a single opening called the "mouth," which also functions as an "anus." Food particles enter the mouth and travel through a tubular, hollow 28 cavity. Food is broken down by digestive enzymes secreted by cells in the cavity. The cells lining the gastrovascular cavity take up the food particles. A more sophisticated system is the alimentary canal, which is made up of a single tube with an anus and a mouth at either end (Fig. 2b). An animal having an alimentary canal is an earthworm. Following ingestion through the mouth, food travels through the oesophagus, where it is stored, and then into the gizzard, where it is broken down and digested. After leaving the gizzard, food travels through the intestine, where nutrients are absorbed, and waste is expelled through the anus as castings, or faeces. Fig. 2: (a) As demonstrated by the hydra and the jellyfish medusa, a gastrovascular cavity has a single opening through which food is consumed and waste is expelled. (b) As demonstrated by this nematode, an alimentary canal has two openings: a mouth for food consumption and an anus for waste removal. Vertebrate Digestive Systems Due to their dietary requirements, vertebrates have evolved increasingly complex digestive systems. While some animals only have one stomach, others have several chambers. Birds' digestive systems have evolved to be suited for consuming partially chewed food. Monogastric: Single-chambered Stomach This kind of digestive system consists of a single stomach chamber, or "monogastric," as the name suggests. Figure 3ab depicts the monogastric digestive system found in humans and many other 29 animals. When food is taken in through the mouth, the digestive process starts. When masticating, or physically breaking down food into smaller particles, the teeth are crucial. Saliva contains enzymes that start the chemical breakdown of food. The mouth and stomach are connected by a lengthy tube called the oesophagus. The oesophageal muscles push food towards the stomach through a process called peristalsis, which is defined as wave-like contractions of smooth muscle. The stomach's pH ranges from 1.5 to 2.5, making it an extremely acidic environment that helps enzymes function more quickly. The stomach's natural digestive juices, which also contain enzymes, work with the food particles to further break down the food. In the small intestine, where enzymes produced by the pancreas, small intestine, and liver further break down food, the process of digestion is completed. The epithelial cells that line the walls of the small intestine allow the nutrients to be absorbed into the bloodstream. The waste material proceeds to the large intestine, where it is compressed into faeces and water is absorbed. It is then held until it is expelled through the rectum. Fig. 3: (a) The monogastric digestive system is found in both humans and herbivores like the (b) rabbit. To give the rabbit more time to digest plant material, the cecum and small intestine have 30 been enlarged. More surface area is available for nutrient absorption thanks to the enlarged organ. Food is broken down twice in the digestive system of rabbits: first, it passes through the cecum, where it gathers, and then it passes out as cecotrophes, which are soft faeces. To aid in its further digestion, the rabbit re-ingests these cecotrophes. Avian It is particularly difficult for birds to get enough nutrition from food. Since they lack teeth, their digestive system needs to be able to handle food that hasn't been fully chewed. Birds' diverse beak types are a reflection of the wide range of foods they eat, which includes fruits, nuts, and seeds as well as insects. Due to their ability to fly, most birds have high metabolic rates, which allow them to digest food quickly and maintain a low body weight. Birds have two chambers in their stomachs: the gizzard, which is where food is stored, soaked, and mechanically ground, and the proventriculus, which produces gastric juices to break down food before it enters the stomach. Food pellets made of the undigested material are occasionally regurgitated. The intestine is where most chemical digestion and absorption takes place, and the cloaca is where waste is expelled. 31 Fig. 4: Food is stored in a pouch called a crop on the avian oesophagus. Food travels from the crop to the proventriculus, the first of the two stomachs, which is equipped with the digestive juices needed to process food. Food travels from the proventriculus into the gizzard, the second stomach, where it is ground. To help with grinding, some birds swallow grit or stones that are kept in the gizzard. Faeces and urine do not exit birds through separate openings. Rather, the kidneys secrete uric acid into the large intestine, where it combines with the waste products of digestion. The cloaca is the opening through which this waste is expelled. Ruminants The majority of ruminants, such as cows, sheep, and goats, are herbivores that only eat a lot of roughage or fibre as part of their diet. They can digest large amounts of cellulose because of the evolution of their digestive systems. The absence of upper incisor teeth in ruminant mouths is an intriguing characteristic. They tear and chew their food using their lips, tongue, and bottom teeth. Food enters the mouth, passes through the oesophagus, and finally enters the stomach. The ruminants' stomachs are multichambered organs that aid in the digestion of the substantial amount of plant material, as shown in Figure 5. The stomach's four sections are referred to as the rumen, reticulum, omasum, and abomasum. Numerous microorganisms that ferment food and break down cellulose are present in these chambers. The monogastric stomach chamber where gastric juices are secreted is analogous to the "true" stomach, or abomasum. The four-compartment gastric chamber gives ruminants more room and the microbial support they need to break down plant matter. Large volumes of gas are produced in the stomach chamber during the fermentation process, and this gas needs to be expelled. Similar to other animals, humans' small intestine is crucial for absorbing nutrients, while the large intestine aids in the removal of waste. 32 Fig. 5: Goats and cows are examples of ruminant animals that have four stomachs. The prokaryotes and protists found in the reticulum and rumen, the first two stomachs, are capable of breaking down cellulose fibre. The reticulum is where the ruminant regurgitates its cud, chews it, and swallows it into the omasum, a third stomach where water is eliminated. After that, the cud travels to the abomasum, the fourth stomach, where ruminant enzymes break it down. Pseudo-ruminants Some animals are classified as pseudo-ruminants, including alpacas and camels. They consume a lot of roughage and plant matter. Because plant cell walls contain the polymeric sugar molecule cellulose, it is difficult to digest plant material. These animals' digestive enzymes are unable to break down cellulose, but the microbes in their digestive systems can. As a result, the digestive tract needs to be capable of processing large quantities of roughage and breaking down cellulose. The digestive system of pseudo-ruminants consists of a stomach with three chambers. However, the roughage is fermented and digested in their large caecum, a pouched organ at the beginning of the large intestine that is home to a variety of microorganisms essential for the digestion of plant materials. These animals have omasums, abomasums, and reticulums instead of rumens. Parts of the Digestive System The purpose of the digestive system in vertebrates is to help break down food materials into the nutrients that keep an organism alive. Oral Cavity 33 The mouth, or oral cavity, is where food enters the digestive system. The process through which food is broken down into smaller pieces by the teeth is called mastication. Mammals of all kinds can chew their food and have teeth. The mouth is where the lengthy chemical process of digestion starts. Saliva, which is secreted by the salivary glands, combines with food as it is chewed. Many animals' mouths produce saliva, which is a liquid material. The parotid, submandibular, and sublingual glands are the three main glands that secrete saliva. Food is moistened and its pH is buffered by the mucus in saliva. Additionally, saliva contains lysozymes and immunoglobulins, which have antibacterial properties that prevent the growth of certain bacteria and hence lessen tooth decay. Additionally, salivary amylase, an enzyme found in saliva, starts the process of breaking down starches in food into maltose, a disaccharide. The cells in the tongue also produce another enzyme known as lipase. A class of enzymes known as lipases is capable of hydrolysing triglycerides. The food's fat components are broken down by lingual lipase. The food is ready for swallowing when it is chewed and moistened by saliva and teeth, creating a mass known as the bolus. By transferring the bolus from the mouth into the pharynx, the tongue facilitates swallowing. The oesophagus, which leads to the stomach, and the trachea, which leads to the lungs, are the two passageways that the pharynx opens to. The glottis, an opening in the trachea, is covered by the epiglottis, a cartilaginous flap. Food enters the oesophagus through the closure of the glottis by the epiglottis during swallowing, not the trachea. Food can be kept out of the trachea thanks to this arrangement. 34 Fig. 6: Food digestion starts in the oral cavity (a). Teeth masticate food, and saliva secreted from (b) salivary glands moisturises it. Salivary enzymes start to break down fats and carbohydrates. The resultant bolus is swallowed, moving into the oesophagus with the aid of the tongue. Oesophagus The tube-shaped organ that joins the mouth and stomach is called the oesophagus. After being chewed and softened, the food is swallowed and travels through the oesophagus. Peristalsis, a sequence of wave-like movements in the smooth muscles of the oesophagus, forces food towards the stomach (Figure 7). Food is moved from the mouth to the stomach by the unidirectional peristalsis wave; reverse movement is not possible. The act of swallowing triggers the involuntary reflex known as peristaltic movement of the oesophagus. Fig. 7: Food is moved through the oesophagus by peristaltic movements from the mouth to the stomach. 35 The sphincter, a muscle that resembles a ring, creates valves in the digestive system. At the end of the oesophagus that leads to the stomach is the gastro-esophageal sphincter. This sphincter opens in reaction to swallowing and the pressure applied by the food bolus, allowing the food to enter the stomach. This sphincter closes and stops the stomach's contents from ascending the oesophagus when there is no swallowing motion. A true sphincter is present in many animals, but humans lack one and instead have an esophageal closure when swallowing is not occurring. "Heartburn," also known as acid reflux, is the result of the stomach's acidic secretions seeping into the oesophagus. Stomach Figure 8 illustrates how the stomach plays a major role in digestion. Gastric digestive juices are secreted by the stomach, an organ that resembles a sac. The stomach's pH ranges from 1.5 to 2.5. The chemical digestion of food and the extraction of nutrients depend on this extremely acidic environment. The stomach is a rather small organ when empty, but when food is inside it, it can swell to a size that is up to 20 times larger than when it is at rest. When food is available, this feature is especially helpful for animals that must eat. Fig. 8: The human stomach has an extremely acidic environment where most of the protein gets digested 36 In animals other than ruminants, the stomach serves as the primary location for the digestion of proteins. Protein digestion is mediated by an enzyme called pepsin in the stomach chamber. The main stomach cells secrete pepsin in an inactive form known as pepsinogen. Pepsin helps activate more pepsinogen, which initiates a positive feedback mechanism that produces more pepsin. It also breaks peptide bonds and cleaves proteins into smaller polypeptides. The main acidic component of the stomach juices, hydrochloric acid, is created in the lumen by the combination of hydrogen and chloride ions secreted by parietal cells, a different type of cell. The inactive pepsinogen is converted to pepsin with the aid of hydrochloric acid. Together with the action of the enzyme pepsin, the extremely acidic environment in the food kills a lot of microorganisms and causes the food's protein to hydrolyse. The churning action of the stomach aids in chemical digestion. Every twenty minutes or so, the contents of the stomach are mixed by the contraction and relaxation of smooth muscles. Chyme is the term for the partially digested food and gastric juice mixture. From the stomach, chyme travels to the small intestine. The small intestine is where further protein digestion occurs. After a meal, the stomach empties two to six hours later. One tiny bit of chyme at a time is released into the small intestine. The movement of chyme from the stomach into the small intestine is regulated by the pyloric sphincter. It is necessary to shield the stomach lining from pepsin digestion when breaking down protein and some fats. When explaining how the stomach lining is shielded, there are two things to take into account. First, as was already mentioned, the inactive form of the enzyme pepsin is synthesised. Because pepsinogen lacks the same enzyme functionality as pepsin, it shields the main cells. Second, the thick mucus lining the stomach shields the underlying tissue from the digestive juices' action. Ruptures in this mucous lining of the stomach can result in ulcers. When the mucous lining 37 of an organ ruptures and does not heal, the result is an ulcer, which is an open wound in or on the organ caused by Helicobacter pylori bacteria. Small Intestine The small intestine receives chyme after leaving the stomach. The organ that completes the digestion of protein, fats, and carbohydrates is the small intestine. The small intestine is a long, tube-shaped organ with highly folded surfaces that are home to projections that resemble fingers and are known as villi. Every villus has numerous microscopic projections known as microvilli on its apical surface. These structures enable nutrients to be taken up from the broken down food and absorbed into the bloodstream on the other side. The luminal side of these structures is lined with epithelial cells. Because of their numerous folds, the villi and microvilli expand the intestine's surface area and improve the effectiveness of nutrient absorption. The hepatic portal vein, which leads to the liver, receives nutrients that have been absorbed from the blood. There, the liver eliminates harmful substances like alcohol, drugs, and certain infections as well as controls how nutrients are distributed throughout the body. The duodenum, jejunum, and ileum are the three sections that make up the human small intestine, which is more than 6 meters long. The duodenum is the fixed, "C-shaped" portion of the small intestine. The pyloric sphincter, which opens to permit chyme to pass from the stomach into the duodenum, divides the stomach from the duodenum. Chyme is combined with pancreatic secretions in the duodenum to form an alkaline solution that is high in bicarbonate, which acts as a buffer and balances the chyme's acidity. Several digestive enzymes are also present in pancreatic juices. The duodenum receives digestive juices from the gallbladder, liver, and pancreas in addition to gland cells found in the intestinal wall itself. The gallbladder is where bile is stored and concentrated after being produced in the liver. While the pancreas produces enzymes that 38 catabolise starches, disaccharides, proteins, and fats, bile contains bile salts that emulsify lipids. The food particles in the chyme are broken down into amino acids, triglycerides, and glucose by these digestive juices. The duodenum is where part of the food's chemical digestion happens. Fatty acid absorption occurs in the duodenum as well. The jejunum is the second segment of the small intestine. Here, the nutrients continue to be hydrolysed, and the majority of the amino acids and carbohydrates are absorbed through the intestinal lining. The jejunum is where most chemical digestion and nutrient absorption takes place. The final segment of the small intestine, the ileum, is where vitamins and bile salts are absorbed into the bloodstream. Through peristaltic muscle movements, the undigested food is transported from the ileum to the colon. At the ileocecal valve, the ileum ends and the large intestine begins. The ileocecal valve is home to the vermiform appendix, which is a "worm-like" structure. Human appendix does not secrete any enzymes and plays a minor role in immunity. Large Intestine The large intestine, shown in Figure 9, breaks down waste materials and reabsorbs water from the undigested food. The human large intestine has a larger diameter than the small intestine, but it is substantially shorter in length. The colon, the rectum, and the cecum are its three components. The cecum serves as the receiving pouch for waste matter and connects the ileum and colon. Numerous bacteria, also known as "intestinal flora," reside in the colon and help with digestion. The ascending colon, transverse colon, descending colon, and sigmoid colon are the four regions that make up the colon. The colon's primary jobs include storing waste products and drawing water and mineral salts from undigested food. Because of their diet, carnivorous mammals have shorter large intestines than herbivorous mammals. 39 Fig. 9: The large intestine retains waste products until they are expelled and reabsorbs water from undigested food. Rectum and Anus As seen in Figure 9, the rectum is the large intestine's terminal end. The rectum's main function is to hold waste until it is expelled. During elimination, peristaltic movements are used to propel the faeces. Waste material leaves the body through an orifice called the anus, which is located at the very end of the digestive system. Elimination is regulated by two sphincters: the outer sphincter is voluntary, and the inner sphincter is involuntary, located between the rectum and anus. Accessory Organs The digestive tract's organs, which food passes through, are the ones that were previously discussed. The organs that produce secretions (enzymes) that catabolise food into nutrients are known as accessory organs. Salivary glands, the liver, the pancreas, and the gallbladder are examples of accessory organs. Hormones react to the food ingested to regulate the liver, pancreas, and gallbladder. The liver, the largest internal organ in humans, is crucial for blood detoxification and fat digestion. Bile, a digestive juice produced by the liver, is necessary for the duodenum to break down the fatty 40 parts of food. In addition, the liver produces a large amount of plasma proteins and processes fats and vitamins. Another significant gland that secretes digestive juices is the pancreas. The pancreatic fluids have high concentrations of bicarbonate, an alkali that balances the acidic chyme that is produced from the stomach. In addition, a wide range of enzymes needed for the digestion of carbohydrates and protein are present in the pancreatic juices. The small organ known as the gallbladder helps the liver by concentrating bile salts and storing bile. When chyme containing fatty acids enters the duodenum, the bile is secreted from the gallbladder into the duodenum. Nutrition and Energy Requirement It makes sense that there would be significant variations in animal diets given the diversity of life on Earth. The building blocks for DNA and other complex molecules required for development, upkeep, and reproduction come from the food that animals eat; these processes taken together are referred to as biosynthesis. Additionally, the diet provides the raw materials needed by cells to produce ATP. For the body to supply the vitamins and minerals needed for proper cellular function, a balanced diet is necessary. Food Requirements What are the basic needs for an animal's diet? A well-balanced diet that includes the minerals and vitamins needed for maintaining the structure and regulation essential for optimal health and reproductive capacity, as well as the nutrients needed for bodily function, should be fed to animals. Figure 10 provides a graphic illustration of these needs for a human. 41  Fig. 10: For humans, a balanced diet includes fruits, vegetables, grains, and protein Organic Precursors Food provides the organic molecules needed to construct tissues and cellular structure. In the body of an animal, sugars or carbohydrates are the main source of organic carbons. Digestible carbohydrates eventually turn into glucose during digestion, which is utilised by metabolic pathways to produce energy. Biochemical modification can convert complex carbohydrates, including polysaccharides, into glucose; however, since humans lack the enzyme cellulase, they are unable to produce glucose from the polysaccharide cellulose. These molecules give humans the fibre needed to pass waste through the large intestine and maintain a healthy colon. These plant fibres provide some nutrients that the human gut's intestinal flora can absorb. The body transforms extra sugars into glycogen, which is then stored for later use in the muscles and liver. Glycogen stores are used as a source of energy during times of food scarcity and to power extended physical activities like long-distance running. Fats, which are stored in mammals' lower skin layers for insulation and energy storage, can be created from excess glycogen. Mammals store excess digestible carbohydrates to help them move around and survive famine. Nitrogen is yet another essential component. Organic nitrogen can be obtained through the breakdown of proteins. The building blocks of proteins are amino acids, which are obtained through the breakdown of proteins and are essential for cellular activity. These provide the carbon 42 and nitrogen needed to make nucleotides, nucleic acids, proteins, cells, and tissues. Since excess nitrogen is toxic, it must be expelled. Food tastes better with fats added, and they also help you feel fuller and sated. Because there are nine calories in one gramme of fat, foods high in fat are also important sources of energy. Dietary fats are necessary to support the synthesis of fat-soluble hormones and the absorption of fat-soluble vitamins. Essential Nutrients Even though the body of an animal can produce many of the molecules needed for function from organic precursors, some nutrients must be obtained through diet. These nutrients are referred to as essential nutrients because the body is unable to produce them and must consume them. Certain membrane phospholipids require the essential fatty acids omega-3 alpha-linolenic acid and omega-6 linoleic acid. Vitamins are classified as co-enzymes because they are another class of essential organic molecules that are needed in small amounts for the proper functioning of many other enzymes. As shown in Tables 1 and 2, low or absent vitamin levels can have a significant impact on health. Vitamins that are both water- and fat-soluble must be consumed through diet. The inorganic essential nutrients known as minerals are found in Table 3 and must be obtained through diet. Minerals serve a variety of purposes, including structure, regulation, and function as co-factors. Additionally, some amino acids are not synthesised by the body and must be obtained through diet. The "essential" amino acids are those listed here. Only 11 of the 20 necessary amino acids can be produced by the human body; the remaining amino acids must be obtained through diet. Table 4 enumerates the amino acids that are necessary. 43 Table 1: Water-soluble Essential Vitamins Vitamin Function Deficiencies Sources Vitamin B1 Required for the body to Weakness in muscles, Meat, dairy, canned (Thiamine) metabolise proteins, carbs, and Beriberi: decreased beans, and whole lipids CO2 is extracted from heart rate, grains organic compounds by neurological issues enzymes. Vitamin B2 Plays a proactive part in Tongue redness and Vegetables, enriched (Riboflavin) metabolism, helping to inflammation; moist, grains, meat, and transform food into energy scaly skin eggs (FAD and FMN) inflammation (seborrhoeic dermatitis); or cracks or sores on the exterior of the lips (cheliosis) Vitamin B3 Used by the body to break Pellagra can cause Potatoes, meat, eggs, (Niacin) down alcohol and release diarrhoea, dermatitis, grains, and nuts energy from carbs; necessary dementia, and even for the synthesis of sex death. hormones; a part of the coenzymes NAD+ and NADP+ Vitamin B5 Helps the body produce energy Weakness, lack of Meat, whole grains, (Pantothenic from food, especially lipids; a coordination, stunted milk, fruits, acid) part of coenzyme A growth, tingling in the vegetables hands and feet, and numbness Vitamin B6 The primary vitamin involved Anaemia, twitching Orange juice, whole (Pyridoxine) in the metabolism of lipids and muscles, mouth sores grains, dairy amino acids; aids in the or ulcers, depression, products, and meat conversion of nutrients into irritability, and energy confusion Vitamin B7 Helps the body use blood sugar; Neuromuscular Vegetables, meat, (Biotin) involved in the metabolism of disorders, dermatitis, eggs, and legumes energy and amino acids, fat depression, tingling synthesis, and fat breakdown. and numbness in the extremities Vitamin B9 Aids in the proper development Pregnancy-related Whole wheat, fruits, (Folic acid) of cells, particularly in foetal deficiencies are linked nuts, legumes, and development; aids in the to birth abnormalities leafy green metabolism of amino and like anaemia and vegetables nucleic acids neural tube defects. Vitamin helps to form new blood cells, neurological Meat and dairy B12 keeps the nervous system conditions, anaemia, products; eggs (Cobalamin) healthy, and is a coenzyme in 44  the metabolism of nucleic numbness, and loss of acids. balance Vitamin C Preserves cartilage, dentin, and Scurvy (characterised Red sweet bell (Ascorbic other connective tissue; boosts by joint pain and peppers, orange acid) immunity swelling), bleeding, fruits, broccoli, and loss of hair and teeth, tomatoes and slowed healing of wounds. Table 2: Fat-soluble Essential Vitamins Vitamin Function Deficiencies Sources Vitamin A Essential for the formation Night blindness, Dark green leafy (Retinol) of bones, teeth, and skin; dermatological vegetables, yellow- supports vision, bolsters the conditions, orange vegetables, immune system, facilitates compromised fruits, milk, and foetal development, and immunity butter influences gene expression. Vitamin D Essential for calcium Osteomalacia, Egg yolk, milk, and absorption, bone immunity, and rickets cod liver oil. development, and strength; sustains a stable nervous system; regulates a normal and robust heartbeat; facilitates blood coagulation. Vitamin E reduces oxidative cell Deficiency is Nuts, seeds, grains, (Tocopherol) damage and protects the uncommon; symptoms wheat germ oil, and lungs from pollution include anaemia and unrefined vegetable damage; essential to the degeneration of the oils immune system nervous system Vitamin K Necessary for blood clotting Loss of blood and Tea and leafy green (Phylloquinone) easily bruised vegetables Table 3: Minerals and Their Function in the Human Body Mineral Function Deficiencies Sources Calcium Essential for heart health, bone Muscle spasms, rickets, Dairy, yoghurt, growth, blood cell synthesis, osteoporosis, and stunted seafood, leafy muscle and neurone function, growth green vegetables, and nerve function and legumes Chlorine Needed for production of Muscle cramps, mood Table salt hydrochloric acid (HCl) in the disturbances, reduced stomach and nerve function; appetite osmotic balance 45 Copper An essential part of numerous A copper deficit is Oysters, cocoa, (trace redox enzymes, such as uncommon. chocolate, nuts, amounts) cytochrome c oxidase; and liver cofactor for the production of haemoglobin Iodine Necessary for the production Goiter Fish, iodised salt, of thyroid hormones and dairy items Iron Necessary to prevent anaemia Anaemia, which impairs Dried fruits, beans, for a variety of proteins and immune system whole grains, fish enzymes, most notably performance, weariness, (tuna, salmon), haemoglobin and concentration. eggs, red meat, and leafy green vegetables Magnesium An essential co-factor for the Mood swings and tense Wholesome grains synthesis of ATP, bone, muscles and leafy greens healthy membrane function, and muscle Manganese A cofactor necessary in trace Low manganese levels Common in the (trace amounts for the activity of are uncommon. majority of foods amounts) enzymes Molybdenum Serves as a cofactor for Lack of molybdenum is (trace xanthine oxidase, aldehyde uncommon. amounts) oxidase, and sulfite oxidase, three vital enzymes in humans. Phosphorus A part of teeth and bones that Weakness, anomalies in Hard cheese, milk, aids in controlling nucleotide the bones, and calcium whole grains, and synthesis and acid-base loss meats balance Potassium Essential for heart, muscle, Abnormal heart rhythm Potato skins, and nerve function and weakness in the tomatoes, bananas, muscles and legumes Selenium A cofactor that is necessary in Selenium deficiency is Common in most (trace trace amounts for the activity rare foods amounts) of antioxidant enzymes such as glutathione peroxidase Sodium Numerous processes, Tiredness, irritability, Table salt including acid-base balance, and cramping in the water balance, and nerve muscles function, depend on systemic electrolyte. Zinc (trace Necessary for the activity of Anaemia and inadequate Common in most amounts) multiple enzymes, including wound healing can result foods carbonic anhydrase, liver in short stature. alcohol dehydrogenase, and carboxypeptidase 46 Table 4: Essential Amino Acids Amino acids that must be consumed Amino acids anabolized by the body isoleucine alanine Leucine aspartate Methionine cysteine Lysine glutamate Histidine selenocysteine Threonine tyrosine Arginine asparagine Valine serine Phenylalanine glycine Tryptophan proline Food Energy and ATP For them to stay healthy and maintain homeostasis, animals require food. The capacity of a system to preserve a steady internal environment despite outside environmental changes is known as homeostasis. Human body temperature, for instance, is normally 37°C (98.6°F). Whether it's hot or cold outside, humans never change this temperature. Animals need energy from their diet to keep their bodies at this temperature. Carbohydrates—primarily glucose—are an animal's main energy source. The body uses glucose as fuel. An animal's diet contains digestible carbohydrates that are transformed into glucose molecules via a sequence of catabolic chemical reactions. The main source of energy in cells is adenosine triphosphate, or ATP; ATP stores energy in phosphate ester bonds. When the phosphodiester bonds are broken and ATP is transformed into ADP and a phosphate group, ATP releases energy. Cellular respiration, the term for the metabolic processes that proteins, fats, and carbohydrates go through in the cytoplasm and mitochondrion of the cell, is what produces ATP. Glycolysis, for instance, is a sequence of chemical reactions in which glucose is transformed into pyruvic acid and a portion of its potential energy is transferred to ATP and NADH. 47 Every single cellular function requires ATP. It is used to build the organic molecules that are required for cells and tissues; it provides energy for muscle contraction and for the transmission of electrical signals in the nervous system. When the body needs less ATP than is available, the extra ATP and extra glucose are used by the liver to create molecules known as glycogen. The liver and the cells of the skeletal muscle store glucose in the polymeric form known as glycogen. The liver releases glucose from glycogen stores when blood sugar levels fall. Intense exercise causes skeletal muscle to convert glycogen to glucose. The process by which glucose and surplus ATP are transformed into glycogen and stored energy is a crucial evolutionary step in assisting animals in coping with famine, food scarcity, and mobility. Digestive System Processes Eating food provides energy and nutrition, but the process takes several steps. Ingestion, or the process of consuming food, is the initial stage for true animals. This is followed by digestion, absorption, and elimination. Ingestion Large molecules are unable to cross cell membranes in intact food. Animals must break down food into smaller pieces in order to absorb the nutrients and organic molecules. Ingestion is the initial stage of this procedure. The act of ingesting food through the mouth is called ingestion. In vertebrates, mastication—the process of breaking down food into boluses—requires the use of the tongue, saliva, and teeth. Salivary enzymes start to chemically break down food while it is being mechanically broken down. These processes work together to change the food from big particles to a soft mass that can pass down the oesophagus and be swallowed. 48 Digestion and Absorption Food is broken down mechanically and chemically into tiny organic fragments during digestion. Macromolecules must be broken down into smaller pieces that can pass through the digestive epithelium and be absorbed. For the digestive epithelial cells to absorb large, complex molecules of proteins, polysaccharides, and lipids, they must first be broken down into smaller particles, like simple sugar. Various organs have distinct functions during the process of digestion. For the animal diet to be nutritionally balanced, it must contain fat, protein, and carbs in addition to vitamins and inorganic elements. Carbohydrates Carbohydrate digestion starts in the mouth. Food starches are broken down by the salivary enzyme amylase into the disaccharide maltose. Carbs are not significantly broken down as the food bolus passes down the oesophagus and into the stomach. The oesophagus secretes mucus for lubrication but no digestive enzymes. The amylase enzyme is inhibited by the stomach's acidic environment. The duodenum is where the next stage of carbohydrate digestion occurs. Remember that the pancreas, liver, and gallbladder all secrete digestive secretions that combine with the stomach chyme as it passes through the duodenum. Amylase, another enzyme found in pancreatic juices, is responsible for converting starch and glycogen into the disaccharide maltose. Enzymes called lactases, sucrases, and maltases break down the disaccharides into monosaccharides. These enzymes are also found in the brush border of the small intestine wall. Maltose is converted to glucose by maltase. Lactase and sucrase, respectively, break down lactose and sucrose, two other disaccharides. Lactase breaks down lactose, also known as "milk sugar," into glucose and galactose, while sucrose, also known as "table sugar," is broken down into glucose and fructose by sucrase. After being absorbed, the monosaccharides (glucose) created in this way can be utilised 49 in metabolic pathways to produce energy. The body's various cells receive the monosaccharides once they have passed through the intestinal epithelium and entered the circulation. Fig. 11: Several enzymes are involved in the digestion of carbohydrates. Amylase and maltase convert starch and glycogen into glucose. Lactase and sucrase break down lactose (milk sugar) and sucrose (table sugar), respectively. Table 5: Digestion of Carbohydrates Enzyme Site of Site of action Substrate End product synthesis acting on Salivary amylase Salivary glands Mouth Polysaccharides Disaccharides (Starch) (maltose), oligosaccharides Pancreatic amylase Pancreas Small intestine Polysaccharides Disaccharides (starch) (maltose), monosaccharides Oligosaccharidases Lining of the Small intestine Disaccharides Monosaccharides intestine; brush (e.g., glucose, border fructose, membrane galactose) Protein The stomach is where most protein digestion occurs. By converting intact proteins into peptides— short chains of four to nine amino acids—the enzyme pepsin plays a crucial part in the digestion of proteins. Other enzymes in the duodenum, such as chymotrypsin, elastase, and trypsin, act on the peptides, breaking them down into smaller pieces. The pancreas produces trypsin elastase, carboxypeptidase, and chymotrypsin, which are then released into the duodenum to act on the 50 chyme. Peptidases, or enzymes that break down peptides, aid in the further breakdown of peptides into single amino acids. Particularly, the enzymes dipeptidase, aminopeptidase, and carboxypeptidase are crucial in breaking down peptides into free amino acids. The small intestine allows the amino acids to enter the bloodstream. Table 6: Digestion of Protein Enzyme Site of synthesis Site of action Substrate End product acting on Pepsin Stomach chief cells Stomach Proteins Peptides Trypsin Elastase Pancreas Small intestine Proteins Peptides Chymotrypsin Carboxypeptidase Pancreas Small intestine Peptides Amino acids and peptides Aminopeptidase Lining of intestine Small intestine Peptides Amino acids Dipeptidase Lipids Lingual and gastric lipases help the stomach start the process of breaking down fats. However, pancreatic lipase is responsible for most of the lipid digestion that takes place in the small intestine. Bile, which is made in the liver and kept in the gallbladder, is released when chyme enters the duodenum due to hormonal reactions. By emulsifying lipids, particularly triglycerides, bile facilitates their digestion. Large lipid globules can split into numerous smaller lipid globules through the process of emulsification. In the chyme, these tiny globules are more widely dispersed than they are in big aggregates. Since lipids are hydrophobic materials, they will group together to form globules when wet in order to reduce our exposure to it. Amphipathic substances, or hydrophobic and hydrophilic portions, are found in bile salts. Hence, the hydrophilic side of the bile salts can interact with water, while the hydrophobic side interacts with lipids. Bile salts emulsify big lipid globules into small lipid globules in this way. 51 Lipases are a type of enzyme found in pancreatic juices that break down lipids. Lipid digestion is incomplete if the chyme's lipids group together into big globules because there will be minimal surface area left for the lipases to work on. Bile salts multiply the lipids' available surface area by several times through the formation of an emulsion. At that point, the lipids can be more effectively broken down by the pancreatic lipases. Lipids are broken down by lipases into glycerides and fatty acids. These molecules have the ability to cross the cell's plasma membrane and enter the intestinal lining's epithelial cells. Long-chain fatty acids and monoglycerides are encircled by the bile salts to form micelles, which are tiny spheres. The long-chain fatty acids and monoglycerides diffuse out of the micelles and into the absorptive cells of the small intestine at the brush border, leaving the micelles behind in the chyme. In the absorptive cells, the long-chain fatty acids and monoglycerides recombine to form triglycerides, which clump together to form globules and get coated in proteins. We refer to these big spheres as chylomicrons. Triglycerides, cholesterol, and other lipids are present in chylomicrons, which also have proteins on their surface. The hydrophilic phosphate "heads" of phospholipids also make up the surface. When combined, they allow the chylomicron to travel through an aqueous medium without coming into contact with the lipids. Chylomicrons are exocytosed from the absorptive cells. Chylomicrons first enter the lymphatic vessels before moving on to the subclavian vein and the blood. Vitamins There are two types of vitamins: lipid-soluble and water-soluble. Vitamins that are fat soluble are absorbed similarly to lipids. A certain amount of dietary fat must be consumed in order to facilitate the absorption of vitamins that are lipid-soluble. Water-soluble vitamins can pass through the intestine and enter the circulation directly. 52 Elimination The removal of undigested food and waste products is the last stage of digestion. The majority of the water is reabsorbed in the colon once the undigested food material has entered. Remember that the "intestinal flora," which are microorganisms that support digestion, are also found in the colon. Peristalsis, or the movement of stool through the colon, stores semi-solid waste in the rectum. The rectum's expansion in reaction to the faecal matter it stores sets off the neural signals that initiate the urge to void. Using peristaltic movements of the rectum, the solid waste is removed through the anus. Common Problems with Elimination Among the most common health issues that impact digestion are diarrhoea and constipation. The condition known as constipation is caused by the colon removing too much water, which causes the faeces to become hard. On the other hand, diarrhoea happens when the faeces do not contain enough water. Excessive diarrhoea is caused by a variety of bacteria, including those that cause cholera, that interfere with the proteins in the colon that are involved in reabsorption of water. Emesis Vomiting, also called emesis, is the forceful expulsion of food through the mouth. It frequently occurs in reaction to an irritant that affects the digestive tract, such as bacteria, viruses, emotions, sights, and food poisoning, among others. The stomach muscles are contracting hard, which is why the food is being forced out of the stomach. The medulla controls the process of emesis. Digestive System Regulation The brain is the primary regulator of hunger and fullness. The nervous and hormonal systems control the digestive system's operations. 53 Neural Responses to Food The first thing that happens when we smell, see, or think about food is salivation. When food stimulates the autonomic nervous system in anticipation of digestion, the salivary glands respond by secreting more saliva. In order to break down the food, the stomach starts to produce hydrochloric acid at the same time. Remember that the brain regulates the peristaltic movements of the oesophagus and other digestive tract organs. These muscles are also primed for movement by the brain. The area of the brain responsible for detecting satiety signals fullness when the stomach is full. The cephalic, gastric, and intestinal phases of gastric control are the three overlapping phases; each is controlled by the nervous system and necessitates a large number of enzymes. Digestive Phases Food triggers a reaction even before it reaches the mouth. The brain's reaction to the stimulus that food provides during the first phase of ingestion, known as the cephalic phase, governs this process. Smell, sight, and other senses all cause neural responses that cause salivation and the secretion of gastric juices. The mere thought of food can also trigger the cephalic phase's gastric and salivary secretion. Currently, salivation is increasing in response to thoughts of chocolate or crispy potato chips, which is a cephalic phase response. The stomach is ready to receive food when the central nervous system kicks in. As soon as the food reaches the stomach, the gastric phase starts. The stimulation from the cephalic phase is expanded upon. Ingested materials are processed by enzymes and gastric acids. The presence of undigested material, a drop in the pH of the gastric contents, and stomach distension all act to stimulate the gastric phase. Local, hormonal, and neural responses make up this phase. Strong contractions and secretions are triggered by these reactions. 54 When chyme enters the small intestine and starts to produce digestive secretions, the intestinal phase starts. This stage regulates how quickly the stomach empties. Chyme enters the small intestine and, in addition to causing the gastrin to empty, it also sets off a series of hormonal and neurological reactions that regulate the function of the pancreas, liver, gallbladder, and intestinal tract. Hormonal Responses to Food The endocrine system regulates the responses of the body's numerous glands as well as the timing of hormone release. The environment of stomach acid is one of the major factors that are regulated by hormones. In reaction to the presence of proteins, G cells in the stomach release the hormone gastrin during the gastric phase. Gastrin promotes the production of hydrochloric acid (HCl), the stomach acid that helps break down proteins. But once the stomach is empty, the production of hydrochloric acid is inhibited by a hormone known as somatostatin, meaning that the acidic environment need not be maintained. A negative feedback mechanism governs this. Digestive secretions from the pancreas, liver, and gallbladder are crucial for the intestinal phase of chyme digestion in the duodenum. A hormone known as secretin causes the pancreas to create an alkaline bicarbonate solution and send it to the duodenum in an effort to neutralise the acidic chyme. Cholecystokinin (CCK), another hormone, and secretin work together in tandem. CCK stimulates the gallbladder to release bile into the duodenum in addition to stimulating the pancreas to produce the necessary pancreatic juices. The makeup of food influences another level of hormonal regulation. Foods with a lot of fat take a while to digest. The small intestine secretes a hormone known as gastric inhibitory peptide, which 55 causes the peristaltic movements of the intestine to slow down and give fatty foods more time to be absorbed and digested. Research on the hormones that regulate the digestive system is still ongoing and very important. Researchers are figuring out how each hormone functions in the digestive system and creating strategies to target these hormones. Developments could result in knowledge that could combat the obesity pandemic. 56  CHAPTER 5 RESPIRATION INTRODUCTION Breathing is an involuntary event. The respiratory centre in the brain tightly regulates how often we breathe and how much air we inhale or exhale. When not exerting themselves, humans breathe around 15 times per minute on average. Canines have a respiratory rate of approximately 15-30 breaths per minute. Every inhalation fills the lungs, and every exhalation pushes air back out. That air does more than simply inflate and deflate the lungs in the chest cavity. The air contains oxygen, which passes through lung tissue, enters the bloodstream, and then travels to organs and tissues. Oxygen (O2) enters cells and is used in metabolic reactions to produce ATP, a high-energy compound. At the same time, these reactions emit CO2 as a byproduct. CO2 is toxic and must be removed. Carbon dioxide leaves the cells, enters the bloodstream, travels back to the lungs, and is expelled from the body during exhalation. The respiratory system's primary function is to deliver oxygen to the cells of the body's tissues while removing carbon dioxide, a cell waste product. The nasal cavity, trachea, and lungs are the three primary structures of the human respiratory system. All aerobic organisms require oxygen to perform their metabolic functions. Throughout the evolutionary tree, different organisms have developed various methods of obtaining oxygen from the surrounding atmosphere. The animal's respiratory system is heavily influenced by its surroundings. The complexity of the respiratory system varies with the size of the organism. As an animal's size increases, diffusion distances increase and the surface area to volume ratio decreases. In unicellular organisms, diffusion across the cell membrane is sufficient to provide oxygen to the cell (Figure 39.2). Diffusion is a slow, passive transport process. For diffusion to be a viable 57 method of providing oxygen to the cell, the rate of oxygen uptake must be equal to the rate of diffusion across the membrane. In other words, if the cell was too large or thick, diffusion would be unable to deliver oxygen to the cell's interior quickly enough. As a result, relying on diffusion to obtain oxygen and remove carbon dioxide is only feasible for small organisms or those with highly flattened bodies, such as many flatworms (Platyhelminthes). To transport oxygen throughout their entire body, larger organisms developed specialised respiratory tissues such as gills, lungs, and respiratory passages, as well as complex circulatory systems. Direct Diffusion The oxygen needs of small multicellular organisms are satisfied by diffusion across the outer membrane. For organisms with a diameter of less than one millimetre, gas exchange through direct diffusion across surface membranes is effective. Every cell in the bodies of simple organisms, like flatworms and cnidarians, is in close proximity to the outside world. Their cells are kept wet, and direct diffusion facilitates the rapid diffusion of gases. Small and essentially flat worms, flatworms "breathe" by diffusing through their outer membrane. These organisms' flat shapes maximise the surface area available for diffusion, guaranteeing that every cell in the body is in close proximity to the outer membrane surface and can obtain oxygen. The central cells of the flatworm could not receive oxygen if it had a cylindrical body. Skin and Gills Amphibians and eart