Microbe Mission: Microbiology & Lab Skills

• Microbe Mission is a hybrid event testing knowledge of microbiology and lab skills
• Teams answer questions, solve problems, and analyze data related to microbes

Topics for 2024-2025

• Microscope types and their advantages/disadvantages
• Use of microscopes for measurements or estimations
• Principles of microscopy (reflection, magnification) and calculations (field of view, object size)
• Structure, function, metabolism (where applicable), and life/replication cycles of:
  • Archaea
  • Bacteria
  • Eukaryotic algae
  • Fungi
  • Parasitic worms
  • Prions
  • Prion-like particles
  • Protozoa
  • Viruses
  • Viroids
• Microbial interactions (competition, mutualism, parasitism)
• Microbial evolution, including horizontal gene transfer and the theory symbiogenesis
• Bacteriostatic vs. bacteriocidal antibiotics
• Methods for assessing antibiotic susceptibility
• Mechanisms of antibiotic resistance and resistance transfer
• Roles of microbes and microbial population explosions in the environment and in microbiomes
• Significance of microbes in agriculture, food production, and other industries (biofuels, bioremediation, phage therapy, pharmaceuticals, wastewater treatment)
• Modern methods for culturing and measuring the growth of microbes
• Modern methods for studying microbial communities and measuring microbial activity
• Use of dichotomous keys to identify microbes
• Data collection, interpretation, and analysis

Stations Format

• There will usually be anywhere from 5 to 20 stations, numbered with Roman (I, II, III...) or Arabic (1, 2, 3...) numerals
• Sections of the test will correspond to each station
• Teams typically have a time limit of anywhere between 2.5 and 10 minutes per station before they must rotate to the next station
• Event coordinators may provide duplicates of the stations

Test Format

• If there are stations, then the test packet will likely be an answer sheet that is divided into pages or sections corresponding to each station
• In many cases, there will be no questions or diagrams in the packet
• At some competitions, the questions may also be included in the test packet
• All answers must be recorded in the packet
• There are additional sections of the test that do not correspond to any station
• If there are not stations, then the test may be given as a normal test packet
• Potential question formats may include: labeling, matching, multiple choice, fill-in-the-blank, short answer, specimen identification, data collection including the use of lab instruments such as microscopes, and calculations

Materials

• Each participant must bring Z87 chemical splash goggles and a writing implement
• Teams may bring two non-programmable, non-graphing calculators and one 2-sided 8.5" x 11" page of notes

Preparing for Microbe Mission

• An AP Biology textbook or college-level microbiology textbook will help with learning important terms and concepts
• It is also helpful to review all of the resources linked on the official Microbe Mission page on soinc.org
• Completing practice tests is extremely helpful when preparing for Microbe Mission and other core knowledge events

Tips for Making the Note Sheet

• Knowing the layout of your note sheet and how to quickly locate information is the most important part of the note sheet
• Effective communication between event partners also important
• Consider using different, readable colors for different topics in order to make locating information during the test easier and faster
• Use as small of a font as possible in order to fit more information, but keep your notes readable
• It can be helpful to create your own diagrams, either by hand or with an image manipulation program
• In addition to diagrams, teams can create custom charts that include specific information and help to maximize space
• Source-check before putting anything on the note sheet to avoid using incorrect information during tests
• Use space efficiently by prioritizing which material to include and which material to leave off
• Laser printers are recommended for smaller font sizes (size 6 or less)

Microscopy

Types of Microscopes

• Optical Microscope: Uses visible light (or UV light in fluorescence microscopy) to magnify samples
  • Light rays refract with optical lenses
  • The first microscopes that were invented were found to belong in this category
  • Compound Microscope: Uses two lens systems (objective and ocular/eyepiece) for greater magnification
  • Utmost useful magnification is about 1000x
  • Stereo Microscope (Dissecting Microscope): Magnifies up to about 100x; provides a 3-dimensional view
    • Useful for observing opaque objects
  • Confocal Laser Scanning Microscope: Scans a sample in depth and eliminates out-of-focus light
    • A computer assembles the data to create a 3D image
• Electron Microscope: Uses accelerated electrons that strike any objects in path, to magnify them up to 2 million times
  • Designed specifically for studying cells and small particles of matter, as well as large objects
  • Has a higher resolving power than a light microscope
  • Scanning Electron Microscope (SEM): Lower magnifying power, provides 3-dimensional viewing
    • Captures black and white image after staining with gold and palladium
  • Reflection Electron Microscope: Detects elastically scattered electrons
• X-ray Microscope: Uses a beam of X-rays to create a high-resolution 3D image
  • Image resolution is higher compared to optical microscopes
  • Allows observation of living cells
• Scanning Helium Ion Microscope (SHIM/HeIM): Uses Helium ions to generate an image
  • The sample is left mostly intact and that it provides a high resolution
• Scanning Acoustic Microscope (SAM): Uses focused sound waves to generate an image
  • Detects small cracks or tensions in materials
  • Used in biology to study physical properties of biological structures
• Neutron Microscope: Experimental; uses neutrons to generate high-resolution images
  • Offers better contrast than other microscopy forms
• Scanning Probe Microscopes: Visualizes individual atoms (computer-generated image)
  • A small tip measures the surface structure of the sample
  • If an atom projects out of the surface, then a higher electrical current flows through the tip
  • The amount of current that flows is proportional to the height of the structure

Microscope Parts

Compound Light Microscopes

• Ocular (Eyepiece): Magnifies the image formed by the objectives
• Nosepiece: Holds the objectives, located below the arm and body tube
• Base: Supports the microscope
• Objectives: Lenses that form the first image by receiving light from the field of view
• Arm: Connects to the base, holds the ocular, body tube, objectives, and nosepiece
• Body Tube: Tube between the ocular and the nosepiece/objectives
• Coarse Adjustment: Adjusts the microscope in lower power
• Fine Adjustment: Adjusts the microscope in high power for fine-tuning
• Stage: Supports the slide and specimen
• Stage Clips: Hold the slide in place
• Illuminator: Light source, usually below the stage; a lumarod may be used instead
• Diaphragm: Controls the amount of light reaching the specimen

Principles of Microscopy

Appearance and Movement of Objects

• Objects appear upside-down and backwards under a microscope
• If a specimen moves forward and right, it appears to move backward and left through the microscope

Magnification and Changing Objectives

• Total magnification = ocular magnification × objective magnification
  • Example: 10x ocular and 12x objective = 120x total magnification
• Typical ocular magnification: 10x or 12x
• Typical objective magnification:
  • Scanning: 5x
  • Low power: 10x or 12x
  • High power: 40x-45x
• Changing objectives to a higher power:
  • Reduces the size of field of view
  • Makes the field of view darker
  • Increases resolution and image size
  • Decreases working distance
  • Reduces depth of focus

Lenses and Refraction

• Many microscopes use lenses to refract light and produce a clear image
• Refraction is the bending of light waves as their phase velocity changes passing through a different medium
• Measured by the angle of incidence
• Each medium has an index of refraction affecting how much light is redirected
  • Hot air has a lower index of refraction than cool air, causing mirages
• Biconvex lenses converge light rays, biconcave lenses diverge light rays
  • More curved biconvex lenses converge light more powerfully
• Electron microscopes use electromagnetic coils to focus electron beams instead of lenses

Mirrors and Reflection

• Not included in summary

Measurements

• Metric ruler smallest measurement: millimeter (mm), or 10^-3 meters
• 1 millimeter (mm) = 1,000 micrometers (μm), or 1 µm = 10^-6 meters
• 1 micrometer (μm) = 1,000 nanometers (nm), or 1 nm = 10^-9 meters

Acellular Microbes and Agents

Prions

• Are pathogenic, misfolded versions of normal cell proteins, major prion protein (PrP) is encoded by the gene PRNP (also called CD230) located on the p arm (shorter arm) of chromosome 20
• PrP is highly conserved in mammals and descended from ZIP proteins
• Human PrP is 253 amino acids long after translation
• The misfolded, disease-causing form (PrPSc) is highly resistant to degradation by proteases
• Exposure to small number of prions can facilitate the conversion of the normal isoform PrPC to the pathogenic isoform PrPSc, resulting in disease
• PrPSc forms insoluble aggregates called amyloid fibrils/plaques in nervous tissue, disrupting normal function
• Prions cause vacuolation, leading to spongiform appearance
• Prion diseases can be acquired, familial, or sporadic; rapidly progressive and always fatal
• Also called transmissible spongiform encephalopathies (TSEs) including Bovine spongiform encephalopathy (BSE, aka mad cow disease), Camel spongiform encephalopathy (CSE), Chronic wasting disease (CWD), Creuzfeldt-Jakob (CJD), Exotic ungulate encephalopathy (EUE), Fatal familial insomnia (FFI), Feline spongiform encephalopathy (FSE), Gerstmann-Straussler-Scheinker Syndrome (GSS), Kuru, Transmissible mink encephalopathy (TME), Scrapie, and Variably protease-sensitive prionopathy (VPSPr)
• Discovered in 1982 by Stanley B. Prusiner, short for "proteinaceous infectious particle"
• Composed solely of protein; no nucleic acid
• Cannot replicate on their own; exploit host cell machinery
• Before prions were discovered, a team of scientists postulated that diseases like scrapie, CJD, and mad cow disease were caused by an infectious agent composed of nucleic acids and coated in a protective layer of proteins derived from host cells, calling this particle a "virino."

Prion-like Proteins

• Misfolded proteins that form amyloid aggregates associated with degenerative diseases
• Do not complete a full infectious cycle
  • Do not have all 6 components involved in the chain of infection:
    • Infectious agent
    • Reservoir
    • Portal of exit
    • Mode of transmission
    • Portal of entry
    • Susceptible host
• Infectious transmission from one host to a new susceptible host has never been recorded
• One example of a prion-like proteins is amyloid-β, is associated with Alzheimer's disease
• Another example is tau proteins, are associated with Alzheimer's disease, frontotemporal dementia, and other degenerative diseases that are collectively called tauopathies
• α-Synuclein amyloids are associated with Parkinson's disease and some types of dementia
• Proteins with expanded polyglutamine (polyQ) tracts can also form prion-like aggregates associated with disease, as in the case of polyQ-expanded huntingtin and Huntington's disease

Viroids

• Small, single-stranded circular RNA molecules without a protein coat
• Infect flowering plants (angiosperms)
• Replicate within host cells by rolling circle amplification using host RNA polymerase II
• Accumulation can lead to plant diseases by disrupting normal cellular processes and gene regulation
• Some of the most famous include Potato spindle tuber viroid (PSTVd), Coconut cadang-cadang viroid (CCCVd), Tomato apical stunt viroid (TASVd), Apple scar skin viroid (ASSVd), Chrysanthemum stunt viroid (CSVd) and the Chrysanthemum chlorotic mottle viroid (CChMVd)

Viruses

• Obligate intracellular pathogens containing DNA or RNA genetic material
• Smaller than bacterial cells (10s to 100s of nanometers)
• Dependent on host cell machinery to replicate
• Genetic material contains instructions for creating viral particles (virions)
  • Virions consist of genetic material + protein coating (capsid) ± lipid layer (envelope)
  • Capsid is made of capsomeres, which are made of protomers
• Infect organisms from all branches of life
• Viruses that infect bacteria are known as bacteriophages
• Responsible for various human diseases (AIDS, chicken pox, chikungunya, the common cold, cowpox, Ebola, hepatitis A-E, influenza, mononucleosis, measles, mumps, rabies, rubella, West Nile fever, yellow fever, Dengue fever, poliomyelitis, shingles, smallpox, and Zika)
• Origins unclear; may derive from plasmids, transposons, or bacteria
• Evolved after cellular life

Viral Capsid Shapes

• Helical: Rod-shaped or filamentous (tobacco mosaic virus, ebola virus)
• Polyhedral: Icosahedron (20-sided) (adenoviruses, picornaviruses like hepatitis A virus and poliovirus)
• Complex:
  • Bacteriophages: Elongated icosahedral head (prolate) + helical sheath + basal plate + tail fibers
  • Bullet-shaped: Rabies virus (Lyssavirus)
  • Brick-shaped: Poxviruses (cowpox, smallpox, mpox)
  • Cone-shaped: HIV-1 and HIV-2 capsids, covered by a viral envelope
• Spherical: HIV-1, HIV-2, influenza A-D viruses and herpesviruses, appear spherical due to viral envelope

Baltimore classification

• Divides viruses into seven groups based on genetic material
• Class I: Double-stranded DNA viruses
• Class II: Single-stranded DNA viruses
• Class III: Double-stranded RNA viruses
• Class IV: Positive-sense single-stranded RNA viruses
• Class V: Negative-sense single-stranded RNA viruses
• Class VI: RNA retroviruses
• Class VII: DNA retroviruses

Lytic and Lysogenic Cycles

• Viruses can be caused by either lytic or lysogenic infections
• Lytic infection:
  • Virus injects genome into host → viral DNA directs production of viral proteins → cell lyses, releasing new viruses
• Lysogenic infection:
  • Virus integrates DNA into host (prophage) → remains dormant for generations → activates, directing new viral protein synthesis
  • HIV is a lysogenic virus, remaining dormant while the host cell undergoes mitosis
• Viruses can be caused by either lytic or lysogenic infections

Satellite Viruses and Nucleic Acids

• Subviral particles that cannot complete the cycle of infection independently
• Dependent on host machinery and helper virus for replication
• Genomes: single-stranded RNA, single-stranded DNA, or double-stranded DNA (not double-stranded RNA)
• Genomes are shorter than viral genomes

Virophages

• Are small DNA viruses that parasitize giant viruses
• Most (if not all) virophages have circular genomes (10-30 kilobases, and usually at least 300 kilobases) and large capsids (200-400+ nm) and belong to phylum Nucleocytoviricota
• Belong to Nucleocytoviricota (nucleocytoplasmic large DNA viruses as they encode enzymes involved in DNA repair, replication, and transcription, which allows them to establish cytoplasmic virus factories that facilitate genome replication in addition to protein synthesis and virion assembly)
• Two famous examples called Sputnik (the Russian word for "satellite)"and Zamilon, which both belong to the family Lavidaviridae and depend on giant viruses belonging to the genus Mimivirus

Virusoids

• Viroids enclosed in a protein capsid of another virus
• Depend on helper virus and host cell RNA polymerase II for replication
• Have circular, single-stranded RNA genomes

Prokaryotic Microbes

• Prokaryote is a type of cell that does not have any nucleus or membrane-bound organelles
• Includes Eubacteria (bacteria) and Archaeabacteria (archaea).
• Archaea are thought to be more ancient than bacteria.
• Archaea have not yet been found to be pathogenic
• Some archaea and bacteria reside in the human gut microbiome, important for digestion and vitamin synthesis.
• Prokaryotic cells divide by binary fission
• DNA replication leads directly to cytokinesis (splitting of cell membrane)
• no agglomeration into chromosomes first

Bacteria

• Single-celled, prokaryotic microorganisms
• Some are beneficial; others are pathogenic
• Originate from first single-celled organisms on Earth
• Have caused epidemics and pandemics
• Negatively impacted by antibiotic drug-resistant strains
• Positively used to create first artificial life
• Impacted study to determine origin of life on Earth
• Used in industry to create familiar products
• Found in plants as nitrogen-fixing bacteria
• Motile may utilize rotating flagella to move, or secrete slime to slide around

Bacterial Cell Shapes

• Cocci (spherical): Staphylococcus, Streptococcus, Pneumococcus
• Bacilli (rod-shaped): Bacillus, Escherichia (E. coli), Lactobacillus, Rhizobium, Streptobacillus
• Spirilla (rigid, corkscrew-shaped): Campylobacter, Helicobacter, Spirllium
• Spirochetes (longer, thinner, more flexible): Borellia, Leptospira, Treponema
• Other shapes: Club-shaped (Cornyebacterium), comma-shaped (Vibrio, Bdellovibrio)
• Pleomorphic: No fixed shape; alter morphology based on environmental conditions
• Streptoccocus bacteria formlinear arrangements of cocci
• Streptobacilli form linear arrangements of rods
• Staphylococcus bacteria form clustered arrangements

Bacterial Processes (Division C Only)

• Transcription; information not present
• Translation; information not present
• DNA replication; information not present
• Gene regulation via operons; information not present

Gram Staining

• Classifies bacteria based on cell wall structure
• Method developed by Hans Christian Gram in 1884
• Heat-fixed bacteria are sequentially treated with four different reagents:

1. Cationic primary stain (crystal violet/methylene blue) that is taken up by both Gram-positive and Gram-negative bacteria

2. Mordant (Gram's iodine solution) creates complex with primary stain inside Gram + cell walls, preventing easy removal of the primary stain with a decolorizer

3. Decolorizer (ethanol/acetone) washes off primary stain from surface of Gram − bacteria

4. Counterstain (safranin, basic fuchsin, carbol fuchsin) stains both Gram + and Gram −, but not visible on Gram + cells due to darker color of primary stain

• Gram + : purple

  • Gram − : red/pink

Gram-positive vs. Gram-negative bacteria

• Gram-positive

  • Exotoxins
  • susceptible to phenol disinfectants which causes thick walls of peptidoglycan to retain crystal violet

• Gram-negative

  • Thinner walls of peptidoglycan
  • Produce red-pink results after Gram staining with safranin

• More difficult to kill Gram-negative bacteria with antibiotics due to complex cell membrane structure

Limitations of Gram Staining

• Not effective for acid-fast bacteria,which usually stain weakly Gram − or Gram-variable
• Similar to Gram −; thinner peptidoglycan + outer lipid membrane
• L-form/L-phase bacteria: Lack cell walls; stain Gram − (from Gram + or Gram −)
• Archaea: Varying results; do not align with archaean's phylogenetic relationships

Horizontal Gene Transfer

• Horizontal Gene Transfer

  • Conjugation: A bacterium can transfer some of its own DNA into other bacteria via pilus.

    • Transduction: A bacteriophage infects a bacterium, and takes some of its DNA after replication.
    • Transformation: After the process of lysis or death, a bacterium can take some of the of DNA fragments that were left behind of the other dead bacteria

Bacterial Motility

• Motility structures and composition; information not present
• Bacterial flagella are made of helical filaments made of protein flagellin
• Bacterial flagella are rotary motors
• Gram − bacteria have 4 basal protein rings

Flagellar Arrangements

• Monotrichous: One flagellum at one pole (Ex: Vibrio cholera)
• Amphitrichous: Single flagellum at each pole (Ex: Alcaligenes faecalis)
• Cephalotrichous: More than one flagellum on each pole of the cell
• Lophotrichous: Multiple flagella at one pole (Ex: Helicobacter pylori)
• Peritrichous: Many flagella across the surface (Ex: Escherichia Coli)
• Atrichous: Lacking flagella entirely (Ex: Lactobacillus delbrueckii)

Archaea

• Single-celled, prokaryotic microorganisms.
• First identified as a separate domain of life
• Thought to share a common ancestor with eukaryotes
• No species of archaea are known to form spores
• Many are extremophiles
• First to be discovered were extremophiles
• Involved in the carbon and nitrogen cycles, assist in digestion, and can be used in sewage treatment
• Play important roles in the human gut microbiome, methanogens
• Not known to cause any diseases in humans/organisms

Eukaryotic Microbes

• A eukaryote (Domain Eukarya) is a type of cell that has a nucleus and membrane-bound organelles
• Humans and plants are also part of the Domain Eukarya
• Examples of eukaryotes are algae, protozoa and fungi

Common Parts of Eukaryotic Cells

• Cell Wall: Plants and fungi, for protection and support, made of cellulose in plants and chitin in fungi
• Plasma Membrane: Semi-permeable, controls movement of substances
• Cilia: Small, beating extrusions to sweep materials
• Flagellum: Propels/moves cell, may have zero, one, two or many flagella
• Cytoplasm: Intracellular fluid with organelles
• Endoplasmic Reticulum (ER): Transports materials, synthesizes lipids, modifies polypeptides, contains rough ER and smooth ER (rough ER is mostly differentiated by the ribosomes on it, hence the term "rough")
• Ribosomes: Site of protein synthesis
• Golgi Apparatus: Modifies proteins and lipids, packs materials into vacuoles
• Mitochondria: Aerobic cell respiration, ATP production
• Hydrogenosomes: Anaerobic respiration in protozoa
• Lysosomes: Digests material or damaged tissue
• Chloroplasts: Store chlorophyll, Photosynthesis occurs here
• Vacuoles: Storage and can increase cell surface area
• Centrioles: Organize spindle fibers during division
• Cytoskeleton: Maintains shape and movement

Fungi

• Heterotrophic eukaryotes that can be single-celled or multi-celled

• More closely related to animals than plants

• Opisthokonts: derived from single posterior flagellum

• Spores of the Chytrids possess flagella

• Most of the types of animals and fungi have lost flagellated cells

• Previously 5 phyla of fungi, there has been 13 recognized more recently including, Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota, and Zygomycota, Basidiobolomycota, Blastocladiomycota, Entomophthoromycota, Entorrhizomycota, Kickxellomycota, Mortierellomycota, Mucoromycota, and Neocallimastigomycota

• Eumycota, also called "true fungi" or Fungi sensu stricto

• Ssister clades to the Eumycota that are now also considered to be fungi include the Aphelidiomycota, Rozellomycota, and Microsporidia

• Unlike animals (lack cell walls), fungi has cell walls = chitin (N-acetylglucosamine)

• Unlike plants (cell walls made of cellulose), both animal and fungi are chemoheterotrophic and lack chloroplasts

• Obtain nutrients by secreting enzymes for extracellular digestion and absorption of the resulting molecules

• Grow best in slightly acidic environments

• Thrive in moist environments but some in low moisture

• Sterols maintains membranes unlike the abundant sterol in plants

• Responsible for diseases in animals/plants with disease = mycosis

  • Examples: athlete’s foot/ringworm, dutch elm disease, early potato blight, ergotism, histoplasmosis, oral thrush, oak wilt

• Rusts (Pucciniomycotina) and smuts (Ustilaginomycotina) are two common types of fungal pathogens that belong to the phylum Basidiomycota and commonly infect plants

• rusts are named for the reddish appearance on infected plants and smuts are named for the black coloration of infected plants

• Play roles in agriculture, food production, industry, and environment

  • Baker’s yeast (Saccharomyces cerevisiae) used for bread/ alcoholic beverages
  • Found in cheeses (Gorgonzola, Stilton blue cheese, and Roquefort, Brie and Camembert) from Penicillium roqueforti/ Penicillium glaucum.

• Penicillin is the product of antibiotic by Penicillium chrysogenum

Lichens

• Symbiotic associations of eukaryotic and prokaryotic organisms
• Include filamentous fungal species (mycobiont) and photosynthetic species (photobiont/phycobiont)
• There is different morphologies - crustose, foliose, fruticose, leprose, squamulose lichens

Protists

• Paraphyletic group of non-fungal ,non-animal, and non-plant microbial eukaryotes.
• Usually divided into protozoa (animal-like, heterotrophic) and eukaryotic algae (plant-like, photosynthetic) but both refer to polyphyletic groups of organisms
• Some groups are fungus-like and now called "pseudofungi", contain the hypochytrids and oomycetes
• Unicellular or multicellular without specialized tissues
• Protists may be either unicellular or multicellular unlike plants
• Unlike plants, protists may contain different types of pigments and plastids, and do not have cuticles that prevent water loss

Eukaryotic Algae

• Photoautotrophic (photosynthetic but heterotrophic) but are not plants or Cyanobacteria (prokaryotes)
• Include coccolithophores (Prymnesiophyceae), diatoms (Bacillariophyceae/Bacillariophyta), dinoflagellates (Dinophyceae/Pyrrophyta), red algae (Rhodophyta), green algae (Prasinodermata, Chlorophyta, Charophyta), brown algae (Phaeophyceae), golden algae (Chrysophyceae), yellow-green algae (Xanthophyceae), and glaucophytes (Glaucophyta).
• Have different types of pigments and plastids (e.g., rhodoplasts in red algae) and aquatic or terrestrial environments

Protozoa

• Non-animal, non-fungal, heterotrophic eukaryotes include apicomplexans, ciliates, diplomonads, euglenids, forams, jakobids, kinetoplastids (including trypanosomes), oomycetes, parabasalids, radiolarians and more.
• Consume protists and bacteria for food
• Have complex life cycles
• Some protozoa, have two nuclei: macronucleus and micronucleus
• Protozoa move with cilia/flagella/pseudopodia
• May exist as a trophozoite (feeding form) or a cyst for protection against environment

Parasitic Worms (Helminths)

• Multicellular heterotrophs
• Flatworms (Platyhelminthes; cestodes, trematodes, monogeneans)
• Roundworms (Nematoda)
• Thorny-headed worms are a grouphighly modified Rotifers (Acanthocephalans, part of the phylum Rotifera)

Flatworms

• Constitute animal phylum Platyhelminthes with bilateraly symmetry; acoelomates
• Lack respiratory/circulatory systems so absorb and excrete gases through diffusion
• Have nervous system with tissues usually located at the worms' apical ends (near the head)
• Contains turbellaria/Neodermata (parasitic groups-cestodes, trematodes, and monogeneans)

Cestodes

• Class Cestoda includes orders Cestodaria/Eucestoda (tapeworms)
• Eucestodes have segmented bodies made up of subunits called proglottids, and strobilia attach to the neck
• Contain scolex (head), rostellum (muscular protrusion), hooks, bothridia ("true suckers"; shaped like a round crater) and bothria ("false suckers"; more of a narrow groove)
• Tegument is an exterior coating plays role in secretion and absorption
• Infect nearly every vertebrate species causing diseases like: taeniasis, cysticercosis, hymenolepiasis, diphyllobothriasis, alveolar echinococcosis, cystic echinococcosis, sparganosis, and dipylidiasis.

Trematodes

• Class of flatworms like blood, liver, lung, intestinal flukes
• Cause diseases such as schistosomiasis and foodborne trematodiases

Monogeneans

• Infect fish; not humans
• Mature are hermaphroditic

Turbellaria

• Paraphyletic clade discovered through phylogenetic analysis
• Now an obsolete and paraphyletic classification of flatworms

Roundworms

• Animal phylum Nematoda, exhibit bilateral symmetry
• Have complete digestive tract.
  • Stoma that functions as mouth
  • Excretory pore -Hydrostatic skeletons and has touqh outer layer
• Responsible for diseases
  • Roundworms parasitize plants often have spears known as a stylet to "drink" contents nutrients
  • Examples of disease: hookworm, pinworm, dog heartworm, whipworm, guinea worm disease, lymphatic filariasis, ascariasis, dioctophymosis, strongyloidiasis, and river blindness

Thorny-headed Worms

• (Acanthocephalans)
• Are a group of highly modified Rotifers often called spiny-headed worms that sometimes infect the human intestinal tract

Types of Extremophiles

• Extremophiles can thrive in extreme conditions and come in different verities such as hot springs, saline lakes, the ocean floor, deep-sea hydrothermal vents, acid mine drainage sites, cold deserts, and subglacial lakes

• Acidophiles and alkaliphiles that prefer lives very low or very high pH