Chapter 12:The Eukaryotes: Fungi,
Algae, Protozoa and Helminths
Kingdom FungiThe Fungi
• Aerobic (molds and yeasts) or facultatively anaerobic (yeasts)
• Chemoheterotrophic
• Most are decomposers
• Mycology is the study of fungi
• >100,000 species
─ ~200 are pathogenic to humans/animals
Fungi vs. Bacteria
asexual
• Filamentous fungi (mostly aerobic)
─ Hyphae: cellular filaments
◦ Vegetative hyphae: responsible for obtaining nutrients
◦ Aerial hyphae: responsible for reproduction (often bear spores)
─ Mycelium: macroscopic mass of hyphae
The Fungi:Molds
Figure 12.2
The Fungi:Molds
Figure 12.1
• Reproduction
─ Fragmentation of hyphae (asexual)
─ Production of spores (sexual or asexual)
◦ Asexual spores: from hyphae of one organism; genetically identical to parent
◦ Sexual spores: from fusion of two nuclei of opposite mating strains of the same species
◦ Released spores will germinate to form a new mold
◦ Spores may be important in identification of fungal species
Figure 12.5
• Nonfilamentous, unicellular, round/oval
• Reproduce by budding or fission
• Capable of facultative anaerobic growth
─ Absence of oxygen, ferment carbohydrates into alcohol and carbon dioxide
The Fungi:Yeasts
Figure 12.3
The Fungi:Dimorphism
• Demonstrate both yeastlike and moldlike growth, depending on environmental conditions (temperature, CO2 levels, etc.)
Figure 24.17
The Fungi:Adaptations
Fungi have adapted to thrive where many bacteria can’t
• Good growth at pH 5
• Tolerant of high osmotic pressure
• Growth in the presence of low moisture
• Metabolize complex carbohydrates that most bacteria cannot
Molds are likely to spoil food that bacteria can’t
Mycoses are typically serious in immunocompromised individuals
• Systemic mycoses Deep within body
• Subcutaneous mycoses Beneath the skin
• Cutaneous mycoses Affect hair, skin, nails
• Opportunistic mycoses Caused by normal microbiota or fungi that
are left unchecked
The Fungi:Infections (mycoses)
The Fungi:Infections (mycoses)• Candidiasis: Candida albicans (Cutaneous
mycosis)
─ Constituent of normal microbiota of the genitourinary tract and mouth (relatively small population)
─ Infection frequently occurs in people treated with broad-spectrum antibacterial drugs
─ Thrush, vaginitis (yeast infections)
Figure 21.17
The Fungi:Infections (mycoses)
• Pneumocystis pneumonia: most common life-threatening infection for AIDS patients
─ Pneumocystis jiroveci
─ Opportunistic fungus
─ Systemic mycosis; uncommon before AIDS epidemic
◦ Considered to be an initial clue for AIDS
Kingdom Protista:The Protozoa
• Unicellular eukaryotes
• Found mostly in soil and water
─ Mostly aerobic
• Chemoheterotrophs
• Vegetative form is a trophozoite
─ Feeding/growing stage, typically motile
• Digestion in vacuoles, waste eliminated through plasma membrane or an anal pore
• Asexual reproduction by fission, budding, or schizogony (multiple fission)
─ Sexual reproduction by some
• Live in areas with large supply of water
• Some produce cysts in adverse conditions
─ Protective capsule
─ Survival in harsh conditions
─ Survival of parasitic species outside of host
Protozoa
• Trichomonas vaginalis
─ Parasite
─ No cyst stage
Parasitic Protozoa:Role of Cysts
Figure 12.17b
Parasitic Protozoa:Role of Cysts• Giardiasis (prolonged diarrhea)
─ Giardia lamblia attaches firmly to human intestinal wall
─ ~7% of humans are healthy carriers; shed cysts in feces
─ Most outbreaks due to contaminated water supplies
─ Diagnosis: presence of cysts in feces or the string test (to detect trophozoites in upper bowel)
Figure 12.17dFigure 25.18www.sciencedaily.com
Protozoa:Mechanisms of Motility
• Mechanisms of motility:
─ Cilia
─ Flagella
─ Pseudopods
◦ May also be used for food ingestion (phagocytosis)
Figure 12.18a
• Some species have complex life cycles
─ Multiple hosts
• Plasmodium (causes malaria)
Parasitic Protozoa:Complex Life Cycles
Plasmodium and Malaria• Malaria: 300-500 mill people worldwide are infected each
year
• Two hosts:
─ Mosquito
◦ Definitive host: harbors sexually reproducing stage
─ Human
◦ Intermediate host: harbors asexually reproducing stage
◦ Destruction of red blood cells (anemia)
◦ Release of toxins (fever/chill cycles)
◦ Alteration of RBC shape can clog tissue capillaries (kidney, liver, brain damage)
Figure 23.25
Parasitic Protozoa with Complex Life Cycles:
PlasmodiumInfected mosquito bites human; sporozoites migrate through bloodstream to liver of human
Schizogony in liver cell; merozoites are produced
Merozoites released into bloodsteam may infect new red blood cells
Merozoites are released when red blood cell ruptures; some infect new red blood cells, and some develop into male and female gametocytes
1 2
3
4
6
Asexual reproduction
Intermediate host
Merozoite develops into ring stage in red blood cell
Ringstage
Merozoites
Another mosquito bites infected human and ingests gametocytes
7
5 Ring stage grows and divides, producing merozoites
Definitive host
In mosquito’s digestive tract, gametocytes unite to form zygote
8
Male gametocyte
Female gametocyte
Zygote
Sexualreproduction
Resulting sporozoites migrate to salivary glands of mosquito
9
Sporozoites in salivary gland
Figure 12.19
Kingdom Animalia:The Helminths
• Helminths (parasitic worms)
─ Multicellular animals
─ Chemoheterotrophic
─ Complex life cycles (often several hosts)
◦ Intermediate and definitive hosts
◦Transmission usually by ingestion
─ Often produce few symptoms
Animalia
Platyhelminthes(Flatworms)
Nematodes(Roundworms)
Flukes Tapeworms
The HelminthsCharacteristics that distinguish parasitic helminths
from other free-living animals:
• May lack a digestive system (can absorb nutrients from host)
• Reduced nervous system (don’t have to search for food or respond much)
• Locomotion may be reduced or absent
• Often complex reproductive system
─ Monoecious: hermaphroditic
─ Dioecious: separate sexes
The Helminths:Flukes
• Flat, leaf-shaped
• Oral and ventral suckers hold fluke in place
• Absorb food through cuticle
Figure 12.25
The Helminths:Lung Fluke life cycle
Figure 12.26
Diagnosis
The Helminths:Tapeworms
• Intestinal parasites
─ Complete lack of digestive system
• Scolex (head) includes suckers and hooks for attachment
• Segmented
─ Proglottids: contain male and female reproductive organs
◦ When mature, they are “bags of eggs”
Figure 12.27
The Helminths:Tapeworms• Beef tapeworm (Taenia
saginata)
─ Cattle ingest proglottids
─ Larvae hatch, bore through intestinal wall and migrate to muscle (meat) and encyst (cysticerci)
─ Humans eat infected meat, and digest all parts except the scolex
─ Scolex latches on to intestinal wall and begins producing proglottids (can grow up to 6 meters!)
◦ Vague abdominal discomfort
• Diagnosis: presence of proglottids/eggs in feces
The Helminths:Roundworms
• Cylindrical, tapered at the ends
• Complete digestive system
• Motile
• Mostly dioecious
Figure 25.21
Figure 25.25
• Ascariasis (Ascaris lumbricoides)
─ Acquired by ingestion of eggs
◦ Eggs, excreted in feces, can survive in soil up to 10 yr
─ Larvae travel to lungs, where they grow
─ Adults up to 1 foot in length, inhabit small intestine
─ Diagnosis: presence of eggs in feces
The Helminths:Roundworms
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