Chapter 4 - Eukaryotic Cell & Microorganisms, Fungi, Protozoa, & Helminths

Fungi, Protozoa, & Helminths

All are Eukaryotic cells

Fungi - Types/Anatomy

• 3 types of fungi:

  • 1. Yeasts

    • Round or oval shape

    • Engage in asexual reproduction (ex. budding)

  • 2. Hyphae

    • Long, threadlike cells found in bodies of filamentous fungi (ex. molds)

  • 3. Dimorphic

    • Some fungal cells that can take either form, depending on growth conditions/environment (human pathogens)

      • So can shift b/w yeast & hyphae shapes

Fungi - Disease

• 3 types of fungal disease (Myocosis) in humans:

  • 1. Community-acquired infections: caused by environmental pathogens

  • 2. Hospital-associated infections: caused by fungal pathogens in clinical settings (HAIs, invasive devices)

  • 3. Opportunistic infections: caused by low-virulence species infecting already-weakened individuals

Fungi - Affecting Human Health

• 1. Harmless spores can cause opportunistic infections in immunocompromised patients (like those w/ AIDs)

• 2. Fungal cell walls give off chemical substances that can trigger allergies

• 3. Toxins produced by poisonous mushrooms can induce neurological disturbances & even death

• 4. Aspergillus flavus synthesizes a poison called aflatoxin, potentially lethal to animals who eat contaminated grain

Fungi - Agricultural Impact

• A number of species are pathogenic to corn & grain

  • Reduces crop production

  • Can cause disease in domestic animals consuming contaminated feed crops

• Fungi rot fresh produce during shipping & storage (spoilage)

  • 40% of yearly fruit crop is consumed by fungi

Fungi - Benefits

• 1. Play an essential role in decomposing organic matter & returning minerals to the soil

• 2. Form stable associations w/ plant roots & increase their ability to absorb water & nutrients

• 3. Fungi have been engineered to produce large quantities of antibiotics, alcohol, organic acids, & vitamins

• 4. Some fungi are eaten or used to provide flavoring to food (ex. mushrooms)

Fungi - Nutrition

• Heterotrophic: acquire nutrients from a wide variety of organic substrates

• Saprobic: these substrates are from the remnants of dead plants & animals in soil or aquatic habitats

• Parasitic: grow on the bodies of living animals or plants, although very few require a living host

• Fungi penetrate the substrate & secrete enzymes that reduces it to small molecules that can be absorbed by the cells

  • Can grow on wood, feathers, rubber, cellulose, & petroleum products

Fungi - Reproductive Strategies

• 2 types of strategies:

  • 1. Most can propagate by the outward growth of existing hyphae or by fragmentation (only hyphae can participate in fragmentation!)

  • 2. Spores: primary reproductive mode of fungi

    • 2 types of spores = asexual & sexual

    • Can be dispersed through the environment by air, water, & living things

    • Will germinate upon finding a favorable substrate & produce a new fungus colony in a short time

Fungal spores vs. Bacterial spores

• Fungal spores = for reproduction

• Bacterial spores = for survival

Protozoa - Anatomy

• Single-celled/unicellular eukaryotes

• Most are harmless, free-living inhabitants of water & soil

  • A few species are pathogens responsible for hundreds of millions of infections each year

• Cytoplasm divided into 2 parts:

  • Ectoplasm: clear, outer layer involved in locomotion (movement), feeding, & protection

  • Endoplasm: granular, inner region housing the nucleus, mitochondria, & food/contractile vacuoles

Protozoa - Characteristics

• Can move through fluids by means of pseudopods (false feet), cilia, & flagella

• Cell membrane regulates food, wastes, & secretions; do not possess cell walls

• Cell shape can remain constant (most ciliates), or change constantly (ameobas)

• Predominant habitats are fresh & marine water, soil, plants, & animals

Protozoa - Life Cycles

• Trophozoite: motile feeding (active) stage requiring ample food & moisture to stay active

• Cyst: dormant, resting stage when conditions in the environment become unfavorable

  • Resistant to heat, drying, & chemicals

  • Can be dispersed by air currents

  • Important factor in the spread of disease

Protozoa - Life Cycles & Transmission

• Some protozoan groups exist only in the trophozoite phase (where they can be easily killed)

  • Ex. Trichomonas vaginalis, a common STD, does not form cysts & must be transmitted by intimate contact

• Many alternate b/w the trophozoite & cyst stage, depending on habitat

  • Ex. Entamoeba histolytica & Giardia lamblia form cysts & are readily transmitted in contaminated water & foods

Protozoa - Types

• 1. Aboeboid Protozoa (2 types)

• 2. Ciliated Protozoa (1 type)

• 3. Flagellated Protozoa (2 types)

• 4. Apicomplexan Protozoa (2 types)

Helminths - Types

• Flatworms (tapeworms, flukes) & Roundworms

• Adult specimens are usually large enough to be seen w/ the naked eye

• Not all flatworms & roundworms are parasites; many live free in soil & water

• Disease-causing helminths spend part of their lives in the gastrointestinal tract

Helminths - Flatworms

• Very thin, often segmented body plan

• Divided into cestodes

• 2 types:

  • 1. Tapeworms

  • 2. Flukes

Helminths - Roundworms

• Also called nematodes

• Elongated, cylindrical, unsegmented body

Reproduction of Helminths

• Complete life cycles includes the fertilized egg, larval, & adult stages

• Adults derive nutrients & reproduce sexually in a host’s body

• 1. Nematodes (roundworms): sexes are separate & different in appearance

• 2. Flukes: sexes can be separate or hermaphroditic (both male & female)

• 3. Tapeworm: generally hermaphroditic (both male & female)

Life Cycle of Helminths

• Must transmit an infective form (egg or larva) to the body of another host

• Sources for human infection are contaminated food, soil, & water or infected animals

Life Cycle of Helminths - Pinworm (Roundworm)

• 1. Microscopic eggs are swallowed - picked up from another infected person or objects they have touched (ex. kids getting infections from toys)

• 2. Eggs hatch in the intestine

• 3. Larvae mature into adults within 1 month

• 4. Male & female worms mate

• 5. Female migrates to the anus to deposit eggs

• 6. Intense itching ensues

• 7. Scratching spreads the eggs