ANP101 Animal Physiology PDF

INTRODUCTION TO ANIMAL PHYSIOLOGY ANP101 / ANP James Ola. Daramola 1 Animal physiology Definition. The study of life How cells, tissues, organs and systems function. Groups of cells with similar characteristics or specializations form tissues Diferent ti...

INTRODUCTION TO ANIMAL PHYSIOLOGY ANP101 / ANP James Ola. Daramola 1 Animal physiology Definition. The study of life How cells, tissues, organs and systems function. Groups of cells with similar characteristics or specializations form tissues Diferent tissues combine to form organs Organs which function together form systems Covers key homeostatic processes the regulation of temperature, blood fow and hormones. 2 Why is it important to study animal physiology? It is the foundation upon which we build our knowledge of what "life" is Crucial for understanding and evaluating underlying biological processes> behavioral states and animal response to diferent biological processes social and environmental stimuli How to manage animals subjected to> stresses by diferent environments disease. 3 Why is it important to learn about animals? Advances in food security & safety keep humans healthy and increase the world's supply of nutritious food. Animal scientists can protect human health. It is important for scientists to study how diseases spread between animals and humans. 4 Physiological functions of cells, tissues, organs & systems Homeostasis Physiological mechanism of cells, tissues, organs & systems that allows maintenance & regulation of the stability required to function properly. maintain steady internal, physical & chemical conditions by living systems. most organ systems contribute to homeostasis maintenance of a constant internal environment in spite of constant change provides for material needs of cells removes wastes from cells 5  Characteristics of living things Movement Respiration Nutrition Irritability Growth Excretion Reproduction Dead 6  Movement  A large number of animals move around using their limbs, and the limbs are moved by muscles.  The muscles are atached to either the endoskeleton or the exoskeleton.  Vertebrates have an endoskeleton and it is located within the body.  The muscles that are used for moving the limbs are atached to the outer surface of the bones.  Arthropods (such as insects and crustaceans) have an exoskeleton made of chitn. In search for food, protecton & shelter 7  Respiration All living things (plants and animals) perform respiration.  In this process oxygen is taken in to oxidize the foods in order to release energy. Carbon dioxide and oxygen are released as by products. To carry out this process, various respiratory organs are found in living organisms 8  Nutrition Every living organism requires food for energy to perform various body functions. Nutrition is a process of taking food. Plants are Autotrophs as they can synthesize food on their own photosynthesis. Animals are Heterotrophs as they are dependent on 9 others for foods Nutrition: Major organs Mouth Chew & break down, saliva secrete to digest Esophagus Muscular tube that carries to stomach Stomach Store tempotarily, digest using enzymes Small Intestine Digestion & absorption of food nutrient into blood stream Large Intestine Remain, Water added, fefes form Liver Decompose & synthesise nutrients, 10  Irritability Sensitivity or Response to Stimuli It's the ability of organism to responds to the stimuli. Any change in the environment is called stimulus and the response of the organism to the stimulus is due to irritability. The movement of plant towards light, contraction & expansion of pupil due to change in the intensity of light , etc. are the examples of sensitivity or irritability 11 Has implication on animal behaviours  Growth  The process of growing or attaining full development i.e attaining maturity.  The term cell growth is used in the contexts of cell development & cell division (reproduction).  When used in the context of cell division, it refers to growth of cell populations,  where a cell, known as the “mother cell”, grows and divides to produce two "daughter cells"  Organisms grow & develop following specifc instructions coded for by their genes.  These genes provide instructions that will direct cellular growth & development, 12  Excretion Waste products of metabolism & other non-useful materials are eliminated from an organism. In vertebrates, this is primarily carried out by the Lungs, Kidneys, liver & Skin. In single celled organisms, waste products are discharged directly through the surface of the cell Wastes from the digestive system (feces) 13  Reproduction  The ability to reproduce & pass genetic information into ofsprings  Single-celled organisms reproduce by frst duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells.  Multicellular organisms often produce specialized reproductive germline cells that will form new individuals.  When reproduction occurs, genes containing DNA are passed along to an organism’s ofspring.  These genes ensure that the ofspring will belong to 14  Sexual reproduction Reproduction resulting from the fusion of male and female gametes is called sexual reproduction. The reproductive organs in the female include ovaries, oviducts and uterus. The reproductive organs in male include testes, sperm ducts and penis. The ovary produces female gametes called ova and the testes produce male gametes called sperms. The fusion of ovum and sperm is called fertilization. The fertilized egg is called a zygote. zygote divides repeatedly to give rise to an embryo. The embryo gets embedded in the wall of the uterus for further development. The stage of the embryo in which all the body parts are identifable is called foetus. 15  Dead No movement No respiration No nutrition No irritability No growth No excretion No reproduction End 16 INTRODUCTORY ANIMAL PHYSIOLOGY DR. ABIONA JOHN 1 MODULE 1: MITOSIS AND MEIOSIS ANP 101 DR. ABIONA JOHN ADESANYA CELL DEATH INTRODUCTORY ANIMAL PHYSIOLOGY DR. ABIONA JOHN 1  Inducers of Apoptosis Physiological activators – TNF family (Fas ligand), transforming growth factor Beta, neurotransmitters (glutamate, dopamine, N-methyl- Dasparatate), growth factor withdrawal, loss of matix attachment, calcium, glucocorticoids Damage-related inducers – heat shock, viral infection, bacterial toxins, oncogenes (myc, rel, E1A), tumor suppressors (p53), cytolytic T cells, oxidants, free-radicals, nutrient deprivation. Therapy-associated agents – Chemotherapeutic drugs (e.g., cispatin, nitrogen mustard), – Antracyclines (doxorubicin), gamma radiation, UV radiation Toxins – Ethanol, Beta-amyloid peptide Anticipate TEAM SYNERGY MODULE 4: CHARACTERISTICS OF LIVING THINGS AND CELLULAR BASIS OF LIFE ANP 101 DR. WILLIAMS T. J ANP101: INTRODUCTORY ANIMAL PHYSIOLOGY (2 UNITS) Course Outline Characteristcs of living things Cellular basis of life: Cell organelles Cell cycle Cell division, Cell growth, Cell death. ANP 101: Introductory Animal Physiology 2 Classifcaton of Animal Kingdom Grades of Organisaton A brief introducton of the various Animal Phyla: Protozoa, Coelenterata Porifera Platyhelminthes Nematoda Annelida Mollusca Arthropoda Echinodermata Chordata ANP 101: Introductory Animal Physiology 3 Characteristics of Living Things Nutriton Respiraton Irritability Movement Excreton Reproducton Growth ANP 101: Introductory Animal Physiology 4  What Is a Cell? Cells - structural and functonal unit of all living organisms Unicellular - single cell, e.g bacteria Multcellular - many cells, e.g animals, humans (up to 100 Trilion cells) Each cell - can take in nutrients, convert these nutrients into energy, carry out specialized functons, and reproduce as necessary. Each cell - stores its own set of instructons for carrying out each of these actvites. ANP 101: Introductory Animal Physiology 5 Prokaryotes and Eukaryotes 2 general categories of cells: Prokaryotes – e.g. Bacteria Unicellular No nuclear membrane Lack cell organelles; plasma membrane performs most of the functons of cell organelles. Consist of 3 parts: Flagella and pili - proteins atached to the cell surface Cell envelope consist of a cell wall, a plasma membrane, and Cytoplasmic region containing the cell genome (DNA), ribosomes, etc. ANP 101: Introductory Animal Physiology 6 Figure 1. Eukaryotes and prokaryotes ANP 101: Introductory Animal Physiology 7  Eukaryotes – Include fungi, animals, plants About 10 X the size of prokaryotes & can be up to 1,000 X greater in volume Has a Nucleus – a membrane-bound compartment which contains the cell’s DNA Have other specialized structures called Organelles: Small structures within cells, performing dedicated functons. ANP 101: Introductory Animal Physiology 8 A EUKARYOTIC CELL ANP 101: Introductory Animal Physiology 9  A EUKARYOTIC CELL – 3 parts 1. The Plasma Membrane (Cell Outer membrane) lining of the cell. Separates and protects the cell from its surrounding environment Made up of a double layer of lipid molecules & protein Embedded proteins act as channels and pumps moving molecules in and out of the cell. ANP 101: Introductory Animal Physiology 10  2. The Cytoplasm Internal, fuid-flled space of the cell Fluid porton of Divided into Cytosol & organelles the cell containing water, All cell organelles reside in the cytosol dissolve solutes It is also home to the cytoskeleton & suspended partcles Contains dissolved nutrients Helps to break down waste products Moves materials around the cell through a process known as cytoplasmic streaming Contains many salts and is an excellent conductor of electricity. ANP 101: Introductory Animal Physiology 11  3.The Nucleus Most conspicuous organelle Contains the cell’s chromosomes Place where almost all DNA replicaton and RNA synthesis occurs Spheroid in shape and separated from the cytosol by the nuclear membrane Nuclear membrane isolates and protects a cell’s DNA from molecules that could accidentally damage its structure or interfere with its processes. DNA is transcribed, forming Messenger RNA (mRNA) mRNA is transported to the cytosol where it is translated into a specifc protein molecule However, DNA processing takes place in the cytoplasm. ANP 101: Introductory Animal Physiology 12  Cell Organelles The Cytoskeleton Complex and dynamic cell component Acts to organize and maintain the cell’s SHAPE Anchors organelles in place Helps during endocytosis – the uptake of external materials by a cell Moves parts of the cell in processes of growth & motlity A great number of proteins are associated with the cytoskeleton, controlling a cell’s structure by directng, bundling and aligning flaments. ANP 101: Introductory Animal Physiology 13  The Ribosome Found in both prokaryotes and eukaryotes Composed of large complex molecules, including RNAs & Proteins Responsible for processing genetc instructons carried by a mRNA Process of convertng the genetc code carried by a mRNA into the correct sequence of amino acids that make up a protein is called TRANSLATION Usually large numbers of ribosomes in a cell as protein synthesis is extremely important for proper functoning of cells Ribosomes foat freely in the cytosol but are sometmes bound to the endoplasmic retculum Ribosomes comprise of one large & one small subunit, each having a diferent functon during protein synthesis ANP 101: Introductory Animal Physiology 14  Mitochondria Self-replicatng organelles found in cytoplasm of all eukaryotc cells Occur in various numbers, shapes and sizes They contain their own genome separate and distnct from the nuclear genome of a cell Have 2 functonally distnct membrane systems separated by a space: Outer membrane which surrounds the whole organelle, & Inner membrane which form folds called CRISTAE Number and shape of cristae in mitochondria vary with tssue and organism in which they are found ANP 101: Introductory Animal Physiology 15 Lysosomes and Peroxisomes Both organelles are spherical, bound by a single membrane and rich in digestve enzymes. Lysosomes contain >36 enzymes for degrading proteins, nucleic acids and polysaccharides. These enzymes are most actve at low pH, reducing the risk of autolysis. This shows the importance of compartmentalizaton in eukaryotc cells. Peroxisomes ofen resemble a lysosome, but: Peroxisomes are self-replicatng while lysosomes are formed in the Golgi complex Peroxisomes also have membrane proteins which are critcal for various functons, such as importng proteins into their interiors and to proliferate and segregate into daughter cells. ANP 101: Introductory Animal Physiology 16 Lysosomes and Peroxisomes, contd. Functons of peroxisome: Rids the body of toxic substances such as hydrogen peroxide or other metabolites Contain enzymes concerned with oxygen utlizaton Present in high numbers in the liver where toxic byproducts are known to accumulate All enzymes found in a peroxisome are imported from the cytosol Each enzyme transferred to a peroxisome has a special sequence at one end of the protein, called peroxisomal targetng signal (PTS) ANP 101: Introductory Animal Physiology 17  Lysosomes and Peroxisomes, contd. Functons of lysosome: Digests foreign bacteria that invade a cell Helps to recycle receptor proteins and other membrane components Degrades worn out organelles such as mitochondria Can help repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. ANP 101: Introductory Animal Physiology 18 Chloroplasts and Mitochondria Chloroplasts are similar to mitochondria but are found only in plants Both are surrounded by a double membrane with an inter- membrane space Both have their own DNA Both are involved in energy metabolism Both have retculatons or foldings flling their inner space Chloroplasts convert light energy from the sun into ATP through photosynthesis ANP 101: Introductory Animal Physiology 19  Endoplasmic reticulum & Golgi apparatus Endoplasmic retculum (ER) – transport network for molecules targeted for certain modifcatons and specifc destnatons within the cytoplasm 2 forms: Rough ER and Smooth ER. Rough ER – has ribosomes adhering to its outer surface Smooth ER – has no adhering ribosomes Translaton of the mRNA for proteins that will either stay in the ER or exported occurs at the ribosomes atached to the RER. The SER serves as the recipient for proteins synthesized in the RER. Proteins for export are passed to the Golgi body for further processing, packaging and transport to other cellular locatons. ANP 101: Introductory Animal Physiology 20 Glycolysis - production of energy from carbohydrates: the breakdown of glucose to pyruvate, with the release of usable energy Play critcal role in generatng energy in eukaryotc cell; process involves complex pathways Glycolysis (1st pathway) requires no oxygen and is referred to as anaerobic metabolism Occurs in the cytoplasm, outside the mitochondria Glucose is broken down into pyruvate; each reacton produces some hydrogen ions which are then used to make ATP 4 molecules of ATP are made from one molecule of glucose in glycolysis In prokaryotes, glycolysis is the only pathway used for convertng energy ANP 101: Introductory Animal Physiology 21 Kreb’s cycle or Citric acid cycle Kreb’s cycle or Citric acid cycle: Occurs inside the mitochondria Capable of generatng enough ATP to run all the cell functons Cycle begins with glucose molecule which is stripped of some of its hydrogen atoms to form two molecules of pyruvic acid Next, pyruvic acid is altered by removal of a carbon and 2 oxygen atoms which form CO 2 When the CO2 is removed, energy is given of and a molecule of NAD+ is converted into the higher energy form, NADH. Another molecule, coenzyme A, then ataches to the remaining acetyl unit to form acetyl CoA Acetyl CoA joins a 4-carbon molecule (oxaloacetate) to form citric acid, a 6-carbon molecule ANP 101: Introductory Animal Physiology 22 Kreb’s cycle or Citric acid cycle, contd. Citric acid is broken down and modifed in a step-wise fashion, a process leading to the release of hydrogen ions and carbon molecules The carbon molecules are used to make more carbon dioxide The hydrogen ions are picked up by NAD and FAD (favin- adenine dinucleotde) Eventually oxalate is again produced and the process starts again. ANP 101: Introductory Animal Physiology 23 Kreb’s cycle is capable of generatng between 24 and 28 THE CELL CYCLE Cell cycle: Sequence of events which occurs between one cell division and the next. It has 3 stages: 1) Interphase period of synthesis and growth Cell produces many materials required for its own growth and for carrying out all its functons DNA replicaton occurs during this stage 2) Mitosis Process by which the cell nucleus divides to produce 2 daughter nuclei containing identcal sets of chromosomes to the parent cell 3) Cell division Process of division of the cytoplasm into 2 daughter cells ANP 101: Introductory Animal Physiology 24  PROPHASE S MITOSI METAPHASE ANAPHASE TELOPHASE G1 + S + G2 = CELLULAR SYNTHESIS G2 CELL DIVISION S M INTERPHAS E G1 THE CELL CYCLE CHART ANP 101: Introductory Animal Physiology 25  Key to the Cell Cycle chart Phase Events within cell G1 Intensive cellular synthesis, including cell organelles. Cell metabolic rate high. Cell growth occurs. Substances produced to inhibit or stmulate onset of next phase as appropriate. S DNA replicaton occurs. Protein molecules called histones are synthesized and cover each DNA strand. Each chromosome becomes two chromatds. At this stage the cell is 4n (4 copies of each DNA molecule, 2 in each homologous chromosome). G2 Intensive cellular synthesis. Mitochondria and chloroplasts divide. Energy stores increase. Mitotc spindle begins to form. M Nuclear division occurs in 4 phases. C Equal distributon of organelles and cytoplasm into each daughter cell. ANP 101: Introductory Animal Physiology 26 MITOSIS Interphase Varies in duraton depending on the functon of the cell DNA of each chromosome replicates just before nuclear division Each chromosome now exists as a pair of chromatds joined together by a centromere The cell is 4n at this stage (4 copies of each DNA molecule, 2 in each chromosome of a homologous pair During this phase chromosome material is in the form of very loosely coiled threads called chromatn Centrioles have replicated. Prophase This is usually the longest phase of division Chromosomes shorten and thicken by coiling and tghter packaging of their components In animal cells the centrioles move to opposite poles of the cell Short microtubules called asters may be seen radiatng from the centrioles The nucleoli disappear as their DNA passes to certain chromosomes. The nuclear envelope breaks ANP up into small 101: Introductory Animalvesicles Physiology which disperse. 27 A spindle is formed. Mitosis contd. Metaphase Chromosomes line up around the equator of the spindle They are atached by their centromeres to the spindle fbres which are microtubules Anaphase Very rapid stage Centromeres split in 2 Spindle fbres pull the daughter centromeres to opposite poles Separated chromatds are pulled along behind the centromeres Telophase Chromatds reach the poles of the cell They uncoil and lengthen to form chromatn again, losing visibility Spindle fbres disintegrate Centrioles replicate A nuclear envelope reforms around the chromosomes at each pole Nucleoli reappear ANP 101: Introductory Animal Physiology 28 Mitosis contd. Cytokinesis Cytokinesis is the division of the cytoplasm Normally follows telophase and leads into the G1 phase of interphase In preparaton for cell division, cell organelles become evenly distributed towards the 2 poles of the telophase cell along with the chromosomes In animal cells the cell surface membrane starts to invaginate towards the region previously occupied by the spindle equator Microtubules probably draw in the cell surface membrane to form a furrow around the outer surface of the cell Cell surface membranes in the furrow eventually join up to completely separate the 2 cells. Signifcance of mitosis Genetc stability Growth Cell replacement Regeneraton Asexual reproducton ANP 101: Introductory Animal Physiology 29 ANP 101: Introductory Animal Physiology 30 ANP 101: Introductory Animal Physiology 31 MEIOSIS Form of nuclear division in which the chromosome number is halved from the diploid number (2n) to the haploid number (n) Like mitosis, it involves DNA replicaton during interphase in the parent cell This is followed by 2 cycles of nuclear divisions and cell divisions known as meiosis I (the 1st meiotc division) and meiosis II (the 2nd meiotc division) Thus a single diploid cell gives rise to 4 haploid cells Meiosis occurs during the formaton of sperm and eggs in animals. ANP 101: Introductory Animal Physiology 32 Meiosis I Prophase I Chromosomes shorten and become visible Homologous chromosomes pair up in a process called synapsis Each pair is called a bivalent One of the pair comes from the male parent and one from the female parent The homologous chromosomes appear to repel each other and partally separate Each chromosome is now seen to be composed of 2 chromatds The 2 chromosomes are seen to be joined at several points along their length, called chiasmata Each chiasma is the site of an exchange between chromatds Genes from one chromosome (e.g. paternal) may swap with genes from the other (maternal) leading to new gene combinatons in the resultng chromatds: This is called crossing over. ANP 101: Introductory Animal Physiology 33 Meiosis I, contd. Metaphase I The bivalents become arranged around the equator of the spindle, atached by their centromeres Anaphase I Spindle fbres pull homologous chromosomes, centromeres frst, towards opposite poles of the spindle Chromosomes are separated into 2 haploid sets, one at each end of the spindle ANP 101: Introductory Animal Physiology 34 Meiosis I, contd. Telophase I Arrival of homologous chromosomes at opposite poles marks the end of meiosis I Halving of chromosome number has occurred but the chromosomes are stll composed of 2 chromatds Spindle fbres usually disappear The chromatds uncoil and a nuclear envelope re-forms at each pole and the nucleus enters interphase Cleavage occurs as in mitosis Interphase II Present only in animal cells Varies in duraton No further DNA replicaton occurs. ANP 101: Introductory Animal Physiology 35 Meiosis II Meiosis II is similar to mitosis Prophase II Stage is absent if interphase II is absent Nucleoli and nuclear envelope disperse Chromatds shorten and thicken Centrioles move to opposite poles of the cells At the end of the phase spindle fbres appear, arranged at right angles to the spindle of meiosis I Metaphase II Chromosomes line up separately around the equator of the spindle Anaphase II Centromeres divide Spindle fbres pull the chromatds to opposite poles, centromeres frst ANP 101: Introductory Animal Physiology 36 Meiosis II, contd. Telophase II 4 haploid daughter cells are formed Chromosomes uncoil, lengthen and become indistnct Spindle fbres disappear Centrioles replicate Nuclear envelopes re-form around each nucleus Each nucleus now contains haploid number of chromosomes Cleavage formaton results in producton of 4 daughter cells. ANP 101: Introductory Animal Physiology 37 ANP 101: Introductory Animal Physiology 38 ANP 101: Introductory Animal Physiology 39 ANP 101: Introductory Animal Physiology 40 ANP 101: Introductory Animal Physiology 41 CELL ADAPTATION, CELL INJURY and CELL DEATH I. DEFINITIONS AND TERMINOLOGY 1) Homeostasis Cells are able to maintain normal structure and functon (e.g. ion balance, pH, energy metabolism) in response to normal physiologic demands. ANP 101: Introductory Animal Physiology 42 CELL ADAPTATION, CELL INJURY and CELL DEATH contd… 2) Cellular Adaptaton As cells encounter stresses, either excessive physiologic demand or some pathologic stmuli, they may make functonal or structural adaptatons to maintain viability / homeostasis. Cells may respond to these stmuli by either increasing or decreasing their content of specifc organelles. Adaptve processes: atrophy, hypertrophy, hyperplasia and metaplasia are forms of adaptaton. ANP 101: Introductory Animal Physiology 43 CELL ADAPTATION, CELL INJURY and CELL DEATH, contd. 3) Cell Injury If the limits of adaptve response are exceeded, or in certain instances when adaptaton is not possible, a sequence of events called cell injury occurs. a) Reversible Cell Injury removal of stress will result in complete structural and functonal integrity to be restored. ANP 101: Introductory Animal Physiology 44 CELL ADAPTATION, CELL INJURY and CELL DEATH, contd. b) Irreversible Cell Injury / Cell Death if stmulus persists (or severe enough from the start) the cell will sufer irreversible cell injury and death. cell death is one of the most crucial events in pathology and can afect any type of cell. two principle morphologic paterns that are indicatve of cell death: Necrosis: type of cell death characterized by severe membrane injury and enzymatc degradaton; always a pathologic process. Apoptosis: regulated form of cell death; can be physiologic or pathologic process. ANP 101: Introductory Animal Physiology 45  ANP 101 Introductory Animal Physiology I Dr. M. O. Abioja 1  Classifcaton of Animal Kingdom Classificaton is identficaton, naming, and grouping of organisms into a formal system are based on similaritis such as intirnal and ixtirnal anatomy, physiological functons, ginitc maki-up, or ivolutonary history There are about 10 to 13 million species on Earth  Taxonomy, a field of science that identfies new organisms and determines how to place them into an existng classificaton scheme Many new types of organisms have evolved while many have gone into ixtncton Scientsts give a new species a scientfic name, typically a two-word name in Latn, to distnguish it from similar organisms The European robin is Erithacus rubecula, while the American robin is Turdus migratorius Features: visibli to thi nakid iyi ditictabli only undir a microscopi ditirminid only by chimical tists ixtirnal shapes and sizis anatomy and functon of organs and systims molicular intiractons  imbryology, ithology, habitat, fossil ricord, hiridity, or ginis play important role in classificaton a spiciis is a group of closily rilatid organisms that are able to interbreed and produce fertle ofspring Similar spiciis are grouped into a broader taxon called a ginus (ginira, plural) Ginira familiis ordirs classis phyla kingdoms domains Scientsts used diferent approach for classificaton PHYLA Phylum Protozoa Phylum Cnidarata/Coilintrata Phylum Porifira Phylum Platyhilminthis Phylum Nimatoda Phylum Annilida Phylum Mollusca Phylum Arthropoda Phylum Echinodirmata Phylum Chordata Phylum Protozoa Protozoa are singli-cillid organisms, some of which may form colonies Placed in the kingdom Protsta with other single-celled organisms with membrane-enclosed nuclei Protozoa have litle or no diferentaton into tssue systems Several phyla are commonly recognized which include: – Flagellated Zoomastgina, many species of which live as parasites in plants and animals; the – Amoeboid Sarcodina, which includes the Foraminifera and Radiolaria both important components of the plankton – Ciliated Ciliophora, many with specialized structures suggestng the mouth and anus of higher organisms – Cnidosporidia, parasites of invertebrates, fish, and a few reptles and amphibians – Sporozoa, many species of which are parasites of animals (including humans)  Mori than 20,000 spiciis ari known  Most species are found in such aquatc habitats as oceans, lakes, rivers, and ponds  They vary in length from 2 to 70 micrometers  Obtain their food by ingestng bacteria, waste products of other organisms, algae, or other protozoa  Amoeba Paramecium  Most species are motle, –Whiplike structures called fagella –Hairlike structures called cilia –Amoeboid moton -pseudopods Dinofagillati Dinofagellates are the 2nd most important group of phytoplankton, responsible for producing energy in the ocean food chain They have a whiplike structure called a fagellum that acts as an organ of locomoton Demonstrate both plant and animal traits Can reproduce rapidly, or bloom Riproducton of protozoans occurs by means of binary fssion or mitosis  Ciliatid Protozoan Propelled by minute, hairlike projectons called cilia Cilia also create currents that help sweep food partcles into a small depression in the body surface through which food is ingested Ciliated protozoans can be found in water or soil and in parasitc or symbiotc relatonships with other organisms In soils, ciliated protozoans functon as decomposing organisms, breaking down organic mater into substances that can be used by other organisms Amoeba is one of the most common protozoans and moves by means of pseudopodia. One of the most agriculturally important species of Protozoans is Babisia This protozoan causes Rid-watir fivir, a disease that afects 100,000 catle a year. Others are Trypanosomi, and Coccidia Phylum Cnidarata Cnidarians, also known as coilintiratis, diverse group of aquatc, invertebrate animals armed with microscopic stnging structures Cnidarians encompasses more than 9,000 species, including corals, hydras, jillyfsh, Portuguese man-of-war, and sea anemones Cnidarians livi in all ocians, and a fiw spiciis inhabit frish watir Although they have various physical characteristcs, all cnidarians exhibit radial symmetry—that is, similar body parts radiate from a central mouth 6-10 tentacles surround a cnidarian’s mouth to aid in the capture and ingeston of the animals they feed on Cnidarians have a saclike body with a single mouth opening The body wall is composed of two sheets of cells—an inner layer (the endoderm) and an outer layer (the ectoderm)  A gelatnous mesoglea layer holds these two cell layers together Cnidarians ari invirtibratis (animals that lack a backboni), but thi ictodirm of somi cnidarians, including hard corals and somi hydrozoans, may form a skiliton-liki structuri ixtirnally The ectoderm of other cnidarians, such as some sof corals, forms an internal skeleton-like structure Thi ictodirm and indodirm layirs contain contractli fbirs that inabli thi animal to movi about Invertebrate zoologists believe these fibers are primitve versions of the muscle cells found in more complex animals Cnidarians lack intirnal organs and thiy do not havi digistvi, circulatory, or rispiratory systims. Sicritons from indodirm cills digist food within thi cintral body cavity and indodirm cills also distributi nutriints and dissolvid oxygin to all parts of thi body. Lacking an anus, cnidarians dischargi wasti matir through thi mouth opining Cnidaria Typis of cnidarians Scientsts divide cnidarians into four classes: Hydrozoa, Scyphozoa, Cubozoa and Anthozoa They base this division partly on whether the polyp or medusa is more conspicuous during an animal’s life cycle Riproducton Reproducton in cnidarians varies among the diferent species Asexual reproducton, sexual reproducton, or both Polyps generally perform asexual reproducton by budding, in which an outgrowth from the body wall separates to form a new polyp or medusa Medusae primarily reproduce sexually—they produce gametes (sex cells), and a gamete (sperm) from a male medusa fuses with a gamete (egg) from a female medusa to form a zygote The zygote develops into a larva, which in turn develops into a polyp or medusa. The medusae of some cnidarians may also form polyps by budding Reproductve life cycle of a typical jellyfish illustrates both asexual and sexual reproducton Males release sperm and females release eggs into the water When an egg and sperm fuse during sexual reproducton, a larva develops that ataches to a rock or other object and develops into a polyp In a type of asexual reproducton, the polyp divides to form a colony of polyps that resembles a stack of saucers Each saucer in the stack develops tentacles and swims away from the colony as a new medusa, and the reproductve cycle repeats A. Exhibit radial symmitry 1. definiton: body parts arranged symmetrically around central axis 2. polyp and medusa forms: a. polyp- sessile, hydrozoans, anemones, and corals have polyps as the predominant body form b. medusa- free-swimming; dispersal stage for many cnidarians c. some cnidarians alternate between an asexual polyp and sexual medusa B. Cills of cnidarians- tssuis livils of organizaton 1. diploblastc: organized into two tssue layers a. epidermis derived from ectoderm b. gastrodermis derived from endoderm c. mesoglea in between (‘jelly-like substance which give jellyfish their common name) 2. cnidocytes-specialized stngy cells which give the phylum its name a. contain harpoon-like structures called nematocysts b. venom which paralyzes prey c. some varietes are toxic to man –Portuguese Man-O-War C. Food procissing 1. tentacles with cnidocytes 2. gastrovascular cavity- incomplete (one opening) 3. digeston by cells—cells engulf food fragments through phagocytosis D. Nirvous systim 1. nerve network in polyps 2. rings of nerve cells in medusas E. Typical lifi Cnidarian cycle 1. characterized by a planula larva stage 2. some alternate between an asexually reproducing polyp and sexually reproducing medusa (true jellyfish) 3. external fertlizaton  Phylum Porifira (spongis) Exclusivily aquatc and, with a fiw ixciptons, a fltir-fiiding group of animals Adult spongis can bi asymmitrical or radially symmitrical (dividid into two idintcal halvis) Thiy comi in a variity of sizis, colours and shapis Thiy includi: – arborisicint (trii-liki) – Flabillati (fan-shapid) – Caliculati (cup shapid) – Tubular (tubi shapid) – Globular (ball shapid) – Amorphous (shapiliss) Habitats: Frishwatir, marini, mangrovis, sia grass icosystims A singli outir layir of cills (pinacodirm) siparatis thi innir cillular rigion (misohyl) from thi ixtirnal invironmint Thi pinacodirm linis thi intirnal canals and is ivintually riplacid by thi choanodirm, a layir of charactiristc fagillatid collar cills (choanocytis) groupid in chambirs Choanocytis maki up thi principli ‘pump’ and’ fltir’, driving watir through thi spongi, trapping, phagocytzing suspindid bactiria and othir partculati food, thin digistid nutriints distributid among thi cills of thi misohyl that facilitati thi functons of fiiding, rispiraton, riproducton  The fow of water inside a sponge is unidirectonal: the water is drawn in through tny pores (osta) in the pinacoderm and exits through one or more larger openings (osculae) The aquiferous system of a sponge is supported by a combinaton of two types of skeletal elements: – Mineral spicules (either calcareous or siliceous) and – Special protein fibers (spongin) – Although either one or both of these elements can be absent Sponges are monophyletc group (common ancestor) Sponge body is unique among animals because it contnuously remolds itself to fine- tune its filter-feeding system Constant rearrangement of the body is accomplished by the amoeboid movements Although ofen considered immobile, Sponges also display several behavioural paterns resultng from coordinated movements of cells, including crawling, producton of filamentous body extensions and body contractons Spongis lack many charactiristcs associatid with othir animals, including a mouth, sinsory organs, organizid tssuis, niurons and muscli cills Thiy ari thi only animals with Skilitons madi of microscopic miniral spikis Thi only onis that fiid by pumping watir through hollow poris Somi of thiir cills ari rimarkably liki frii-living protozoans callid collar fagillatis To ivolutonary biologists, this risimblanci strongly suggists that spongis and othir invirtibratis arosi from protozoan-liki ancistors Phylum Platyhilminthis Means “fat worms” and all the members of this phylum are fat worms! Classified into three classes: Turbellaria (Free living); Trematoda (Parasitc Flukes); Cestoda (Parasitc Tapeworms) A. Exhibit bilatiral symmitry 1. Efcient locomoton 2. Dorsal and ventral surfaces 3. Anterior and posterior ends 4. Cephalizaton-head region with sensory organs: – a. sensory cells at anterior end; – b. ganglia as forerunner of brain B Triploblastc 1. Mesoderm between ectoderm and endoderm 2. Give rise to specialized adult tssues 3. Solid body with no internal body cavity- acoelomate Flatworm (Turbellaria) Liver Fluke (Trematoda) C. Frii-living fatworms-planaria 1. Food processing-incomplete digestve tract 2. Muscular pharynx 3. Sensory system-eyespots ‘ocelli’ 4. Musculature-muscle cells 5. Excretory structure-fame cells 6. Reproductve organs-hermaphroditc D Parasitc fukis and tapiworms 1. Organism which causes schistosomiasis- disease in which the fuke live in the intestnal tract, liver, or bladder causing injury to the organs 2. 1 in 20 people in tropical Africa, Asia, South America and the Middle East are aficted with schistosomiasis 3. Tapeworms- important parasite of livestock and pets All platyhelminths are hirmaphroditis (are both male and female) and can, if required, can fertlize themselves The most important agricultural species of platyhelminths is the Livir Fluki or Fasciola hepatca The life cycle of the liver fuke is very important in finding ways of controlling the disease. The Life cycle is complicated and the fuke must lay huge amounts of eggs to survive The lifecycle takes place in the cow, on grass and in a secondary host (the mud snail) Thi Lificycli of thi Livir Fluki The Liver fuke lives in the ducts of the liver The fuke lays eggs in the bile ducts (20,000 or so a day) The eggs pass in the faeces and hatch two weeks later in water and form a ciliated Miracidium The Miracidium enters the foot of the mud snail and changes into a Sporocyst Stll inside the snail, the Sporocyst changes into a Ridia The Redia then produce very small tadpole shaped Circaria For every Miracidium that enters the snail, 10,000 Cercaria can be produced The Cercaria then leaves the snail and goes onto grass There it becomes encysted (forms a shell) and waits to be eaten by a sheep or cow If eaten, the stomach acids dissolve the cyst and the liver fuke moves to the liver and restarts the cycle Understanding the lifecycle of the liver fuke allows us control the spread in the following ways: – Dosing any animals to kill the adult fuke – Spraying molluscicides to kill the snail – Draining land (the snail only lives in water) Fencing fooded areas Don’t graze wet lands afer August Phylum Nimatoda AKA roundworms or eelworms Reproduce by laying thousands of eggs, which become encysted in the grass and wait to be ingested. The most important species are: Lungworms (causes hoose) Hairworms (worms in school children) Potato eelworm Stomach worms Largest group of invertebrates in terms of sheer number Unsegmented roundworms Charactiristcs: 1. triploblastc 2. first group to have a complete digestve tract 3. pseudo-coelomates- fuid-filled cavity located between mesoderm and endoderm: – a. increases the efectveness of muscles – b. functons as a hydrostatc skeleton 4. dioecous Important parasitis of man, livistock, pits and iconomically important crop plants 1. Trichinella- contracted from eatng poorly cooked pork 2. Heart worms in dogs 3. Elephantasis 4. Thick cutcle which prevents digestve enzymes of the host organism from damaging the round worm Phylum Annilida Sigmintid worms , including earthworm – Lumbricus terrestris and leeches On each segment, earthworms have four bristles or Chaitai, which they use to move Important to the farmer: – they improve the soil in the following ways: – they eat their way through the soil and mix the ingested material with mucus in their guts, improving soil crumb structure – Depositng soil in diferent places and mixing horizons. Improve drainage of heavy clay soils – Introduces more air into the soil – When they die they further increase the amount of organic mater ABody dividid into sigmints 1. Segments are advantagous– allow for specialized movement 2. Internal structures—nerves, nephridia, blood vessels, and reproductve organs are repeated in several segments– damage to one segment is less harmful to the functoning of a segmented organism B Evolutonary link with mollusks 1. Trochophore larva 2. Coelomate 3. Triploblastc 4. Protostome development  C. Charactiristcs 1. segmented muscles and coelomic compartments: a. Longitudinal and circular musclis b. Bristli (sitai) assist in burrowing 2. Complete digestve tract and closed circulatory system 3. Paired nephridia in each segment for excretory system 4. Chainlike nervous system 5. Hermaphroditc 6. Dorsal blood vessel and ventral nerve cord D. Liichis: Substances in the salivary gland which is an antcoagulant– hirudin (first commercially available blood thinner); stll used in the treatment of burns and the reatachment of body parts Phylum Mollusca The molluscs include slugs, snails, squid, mussels, clams and octopus These animals generally have a foot, which excretes a slimy mucus. They also have a rasping tongue. The most agriculturally important mollusc is the mud snail (Lymnaea truncatula) Archachatna marginata Giniralizid Anatomy of a Mollusk Around 50,000 spp, ranging from < 1 cm to 18m Most mollusks have the same basic body structure Have a glandular body covering, called the mantle In some mollusks, such as clams and snails, the mantle secretes a hard shell. Most mollusks have a large muscular organ, called the foot-for burrowing or for moton. Feed by means of the radula, a fexible organ that bears many sharp teeth Mollusks use gills to absorb nutrients from water and release waste products from cells They make up the 2nd largest group of invertebrates Include snails, clams, octopuses, and squid, as well as some lesser-known animals, such as chitons and monoplacophorans Bivalves- sedentary, Squids are jet-propelled predators -swifest swimmers in the invertebrate world Most sedentary mollusks are filter- feeders, Other, (snails and other gastropods), scrape up their food using a radula—a ribbon-like mouthpart that is unique to mollusks and covered with rows of microscopic teeth Major Groups of Mollusks The mollusks represent a diverse group of marine, freshwater, and terrestrial invertebrates, including such varied forms as snails, chitons, limpets, clams, mussels, oysters, octopuses, squid, cutlefish, tusk shells, slugs, nudibranchs, and several highly modified deep-sea forms They all have one anatomical feature in common, the presence of a shell at some stage in the life cycle. Although most mollusks have a shell as adults, the octopus, squid, and deep-sea forms do not. They do however have a small, shell-like structure, called a shell gland, present for a short tme during embryonic development. A. Shills 1. one piece shells: snail 2. two piece shell: clams 3. eight piece shells: chitons B. Mantli forms a mantli cavity which may housi: 1. gills 2. lungs 3. reproductve systems C. Muscular ‘foot’ 1. fat sole (snails) 2. compressed (clams) 3. arms or tentacles (squid) Typis of mollusks 1. Gastropod 2. Bivalve 3. Cephalapode  Classis of mollusks 1. Gastropoda- coiled shell; including snails and slugs 2. Peleypoda (bivalves)- hinged shells: clams and oysters 3. Cephalopoda- head with tentacles: squid, octopus Kingdom: animalia; Phylum : mollusca; Class: gastropoda; Order: pulmonata; Family: achatnidae; Genera: achatna and achachatna; Species: achatna fulica, achatna achatna, achachatna marginata Phylum Arthropoda This is the largest phylum containing nearly a million species. Therefore it is necessary to sub classify the phylum into classes All Arthropods have jointed legs and an exoskeleton (outer skeleton) Members of the phylum include scorpions, insects, spiders, shellfish (crustaceans), woodlice, centpedes and millipedes. The most important classes of Arthropods are the spiders and insects. Arthropods live in every habitat on Earth from mountaintops to hydrothermal vents, springs of hot water located on the deep ocean foor. Surrounded by protectve exoskeletons, arthropods have tubular legs that bend at fexible joints. This unique characteristc sets them apart from all other invertebrates, and it enables them to hop, walk, and run. Insicts dominati thi arthropod phylum. Making up 90% of all arthropods, insects have a strong claim to be the most successful animals in the world On land, they live in almost every habitat, aided by their small size and, for many, their ability to fy They also live in fresh water, but remarkably, they have failed to colonize the sea. Some zoologists believe this is because crustaceans have already exploited this habitat to its fullest a. Marine, fresh water, and terrestrial b. Segmentaton: segmented bodies c. External skeleton: exoskeleton d. Ventral nerve cord e. Open circulatory system: gills, tracheae (insect) A lot of the members of phylum Arthropoda are Parasitis Main groups 1. Class Crustacia (lobster, crayfish, shrimp, and barnacles) 2 pair of antennae Respire by gills Lobster: Their claws are modified legs, and they really taste good, cooked properly, especially in New Orleans, Preying Mants. The female, who is bigger, bites of the head of the male, and then copulates with the headless male. Then the female eats the male’s body. Thus, reproducing and finding its food at the same tme 2. Class Arachnida (spiders, horseshoe crabs, mites, and tcks) No antennae Reduced segmentaton 4 pair of legs No jaws Poison gland- a. immobilize their prey, b. Digest contents of their prey in the sucking stomach c. They are scary to some; who might consider themselves arachnophobics The spider has two main body segments, the cephalothorax and the abdomen. Some of the diseases spiders cause on the farm are mange (scabies) and fea (mites). Ticks are blood sucking spiders that can atack sheep and spread disease (red water fever) 3. Class Insicta (aphids, lice, feas, crane-fies and buterfies) There are more organisms in this class than any other Have a head, thorax, and abdomen 1 pair of antennae Usually 2 pairs of wings 3 pairs of legs The life cycle of all insects follows this path: Egg Larvai Pupa Adult  Mitamorphosis This is the process where an organism starts as a small larvae and develops into adult. The larvae collects organic material and then molts into a pupa stage. Afer a certain tme the pupa molts to form the mature larger adult. Fleas: Wingless, go through complete metamorphosis and can carry disease  http://www.unaab.edu.ng COURSE CODE: ANP 101 COURSE TITLE: Introductory Animal Physiology NUMBER OF UNITS: 2 Units COURSE DURATION: Two hours per week OUR COURSE DETAILS: Course Coordinator: Dr. J.O. Daramola, B.Ed., M.Sc., PhD Email: [email protected] Office Location: ANP Staff Office, COLANIM Other Lecturer: Professor O.A. Osinowo, Dr. I. J. James, Dr. T. J. Williams COURSE CONTENT: Characteristics of living things; Cellular basis of life: Cell organelles; Cell cycle, Cell division, Cell growth, Cell death; Classification of Animal Kingdom, Grades of Organisation, A brief introduction of the various Animal Phyla: Protozoa, Coelenterata, Porifera, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata. COURSE REQUIREMENTS: This is a compulsory course for all B. Agriculture students in the University of Agriculture, Abeokuta, Nigeria. Students are expected to participate in all the course activities and have a minimum of 75% of attendance to be able to write final examination. READING LIST: 1. http://www.cliffsnotes.com/study_guide/Characteristics-of-Living- Things.topicArticleId-8741,articleId-8578.html 2. http://hyperphysics.phy-astr.gsu.edu/hbase/biology/life.html 3. http://lisacruz2.tripod.com/id30.html 4. http://www.saburchill.com/chapters/chap0001.html 5. Wikipedia 6. Encyclopædia Britannica 2010. 1  http://www.unaab.edu.ng 7. Microsoft ® Encarta ® 2009. LECTURE NOTE: Characteristics of living things Living things have a level of complexity and organization not found in lifeless objects. At its most fundamental level, a living thing is composed of one or more cells. These units, generally too small to be seen with the unaided eye, are organized into tissues. A tissue is a series of cells that accomplish a shared function. Tissues, in turn, form organs, such as the stomach and kidney. A number of organs working together compose an organ system. An organism is a complex series of various organ systems. A living organism must possess all the following characteristics: Organization Living things are highly organized. The smallest part of an organism is a cell. Some single- celled organisms are free-living and contain structures, called organelles, that allow them to be self-sufficient. More complex organisms are multicellular. In the case of a human, cells are organized into tissues. These have a common function like a muscle. Tissues are organized into organs like the heart. Organs are organized into organ systems, like the cardiovascular system. Organ systems functioning together make up a living organism. A population is an organization of more than one individual. This is generally all of one species in a particular area. We could talk about the population of squirrels in our area or dogs or cats. Enlarging our view next comes a community. An example of a community is the town or place we live. A more accurate biological description would include all the living things in that area. A community is composed of many species, including plants and animals An ecosystem not only considers the living things in an area, but also the physical environment and the interrelated flow of energy. You may live in a desert ecosystem, a forest ecosystem, or another kind of ecosystem. Most complex of all is the biosphere. In our case, this includes the all the areas of our planet where living things are found. Metabolism Most of us call this eating! Living things exhibit a rapid turnover of chemical materials, able to convert our food, a form of energy, to chemicals our cells can use through a process which is referred to as metabolism. It is the transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life. Metabolism involves exchanges of chemical matter with the external environment and extensive transformations of organic matter within the cells of a living organism. Some organisms like plants, algae, and some microorganisms are 2  http://www.unaab.edu.ng autotrophs. The autotrophs we are most familiar with are the green plants that use photosynthesis to make their own "food." Some bacteria use chemosynthesis for their energy source. Animals and fungi are heterotrophs and capture their food in a variety of ways. The ability to acquire and use energy is extremely important. Without a constant input of usable energy, organisms would quickly become "disorganized" and die. In order to survive, organisms must be able to achieve homeostasis. Each type of organism has a specialized way to stay in balance with its outside and inside environments. A paramecium has a contractile vacuole that pumps excess water out of its cell in order to survive in a fresh water environment. You and I have an internal "thermostat" that helps us maintain a body temperature of about 98.6 degrees Fahrenheit (37 oC) Nonliving things do not display metabolism. Responsiveness All living things are able to respond to stimuli in the external environment. This often results in movement of the individual toward safety. This helps to ensure survival of the organism. For example, living things respond to changes in light, heat, sound, and chemical and mechanical contact. To detect stimuli, organisms have means for receiving information, such as eyes, ears, and taste buds. As young children, for example, we learned to avoid hot stoves and busy streets To respond effectively to changes in the environment, an organism must coordinate its responses. A system of nerves and a number of chemical regulators called hormones coordinate activities within an organism. The organism responds to the stimuli by means of a number of effectors, such as muscles and glands. Energy is generally used in the process. Organisms change their behaviour in response to changes in the surrounding environment. For example, an organism may move in response to its environment. Responses such as this occur in definite patterns and make up the behaviour of an organism. The behaviour is active, not passive; an animal responding to a stimulus is different from a stone rolling down a hill. Plants also have some limited ability to move. They grow up toward the sun, and some have leaves able to turn to follow the sun (phototropism), allowing them to photosynthesize better. Their roots grow down to search for water and minerals. If a plant doesn't get enough sunlight, water or minerals it will die. Living things display responsiveness; nonliving things do not. Growth Growth requires an organism to take in material from the environment and organize the material into its own structures. It is the maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter. To accomplish growth, an organism expends some of the energy it acquires during metabolism. An organism has a pattern for accomplishing the building of growth structures. During this period organisms also undergo a cycle of changes called development. 3  http://www.unaab.edu.ng During growth, a living organism transforms material that is unlike itself into materials that are like it. A person, for example, digests a meal of meat and vegetables and transforms the chemical material into more of himself or herself. A nonliving organism does not display this characteristic. Reproduction A living thing has the ability to produce copies of itself by the process known as reproduction. These copies are made while the organism is still living. Among plants and simple animals, reproduction is often an extension of the growth process. For example, bacteria grow and quickly reach maturity, after which they split into two organisms by the process of asexual reproduction. Asexual reproduction involves only one parent, and the resulting cells are generally identical to the parent cell. All living things, even the smallest bacteria, have a chromosome containing DNA. Prokaryotes like bacteria only have one circular chromosome, called a plasmid. Eukaryotes, multicellular organisms like plants and humans, have a species-specific number of chromosomes. As humans, we have 46 chromosomes, in 23 pairs. Genes on chromosomes contain the instructions for the organism's structure and function. However, most organisms reproduce sexually. Some, like earthworms and snails are hermaphrodites. Most others have separate sexes, male and female, like marijuana plants, fish, birds, cattle and humans. In order for two organisms to combine their genetic information without doubling the number of chromosomes given to offspring, Mother Nature came up with a way to reduce the number of chromosomes. Without it, each new generation would have double the number of its parents' chromosomes. This halving is done by meiosis in the sex organs. In the female, the ovary produces haploid eggs and in the male the testes produces haploid sperm. Each of these gametes contains only one chromosome from each of the pairs of chromosomes. During fertilization, the sperm and egg unite to form a zygote, a diploid individual. This new individual is different from either parent, although it contains characteristics from both. This is what gives us the great diversity of life. In living things, we call this genetic biodiversity Nonliving things have no such ability or requirements. Adaptation Modifications enable an organism to survive in its environment. Natural selection allows individuals with better adaptations to survive better and reproduce more. Thus, their characteristics are passed into future generations and that makes the species stronger. However, it is important to note that individuals can only adapt to their environment, and species don’t adapt, they evolve. During evolution, changes occur in populations, and the organisms in the population become better able to metabolize, respond, and reproduce. They develop abilities to cope with their environment that their ancestors did not have. 4  http://www.unaab.edu.ng Evolution also results in a greater variety of organisms than existed in previous eras. This proliferation of populations of organisms is unique to living things. Death Death is the permanent termination of all vital functions or life processes in an organism or cell. Death involves a complete change in the status of a living entity—the loss of its essential characteristics. After death, the remains of an organism become part of the biogeochemical cycle. Organisms may be consumed by a predator or a scavenger and leftover organic material may then be further decomposed by detritivores, organisms which recycle detritus, returning it to the environment for reuse in the food chain. Definition of Biology Biology is the science that is focussed on the study of living things. The major branches of biology are:  Anatomy, which deals with gross structure  Physiology, which is the study of gross function or how the organism works  Histology, the study of tissues  Cell biology, the study of cells  Microbiology, concerned with the study of fungi (mycology), bacteria (bacteriology) and viruses (virology)  Biochemistry and Molecular Biology, study of living systems at the molecular level  Genetics, study of inheritance  Zoology, study of animals  Botany, study of plants Definition of Physiology  Characteristics of Living Things o Nutrition o Respiration o Irritability o Movement o Excretion o Reproduction o Growth  Cellular Basis of Life o Cell Organelles o Cell Division o Cell Growth o Cell Death 5  http://www.unaab.edu.ng  Physiological Systems in Mammals o Respiratory System o Digestive System o Reproductive System o Excretory System o Nervous System o Endocrine System  Concepts of Homeostasis What Is a Cell? Cells are the structural and functional unit of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, or have many cells—an estimated 100,000,000,000,000 cells! Each cell is an amazing world unto itself: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Even more amazing is that each cell stores its own set of instructions for carrying out each of these activities. Cell Organization Before we can discuss the various components of a cell, it is important to know what organism the cell comes from. There are two general categories of cells: prokaryotes and eukaryotes. 6  http://www.unaab.edu.ng Prokaryotic Organisms It appears that life arose on earth about 4 billion years ago. The simplest of cells, and the first types of cells to evolve, were prokaryotic cells—organisms that lack a nuclear membrane, the membrane that surrounds the nucleus of a cell. Bacteria are the best known and most studied form of prokaryotic organisms, although the recent discovery of a second group of prokaryotes, called archaea, has provided evidence of a third cellular domain of life and new insights into the origin of life itself. Prokaryotes are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of our bodies. Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most of the functions of organelles, such as mitochondria, chloroplasts and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. 7  http://www.unaab.edu.ng Eukaryotic Organisms Eukaryotes include fungi, animals, and plants as well as some unicellular organisms. Eukaryotic cells are about 10 times the size of a prokaryote and can be as much as 1000 times greater in volume. The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bounded compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, a membrane-delineated compartment that houses the eukaryotic cell’s DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name. Eukaryotic organisms also have other specialized structures, called organelles, which are small structures within cells that perform dedicated functions. As the name implies, you can think of organelles as small organs. There are a dozen different types of organelles commonly found in eukaryotic cells. In this primer, we will focus our attentions on only a handful of organelles and will examine these organelles with an eye to their role at a molecular level in the cell. The origin of the eukaryotic cell was a milestone in the evolution of life. Although eukaryotes use the same genetic code and metabolic processes as prokaryotes, their higher level of organizational complexity has permitted the development of truly multicellular organisms. Without eukaryotes, the world would lack mammals, birds, fish, invertebrates, mushrooms, plants, and complex single-celled organisms. This figure illustrates a typical human cell (eukaryote) and a typical bacterium (prokaryote). The drawing on the left highlights the internal structures of eukaryotic cells, including the nucleus (light blue), the nucleolus (intermediate blue), mitochondria (orange), and ribosomes (dark blue). The drawing on the right demonstrates how bacterial DNA is housed in a structure called the nucleoid (very light blue), as well as other structures normally found in a prokaryotic cell, including the cell membrane (black), the cell wall (intermediate blue), the capsule (orange), ribosomes (dark blue), and a flagellum (also black). Cell Structures: The Basics The Plasma Membrane—A Cell's Protective Coat The outer lining of a eukaryotic cell is called the plasma membrane. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of proteins and lipids, fat-like molecules. Embedded within this membrane are a variety of other molecules that act as channels and pumps, moving different molecules into and out of the cell. A form of plasma membrane is also found in prokaryotes, but in this organism it is usually referred to as the cell membrane. 8  http://www.unaab.edu.ng The Cytoskeleton—A Cell's Scaffold acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell; and moves parts of the cell in processes of growth and motility. There are a great number of proteins associated with the cytoskeleton, each controlling a cell’s structure by directing, bundling, and aligning filaments. The Cytoplasm—A Cell's Inner Space Inside the cell there is a large fluid-filled space called the cytoplasm, sometimes called the cytosol. In prokaryotes, this space is relatively free of compartments. In eukaryotes, the cytosol is the "soup" within which all of the cell's organelles reside. It is also the home of the cytoskeleton. The cytosol contains dissolved nutrients, helps break down waste products, and moves material around the cell through a process called cytoplasmic streaming. The nucleus often flows with the cytoplasm changing its shape as it moves. The cytoplasm also contains many salts and is an excellent conductor of electricity, creating the perfect environment for the mechanics of the cell. The function of the cytoplasm, and the organelles which reside in it, are critical for a cell's survival. Genetic Material Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms are made of DNA, but a few viruses have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence. Prokaryotic genetic material is organized in a simple Interestingly, as circular structure that rests in the cytoplasm. Eukaryotic much as 98 percent genetic material is more complex and is divided into of human DNA does discrete units called genes. Human genetic material is made up of two distinct components: the nuclear genome not code for a and the mitochondrial genome. The nuclear genome is specific product. divided into 24 linear DNA molecules, each contained in a different chromosome. The mitochondrial genome is a circular DNA molecule separate from the nuclear DNA. Although the mitochondrial genome is very small, it codes for some very important proteins. 9  http://www.unaab.edu.ng Organelles The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs", called organelles, that are adapted and/or specialized for carrying out one or more vital functions. Organelles are found only in eukaryotes and are always surrounded by a protective membrane. It is important to know some basic facts about the following organelles. The Nucleus—A Cell's Center The nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes and is the place where almost all DNA replication and RNA synthesis occurs. The nucleus is spheroid in shape and separated from the cytoplasm by a membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or synthesized, into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. In prokaryotes, DNA processing takes place in the cytoplasm. 10  http://www.unaab.edu.ng The Ribosome—The Protein Production Machine Ribosomes are found in both prokaryotes and eukaryotes. The ribosome is a large complex composed of many molecules, including RNAs and proteins, and is responsible for processing the genetic instructions carried by a mRNA. The process of converting a mRNA's genetic code into the exact sequence of amino acids that make up a protein is called translation. Protein synthesis is extremely important to all cells, and therefore a large number of ribosomes—sometimes hundreds or even thousands—can be found throughout a cell. Ribosomes float freely in the cytoplasm or sometimes bind to another organelle called the endoplasmic reticulum. Ribosomes are composed of one large and one small subunit, each having a different function during protein synthesis. Mitochondria and Chloroplasts—The Power Generators Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. As mentioned earlier, mitochondria contain their own genome that is separate and distinct from the nuclear genome of a cell. Mitochondria have two functionally distinct membrane systems separated by a space: the outer membrane, which surrounds the whole organelle; and the inner membrane, which is thrown into folds or shelves that project inward. These inward folds are called cristae. The number and shape of cristae in mitochondria differ depending on the tissue and organism in which they are found, and serve to increase the surface area of the membrane. Mitochondria play a critical role in generating energy in the eukaryotic cell, and this process involves a number of complex pathways. Let's break down each of these steps so that you can better understand how food and nutrients are turned into energy packets and water. Some of the best energy-supplying foods that we eat contain complex sugars. These complex sugars can be broken down into a less chemically complex sugar molecule called glucose. Glucose can then enter the cell through special molecules found in the membrane, called glucose transporters. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, via two different pathways. The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Glycolysis occurs in the cytoplasm outside the mitochondria. During glycolysis, glucose is broken down into a molecule called pyruvate. Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets (ATP). However, only four ATP molecules can be made from one molecule of glucose in this pathway. In prokaryotes, glycolysis is the only method used for converting energy. The second pathway, called the Kreb's cycle, or the citric acid cycle, occurs inside the mitochondria and is capable of generating enough ATP to run all the cell functions. Once again, the cycle begins with a glucose molecule, which during the process of glycolysis, is stripped of some of its' hydrogen atoms, transforming the glucose into two molecules of pyruvic acid. Next, pyruvic acid is altered by the removal of a 11  http://www.unaab.edu.ng carbon and two oxygen, which go on to form carbon dioxide. When the carbon dioxide is removed, energy is given off, and a molecule called NAD+ is converted into the higher energy form NADH. Another molecule, coenzyme A, then attaches to the remaining acetyl unit, forming acetyl CoA. Acetyl CoA enters the Kreb's cycle by joining to a four-carbon molecule called oxaloacetate. Once the two molecules are joined, they make a six-carbon molecule called citric acid. Citric acid is then broken down and modified in a stepwise fashion. As this happens, hydrogen ions and carbon molecules are released. The carbon molecules are used to make more carbon dioxide. The hydrogen ions are picked up by NAD and another molecule called flavin-adenine dinucleotide (FAD). Eventually, the process produces the four-carbon oxaloacetate again, ending up where it started off. All in all, the Kreb's cycle is capable of generating between 24 and 28 ATP molecules from one molecule of glucose converted to pyruvate. Therefore, it is easy to see how much more energy we can get from a molecule of glucose if our mitochondria are working properly and if we have oxygen. Chloroplasts are similar to mitochondria but are found only in plants. Both organelles are surrounded by a double membrane with an intermembrane space; both have their own DNA and are involved in energy metabolism; and both have reticulations, or many foldings, filling their inner spaces. Chloroplasts convert light energy from the sun into ATP through a process called photosynthesis. The Endoplasmic Reticulum and the Golgi Apparatus—Macromolecule Managers The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and The Golgi apparatus specific destinations, as compared to molecules that will was first described in float freely in the cytoplasm. The ER has two forms: the 1898 by an Italian rough ER and the smooth ER. The rough ER is labelled anatomist named as such because it has ribosomes adhering to its outer surface, whereas the smooth ER does not. Translation of Camillo Golgi. the mRNA for those proteins that will either stay in the ER or be exported (moved out of the cell) occurs at the ribosomes attached to the rough ER. The smooth ER serves as the recipient for those proteins synthesized in the rough ER. Proteins to be exported are passed to the Golgi apparatus, sometimes called a Golgi body or Golgi complex, for further processing, packaging, and transport to a variety of other cellular locations. 12  http://www.unaab.edu.ng Lysosomes and Peroxisomes—The Cellular Digestive System Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally occurring proteins that speed up biochemical processes. For example, lysosomes can contain more than three dozen enzymes for degrading proteins, nucleic acids, and certain sugars called polysaccharides. All of these enzymes work best at a low pH, reducing the risk that these enzymes will digest their own cell should they somehow escape from the lysosome. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system. What Is pH? The term pH derives from a combination of "p" for the word power and "H" for the symbol of the element hydrogen. pH is the negative log of the activity of hydrogen ions and represents the "activity" of hydrogen ions in a solution at a given temperature. The term activity is used because pH reflects the amount of available hydrogen ions, not the concentration of hydrogen ions. The pH scale for aqueous solutions ranges from 0 to 14 pH units, with pH 7 being neutral. A pH of less than 7 means that the solution is acidic, whereas a pH of more than 7 means that the solution is basic. One function of a lysosome is to digest foreign bacteria that invade a cell. Other functions include helping to recycle receptor proteins and other membrane components and degrading worn out organelles such as mitochondria. Lysosomes can even help repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. Peroxisomes function to rid the body of toxic substances, such as hydrogen peroxide, or other metabolites and contain enzymes concerned with oxygen utilization. High numbers of peroxisomes can be found in the liver, where toxic byproducts are known to accumulate. All of the enzymes found in a peroxisome are imported from the cytosol. Each enzyme transferred to a peroxisome has a special sequence at one end of the protein, called a PTS or peroxisomal targeting signal, that allows the protein to be taken into that organelle, where they then function to rid the cell of toxic substances. Peroxisomes often resemble a lysosome. However, peroxisomes are self replicating, whereas lysosomes are formed in the Golgi complex. Peroxisomes also have membrane proteins that are critical for various functions, such as for importing proteins into their interiors and to proliferate and segregate into daughter cells. 13  http://www.unaab.edu.ng Where Do Viruses Fit? Viruses are not classified as cells and therefore are neither unicellular nor multicellular organisms. Most people do not even classify viruses as "living" because they lack a metabolic system and are dependent on the host cells that they infect to reproduce. Viruses have genomes that consist of either DNA or RNA, and there are examples of viruses that are either double-stranded or single-stranded. Importantly, their genomes code not only for the proteins needed to package its genetic material but for those proteins needed by the virus to reproduce during its infective cycle. Making New Cells and Cell Types For most unicellular organisms, reproduction is a simple matter of cell duplication, also known as replication. But for multicellular organisms, cell replication and reproduction are two separate processes. Multicellular organisms replace damaged or worn out cells through a replication process called mitosis, the division of a eukaryotic cell nucleus to produce two identical daughter nuclei. To reproduce, eukaryotes must first create special cells called gametes—eggs and sperm—that then fuse to form the beginning of a new organism. Gametes are but one of the many unique cell types that multicellular organisms require to function as a complete organism. Making New Cells Most unicellular organisms create their next generation by replicating all of their parts and then splitting into two cells - a type of asexual reproduction called binary fission. This process spawns not just two new cells, but also two new organisms. Multicellullar organisms replicate new cells in much the same way. For example, we produce new skin cells and liver cells by replicating the DNA found in that cell through mitosis. Yet, producing a whole new organism requires sexual reproduction, at least for most multicellular organisms. In the first step, specialized cells called gametes-- eggs and sperm--are created through a process called meiosis. Meiosis serves to reduce the chromosome number for that particular organism by half. In the second step, the sperm and egg join to make a single cell, which restores the chromosome number. This joined cell then divides and differentiates into different cell types that eventually form an entire functioning organism. Mitosis is the process by which the diploid nucleus (having two sets of homologous chromosomes) of a somatic cell divides to produce two daughter nuclei, both of which are still diploid. The left-hand side of the drawing demonstrates how the parent cell duplicates its chromosomes (one red and one blue), providing the daughter cells with a complete copy of genetic information. Next, the chromosomes align at the equatorial plate, and the centromeres divide. The sister chromatids then separate, becoming two diploid daughter cells, each with one red and one blue chromosome. 14  http://www.unaab.edu.ng Mitosis Every time a cell divides, it must ensure that its DNA is shared between the two daughter cells. Mitosis is the process of "divvying up" the genome between the daughter cells. To easier describe this process, let's imagine a cell with only one chromosome. Before a cell enters mitosis, we say the cell is in interphase, the state of a eukaryotic cell when not undergoing division. Every time a cell divides, it must first replicate all of its DNA. Because chromosomes are simply DNA wrapped around protein, the cell replicates its chromosomes also. These two chromosomes, positioned side by side, are called sister chromatids and are identical copies of one another. Before this cell can divide, it must separate these sister chromatids from one another. To do this, the chromosomes have to condense. This stage of mitosis is called prophase. Next, the nuclear envelope breaks down and a large protein network, called the spindle, attaches to each sister chromatid. The chromosomes are now aligned perpendicular to the spindle in a process called metaphase. Next, molecular motors pull the chromosomes away from the metaphase plate to the spindle poles of the cell. This is called anaphase. Once this process is completed, the cells divide, the nuclear envelope reforms, and the chromosomes relax and decondense during telophase. The cell can now replicate its DNA again during interphase and go through mitosis once more. Cell Cycle Control and Cancer As cells cycle through interphase and mitosis, a surveillance system monitors the cell for DNA damage and failure to perform critical processes. If this system senses a problem, a network of signalling molecules instructs the cell to stop dividing. These so called "checkpoints" let the cell know whether to repair the damage or initiate programmed cell death, a process called apoptosis. Programmed cell death ensures that the damaged cell is not further propagated. Scientists know that a certain protein, called p53, acts to accept signals provoked by DNA damage. It responds by stimulating the production of inhibitory proteins that then halt the DNA replication process. Without proper p53 function, DNA damage can accumulate unchecked. A direct consequence is that the damaged gene progresses into a cancerous state. Today, defects in p53 are associated with a variety of cancers, including some breast and colon cancers. Meiosis, a type of nuclear division, occurs only in reproductive cells and results in a diploid cell (having two sets of chromosomes) giving rise to four haploid cells (having a single set of chromosomes). Each haploid cell can subsequently fuse with a gamete of the opposite sex during sexual reproduction. In this illustration, two pairs of homologous chromosomes enter Meiosis I, which results initially in two daughter nuclei, each with two copies of each chromosome. These two cells then enter Meiosis II, producing four daughter nuclei, each with a single copy of each chromosome. 15  http://www.unaab.edu.ng Meiosis Meiosis is a specialized type of cell division that occurs during the formation of gametes. Although meiosis may seem much more complicated than mitosis, it is really just two cell divisions in sequence. Each of these sequences maintains strong similarities to mitosis. Meiosis I refers to the first of the two divisions and is often called the reduction division. This is because it is here that the chromosome complement is reduced from diploid (two copies) to haploid (one copy). Interphase in meiosis is identical to interphase in mitosis. At this stage, there is no way to determine what type of division the cell will undergo when it divides. Meiotic division will only occur in cells associated with male or female sex organs. Prophase I is virtually identical to prophase in mitosis, involving the appearance of the chromosomes, the development of the spindle apparatus, and the breakdown of the nuclear membrane. Metaphase I is where the critical difference occurs between meiosis and mitosis. In mitosis, all of the chromosomes line up on the metaphase plate in no particular order. In Metaphase I, the chromosome pairs are aligned on either side of the metaphase plate. It is during this alignment that the chromatid arms may overlap and temporarily fuse, resulting in what is called crossovers. During Anaphase I, the spindle fibers contract, pulling the homologous pairs away from each other and toward each pole of the cell. In Telophase I, a cleavage furrow typically forms, followed by cytokinesis, the changes that occur in the cytoplasm of a cell during nuclear division; but the nuclear membrane is usually not reformed, and the chromosomes do not disappear. At the end of Telophase I, each daughter cell has a single set of chromosomes, half the total number in the original cell, that is, while the original cell was diploid; the daughter cells are now haploid. Meiosis II is quite simply a mitotic division of each of the haploid cells produced in Meiosis I. There is no Interphase between Meiosis I and Meiosis II, and the latter begins, with Prophase II. At this stage, a new set of spindle fibers forms and the chromosomes begin to move toward the equator of the cell. During Metaphase II, all of the chromosomes in the two cells align with the metaphase plate. In Anaphase II, the centromeres split, and the spindle fibers shorten, drawing the chromosomes toward each pole of the cell. In Telophase II, a cleavage furrow develops, followed by cytokinesis and the formation of the nuclear membrane. The chromosomes begin to fade and are replaced by the granular chromatin, a characteristic of interphase. When Meiosis II is complete, there will be a total of four daughter cells, each with half the total number of chromosomes as the original cell. In the case of male structures, all four cells will eventually develop into sperm cells. In the case of the female life cycles in higher organisms, three of the cells will typically abort, leaving a single cell to develop into an egg cell, which is much larger than a sperm cell. 16  http://www.unaab.edu.ng Recombination—The Physical Exchange of DNA All organisms suffer a certain number of small mutations, or random changes in a DNA sequence, during the process of DNA replication. These are called spontaneous mutations and occur at a rate characteristic for that organism. Genetic recombination refers more to a large-scale rearrangement of a DNA molecule. This process involves pairing between complementary strands of two parental duplex, or double-stranded DNAs, and results from a physical exchange of chromosome material. The position at which a gene is located on a chromosome is called a locus. In a given individual, one might find two different versions of this gene at a particular locus. These alternate gene forms are called alleles. During Meiosis I, when the chromosomes line up along the metaphase plate, the two strands of a chromosome pair may physically cross over one another. This may cause the strands to break apart at the crossover point and reconnect to the other chromosome, resulting in the exchange of part of the chromosome. Recombination results in a new arrangement of maternal and paternal alleles on the same chromosome. Although the same genes appear in the same order, the alleles are different. This process explains why offspring from the same parents can look so different. In this way, it is theoretically possible to have any combination of parental alleles in an offspring, and the fact that two alleles appear together in one offspring does not have any influence on the statistical probability that another offspring will have the same combination. This theory of "independent assortment" of alleles is fundamental to genetic inheritance. However, having said that, there is an exception that requires further discussion. The frequency of recombination is actually not the same for all gene combinations. This is because recombination is greatly influenced by the proximity of one gene to another. If two genes are located close together on a chromosome, the likelihood that a recombination event will separate these two genes is less than if they were farther apart. Linkage describes the tendency of genes to be inherited together as a result of their location on the same chromosome. Linkage disequilibrium describes a situation in which some combinations of genes or genetic markers occur more or less frequently in a population than would be expected from their distance apart. Scientists apply this concept when searching for a gene that may cause a particular disease. They do this by comparing the occurrence of a specific DNA sequence with the appearance of a disease. When they find a high correlation between the two, they know they are getting closer to finding the appropriate gene sequence. 17  http://www.unaab.edu.ng Binary Fission—How Bacteria Reproduce Bacteria reproduce through a fairly simple process called binary fission, or the reproduction of a living cell by division into two equal, or near equal, parts. As just noted, this type of asexual reproduction theoretically results in two identical cells. However, bacterial DNA has a relatively high mutation rate. This rapid rate of genetic change is what makes bacteria capable of developing resistance to antibiotics and helps them exploit invasion into a wide range of environments. Similar to more complex organisms, bacteria also have mechanisms for exchanging genetic material. Although not equivalent to sexual reproduction, the end result is that a bacterium contains a combination of traits from two different parental cells. Three different modes of exchange have thus far been identified in bacteria. Conjunction involves the direct joining of two bacteria, which allows their circular DNAs to undergo recombination. Bacteria can also undergo transformation by absorbing remnants of DNA from dead bacteria and integrating these fragments into their own DNA. Lastly, bacteria can exchange genetic material through a process called transduction, in which genes are transported into and out of the cell by bacterial viruses, called bacteriophages, or by plasmids, an autonomous self-replicating extra chromosomal circular DNA. Viral Reproduction Because viruses are acellular and do not use ATP, they must utilize the machinery and metabolism of a host cell to reproduce. For this reason, viruses are called obligate intracellular parasites. Before a virus has entered a host cell, it is called a virion--a package of viral genetic material. Virions—infectious viral particles—can be passed from host to host either through direct contact or through a vector, or carrier. Inside the organism, the virus can enter a cell in various ways. Bacteriophages—bacterial viruses—attach to the cell wall surface in specific places. Once attached, enzymes make a small hole in the cell wall, and the virus injects its DNA into the cell. Other viruses (such