The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

Ch 12 

The Eukaryotes: 

Fungi, Algae, 

Protozoa, and 

Helminths 

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Student Learning Outcomes 

• List the defining characteristics of fungi. 

• Identify two beneficial and two harmful effects of fungi. 

• List the defining characteristics of protozoa. 

• Differentiate an intermediate host from a definitive host. 

• List the distinguishing characteristics of the two classes of 

parasitic helminths, and give an example of each. 

• Provide a rationale for the elaborate life cycles of parasitic 

worms. 

• Define arthropod vector. 

• Differentiate between a tick and a mosquito, and name a 

disease transmitted by each. 


FUNGI 

• Chemoheterotroph, aerobic 

(molds) or facultatively 

anaerobic (yeasts) 

• Mycology: Study of fungi 

• Most fungi decomposers, few 

are parasites of plants and 

animals. 

• # of serious fungal infections 

increasing 

Fig. 12.1 

Review Table 12.2 


Characteristics of Fungi 

• Hyphae: Filaments of cells, 

mostly septate 

• Mycelium: Mass of hyphae. 

• Molds: mostly filamentous. 

• Yeasts: nonfilamentous, unicellular fungi. 

• Budding yeasts divide asymmetrically. 

• Dimorphic fungi: yeasts like 37C, molds 25C. 

• Fungal spores differ from bacterial spores. Form from 

aerial hyphae. 

• Growth in acidic, low-moisture, high osmotic pressure 

environments. 

• Copyright Metabolize © 2010 Pearson Education, Inc. complex carbohydrates (e.g.: lignin).

Economic Effects of Fungi 

• Saccharomyces cerevisiae: Bread, wine, HBV 

vaccine 

• Trichoderma: Cellulase 

• Taxomyces: Taxol 

• Entomophaga: Biocontrol 

• Paecilomyces: Kills termites 

• Mold spoilage 


Fungal Diseases – Mycoses 

1. Systemic mycosis: infection deep within body, 

affects many tissues and organs. Histoplasmosis and 

coccidiomycosis. 

2. Subcutaneous mycosis: Saprophytic fungi, e.g.: 

Sporotrichosis. 

3. Cutaneous mycosis = Dermatomycosis: affects 

keratin-containing tissues (hair, nails, skin). 

4. Superficial mycosis: localized on hair shafts and 

superficial skin cells. 

Opportunistic mycoses: 

• caused by normal microbiota or fungi that are not 

usually pathogenic (E.g.: Candidiasis and 

Pneumocystis pneumonia) 

• usually systemic. 


Human eyelash 

with unknown 

fungus infection. 

Minimal damage to 

skin or underlying 

tissues. 

However, impaired 

IS can encourage 

the infecting fungus 

to proliferate. 


ALGAE 

Mostly photoautotrophs, 

mostly in ocean 

Diatoms 

• Unicellular, store 

energy in form of oil 

• Domoic acid Neurological disease 

• Ingestion of mussels that fed on diatomes (also 

affects birds and sealions) 

Dinoflagellates (plankton) 

• Some produce neurotoxins: red tide 

• Kills fish, marine mammals, and humans, e.g.: 

parasitic shellfish poisoning (PSP) 


PROTOZOA 

Unicellular, 

eukaryotic 

chemoheterotrophs. Large and diverse group. Few 

are pathogenic. 

Found in soil and water and as normal microbiota in 

animals. 

Trophozoite: Vegetative form (feeding and growing). 

Asexual reproduction via fission, budding, or 

schizogony (multiple fission). 

Sexual reproduction via conjugation. 

Some protozoa can produce a cyst that provides 

protection during adverse environmental conditions. 


Medically Important Protozoa 

1. Arcaezoa (lack mitochondria) 

• Trichomonas and 

• Giardia 

2. Microspora (no mitochondria and no microtubules) 

– diarrhea and keratoconjunctivitis in AIDS patients 

3. Amoebozoa (move via pseudopodia) 

• Entamoeba (dysentery) and Acanthamoeba 

4. Apicomplexa: not mobile, intracellular 

• Plasmodium, Babesia, Toxoplasma, Cryptosporidium 

5. Euglenozoa: Hemoflagellates 

• Trypanosoma 


Amoebozoa 

• Move by 

pseudopods 

• Entamoeba 

• Acanthamoeba 


The Life Cycle of Plasmodium vivax 

2 

3 

8 

7 

6 

Fig 12.18

Euglenozoa 

• Move by flagella 

• Hemoflagellates 

• Trypanosoma spp. 

Sleeping 

sickness 

Chagas’ 

disease 

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Fig 23..22

HELMINTHS (Parasitic Worm) 

• Kingdom: Animalia 

• Phylum: Platyhelminthes 

(flatworms) 

Class: Trematodes (flukes) 

Class: Cestodes (tapeworms) 

• Phylum: Nematoda (roundworms) 

• few are human parasites 

• Anatomy and life cycle modified for 

parasitism 

• Adult stage in definitive host. 

• Each larval stage in specific 

Copyright intermediate © 2010 Pearson Education, Inc. host.

Life Cycle of Helminths 

• Monoecious (hermaphroditic) 

• Male and female reproductive systems in one animal 

• Dioecious 

• Separate male and female 

• Egg larva(e) adult 


Platyhelminths 

• Dorsoventrally flattened 

Trematode, or fluke: Oral and ventral sucker attaches 

to host tissue 

• Cestode, or tapeworm: Scolex (head), proglottids 

4 suckers and 

rostellum with hooks 

Fig 12.26 

Gravid proglottid with 

uterine branches

Taenia solium 

Taenia saginata 


Human definitive host; 

pig or cattle intermediate host.

Echinococcus granulosus 

Fig. 12. 27

Human as 

Human is …. 

Definitive Host 

Taenia saginata 

Cysticerci in beef 

muscle 

Intermediate Host 

Echinococcus 

granulosus 

Adult in dog

. 

Nematodes 

Roundworms have a complete digestive system 

Eggs infective for humans: 

• Ascaris lumbricoides: Ascariasis. 2 nd most 

common worm infection in US. (Most common 

worldwide; > 1 bio infected) 

• Enterobius vermicularis (pinworm). Most 

common worm infection in US (30% of 

children, 16% of adults infected) 

• 


Pinworm / Enterobius vermicularis 


Fig12.28

Do test immediately 

after waking up. 

Several samples 

might need to be 

examined. 

Since scratching of 

the anal area is 

common, samples 

taken from under the 

fingernails may also 

contain eggs. 

Diagnosing Pinworm Disease 

pinworm paddle

Larvae Infective for Humans 

Fig 25.23 

Hookworms 

Ancylostoma duodenale and 

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Inc.

Trichinellosis: 

The Life Cycle of Trichinella spiralis

The Heartworm Dirofilaria immitis 

Primarily in dogs and cats human heart failure, 

also in human lungs 

Spread via mosquitoes 


Fig 12.29

ARTHROPODS AS VECTORS 

Kingdom: Animalia 

• Phylum: Arthropoda (exoskeleton, jointed legs, segmented body) 

Class: Insecta (6 legs) 

Lice, fleas, mosquitoes 

Class: Arachnida (8 legs) 

Mites and ticks 

• Arthropods that carry diseases are called vectors. 

• Elimination of vectorborne 

diseases best via control or 

eradication of vectors. 


Arthropod Vectors 

• Mechanical transmission 

• Biological transmission 

• Microbe multiplies in vector 

• Definitive host 

• Microbe’s sexual reproduction in vector 

Fig 12.32

The Eukaryotes: Fungi, Algae, Protozoa, and Helminths

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