General Biology I Lecture 2 PDF

BAZE UNIVERSITY ABUJA DEPARTMENT OF BIOLOGICAL SCIENCES General Biology I BIO 101 LECTURE 02 The Diversity and the characteristics of Living Things. CONTENTS 2.0 – Introduction...

BAZE UNIVERSITY ABUJA DEPARTMENT OF BIOLOGICAL SCIENCES General Biology I BIO 101 LECTURE 02 The Diversity and the characteristics of Living Things. CONTENTS 2.0 – Introduction 2.1-Animal Diversity 2.2-Plant Diversity 2.3– Characteristics of Living Things. 1 2.0 – Introduction Understanding the diversity and characteristics of living organisms is crucial, as it provides insights into human biology, disease mechanisms, and the evolution of treatments. This lecture will cover the diversity of life, including both animal and plant kingdoms, with a focus on characteristics relevant to medicine. Scientist estimate that there are about 10-50 million organisms living on planet earth today, of which only about 18 % (1.8 million) have been identified and named. Tropical forests e.g., the Amazon and deep oceans like the Pacific and Atlantic oceans likely hold the highest population of still unknown species. The total population of living organisms in a particular habitat is known as biodiversity. According to the hierarchial classification system, biodiversity on earth have been grouped into 3 domains of: Archaea; Eubacteria and Eukarya. These domains are further divided into 6 kingdoms of: Archaea; Eubacteria; 2 Protista; Fungi; Plantae and Animalia. For the purpose of this study this unit will focus on the kingdoms of Animal Diversity and Plant Diversity. 2.1-Animal Diversity The Animal Kingdom: The animal kingdom consists of a diverse range of organisms which share common properties that define animals as a distinct group of life forms. Animals are multicellular; eukaryotic; aerobic; heterotrophic organisms; capable of reproducing sexually or asexually; mostly motile and live on land or water habitats.  Levels of organization: The patterns of organization of cells vary in animals in spite of their multicellular nature. The patterns of cellular organization seen in animals are: 1. Cellular level of organization - In these animals, the cells of the body form loose aggregates e.g., Sponges. 2. Tissue level of organization: In these animals, cells of the animal carrying out the same function are arranged in tissues e.g., Coelenterates. 3. Organ system level of organization: In these animals, tissue are grouped together to form organs, each specialized for a particular function e.g., members of Platyhelminthes and other higher phyla. Animals are classified based on some certain fundamental features and similarities, such as cellular arrangement; body symmetry, segmentation, presence or absence of notochord etc. These features help to identify and 3 organize the various animals into specific groups. Below are some of the fundamental features:  Body symmetry: The arrangement of body parts around a central point or line determines symmetry. Some animals are asymmetrical which cannot be divided into two equal halves along any plane passing through the centre e.g., sponges. Some exhibit radial symmetry where the animal can be divided into two equal halves along any plane passing through the central axis e.g., Coelenterates, Echinoderms, etc. Others exhibit bilateral symmetry where the body can be divided into identical left and right halves along only one plane. e.g., Annelids, Arthropods, Chordates etc. In most bilateral animals nerve cells are concentrated at the head end; this process is known as cephalization - concentration of nerve cells at one end of the body. 4  Body wall/ Germ layers: The body wall of an animal may be arranged in two or three embryonic layers. Accordingly the animals are called diploblastic (having outer ectoderm and inner endoderm and undifferentiated mesoglea in between them) animals. E.g., Coelenterates, and triploblastic (having outer ectoderm, middle mesoderm and inner endoderm) animals. E.g., Platyhelminthes to Chordates. Fig.2 Body layers (a) Diploblastic (b) Triploblastic.  Coelom/ Body cavity: The presence or absence of a cavity called coelom in between body wall and gut is important for classification. Animals are grouped into 3 types based on the presence or absence of a coelom: 1. Acoelomates: Body cavity in this group of animals is absent e.g. Platyhelminthes. 5 2. Pseudocoelomates: Body cavity in this group of animals is not lined by a mesoderm e.g. Rotifers, Nematodes. 3. Eucoelomates: Animals in this group possess true coeloms lined by a mesoderm e.g., from Annelids to Chordates..  Segmentation: Also called metamerism. The body is externally and internally divided into repeated, linear series of body units called metameres or somites, e.g., Earthworms. In other animals, the segments are modified, such as with insects. They essentially have three segments- the head, thorax and abdomen. 6  \  Notochord: Is a supporting rod-like structure derived from mesoderm. It may be present in embryonic or adult stages. The animals which possess notochord are called chordates, e.g. Chordata. The animals in which notochord is absent are called non chordates, e.g., Porifera to Hemichordata.  7  CLASSIFICATION OF THE ANIMAL KINGDOM The animal kingdom is further divided into groups of approximately 35 Phyla, below are the 10 major phyla of the animal kingdom:  Porifera: These are the salt-water sponges, approximately 8,000 exists today. Characteristic features of Porifera:  They are all aquatic – mostly marine, some freshwater;  They are sessile;  They are asymmetrical;  They have no true tissues (no mouth, no digestive cavity, no muscles, no nervous system); hence known as the Parazoans;  They have epithelial, collar, and amoeboid cells;  They reproduce both asexual and sexual  They are mostly hermaphrodites;  They serve as food and shelter for many organisms;  Their body is made up endoskeleton – made of CaCO3 or silica; 8  Cnidaria: Organisms in this group include jellyfish, anemone, sea corals etc., and approximately 15,000 species exist today. Features include:  Characteristic features of Cnidaria:  Their body is radial symmetry;  They have two layers of tissue – endoderm and ectoderm with a jellylike mesoglea layer in between;  They have specialized nerve, muscle, digestive, and reproductive tissue;  They have tentacles with nematocysts;  Many species are considered at risk;  They have 2 life cycle stages – polyp (asexual) - mostly sessile; and medusa (sexual) - free swimming. 9  Platyhelminthes: These are flatworms e.g., tapeworm, fluke worm, etc., approximately 15,000 species exist today. Characteristic features of Platyhelminthes:  They are Flattened;  They are Un-segmented;  They are bilateral symmetry;  They have hydrostatic skeleton;  Their body is made of three cell layers;  They have 3 cell layers but acoelomates;  They do not have circulatory or respiratory systems;  They have degree of cephalization;  There are mainly parasites. 10  Nematodes: These are the round worms, consists mainly of parasitic worms e.g., hook worm, trichenella, etc., there are about 80,000 known species. Characteristic features of Nematodes:  They are Round / cylindrical shapes;  They are found in the soil and aquatic habitat ;  They are un-segmented;  Their mouth is separated from the anus;  Their body is divided into 3 cell layers but pseudocoelomates;  They do not have circulatory or respiratory systems ;  They have hydrostatic skeleton;  They are mostly scavengers or parasites; 11  Rotifers: These are microscopic freshwater and moist soil invertebrate animals. There are about 1,800 known species.  Characteristic features of Rotifers:  They are bilateral symmetry;  Their body has more than two cell layers, tissues and organs;  Their body cavity is a pseudocoelom;  Their body possesses a through gut with an anus;  Their body was covered in an external layer of chitin called a lorica;  There have a nervous system with a brain and paired nerves;  They do not have circulatory or respiratory organs;  They reproduction mostly by parthenogenetic, otherwise sexual and gonochoristic;  They feed on bacteria, and protista, or they can act as parasitic;  They are free swimming or attached to another organisms.  Mollusca: This group includes organisms such as snails, clams, squids and octopus. Over 100,000 species are known today.  Characteristic features of Mollusca:  They are mostly marine and live freely;  Some of them are swimmer, some creep slowly, some are terrestrial;  Their body plan contains a foot (muscular, used for motion), mantle (covers gills and secretes shell), and visceral mass (contains organs); 12  They have a varying degrees of cephalization;  Their body is bilateral symmetry;  They have 3 cell layers; coelomates;  They possess radulas used for scraping and burrowing. Mollusca  Annelida: these are the segmented worms; organisms in this group include earthworms, leeches, etc. Characteristic features of Annelida:  Their body is segmented;  Thy can be terrestrial, marine, freshwater;  They have 3 cell layers; coelomates;  They can grow larger than non-segmented worms;  They have hydrostatic skeleton;  Their body is bilateral symmetry;  They have a complete digestive and circulatory system;  Some of them are hermaphrodites. 13  Arthropoda: This large group consists of insects, spiders, crustaceans, etc; scientists estimate that there are more than 1 million species of insects. Characteristic features of Arthropoda:  They have segmented body with jointed appendages;  They are both aquatic and terrestrial;  Their body have 3 cell layers; reduced coelom;  They mostly dominant animals on Earth;  Their body is made of exoskeleton with chitin;  They have efficient gas exchange allows rapid supply of oxygen to muscles;  They have a well-developed sensory (some with antennae), nervous, and circulatory systems. Arthropoda  Echinodermata: Organisms in this group include star fish, sea urchins, etc., there about 6,000 known species, 14  Characteristic features o Echinodermata:  They have Spiny-skinned;  Their larvae are bilaterally symmetrical, adults are radial;  They Have digestive and circulatory systems, but no respiratory or excretory systems;  endoskeleton;  Their have 3 cell layers, coelomates;  They reproduce sexually  They move by using ‘hydraulics’;  They have no head (no cephalization). Echinodermata  Chordata: This group consists of animals that are classified based on the 3 common embryological features: dorsal nerve cord; notochord (supportive structure); and pharyngeal gill pouches. The phylum chordate is further divided into 3 subphyla as follows: 1. Tunicata (Urochordata): large group of unusual invertebrates that start life as larvae with notochord in the tail region, while adult life is sedentary (attached) forms without notochord. Eg: - Ascidia, Doliolum. 15  Tunicata 2. Cephalochordata: Animals of this subphylum have fish-like appearance with notochords extending from the head to tail region. They lack bones, brains, eyes, and most organs associated with the brain. eg: - Brcmchiostoma (Amphioxus or Lancelet). Subphyla Urochordata and Cephalochordata are called protochordates and are all marine organisms. Cephalochordata 3. Vertebrata: The largest subphylum composed of members which possess notochord only in the embryonic stages. In adults it is replaced by Vertebral column. All vertebrates have a skeleton of either bone or cartilage, with brains protected by a boney cranium. They have ventral 16  heart with 2-4 chambers; a closed circulatory system; kidney for excretion; and paired appendages which may be fins or limbs. There are 7 classes within the subphylum Vertebrata: 1. Agnatha: These are ancient animals similar to fish, but noticeably different. They have suctorial and circular mouth without jaws, lack paired fins and scales. E.g. Lamprey, Hag fish, etc. 2. Chondrichthyes: They are marine fishes with cartilaginous endoskeleton. The exoskeleton has placoid scales. E.g. Shark, Saw fish, Sting ray, Electric ray, etc. 3. Osteichthyes: The largest class of vertebrates with over 20,000 species. They are marine or freshwater fishes with bony endoskeleton. The exoskeleton has cycloid or ctenoid scales. Ovoviviparous reproduction – hatched egg birthing, e.g. Sardine, Mackerel, Flying fish. 4. Amphibia: They are the vertebrates adapted to land and water. The word ‘amphibian’ is derived from two Greek words amphi (double) and bios (life), which refers to the two phases in the life cycle of most amphibians: an aquatic larval stage and a terrestrial adult stage. They do not possess exoskeleton. E.g. Frog, Toad, Salamander. 5. Reptilia: They are the creeping or crawling vertebrates having dry- cornified skin without skin glands; ectothermic – need outside source of heat to generate adequate body heat. The exoskeleton has horny scales or scutes. E.g. Tree lizard (Chameleon), Garden lizard, Turtle, Tortoise, Cobra. 6. Aves: They are animals with wings and are adapted for flight. They have feathers as exoskeleton and their jaws are modified into beaks. They are oviparous – egg-laying. E.g. Crow, Pigeon, Peacock, Parrot, Ostrich, Penguin. 7. Mammalia: Represent only about 9% of the known vertebrates. They possess breast glands (mammary glands) and majority of them are 17  viviparous – live birthing. They have hair as exoskeleton. E.g. Platypus, Kangaroo, Camel, Monkey, Humans, Elephants, Dogs, Cats. 2.2-Plant Diversity Scientists estimate that there about 315 thousand species of plant today, that evolved from a small group of aquatic green algae called Charophytes to modern terrestrial plants roughly 500 million years ago. General Characteristic of plants  Plants are multicellular; eukaryotic and autotrophic ,  Plant reproduce through spores or seeds.  Their cells possess cell walls made of a carbohydrate called cellulose  Plant store their food in the form of starch.  They have chloroplasts containing chlorophyll and other pigments.  Most plants are terrestrial although there are some exceptions.  Plant life cycles have two alternating phases, a haploid (n) phase and a diploid (2n) phase.  The diploid phase is called the sporophyte and produces spores, while the haploid is called the gametophyte and produces gametes. Plants are classified based on some common characteristics and similarities, such as differentiated body parts; presence of vascular tissues; method of reproduction; seed forms and availability; the presence of Chlorophyll a & b, and Carotenoid pigments; alternation of generations (Gametophyte > Sporophyte > Gametophyte); etc. These characteristics help to identify and organize the diverse range of plants into specific groups; some of the fundamental characteristics are discussed below: Plant body plan: The plant body may be thalloid e.g., algae; fungi; lichens (Thallophyta) or differentiated into root, stem and leaves. 18 Presence of vascular tissue: a vascular tissue is a complex conducting tissue composed of xylem and phloem, which function in the transport of water and dissolved substances. All plants are classified using the availability of the vascular tissue and could be: i. Non-vascular - plants (e.g., mosses) that have no system for transporting water or nutrients. ii. Vascular - plants that have a system through which they can transport water and nutrients throughout the plant, e.g., ferns, maize, oaks, etc. 19 Seeds: Plants could either be seedless plants (Cryptogamae), examples include ferns, moss, etc., - though some (ferns) have a vascular system, they reproduce using spores; or seed plants (Phanerogamae) – flowering plants that reproduce using seeds, and based on their morphology can be further divided into two types: 20  1. Gymnosperms (e.g., pine) have seeds that are not enclosed, i.e., naked seeds. 2. Angiosperms (i.e., flowering plants) have seeds that are enclosed in fruits. Angiosperms are further arranged into two groups:  Monocotyledons: examples are grasses, palms, etc., characteristics include:  Leaves have parallel venation;  Embryos have one cotyledon;  Fibrous root system;  Flowers are in multiples of three.  Dicotyledons: examples are trees and most common plants, characteristics include:  Leaves have netlike venation;  Embryos have two cotyledons;  Tap-root system;  Flowers are in multiples of four or five.  2.3- Characteristics of Living Things. Living things are called organisms. Living organisms are comprised of the same chemical elements that make up nonliving things and both obey the same laws of physics and chemistry. We can better understand what distinguishes living 21 from nonliving by examining the processes and characteristics that all living organisms have in common. Some of these characteristics are discussed below:  Living organisms are composed of cells. This is the single most fundamental difference between living and non-living things. Small organisms such as bacteria and many protists are composed of a single cell. Larger organisms are composed of many cells; they are multicellular.  Living organisms carry out various kinds of life processes, such as: 1. Nutrition 2. Synthesis and assimilation 3. Transport 4. Respiration 5. Growth 6. Excretion 7. Reproduction 8. Regulation These life processes are necessary for maintaining a fairly constant environment within an organism in spite of its constantly changing external environment. The condition of a constant internal environment is known as homeostasis. Nutrition: Every organism takes in (ingest) substances from their external environment and convert them into useable forms. Nutrition is defined as the ingestion of nutrients (e.g. organic substances and mineral ions) containing the raw materials for growth and tissue repair, absorbing and assimilating them. Organisms such as green plants; cyanobacteria etc.; produce complex nutrients from simple substances (e.g. carbon dioxide; water) found in the environment, they are known as producers. 22 Most animals on the other hand, obtain nutrients ready-made from the environment by consuming other organisms in their environment. Synthesis and assimilation: Organisms are able to combine simple substances chemically to form more complex substances. This process is called synthesis. Synthesis produces materials that can become part of the structure of an organism. In this way, the organism can repair or replace worn-out parts. These materials also allow the organism to grow. The incorporation of materials into the organism's body is called assimilation. Knowledge of metabolism is crucial for understanding drug interactions and nutrition. Transport: The process by which substances enter and leave cells and become distributed within the cells is known as transport. In the smallest and simplest organisms, materials are exchanged directly with the external environment. Useable materials enter the cells directly from the environment; waste materials pass from cells directly into the environment. In larger, multicellular organisms, however, most cells are not in direct contact with the external environment. In many animals, for example, a circulatory system transports materials to, and wastes away from, the cells of the organism. The fluid, or blood, of the circulatory system is kept in motion, distributing these materials among the cells of the organism. In plants, specialized conducting structures transport substances from the roots and leaves to all parts of the plant. Respiration: All living organisms need energy. They get this by breaking down nutrients, such as glucose, inside their cells. This releases the energy from the nutrients. Respiration is the chemical reactions that break down nutrient molecules in living cells to release energy. Growth: Some of the nutrients that living organisms ingest are used to help cells to grow, and to help to make more cells. Growth can be defined as a 23 permanent increase in size and dry mass by an increase in cell number or cell size or both. Excretion: Every organism produces waste substances that it cannot use and that may be harmful if accumulated in the body. These wastes are the products of many of the chemical / reactions that occur within cells. The removal of these wastes from the organism's body is called excretion. Reproduction: is the process by which living things produce new organisms of their own kind. Reproduction can take different forms of multiplication and division:  Asexual (e.g. microorganisms);  Sexual (e.g. humans). Regulation: All the activities that help to maintain an organism's homeostasis make up the process of regulation. In animals, systems such as the digestive, transport, excretory, nervous, and endocrine systems are involved in some part of the process of regulation. Each of these systems contributes to maintaining homeostasis. Plants do not have nervous systems, but they do have parts that produce hormones. These hormones allow a plant to respond to various changes in its environment. Relevance to Medicine A. Understanding Diseases Zoonotic Diseases: Many human diseases originate from animals (e.g., rabies, COVID-19). Knowledge of animal classification aids in understanding these pathogens. B. Drug Development 24 Many pharmaceuticals are derived from plant and animal sources. Understanding biodiversity helps in discovering new drugs. C. Evolutionary Medicine Studying the evolutionary relationships among species can provide insights into human health and disease susceptibility. D. Ecosystem Health Understanding plant and animal diversity is essential for addressing environmental health issues, which directly affect human health. Conclusion The diversity and characteristics of living organisms form the foundation of biological knowledge essential for medical practice. As future healthcare providers, students must appreciate the interconnectedness of all life forms, their classifications, and their relevance to human health and disease. 25