Ch. 23.4 Ecology of Protists

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Was are the major ecological roles of protists?

Protists can be primary producers, food sources, decomposers, human pathogens, and plant pathogens.

Why are protists important as primary producers?

Photosynthetic protists produce organic matter that supports aquatic food webs.

Approximately what percentage of the world’s photosynthesis is preformed by photosynthetic protists?

About 25%

Which major group of protists are especially important photosynthetic producers?

Dinoflagellates, diatoms, and multicellular algae.

What is a mixotroph?

An organism that can obtain nutrition through both photosynthesis and heterotrophic feeding.

How can ciliates such as Paramecium bursaria become mixotrophic?

They can form symbiotic relationships with green algae that provide photosynthetic nutrients.

What are zooxanthellae?

Photosynthetic dinoflagellates that live symbiotically with organisms such as corals.

What do zooxanthellae provide corals?

They provide nutrients/energy from photosynthesis that help corals build their calcium carbonate skeletons.

What do corals provide their dinoflagellate symbionts?

A protected environment and compounds needed for photosynthesis.

What is coral bleaching?

The loss of algal pigments/symbiotic algae from coral, which can eventually cause th coral to die.

Why are reef-building corals generally not found much deeper than about 20 meters?

There is not enough light for their photosynthetic dinoflagellates at greater dephs.

Why are protists important to aquatic food chains?

They serve as primary producers and food sources for many aquatic organisms.

How do anaerobic parabasalids help termites and wood-eating cockroaches?

They help digest cellulose from wood.

What is a pathogen?

An organism that lives in or on a host and harms the host.

What major human diseases are caused by protists?

Malaria, African sickness, changes disease, amoebic encephalitis, and some forms of waterborne gastroenteritis.

What organism causes malaria?

Species of the protist genus Plasmodium

What type of protist is Plasmodium?

An apicomplexan.

What two types of hosts are required to complete the Plasmodium life cycle?

A mosquito and a vertebrae host, such as a human.

What happens to Plasmodium in the human liver?

It developed and multiplies in liver cells during the exoerythrocytic stage.

What happens during the erythrocytic stage of malaria?

Plasmodium infects red blood cells, multiplies, and causes them to burst.

What species of Plasmodium is the deadliest cause of human malaria?

Plasmodium falciparum

Why can P. falciparum cause severe amen?

It can infect and destroy a large proportion of a person’s red blood cells.

What causes the fever episodes associated with malaria?

Parasites bursting from red blood cells release waste products that trigger a strong immune/inflammatory response.

Which mosquito transmits Plasmodium falciparum?

The African mosquito Anopheles gambiae.

What genetic trait can provide some resistance to malaria?

Having one copy of the HbS beta-goblin allele.

What is the disadvantage of having two copies of the HbS allele?

Homozygosity causes sickle cell disease.

What disease is caused by Trypanosome brucei?

African sleeping sickness in humans.

What disease does Trypanosome brucei cause in cattle and horses?

Nagana.

How is Trypanosome brucei transmitted?

By tsetse flies.

How does T. brucei evade the human immune system?

It repeatedly changes its surface glycoproteins, allowing it to evade antibodies.

What can happen if African sleeping sickness caused by T. brucei is untreated?

The parasite can affect the centra nervous system, causing coma and eventually death.

What protist causes Chagas disease?

Trypanosoma cruzi

What insect primarily transmits Trypanosome cruzi?

The blood-sucking kissing bug (Triatoma)

What organs can be severely affected during chronic Chagas disease?

Especially the heart and digestive system.

What is Plasmopara viticola?

An oomycete that causes downy mildew in grape plants.

What effect did downy mildew have on the French wine industry?

It nearly collapsed the French wine industry in the 19th century.

What organism causes potato late blight?

Phytophthora infestans, a pathogenic oomycete.

What historical event was strongly associated with Phytophthora imfestams?

The Irish potato famine of the 19th century.

How does Phytophthora infestans affect potato plants?

It causes light blight, causing tissues to decay.

What were major consequences of the Irish potato famine?

Approximately 1 million people died and at least 1 million emigrated from Ireland.

Are oomycetes actually fungi?

No. They have fungus-like appearances, but molecular evidence shows they are not closely related to fungi.

What are saprobes?

Organisms that obtain nutrients by absorbing nutrients from dead organisms or organic wastes.

What is the ecological role of saprobic protists?

They decompose organic matter and recycle inorganic nutrients into soil and water.

Why are protist decomposers important to ecosystems?

They return nutrients to the environment so they can be reused by plants and other producers.

What would happen without decomposers such as protists, fungi, and bacteria?

Organic carbon and nutrients would become locked in dead organisms, disrupting ecosystems.

What is the difference between Plasmodium and Trypanosome brucei?

Plasmodium causes malaria and is transmitted by mosquitoes; T. brucei causes African sleeping sickness and is transmitted by tsetse flies.

What is the difference between a primary producer and a decomposer?

A producer creates organic matter, usually through photosynthesis; a decomposer breaks down dead organic matter and recycles nutrients.

What is the relationship between coral and zooxanthellae?

It is a symbiotic relationship: dinoflagellates provide photosynthetic nutrients to coral, while coral provides protection and materials needed for photosynthesis.

What a re the two major categories of protist roles emphasized in this section?

Beneficial ecological roles ( producers, food sources, decomposers) and harmful roles (human and plant pathogens)