Chapter 15

Question 1

What is a parasite?

Answer 1

Lives in or on another organism (host)

Consumes host resources

Causes harm to host

A pathogen is a type of parasite that causes infecBous disease.

Question 2

Ectoparasites

Answer 2

live on the outside of an organism.

Mostly arthropods (e.g., ticks, mites, lice, fleas)
Includes some leeches, lampreys
Nematodes
~4000 plants (e.g., mistletoe)

Question 3

Endoparasites

Answer 3

live inside organisms.

Question 4

Types of endoparasites

Answer 4

Viruses 
Prions
 Protozoans
 Bacteria
 Fungi 
Helminths

Question 5

Prions

Answer 5

They begin as beneficial brain proteins.

A protein folds into an incorrect shape and becomes pathogenic.

It replicates by coming into contact with other proteins.

Transmission occurs through consumpBon of infected dead animals or their feces.

Question 6

Bacteria

Answer 6

single-celled prokaryotes

Examples:
“Shot hole” plant bacteria “Crown gall”
Anthrax
Plague
Pneumonia Salmonella Leprosy

Question 7

Fungi

Answer 7

Devastates many plant species

Examples:
Loss of American elm from Dutch elm disease
Loss of American chestnut from Cryphonectria parasitca

Question 8

Batrachochytrium dendrobatidis

Answer 8

Fungus that lives in the outer layer of amphibian skin; causes ion imbalance.

It rapidly spread across Central America.

It is now the suspected cause of dozens of amphibian extinctions.

Question 9

Helminths

Answer 9

Include several species of roundworms and flatworms

Examples:
Hookworms that feed on blood of intestines
Lungworms that live in the lungs
Echinostomes that live in kidneys
Liver flukes that infect livestock, resulting in death

Question 10

Emerging infectious disease

Answer 10

a newly discovered or rare disease that increases in abundance.

Oben occurs when a mutaBon allows a pathogen to jump to a new host species.

Question 11

Factors that influence the probability of host infection

Answer 11

Mechanism of transmission

Mode of entering the host

Ability of parasite to jump between specie

Existence of reservoir species

Counterahacks to host’s immune system

Question 12

Horizontal transmission

Answer 12

When a parasite moves between individuals other than parents and offspring.

Question 13

Vertical transmission

Answer 13

When a parasite is transmitted from a parent to its offspring.

Question 14

Mode of entering the host

Answer 14

Piercing tissue (e.g., leeches)
 Reliance on a vector (e.g., malaria)

Question 15

Ability of parasite to jump between species

Answer 15

A lethal parasite that specializes on one host may face exBncBon; soluBon is to infect mulBple species (e.g., bird flu, HIV)

Question 16

Reservoir species

Answer 16

Species that carry a parasite but do not succumb to disease.

They can be a continuous source of parasites as other hosts become rare.

Question 17

Counterahacks to host’s immune system

Answer 17

Avoiding detection by incorporating into chromosomes (e.g., HIV)
Form protective outer layer (e.g., schistosomes)

Question 18

Vector

Answer 18

an organism that disperses a parasite between hosts.

Some parasites require multiple hosts to complete their life cycle.

Example: Lyme disease

Question 19

Parasites can evolve adaptations that increase the probability of transmission…

Answer 19

Example:
The yellow dungfly is infected by a fungus.

The fungus causes the fly to perch upside-down on an upper leaf of a plant.

Spores are released, carried by the wind, and infect more flies.

Question 20

The parasitic worm Acanthocephalus dirus

Answer 20

requires two hosts: an isopod and a fish.

Infected isopods increase their visibility to fish predators by spending more time in open water.

Worms develop in the fish, and parasites leave the fish with waste products that isopods consume.

Question 21

Hosts have developed a range of responses to combat parasites.

Answer 21

Immune system responses

Production of antibacterial/antifungal compounds

Mechanical/biochemical defenses

Question 22

Self-medication

Answer 22

When infected with nematode parasites, chimpanzees will consume Aspilia leaves, which are covered with any hooks that pull nematodes out of the digestive tract.

They also chew biher twigs from the Vernonia plant, which contain chemical compounds that kill parasites.

Question 23

When two or more species continue to evolve in response to each other’s evolution

Answer 23

Invasive rabbit populations in Australia cause massive crop damage.

The government released a virus (Myxoma) into the populaBon that killed 99.8% of the rabbits.

This favored resistant rabbits and less lethal viruses.

Over time, both virus and rabbit populaBons coevolved and began increasing in abundance.