Eukaryotes: Fungi, Algae, Protozoa, and Helminths Notes

Fungi

• Kingdom: Fungi
• Chemoheterotrophs: Acquire food by absorption.
• Mostly multicellular (except yeasts).
• Reproduce with sexual and asexual spores.
• Mycology: The study of fungi.

Structure of Fungi

• Includes unicellular yeasts and multicellular molds (e.g., Rhizopus stolonifer).

Characteristics of Fungi

• Heterotrophic: Obtain energy by decomposing organic material.
• Structures: Made of filamentous cells.
• Cell walls: Contain chitin.
• Nuclear Mitosis: Nucleus divides without cytokinesis.

Structures

• Hyphae: Slender woven filaments.
• Mycelium: Tangled mass of hyphae making up fungal structures.

Types of Hyphae

• Septate Hyphae:
  • Multicellular.
  • Walls divided by septa.
• Coenocytic Hyphae:
  • Continuous cytoplasm mass.
  • Multinucleate.
  • No septa.

Mycelium

• Mass of branching intertwined hyphae.
  • Vegetative Mycelium: Hyphae penetrate the supporting medium and absorb nutrients.
  • Aerial Mycelium: Hyphae project above the surface and bear reproductive structures (conidia).

Mold

• Main body: Made of fine, branching hyphae.
• Mycelium: Tangled web formed by intertwined hyphae.
• Septum: Divides hyphae into cells or compartments with central pores for cytoplasm movement.

Yeast

• Microscopic, unicellular fungi with a single nucleus and eukaryotic organelles.
• Shape: Oval or round.
• Reproduction: Asexual budding; a new cell forms, enlarges, and breaks free.

Yeast vs. Mold: Characteristics

Nutrients

• Fungi are decomposers.
• Obtain energy by secreting digestive enzymes and absorbing decomposed nutrients.

Reproduction

• Most fungi reproduce by releasing spores (asexual or sexual).
• Spores are haploid and fuse to create a diploid stage.
• Spores are small and lightweight to stay suspended in the air.

Asexual Spores

• Sporangiospores:
  • Example: Rhizopus species (Zygomycete).
• Conidia:
  • Example: Aspergillus species.

Reproduction in Fungi

• Sexual Reproduction:
  • Compatible nuclei unite within the mycelium to form sexual spores.
  • Can occur within a single mycelium or require different mycelia.
  • Cell union leads to nuclear fusion and diploid nucleus formation.

Classification of Fungi

• Four divisions:
  1. Ascomycetes
  2. Basidiomycetes
  3. Zygomycetes
  4. Deuteromycetes

Ascomycetes

• Sexual spores: Ascospores produced within a sac-like structure (ascus).
• Asexual reproduction: Conidia.
• Hyphae: Generally septated.
• Examples: Saccharomyces, Arthroderma.

Basidiomycetes

• Sexual spores: Basidiospores produced externally on a basidium.
• Asexual reproduction: Budding, fragmentation, or conidia formation.
• Commonly called mushroom group.
• Hyphae: Generally septated.
• Examples: Amanita, Agaricus.

Zygomycetes

• Sexual spores: Zygospores formed by fusion of two similar cells.
• Asexual reproduction: Sporangiospores.
• Hyphae: Generally aseptated.
• Examples: Rhizopus, Mucor.

Deuteromycetes

• No sexual stage present (Fungi Imperfecti).
• Asexual reproduction: Conidia.
• Most human and animal pathogens.
• Examples: Candida, Cryptococcus, Trichophyton, Epidermophyton, Histoplasma.

Nutritional Adaptations

• Adapted to hostile environments for bacteria.
• Chemoheterotrophs: Absorb nutrients.
• pH Preference: Grow better at pH 5 (too acidic for most bacteria).
• Aerobic: Almost all molds; most yeasts are facultative anaerobes.
• Osmotic Pressure: More resistant than bacteria (grow in high sugar/salt concentrations).
• Moisture Content: Can grow on substances with low moisture content.

Medically Important Fungi

• Common as contaminants in foods and lab cultures.

Zygomycota

• Conjugation fungi.
• Saprophytic molds with coenocytic hyphae.
• Example: Rhizopus stolonifer (black bread mold).
• Role in carbon cycle: Decompose soil, plant matter, and dung.

Microsporidia

• Unusual eukaryotes lacking mitochondria and microtubules.
• Obligate intracellular parasites.
• Cause human diseases including chronic diarrhea and keratoconjunctivitis, especially in AIDS patients.

Ascomycota

• Largest and most diverse group.
• Sac fungi, include molds with septate hyphae and some yeasts.
• Asexual spores: Conidia (dust-like).
• Examples: Morel and truffles.

Basidiomycota

• Club fungi, possess septate hyphae.
• Include fungi that produce mushrooms.
• Importance: Some are poisonous, high in protein/calcium/phosphorous, nutrient cycling, pharmaceuticals.

Fungal Diseases

• Mycosis: Any fungal infection (generally chronic due to slow growth).
• Classification: Systemic, subcutaneous, cutaneous, superficial, or opportunistic based on tissue involvement and mode of entry.

Fungal Infection of Humans

• Subcutaneous Mycoses: Infections beneath the skin caused by saprophytic fungi in soil and vegetation.
  • Example: Sporotrichosis (rose gardener’s disease).
• Cutaneous Mycoses: Infections of the epidermis, hair, and nails (dermatophytes).
  • Transmission: Human to human or animal to human by direct contact.
• Opportunistic Mycoses: Infections in immunocompromised hosts.
  • Causes: Overuse of antibiotics, corticosteroids, and immunosuppressive drugs.

Economic Effects of Fungi

• Aspergillus niger: Citric acid production for foods and beverages.
• Saccharomyces cerevisiae: Bread and wine making, genetically modified for protein production (e.g., hepatitis B vaccine).
• Trichoderma: Cellulase enzyme production for clear fruit juice.
• Coniothyrium minitans: Biological control for fungi that destroy soybeans and bean crops.
• Paecilomyces fumosoroseus: Termite control in trees.

Harmful Effects of Fungi

• Human illness: Poisonings, parasitic infections, and allergic reactions.

Lichens

• Combination of green alga (or cyanobacterium) and a fungus (typically an ascomycete).
• Mutualistic relationship (both partners benefit).
• Can colonize newly exposed soil or rock where neither fungi nor algae could survive alone.

Characteristics

• Secrete organic acids to weather rock and accumulate nutrients for plant growth.
• Slow-growing organisms found on trees, concrete, and rooftops.

Morphologic Categories

• Crustose: Grow flush or encrusted onto the substratum.
• Foliose: Leaflike.
• Fruticose: Fingerlike projections.

Economic Importance

• Ancient Greece and Europe: Dyes for clothing.
• Usnic acid (from Usnea): Antimicrobial agent in China.
• Erythrolitmin: Dye used in litmus paper.
• Some lichens: Cause allergic contact dermatitis in humans.

Algae

• Photoautotrophs lacking roots and stems of plants.
• Mostly aquatic.
• Can be unicellular, filamentous, or thalli.

Characteristics of Algae

• Vegetative Structures:
  • Thallus: Body of multicellular alga.
  • Seaweeds: Branched holdfasts, stipes, and leaflike blades.
  • Photosynthesis: Carried out by cells covering the thallus.
  • Nutrient Absorption: Occurs over the entire surface due to lack of conductive tissue.
  • Stipe: Not lignified, supported by surrounding water; some have pneumatocysts (gas-filled bladders).

Life Cycle

• Asexual Reproduction:
  • Multicellular algae: Fragmentation.
  • Unicellular algae: Mitosis and cytokinesis.
• Sexual Reproduction:
  • Some species alternate between asexual and sexual reproduction.
  • Other species have alternating generations.

Nutrition

• Most algae are photosynthetic.
• Oomycotes (fungal-like algae) are chemoheterotrophs.
• Photosynthetic algae are found in the photic zone.
• Chlorophyll a and accessory pigments give algae their distinct colors.

Roles of Algae in Nature

• Important in aquatic food chains: Fix carbon dioxide into organic molecules.
• Convert atmospheric carbon dioxide into carbohydrates via photophosphorylation.
• Produce molecular oxygen (O2) as a byproduct of photosynthesis.
• Algal blooms: Periodic increases in planktonic algae due to seasonal changes.
  • Dinoflagellates: Responsible for seasonal red tides.
  • Certain species indicate polluted water due to high concentrations of organic materials.
• Decomposition of algal blooms: Depletes dissolved oxygen in water.
• Petroleum Formation: Diatoms and planktonic organisms buried by sediments millions of years ago.
  • Organic molecules transformed into hydrocarbons (petroleum and natural gas) by heat and pressure.

Protozoa

• Diverse group of unicellular eukaryotic organisms (“first animals”).
• Heterotrophic organisms without chlorophyll.
• Examples: Amoeba, paramecium, euglena.

Characteristics

• Acellular or non-cellular: Body consists of mass of protoplasm.
• Habitat: Mostly aquatic, free-living or parasitic.
• Size: 1 to 10 micrometers (Balantidium coli may measure up to 150 micrometers).
• Body: Naked or covered by a pellicle.
• Locomotion: Pseudopodia, cilia, or absent.
• Nutrition: Holophytic, holozoic, saprophytic, or parasitic.
• Digestion: Intracellular, in food vacuoles.
• Respiration: Through the body surface.

Cytoplasm

• Differentiated into ectoplasm (outer layer) and endoplasm (inner layer with organelles).
• Structure prominent in species with pseudopodia, like amoebas.

Reproduction

• Both sexual and asexual reproduction.
  • Asexual: Binary fission.
  • Sexual: Conjugation.
• Nucleus: Compact with diffuse chromatin or vesicular with karyosome and peripheral chromatin.

Encystment

• Protective capsule (cyst) produced under adverse conditions.
• Allows survival without food, moisture, or oxygen, or in unsuitable temperatures or toxic chemicals.
• Enables parasitic species to survive outside a host and move between hosts.
• Oocyst: Cyst formed in Apicomplexa, reproductive structure for asexual cell production.
• Excystation: Cyst wall ruptures to release the organism in favorable conditions.

Beneficial Protozoa

• Food: For insect larvae and worms, which feed fishes, crabs, and humans.
• Insect control: Control harmful insects by persisting in their bodies.
• Sanitation: Feed on organic matter in polluted water, thus purifying it.
• Oil exploration: Indicators of oil deposits.
• Scientific study: Used in biological and medical researches.

Harmful Protozoa

• Pollution of water: Make drinking water unpalatable.
• Destruction of wooden articles: Flagellates in termite guts aid cellulose digestion.
• Reduction in Soil fertility: Protozoa feed on nitrogen-fixing bacteria.

Slime Molds

• Have both fungal and amoebal characteristics, more closely related to amoeba.
• Two taxa: Cellular and plasmodial.

Cellular Slime Molds

• Live as ameboid individual cells.
• Cluster in times of stress to sexually reproduce.

Plasmodial Slime Molds

• Move as a group.
• Live mostly on forest floors.
• Not made from individual cells.
• Form sexually reproductive structures in times of stress.

Water Molds

• Branching cells grouped together.
• Mostly live in fresh water.
• Infamous for causing the Irish Potato Famine (Phytophthora infestans).

Helminths

• Parasitic animals that spend part or all of their lives in humans.
• Phylum Platyhelminths: Parasitic flatworms.
• Phylum Nematoda: Parasitic roundworms.
• Multicellular animals.

Characteristics of Helminths

• Multicellular eukaryotic animals with digestive, circulatory, nervous, excretory, and reproductive systems.
• Parasitic helminths are highly specialized to live inside hosts.
  1. Lack of digestive system: Absorb nutrients from host’s food, body fluids, and tissues.
  2. Reduced nervous system: Less need to search for food or respond to the environment.
  3. Reduced locomotion: Transferred from host to host.
  4. Complex reproductive system: Produce large numbers of eggs to infect suitable hosts.

Platyhelminths (Flatworms)

• Parasitic flatworms may lack a digestive system.
• Classes: Trematodes and cestodes.
  1. Trematodes (Flukes):
     • Oral and ventral sucker to attach to host tissue.
     • Obtain food by absorbing through the cuticle.
  2. Cestodes (Tapeworms):
     • Intestinal parasites with a scolex (head) and proglottids (body).
     • Scolex has suckers and hooks for attachment.
     • Lack a digestive system and absorb food through their cuticle.

Humans as Definitive Hosts

• Taenia saginata (beef tapeworm): Adults live in humans, can reach 6 m in length.
• Feces of infected humans contain mature proglottids with thousands of eggs.

Nematodes (Roundworms)

• Complete digestive system (mouth, intestine, and anus).
• Nematode infections of humans:
  • Infection via Eggs: Ascaris, Trichuris, and Enterobius.
    • Adult Ascaris lives in the small intestine, feeds on partially digested food, can cause intestinal blockage.
  • Infection via Larvae: Hookworms and Trichinella.
    • Larva penetrates host skin, enters blood or lymph, travels to lungs, is coughed up, swallowed, and ends up in the small intestine.
    • Trichinellosis: Acquired by eating encysted larvae in undercooked meat.

Arthropods as Vectors

• Arthropods: Animals with segmented bodies, hard external skeletons, and jointed legs.
• Vectors: Arthropods that carry pathogenic microorganisms.
• Classes:
  • Arachnida (eight legs): Spiders, mites, ticks.
  • Crustacea (four antennae): Crabs, crayfish.
  • Insecta (six legs): Bees, flies, lice.
• Some vectors act as mechanical transporters of pathogens (e.g., houseflies).
• Some parasites multiply in vectors and accumulate in feces or saliva.
• Vectorborne disease elimination: Focus on eradicating the vectors.