BH/Unit 1: Introduction to Biology PDF

**.BH/Unit 1: Introduction to Biology** 1. **Definition of Biology** - **Biology** - Came from two Greek words bios means life, and logos meaning study. - the scientific study of **life or living things** - Living organisms interact with themselves and the environment at all levels...

**.BH/Unit 1: Introduction to Biology** 1. **Definition of Biology** - **Biology** - Came from two Greek words bios means life, and logos meaning study. - the scientific study of **life or living things** - Living organisms interact with themselves and the environment at all levels of biological organizations. - Life recognized mainly by common characteristics shared by living systems. - Living things are - Composed of one or more cells, - can grow, reproduce, - transmit genetic information to their offspring, - need the energy to accomplish work, - can maintain relatively constant internal conditions (homeostasis) - Capable of evolutionary adaptation to the environment etc. **What is a scientific study?** - **Scientific Study** - **A** systematic investigation that aims to answer questions or explore phenomena through the empirical (observed) evidence - It follows the principles of **scientific methods** - Scientists who studies living organisms and their relation to their environments are called **biologists** - Biologists study about living things using a scientific method - Biological **inquiry** depends on a **scientific method**. - Scientists follow a method while performing scientific experiments and writing up the results. - scientific study follows the study of structures and processes - we can verify observe and measure, either directly or indirectly with the help of tools and technology, such as microscope - The **study of biology** is a point of merging information and tools from all natural sciences. Example - information about naturally occurring elements in living organisms, chemical bonding, molecules, acids ,bases and other related things can be studied using - **the tools and principles of chemistry.** - Scientific concept like conversion of radiant energy into organic molecules by photo-synthesis using = - **the knowledge of chemistry and Physics.** 2. **Why do we study Biology?** - Human beings have **an inborn curiosity** about the natural world - Leads them to study about **living organisms and their habitats**. - **Studying biology helps to** understand - how living things work - How living things function and interact with the environment. - How to treat different human diseases using drugs - Eg Antibiotics, such as penicillin, are produced by mould fungi or bacteria. - How our animals and plants body work and how critically affect our lives - How ecosystems work - How advancements in genetics( **Gene or DNA )** and cell biology are transforming to **medicine and agriculture** - The use of **forensics biology** to investigate crime **using DNA structure** as sample - How ecology is helping societies evaluate environmental issues, such as **global warming,** - How fermentation is used to produce alcoholic drinks such as **beer and wine making** , the baking of bread , the production of cheese by - **yeasts, other fungi and bacteria, or enzymes from these organisms.** - how to treat patients suffering from AIDS, tuberculosis, and some types of cancer - for the production of industrial chemicals such as citric acid or lactic acid needs bacteria or fungi to bring about essential chemical changes - For Sewage disposal depends on bacteria in the filter beds to form the basis of the food chain that purifies the effluent **1.3. The Scientific Method** - Biology is a science of inquiry (ask question or investigation). - Biologists are always **curious** about why things happen or how things happen. - Biologists come up with new theories to explain new findings by asking questions and seeking science-based responses known as the **scientific method** - **The scientific method** - The process by which biologists and all other scientists approach their work - A series of logical steps scientists use to solve problems in a scientific way or a series of steps that guide scientists through such scientific investigations - It is a powerful method of problem solving - **The general steps of the scientific method** - The main steps (stages ) of the scientific methods are 1. **Observation** - Can be made either **directly** using your sense organs or **indirectly** using scientific tools such as microscopes. 2. **Asking Questions** - The observations usually lead the scientist to ask questions (inquiry). - Leads to **do back ground of research** ( identification of problem, gathering information ) 3. **Forming of a hypothesis( constract hypothesis )** - A hypothesis is proposed scientific explanations (possible answers) for a set of question (s). - **Hypothesis** is an educated guess about what a biologists think the explanation of an observation will be - To solve a problem, one can propose several hypotheses. - Scientific hypotheses should be **testable** ( by **experiment**) 4. **Testing the hypothesis with experiment** - Hypothesis can be tested through experimentation. - Can be **supports or rejects** the original hypothesis - If a hypothesis is not supported by experimental data, one can propose a new hypothesis. **NB. Prediction =** an educated guess as how the biologists think his /her experiment will turn out 5. **Making conclusions about the findings( Analyze result and draw conclusion)** - **The** possible explanations for how things work to accept (true hypothesis ) or reject (false hypothesis) - If not, scientists reject the hypotheses and try to come up with alternate explanations (new hypotheses) that can explain what they've seen 6. Communicating the findings (report results ) - When scientists complete some work - they write a paper that explains exactly what they did and the results they obtained. - Then, they submit the paper to a scientific journal in their field. - the findings will be printed in scientific journals and assist teachers and students in the fiel **Example.** Suppose you want to use your torch (hand lamp) to find a missing pen in your bedroom  **Main Steps on how we write repot on scientific experiment** - **Experiment** = a kind of test or at rail to find out some things - **scientific experiment** - planned inquiry to obtain facts or to confirm deny a hypothesis - try to establish case and effect - two groups in the scientific experiment - control group (untreated or placebo unit or inert or innocus) - experimental group (treatment group) - we can write a report on a scientific experiment (lab) as follows 1. Title 2. Objective 3. Introduction (includes hypothesis and prediction ) 4. Materials required (apparatus ) 5. Procedure 6. Result 7. Conclusion 8. Evaluation 9. Acknowledgement 10. Reference **1.4.1. Laboratory tools of biologist** - Biologists can divide the tools (apparatus in to two groups I. Tools used for laboratory work II. Tools used for field work **I. Tools used for laboratory work** - **Hand lens** - has a higher magnification than our naked eye - Provide an enlarged image of the object placed under it. - It consists of a convex lens fixed within a circular metallic loop - **Autoclave** - the equipment used to **sterilize** (kill micro-organisms) different biological samples - Sterilizes contaminated materials including ***culture media, and bacterial spores*** by exposing them to - High temperatures - Highly pressurized steam. - **Culturing** is the procedure used to grow microorganisms in a controlled environment to reproduce very quickly. - Have important function food- cheese making ,beverage like Wine and beer, medicine (Penicillin) and bio-fuel production - Used in hospitals ,laboratories and industries - The effective sterilization techniques using autoclave is - **Moist heat sterilization ( autoclaving ) or gravity displacement autoclave** - Can be used for a variety of items including glassware, media, and surgical instruments - the most common method ,involving exposure to saturated steam under pressure at 121^o^c for 15-20min - effectively kills all microorganisms including bacteria, viruses and spores **NB. The other commonly used sterilization methods besides autoclaving for killing microorganisms are** - **Heat Sterilization** **-dry heat** sterilization use hot air oven at temperature160-170^o^c for 1-2hrs - **Chemical sterilization** - **Disinfectants =** kill or inhibit growth microbs in surfaces **Eg.** Bleach, alcohol, H~2~O~2~, phenol - **Antiseptics =** applied to living tissue to kill or inhibit microorganism **Eg** Ethanol, iodine, chlorhexidine, H~2~O~2~ - **Ionization radiation sterilization** - Used for sterilizing medical devices and pharmaceuticals that cannot sterilized by heat or chemical - Penetrats deeply and kill microorganisms Eg. gammary ,x-rays - **Ultraviolet(Uv) Light sterilization** - Used to kill microorganisms on surface and in air frequently utilized in hospitals and lab - Flame sterilization (flaming ) - The high temperature of the flame rapidly destroys the cell structure of microorganisms including bacteria ,viruses and spores by denaturing their proteins. - **Incubator** - a device used to maintain a specific environment for culturing. - An incubator is an instrument that maintains the temperature best suited for the growth of different types of microorganisms. - **Petri dishes** - Flat dishes with a matching cover of a slightly larger diameter. - Available in glass and plastic form. - Used with gelling culturing media, such as agar, and placed in the autoclave to sterilize it. - Used for propagate (culturing ) plants from plant cells by micro propagation - Show how effective d/t antibiotic against certain types of bacteria - Show how well d/t concentration of enzymezs digest a substrat - **Culture tubes** - Available in a huge range of sizes, shapes, materials, and so on. - Used to culture micro-organisms. - May be used with solid (gel) culturing media or with liquid (broth) culturing media, and then placed in the autoclave for sterilization. NB. **Culturing** - The procedure used to grow microorganisms in a controlled environment. - Culturing of micro-organisms have important function like in medicine (Penicillin) and for food (beverage) preparation. - Wine and beer making uses culturing on a large scale, as it does in cheese making, bio-fuel production - **Measuring things** - Micrometers - Rulers - Measuring cylinder - Balance = for spring balance and chemical balance - Calculator - **Burette** = for volume of liquid - **Pipette or droper** =for volume - Used to control the amount of solution being added to a reaction. - **Syrings** = for volume gas - **D/T Flask** - An apparatus having a flat bottom and a long narrow neck, which allows easy mixing of the solution without spilling out the content - Are available in a variety of shapes and sizes - used to gently heat the content inside with a gentle swirling motion of the flask - Used to produce large populations of micro-organisms. - **Tongs** - metallic scissors-shaped laboratory instruments - It is used to Lifting or picking up hot objects such as heated crucible, beakers, dishes, or flasks. - **Dissecting Tool Kit** - used to dissect animals such as frogs, fetal pigs, mice, etc - It consists of all the necessary tools required to carry out the process of dissection - Includes - **a catheter, groove probe, scalpel** - **surgical scissors** (straight and curved), = for cut - **mayo scissors** (straight and curved), = for cut - **dissecting forceps** (with and without teeth) =for hold - dissecting pin= hold specimen within the dissecting pan - mounting needle= to separate - brush =removing or washing - **Dissecting pan =** used for holding or kept specimens during dissection of internal organs (hold specimen and dissection process) - **Crucible** - a small container made up of ceramic or metal(platinum or nickel) - used to heat substance to high temperature (withstand high temperature(without breaking) - **Generally used to melt elements(metals and alloys)** - **Beaker** - a cylindrical glass container used for making up solutions, holding hot or cold water or ice baths - **Hotplate** - Useful for heating solutions, making up an agar culturing medium - **pH meter** - Used to m**e**asure the pH (acidity or basicity) of substances. - **Thermometer** - an instrument that measures the temperature of substance - **Forceps** - Used to hold or pick up small objects. - They are available in a variety of shapes and sizes. - **Spatula** - Used for mixing substances into a solution, stirring the solution, and scrapping objects. - It is shaped like a spoon - **Wash Bottles** - Mainly used to rinse various laboratory materials. - flexible in nature that allows the user to adjust the water pressure as per the need by squeezing the bottle accordingly - **Bunsen burner or alcohol burner** - Apparatus produces a single open flame - Used for heating and sterilization purposes in the various experiments conducted in labs. - **Centrifuge** - A tool used to spines to separate solid from liquids without the need to filter - **Mortar and pestle** - Used to grind things and make them smaller - **Glass slides and cover slips** - The **microscope slides** are used to support an specimens being examined under the microscope. - The **cover slips** are the small square or circle shaped thin glass sheets that are used to cover specimens on the glass slide - **The Microscope** - an instrument that is used to see very small objects by a process called **magnification** - an instrument used to study objects that are too small to be seen with a naked eye - It magnifies the image of small objects - eg used to observe the shape of bacteria, fungi and parasites - The important function of microscope is **magnification and resolution.** - **Magnification** - The number of times larger an image is, than the real size of the object. - The multiplication or enlarging of the size of an object - **Resolution** - The ability to distinguish between two separate points that are close tighter - The scattering of parts of the object so that the details are seen clearly **Types of microscope** - There are several kinds of microscopes. - The major types are: A.Light microscope B. Electron microscope **A. Light microscope (optical microscope)** - It uses a beam of light to view specimens. - Use beam of light to view specimens. - Show living and non living things - Uses glass lens specimen - Use colored dyes like methyl blue, iodine, acetocramine,haematexyline - **Two** types of light microscopes - **Simple microscope (**one lens **)** - **Compound microscope (**two or more lens**)** - **Compound microscope** - the most common microscope used in biology - It consists of two lens systems (a combination of lenses) to magnify the image of an object up to 2000x - A compound light microscope with a single eyepiece is called **monocular** - One compound light microscope with two eye-pieces is said to be **binocular.** - In the compound light microscope light rays are focused on to the image on a **microscope slide**. - Light which **transmitted through the specimen** is then focused by **two types of lenses** - **Eye piece lens** - **Objective lenses** - A compound light microscope magnification is the product of eye and objective lenses **Magnification power of microscope = Eye piece lens x Objective lenses x actual size of an object** **MPM = or Eye piece lens x Objective lenses** - Used for magnification and viewing of the specimen images. **The parts and function of the light microscope** - **Eyepiece** - Found at the top of the microscope and is used to look through the microscope. - It is also named as the ocular. - Its standard magnification is 10x with an optional eyepiece having magnifications from 5X to 30X. - **Eyepiece tube** - The eyepiece holder. It carries the eyepiece just above the objective lens. - In some microscopes such as the binoculars, the eyepiece tube is flexible and can be rotated for maximum visualization. - **Objective lenses** - Major lenses that further magnify the specimen at different intensities with multiple objective lenses. - Mostly they have a magnification power of 4X-100X. - Are lower, Middle ,Higher, and oil immersion objectives - **Arm** - a holder connected to all components that function as a support for the microscope - so that the microscope can be used properly. - **Body tube** - connects the eyepiece to the objective lenses. - **Nose piece** - Rotating mount that holds many objective lenses. - It is movable hence it allows to change the magnification. - **The Adjustment knobs** - knobs that are used to focus the microscope. - are two types of adjustment knobs - **Fine adjustment:** - regulate the distance between object and objective - to achieve the necessary sharpness. - The fine focus moves the stage only minimally. - **Coarse adjustment**: - Brings specimen into general focus. - Moves the stage to adjust the difference between the object and the objective. - The function of the coarse focus is to capture the exact distance roughly and quickly. - **Stage** - the section in which the specimen is placed for viewing. - **Stage clip** - a holder for the object plate and ensures that it doesn't fall out of place accidentally. - **Aperture** - a hole on the microscope stage, through which the transmitted light from the source reaches the stage. - **Microscopic illuminator mirror** - the microscopes light source, located at the base. - It is used instead of a mirror. - It captures light from an external source of a low voltage of about 100v. - **Condensers** - Are lenses that are used to collect and focus light from the illuminator into the specimen. - Are found under the stage next to the diaphragm of the microscope. - Play a major role in ensuring clear sharp images are produced with a high magnification of 400X and above. - **Diaphragm** - Also known as the iris. - It is found under the stage of the microscope - Control the amount of light that reaches the specimen. - It's an adjustable apparatus, hence controlling the light intensity and the size of the beam of light that gets to the specimen. - **Base** - The very bottom part. - Serves to accommodate all parts of the light microscope. **B. Electron microscopes** - Use a beam of electrons (instead of a beam of light) to produce magnifying image - Use electromagnets (instead of glass lenses) to enlarge the image of an object. - Provide a higher **magnification and resolution** than light microscopes - Used for observing extremely **small micro-organisms such as viruses.** - It has a vacuum system which is used for electrons easly scattered by air molecules - Are two types - **Scanning Electron Microscope (SEM)** - Scan the surface of the sample bite by bite - Can produce the detailed picture of the surface of objects - Can provide a realistic three-dimensional image - **Transmission Electron Microscope (TEM)** - Used very thin sample - The beam of electrons is directed on to the object to be magnified - Most common than scanning - Allows researchers to view the structures of cells in detail **The difference b/n electron and light microscope** **Feature [Electron] [Light]** - Radation source electron light - Wave length about 0.005nm 400-700nm - Lens electron magnets glass - Specimen non living living or non living - Common stain heavy metal to reflect electron colored dyes - Image blackand white usually colored - Resolution high low - Magnification 250,000or 2,000,000 1500 or 2000 II. **Tools used for field work** - **Insect nets** (sweep net) - Used to collect insects and other invertebrates - composed of some sort of net bag made of cloth or fine mesh that is attached to a wire loop - it is attached to a wooden or metal pole. - **Fishing net** - a net used for fishing. - Nets are devices made from fibres woven in a grid-like structure. - Some fishing nets are also called fish traps. - **Quadrate (metal squer)** - Used to estimate the abundance of organisms in an area - **Plant press** - Used to preserve plant parts - **Theodolite** - To measure height of tree or slop of an area - **Flow meter** - To measure the rate of flow of water - Field microscope - To investigate the structure of specimens in the field while they are fresh - Pitfall traps (plastic carton ) - A container that is sunk in to the ground in order to collect insects (small ground dwelling animals ) that crawl on the ground. - PH kit - Measuring the PH of soil - **GPS** - Used for recording positioning quickly and accurately to draw an accurate map of an area - Data logger - For recording information **1.5.2 Handling and using a light microscope** - Be very careful when removing the Microscope from the cabinet - Carry the microscope properly, always grip the microscope by the arm and put your hand beneath its base. Hold the microscope upright at all times. Do not bump it against anything. - Make sure that the slide is clean and dry before putting it on the stage. - Put the slide on the stage, with the most promising region exactly in the middle of the hole in the stage that the light comes through. - Always focus on low power (4X objective) first even if eventually you need high power magnification. - Focus with the larger coarse-focusing knobs first, then when you have nearly got the image in focus make it really sharp using the smaller fine-focusing knobs. - If you want to increase the magnification, move the slide so the most promising region is exactly in the middle of the field of view and then change to a higher magnification lens. - Use immersion oil only with the 100X objective (oil immersion lens) in place. - Use only one drop of oil. - Always focus by moving the lens and the specimen further apart, never closer to each other. - Never touch the surfaces of the lenses with your fingers or anything else. - Lower the stage and then remove the slide when you are done. - Always clean the microscope when you are done. (use a lens paper and the alcohol) - Always place the 4X objective over the stage and be sure the stage is at its lowest position before putting the microscope away - Always turn off the light before putting the microscope away. - Always return the microscope to the correct cabinet. - Always place the oculars toward the back of the cabinet - Always wrap the cord correctly before putting the microscope away **1.6. General Laboratory Safety Rules** - **Safety** - The condition of being protected from harm or other danger. - Can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. - **Laboratory safety** is important before we do any activities in the laboratory: - working carefully in the laboratory - Dealing with minor problems before they become major problems - Keeping safety constantly in mind are some of the safety rules. - **Important general laboratory safety rules are** 1. Following the instructions 2. Knowing the location of safety equipment 3. Dressing for the laboratory 4. Never eat or drink in the laboratory. 5. Never taste or sniff chemicals 6. Act responsibly in the laboratory. 7. Cleaning the experiment area in the laboratory and storing the waste properly. 8.. Handling chemicals properly 9. knowing what to do with laboratory accidents 10. All laboratory personnel should place emphasis on safety and chemical hygiene at all times. **Unit 2: Characteristics and Classification of Organisms** **2.1 Characteristics of living things** **What are the characteristics of living things?** - Living things, or organisms ,share several key characteristics that distinguish them from non living entities Some of the properties that are shared by all living things are 1. **Cellular organization (cellular structure and composition)** - **All living things are made up of one or more cells** - One cell= unicellular eg bacteria and many cell = multicellular eg plants 2. **Metabolism (energy utilization)** - **All living things require energy** - All organisms use a source of energy for their metabolic activities. - Plants (autotrophs or producers) use light energy for photosynthesis - Animals (consumers or heterotrophs) consume others - Decomposers (saprophytes) break down dead organisms and organic wastes eg soil bacteria ,yeast - Parasites (host dependence) derive their nutrition from another living organism eg ticks ,lice, tapeworm 3. **Response to stimuli** - **All living organisms respond to stimuli** - Organisms can detect or sense stimuli (change) in the internal or external environment and make appropriate responses. 4. **Growth and Development** - **All living things can grow** - **Growth** - a permanent increase in size and mass due to an increase in cell number or cell size or both. - Bacteria and single-celled creatures show an increase in size. - Multicellular organisms = increase the number of cells in their bodies become more complicated and change their shape and size. - **Developmen**t --undergo change in their lifecycle such as differentiation and maturation 5. **Reproduction** - **All living things can reproduce** - **Reproduction -**the process that makes more of the same kind of organism. - **Living things can reproduce to create offspring by** - **Asexually (no fusion of gamete)** - **Sexually (fusion of gamete)** 6. **Excretion** - **All living things can excrete** - **Excretion** - the removal of the metabolic wastes produced in cells as a result of chemical reactions (metabolism) - Example, respiration and other chemical reactions in the cells produce waste products such as carbon dioxide 7. **Ordered Complexity** - **All living things display ordered complexity** - All living things are both complex and highly ordered. - The levels of organization in biological systems begin with atoms and molecules and increase in complexity. 8. **Homeostasis** - **Most living things maintain homeostasis (regulation)** - Homeostasis is the regulation of an organism's internal conditions to maintain stability - Most organisms maintain relatively constant internal conditions that are different from their environment - body temperature remains stable despite changes in outside temperature  **2.2 Taxonomy of living things** 2.2.1 **Principles of classification** - **Classification** - the process of grouping things based on their similarities - One tool biologists use to organize and understand living organisms - **Taxonomy**. - The science of naming, identifying and classifying organisms - Scientists who study taxonomy are called **taxonomists**. - Biologists classify organisms into different categories mostly by - judging the degrees of their apparent similarities and differences. These - include the external and internal structures of the organism as well as where the organism lives. - Can classify living things for several things - Organization (help to organize the vast diversity of life in manageablegroups) - Identification (basedon their characteristic) - Evolutionary relationships(based on shared characteristics - Communication(common language for scientists &helps to avoid confusion - Conservation (helps to identify endangered spp and prioritize conservation effort) - Taxonomists also consider - the genetic makeup of organisms to reveal their evolutionary relationships to other organisms. - the greater the degree of physical similarity between them, the closer their biological relationship i - They try to identify and classify organisms based on a number of features - **Morphologica**l=external and internal anatomy - **Physiological**=metabolic process, biochemical process, physiological response to temp, light, humidity - **Molecular**=DNA sequence, protein structure ,gene expressiion - **Behavioral**=matig, social behavior, learningn - **ecologica**l characters)=habit ,nich,interaction withother organism 2. **Taxonomic hierarchies in biological classification** - **The contribution of Aristotle (384-322 BC) to biological classification** - Developed the first widely accepted **biological classification systems**. - Used simple morphological characters to classify plants into - **trees, shrubs and herbs** - Divided animals into two groups based on similarities - Had red blood ( mammals, birds, amphibians, reptiles and fish) - did not have or without (insects and crustaceans). - Grouped some organisms that had very little in common - For example, he grouped **birds, bats, and flying insects** because they could **fly.** - **Carolus Linnaeus** (1707--1778) - the father of taxonomy - The first person to propose an **orderly system** for classifying organisms - Introduced a **taxonomic hierarchy** of classification - **Taxonomic hierarchy** - the process of arranging various organisms into successive levels of the biological classification either in a decreasing or an increasing order - In the Linnaean classification system, **all organisms are placed in a ranked hierarchy** - According to linnaean **kingdom** is ranked the highest followed by **Phylum (division), class, order, family, genus, and species** - Each rank in a taxonomic hierarchy is termed taxon (plural, taxa). - Developed a two Kingdom system of classification - All living organisms under - Kingdoms Plantae = all plants - Kingdoms Animalia = animals - This system **did not distinguish** between the - Eukaryotes and prokaryotes, - unicellular and multicellular organisms; and - Photosynthetic (green algae) and non-photosynthetic (fungi) organisms. - **The recent(modern) taxonomic hierarchy in biological classification** - From broadest level, biologists divide the diversity of life in to - **Domain,** **kingdom** , **Phylum (division), class, order, family, genus, and species** - **Domain** - Proposed by **Carl Woese**, **Otto Kandler** and **Mark Wheelis** in 1990 - The highest level, encompassing all life. - the rank above kingdom - divide the diversity of life into three domains based on fundamental genetic and biochemical characteristics or evolutionary history 1. **Archaea** - Are prokaryotic - Their range of size is similar to that of bacteria. - Cells with no membrane-bound organelles. - DNA exists as a circular 'chromosome' - Ribosomes are similar to bacteria. - Cell wall does not contain peptidoglycans - Cells divide by binary fission - Are unicellular/ coloni - Inhabit extreme environments. - No longer grouped under the kingdom **monera** - instead ,they are recognized as a separate domain due to their unique characteristics 2. **Bacteria** - Cells with no nucleus or prokaryotic - DNA exists as a circular 'chromosome'. - No membrane-bound organelles - Ribosomes are similar to archaea - Cell wall contains peptidoglycans - Cells divide by binary fission - Are unicellular/ colonial The major difference b/n Bacteria and Archaea **Feature Bacteria Archaea** Cell wall composition composed of peptidoglycan lack, but have pseudo peptidoglycan (has charbohydrat &protein Cell membrane ester linkage b/n glycerol and fatty acid ether linkage b/n fatty acid and glycerol or isoprenoid chain Chlorophylll have in some example cyano bacteria had no but some can photosynthesis by pigment eg bacteriorhodopsin Methane generation occur in some bacteria occur in many archaea(methanogens ) Sensitivity to antiobiotic sensitive to antibiotics resistant to antibiotics 3. **Eukarya** - relatively large and complex cells - Cells with a nucleus and membrane-bound organelles. - DNA in the nucleus arranged as linear chromosomes with histone proteins - Ribosomes are different from both bacteria and archaea - Have a great diversity of forms - are unicellular , colonial and multicellular organisms - Cell division is by mitosis - Many different ways of reproducing -- asexually and sexually. - includes groups such as **protists, fungi, plants and animals** **Summary of the taxonomic Hierarchies** - the major taxonomic ranks from broadest to most specific are 1\. Domain - the highest taxonomic rank (contain **Archaea Bacteria Eukarya)** 2\. **Kingdom** - a taxon of similar phyla (plural for phylum). - A major sub division of domain (Animalia,plantae,fungi,protista,monera) 4. **Phylum**( or division) - a taxon of similar classes. (Plant taxonomists use the taxon division instead of phylum). - A group of closely related class(chordate,arthropoda) 5. **Classes**: - a taxon of similar orders. Or A group of closely related orders(mammalia ,aves,reptilia) **6.Orders:** - a taxon of similar families. or A group of closely related families(primates,carnivore) 7.Family: - a taxon of similar genera or A group of closely related genera(felidae,canidae) 8**.Genera**: - a taxon of similar species. or A group of closely related species(homo,panethera) **9.Species:** - unique type of organism - the basic unit of classification - The smallest natural group of organisms is the species. - a group of organisms that can reproduce to produce fertile offspring. - Members of a species also often resemble each other very closely in appearance ( biological spp) - There are many other definitions of species; Example, phylogenetic species, morphological species, evolutionary species, systematic species, recognition species etc. However, for a biological species, members could reproduce to produce fertile offspring. Members of a species also often resemble each other very closely in appearance NB **Taxon**: is a group of organisms that share a unique set of traits. 3. **Relevance of classification** **What are the relevancies of biological classification?** - The applications of classification are manifold: - Identification of harmful and beneficial organisms, - reduce energy and time to study organisms - help us understand the relationship between organisms - For example, biologists to study the relationship between birds and dinosaurs. - Biologists have found that the bones of some dinosaurs have large internal spaces. So do the bones of birds. - Because of these findings, some biologists believe that dinosaurs are more closely related to birds than to reptiles - Taxonomy can also be a useful tool for scientists who work in such areas as agriculture, forestry, and medicine. - Taxonomy can also help the economy. - For example, taxonomists can discover new sources of lumber, foods, medicines, and energy. - For example, a taxonomist might know that a certain species of tree contains chemicals that make good disinfectants (e.g., Shiferaw/ Moringa- Moringa stenopetala). - It is possible that a closely related plant species could have the same useful substances. - So instead of having one source of chemicals, there may be two or more sources. 4. **Linnaean system of nomenclature** **How did Carl Linnaeus classify living organisms?** - **Linnaeus** - A Swedish naturalist who initially graduated in **medicine** but became interested in **plants**. - Discovering and naming new plant species. - he published his Systema Naturae( in 1735) - He accurately described **7700 plant** species and classified them. - Further grouped species into genera, genera into classes, and classes into orders. - He also classified over 4000 animals, but rather less successfully into mammals, birds, insects and worms. - Linnaeus refined and popularized the **binomial system of naming organisms** - **Binomial nomenclature** - An internationally agreed system in which the scientific name of an organism is made up of two parts showing the **genus and the species.** - A formal system of naming species of living things by giving each a name composed of two parts or **two part name** - The two names of an organisms are in **Latin** - The Latin form of the name allows it to be used in all over the world irrespective of language barriers. - The similarity in **size, shape, behavior and colour** makes it difficult to differentiate one species from the other. - The use of the **scientific name** avoids such confusion. - **The simple rules for writing scientific names** 1. The first name represents the **genus** - **Genus** (plural, genera) consists of a **group of similar species.** - **It is written with capitalized letter** 2. The second name represents specific **epithet.** - The **specific epithet** sometimes describes a **characteristic of the organism** - It is written with **small letter** 3. The scientific names (two names) are **underlined when handwritten** or **italicized when printed.** - This system is still the official starting point for naming or revising the names of organisms. - **For example** - The scientific name of **human beings** is **Homo sapiens** **= Homo-genus name ,sapiens --specific epithet** - Scientific name of Dog......\... *Canis familiaris* - scientific name of Cat...........*Felis domesticus* - scientific name of housefly.....*Musca domestica* - Scientific name of Mouse...........Mus *musculus* - scientific name of Goat............*Capra hircus* - scientific name of honey bee........*Apis mellifera* - scientific name of sheep.......*..Ovis aries* - scientific name of Cow...........*Bos taurus* 5. **Common Ethiopian animals and plants** - Ethiopia is endowed with high biological diversity (biodiversity) due to - its geographical location - topographical diversity - Diverse climatic features. - The country is a hot spot for a diversity of wild plant and animal species with a high degree of endemicity. - Ethiopia is a primary centre of diversity for field crops such as - noug (Guizotia abyssinica), tef (Eragrostis tef) and the Ethiopian mustard (Brassica carinata). - Besides, field crops such as barley, sorghum, durum wheat, finger millet, faba bean, chickpea, lentil, and cowpea have wide diversity in Ethiopia - Ethiopia has served as a gateway to domestic animals from Asia to Africa - Its diverse ecology favoured diversification of these resources. - The scientific and common names of some plants and animals in Ethiopia are  - **Dichotomous keys ( Two branching )** - The simplest type of identification key - Type of keys based on making choices between two statements or alternatives - Statements are description of external features of specimens - Simplify the process of identification - Used to identify unfamiliar organisms - Each key is made up of pairs of contrasting features - Starting with quite general characteristics and progressing to more specific ones. - By following the key and making appropriate choices it is possible to identify the organism correctly - **An example1** of a dichotomous key that could be used to place an unknown vertebrate and unknown invertebrate in the correct class. - **Example 2** **dichotomous key for vertebrates and invertebrates** 1. Does the organism have a back bone? - Yes :Goto2 - No:Goto 6 2. Does the organism have hair or fur? - Yes :Mammal (dog ,cat, human) - No:Goto 3 3. Does the organisms have feather? - Yes :bird - No:Goto 4 4. Does the organism have scales? - Yes :reptile (snak, lizard, turtle) - No:Goto 5 5. Does the organism live part of its life in water and part on land? - Yes :Amphibia (frog, toad, salamander ) - No: fish 6. Does the organism have an exoskeleton? - Yes :Goto7 - No:Goto 8 7. Does the organism have jointed legs? - Yes :Arthropod(insect, spider, crab) - No: other invertebrate (worm, snail, jelly fish) 8. Does the organism have a soft unsegmented body? - Yes :Worm or snail - No: Other invertebrate (jelly fish, starfish) 6. **The five-kingdom system of classification** - **Historical classification system** 1. Two kingdom classification *system* - ***Proposed by*** :Carolus Linnaeus - **Division** :Plantea(plants),Animalia (animals) - **Based on** :morphological difference ,such as the ability to move and the presence of cell wall 2. Three kingdom classification system - **Proposed by :**Ernst Haeckel - **Division** :Plantae, Animalia, protista - **Based on** :Cellular organization ,recognizing the distinict nature of single-celled organisms 3. Four kingdom classification system - **Proposed by** :Herbert Copeland - **Division** :Monera, Protista, Plantae, Animalia - **Based on** :Cellular organization, distinguishing b/n prokaryotes(monera) and eukaryotes 4. Five kingdom classification system - **Proposed by** :Robert Whittaaker - **Division** : Monera, Protista, Fungi , Plantae, Animalia - **Based on** :Cellular organization, mode of nutrition ,and body organization - The five kingdom classification system was proposed by **Robert H. Whittaeker** to solve the pitfalls of the two kingdom system of classification. - The main criteria for classification used by **Robert H. Whittaeker** include - Cell structure - distinguishing b/n **prokaryotes(monera) and eukaryotes** - Body organization - Distinguishing b/n **unicellular and multicellular organism** - Mode of nutrition - categorizing organisms as -**Autotroph**y(photosynthetic or chemosynthetic ) **Heterotrophs** (absorptive or ingestive) - Reproduction - **asexual** (with out fusion of gamete like mitosis, budding, fragmentation) - **sexual** (fusion of gametes like meiosis, fertilization) - Phylogenetic relationships - evolutionary relationships b/n different groups of organisms - Whittaker's five-kingdom scheme consists of **animals, plants, fungi, monera and protists**  Figure 2. 4. The five kingdoms of life **2.6.1. Kingdom Monera** - **Important characteristics of monera**: - Simple prokaryotic unicellular organisms - Lack a well-defined nucleus or any membrane bound organelles - Most have a rigid cell wall called peptidoglycan - Have various modes of nutrition. - Could **autotrophs** (photosynthetic and chemosynthetic) and **heterotrophs** - Known as decomposers and mineralizers in the biosphere - Are motile (through flagella ) and non motile - Are found at ever were (soil, **animal ,plant air ,water**) - All are microscopic - Reproduced through - asexually by **Binary fission** - sexually like by **conjugation (means genetic transfer)** - Some of the are harmful and cause disease to humans , plants and animals - Monera includes **1**. **Eubacteria 2 Archaebacteria** 1. **Eubacteria ( True Bacteria)** - Have strong cell walls. - Some eubacteria are - Heterotrophs - **Autotrophs** - Photoautotrophs = synthesis food using pigment(cyanin) and light energy **eg** **Cyano bacteria(blue green algae like )** - Chemoautotrophs = synthesis food using chemical reaction. **eg** sulpher bacteria - Can be live in most habitats, except the most extreme. - Some are harmful and cause diseases, like - strep throat , pneumonia, , Haemophilus ducreyi, chancroid - Bacterial diseases harm people. - First, the growth of bacteria can interfere with the normal function of body tissues - Second, the bacteria can release a toxin that directly attacks the host. - Most eubacteria are harmless and helpful - Some bacteria help with human digestion - Other bacteria also help produce cheese, yogurt, and sourdough bread. - They exist in various shapes and forms like - Cocci(sg-coccus) = spherical bacteria - Bacilli(sg --bacillus) = rod shaped bacteria - Spirillum or spirochaetes = spiral or cork screw shaped bacteria - They can occur in different arrangements or patterns like - Pair =diplo - eg diplococusand diplobacillus - Chian=strepto- eg streptococcus pneumoniae - Cluster =staphylo - eg staphylococcus aureus - Examples for the different arrangements of the bacteria  **2 Archaebacteria (Archaea)** - A group of microorganisms considered to be an ancient form of life that evolved separately from the bacteria - have very different cell walls (pseudopeptido glycan ) than bacteria - can be make their own food like bacteria through - Chemosynthetic and photosynthetic ( have **bacteriorhodopsin which traps light** ) - Can be also heterotrophic - Can be live in extreme environments. - Such places as swamps, deep-ocean hot water vents and seawater evaporating ponds. - The environments in which the archaebacteria live often have no oxygen - Have genetic similarity to Eukaryote - Have closer evolutionary relationship with eukaryote (based on ribosomal RNA gene sequences) - Have similar mode of reporoduction with bacteria but some archaea use **budding and fragmentation** **2.6.2. Kingdom Protista (protozoa and algae)** - **What are protists?** - contains the most diverse organisms of all the kingdoms - Are single-celled (most are unicellular) and many-celled (multicellular) protists. - Some are microscopic, others are very large - Are heterotrophic and autotrophic - all eukaryotes(common for all) - Most of their metabolic processes (chemical reactions) take place inside their membrane-bound organelles. - Many protists are motile (using flagella, cilia pseudopodia) and some are non motile - Can reproduce by - **Asexually** - bina fission eg amoeba , paramecium, chlamydomonas, giardia - multiple fission(schizogony) eg plasmodium , dinoflagelllate - fragmentation eg multiple algae (spirogyra) - spor formation eg some algae (ulothrix or filamentous grren algae) - budding eg some algae(protosiphon) - **Sexually** - conjugation **eg** paramecium - gamet formation eg chlamydomonas - Some can cause serious disease to humans - Can classifeied in to - **Phylum protozoa** (**animal like** except only have **one cell**) - all are unicellular - eg amoeba , euglena, paramecium, plasmodium ,giardia - **Phylum bacillerophyta** Eg diatoms - have unique characteristics different from protozoa and algae - have **silica cell wall** (hydrated silicon dioxide ) - **Frustule structure** -- cell wall have two overlapping halves that fit together like petridish - **Photosynthetic pigments** --have unique blends of photosynthetic pigment include *chll a,chll c ,fucoxanthin , diatoxanthin* - **Oil storage -** storage energy in the form of oil droplets - **Algae** (**plant like** except they do not have **roots, stems, or leaves).** - Muli and uni cellular - Photosynthetic and autotrophic. - Unicellular algae are the basis of aquatic food chains and produce much of the oxygen in Earth's atmosphere. - Example - Phylum **phaeophyta (brown algae)** - Phylum Rhodophyta **(red algae)** - Phylum chlorophyta **(green algae )** - **Phylum cyanophyta (blue green algae )** **[NB.]** Other protists **fungil like** ( eg slime mold and water mold )  **2.6.3. Kingdom Fungi** - **Fungi** - Are eukaryotic microorganism - are filamentous multicellular organisms except yeast ( only unicellular) - Nearly all fungi are **multicelled** eukaryotic species - Are non motile organism - Are **heterotrophic**(non photosynthetic ) organism - They can be - **Saprophytic fungus** - obtains food from dead organic matter - Most fungi absorb soluble organic matter from dead substrates - act as decomposers - secreting powerful enzymes into their surroundings and digest compounds - fungi do not ingest (eat) their food - Fungi use a process called extracellular digestion to obtain nutrients. - Food is digested outside a fungus's cells and then the digested food is absorbed. - **Example** -Some hyphae of a fungus will grow into an orange. They release digestive enzymes into the orange that break down the large organic molecules into smaller molecules. - **Parasitic fungus** - feeds up on a living organism host from the cells of living hosts - Some parasitic fungi are pathogenic, causing diseases in humans - Example : -Candida albicans cause rush \- Tinea pedis cause athlete's foot), animals and plants. \- ring warm fungi - **Symbiotic fungi (mutualists)** - Live in close association with other organism or live in a mutually beneficial relationship with a host - Example - Fungi + algae = **lichen** \- Fungi + roots of higher plant = **Mycorrhizae** - Fungi possess a cell wall that is made up of **chitin and polysaccharides**. - Are achlorophyllous( without chlorophyll) - Can be utilize **glycogen** as their reserve food - Their bodies consist of long, slender thread-like structures called hyphae. - Hyphae play an important role in how they obtain food. - An interconnected mass of hyphae called mycelium - The distribution of fungi is cosmopolitan - Can grow over a wide range of temperature of 22-30c and 30-37oc - Some fungi can survive at 0cand spoil frozen **meat and vegetables** - Fungi can reproduce either asexually by vegetative means - Fungi can reproduce - **asexuall**y by vegetative means(spores , fragmentation, fission and budding) - **sexually** by spores **NB.** The various spores are produced in distinct structures called fruiting bodies. - Yeast (saccharomyces service) is used for making injera rise and allows us to make alcohol (Tej, Tella, Beer etc.). - The branch of microbiology that deals with the study of fungus is known as **mycology** - Fungi can be classified based on the identification of sexual reproduction in to 1**. Imperfect fungi** **2. Perfect fungi** 1**. Imperfect fungi (Duetromycetes or duetromycota )** - Sexual reproduction not identified - Primarily reproduced by asexually often by producing spores called conidia Eg Cercospora fusarium or plant fungi 2. **Perfect fungi** - Fungi that reproduce both sexually and asexually - Can be grouped in to A. **Oomycata(** - Are primitive fungi - Classified as **phycomycetes (algal fungi )** - Are not true fungi - Reproduce by - asexually through motile spores (zoospores - **Are saprophytic (**decomposer**s)and parasitic (**infect plants and animals) - Have cellulose cell wall like algae - Their hyphae typically lack internal cross walls (septa) **Eg Phytophthora albugo(**white rust in leave plants **) , plasmopara viticola(**downy mildew of grapes **)** B. **Eumycota(true fungi)** - Can be classified in to - **Phylum chytridiomycota (Chytrids)** - The simplest group of true fungi - Primarly aquatic ,saprobic decomposers or parasites that produce flagellated spores(zoospores) by asexually and sexully Eg. Chytridium - **Phylum zygomycota(zygomycetes)** - Producers of zygospors (zygotes in side thick well)by ways of sexual reproduction and produce spores asexually Eg Bread molds rhizopus,philobolus - **Pyllum ascomycota(ascomycetes)** - Sac fungi - Can reproduce asexually by **conidia** - Sac shaped cells form sexual spores (ascospores) Eg most yeast , mold , candida,pencillium,aspergillus, morchella - **Phylum** basidiomycota **(basidiomycetes** - Club fungi - Most divers group - Produce basidiospores by sexually inside club shaped structures Eg mushroom ,shelf fungi ,stinkhorns, agaricus,craterellus gymnophilus,rust **2.6.4. Kingdom Plantae** - **What are plants?** - Kingdom Plantae includes all eukaryotic and multicellular autotrophic organisms. - Plants make their own food through the process of photosynthesis. - Photosynthesis provides oxygen in the atmosphere - Plants have chloroplast and chlorophyll pigment - Some plants parasitic. - Are heterotrophic because they lack chlorophyll - For example Viscumspp (eg mistletoe), cuscuta spp (eg dodder) - Many plants exhibit indeterminate growth - They can continue to grow throughout their lifespan - Nearly all live on land. - Sexual reproduction predominates. - They do not move from place to place - they are stationary. - Their cells contain a rigid cell wall made up of cellulose. - Their cells contain a large central vacuole that stores water, nutrients and waste products - They reproduce through - asexually by vegetative propagation - like runner,tuber,bulbs,cutting ,grafting,rhizomes - sexually - gamete formation - There are over 250 000 species of plants. - These include flowering plants, mosses, ferns, and coniferous plants - They are generally described as **Embryophyta** - land plants; photosynthetic species that protect and nourish the embryo on the parental body - **Embryophyta can be divided in to** Vascular and non-vascular plants - **non-vascular plants** (no specialized conducting tissue): - Bryophyta -- Liverworts , horn worts and Mosses - **Vascular plants**(well developed xylem and phloem tissue) - **Pteridophayte** (also known as the Filicinophyta - the ferns) - **Spermatophyte** - **Gymnospermae** (also known as the Coniferophyta) -- the conifers - Seed plant that does not make flowers or fruits - **Angiospermae** (also known as the Angiospermophyta) -- the true flowering plants - Most diverse seed plant group. Only group that makes flowers and fruits. - Can be divided in to dicots and monocots - Dicots: Most diverse groups of angiosperms; members have two seed leaves, branching leaf veins. - Monocots: Highly diverse angiosperm group; includes plants such as grasses that have one seed leaf and parallel veins  **2.6.5 Kingdom Animalia** - **What is an Animal?** - An animal is a multicellular ,eukaryotic organism belong to the biological kingdom animalia - Kingdom Animalia includes **all multicellular, heterotrophic, eukaryotic organisms** - Unlike plants, animals are not photosynthetic. - Animals consume food obtained from other organisms (i.e. they are heterotrophy) - Unlike fungi, most animals do not feed by absorption; - Animals ingest their food and then use enzymes to digest it within their bodies - **Unlike** plants and fungi, animals lack the structural support of rigid cell walls - Animal cells are held together by structural proteins - the most abundant being collagen, which is found only in animal - Many animals have **specialized cells or specialized tissue** **not seen** in other multicellular organisms(plant and fungi) - The specialized cells or specialized tissue are muscle tissue, nervous tissue and connective tissue - These have specific functions - muscle tissue for body movement - nervous tissue for conducting nerve impulse - connective tissue supporting and connecting various body parts - most animals are capable of movement (motile) but some animals cannot move like **sponges and corals** - most animals reproduce sexually by **fusion of gametes** (sperm+egg) - Animals are very diverse - are generally classified into two groups based on the presence or absence of backbone 1. Invertebrates (**animals with no backbone**) 2. Vertebrates (**animals with a backbone**) **Comparison between Invertebrates and Vertebrates'** **[Characteristics] [Invertebrates] [vertebrates]** - Back bone - do not possess a back bone or - possess a back bone and internal skeleton an internal skeleton - Body support -by exoskeleton - by endoskeleton - Body size - Generally smaller than vertebrates - Comparatively larger than invertebrates' - organ system -simpler -more complex - Eye -Majority have compound eye - Do not have compound eye - Nervous system -Presence of simple and unorganized - Presence of complex and highly specialized Nervous system organ system with specific function - Mode of nutrition - Includes heterotrophic and Parasitic (in some) - Usually heterotrophic - Diversity - **most diverse** group of animals in the world. -- less diverse but most advanced group - **Invertebrates** - Can be grouped in to different phylum's - **Annelids (** **segmented worms**) - Have two body opening , simple nervous system - eg earth warm, Leech, sand warm - **Cnidarians** (**stinging cells**) - Have tentacles with stinging cells ,one body opening ,live in water - eg jelly fish, corals, sea anemones, hydra - **Echinidermata** (**spiny skinned**) - Have bodies in five parts covered in spins or spikes - Have endoskeleton composed of calcareous plates called ossicles - eg starfish ,echinus, sea cucumber ,asteris sea urchins - **mollusks** (**soft bodied** ) - have soft bodied and unsegmented - have external and internal shells ,most have shells - have a foot of tentacles - eg slugs, squids, octopuses ,marine mussel, snail, oyster - **Porifera**(sponges ) - Nobody opening ,no muscles ,no nerves ,live in water - **eg** sponges - **Arthropods(jointed legs)** - Have more than one body section , have exoskeleton - are classified in to - **Crustacean** eg crab,losters, shrimp,water flea, wood lice - **Arachinida** eg spiders, scorpion, ticks - **Insects eg** butterflies,weevils, locust, cockroach ,wasp ,bees, beetles - **Myriapoda or many-legs** eg centipedes ,millipids - **Platy helminthes** (***flat worms**)* - Have flattened body with mouth but no anus - Eg tape worm, fluks, planarian - **Vertebrate classification** - Highly advanced group of animals. - Have more complex and specialized organ systems - Can be grouped in **phylum chordate** - Phylum chordate have 3 sub phylums - **Sub phylum urochordata** eg marine animals suchas Tunicate - **Sub phylum cephalochordate** eg animals like lancelets and amphioxus - **Sub phylum vertebrates** - Animals have vertebral column /back bone - Can be divided in to classes A. Class Pisces.........\...\.... **Fish** (eg tiplaia,nileperch, cat fish ,shark, skates B. Class Amphibian.........**.Ampmibians** (eg frog,salamander , toad) C. Class Reptilia..........**.Repitiles** (eg snakes, crocodiles,lizards,turtles,alligators,tortouises) D. Class Aves............**.Birds** (agles, pegion, fowls ) E. Class Mammalian.......**Mammals** ( Egglyingmammals , marsupials mammals , placental mammals A. **Class Pisces.........\...\.... Fish** - They live under water - They breath throughout gills - Some of them have scales covering their bodies - Fins help them to move under water - Cold blooded animals - They are born from eggs - Example Tiplaia, Nileperch, Cat Fish ,Shark, Skates B. **Class Amphibian..........Amphibians** - Have thin and humid skin - Transformation throughout their life cycle - They change their breathing method by lung ,gills and skins - They are born from eggs - Cold blooded animals - They live on ground and water - Example Frog, Salamander , Toad C. **Class Reptilia...........Repitiles** - The longest lived species on the planet - Cold blooded animals - Body covered with scales or shells - They cannot chew - They are born from eggs - They live on the ground or in water - Example Snakes, Crocodiles,Lizards,Turtles,Alligators,Tortouises D. **Class Aves.............Birds** - Body covered with feathers - They usually have porous light weight bones to allow them so fly - They live flying or on the ground - Have wings to fly - Their mouth are toothless beaks - Warm bloodedvvvv animals - They are hatched from eggs - Example Agles, Pegion, Fowls E. **Class Mammalian.......Mammals** - They are born alive from the mother - They breathe through the lung - They live in the water , the air , on the ground - They have fur covered their body - Worm blooded - Example - Egg lying mammals ( eg duck billed platypus,spiny anteater) - Marsupials mammals (Kangaroo,opossum,koala bear) - Placental mammals(human ,cow, lion ,elephant etc) 7. **Renowned Taxonomists in Ethiopia** - The renowned taxonomists that contributed the publication of volumes of books on the **Flora of Ethiopia are** Dr. Mesfin Taddese, Professor Sebsebe Demissew, Professor Ensermu Kelbessa and Professor Silesh Nemomissa - There are few other zoologists like **Professor Abebe Getahun**; who contributed to the field of **animal taxonomy.** **Unit 3: Cells** 1. **What is a cell?**