2.5 b) + c) Parasitic Life Cycles + Transmission and Virulence

Question 1

Some parasites only require ___ host to complete their ___ ___.

Answer 1

one, life cycle

Question 2

Many parasites require more than one ___ to complete their ___ ___.

Answer 2

host, life cycle

Question 3

What is meant by the term…
Intermediate host?
Definitive host?

Answer 3

an intermediate host is a host which helps some parasites complete their life cycles
A definitive host is a host in or on which a parasite reaches sexual maturity

Question 4

A vector plays an ___ role in the ___ of a parasite, and may also be a ___.

Answer 4

active, transmission, host

Question 5

The two parasite life cycles to study are:
___, which cause malaria, and
___, which cause schistosomiasis.

Answer 5

plasmodium (plural - plasmodia)
schistosome(s)

Question 6

The life cycle of a plasmodium has 6 steps. Give a brief summary of each:
1.
2.
3.
4.
5.
6.

Answer 6

1. an infected mosquito bites a human
2. the plasmodia enter the blood
3. the plasmodia reproduce asexually in red blood cells and liver
4. the red blood cells burst, releasing gametocytes
5. another mosquito bites the human, the gametocytes enter the mosquito, mature into gametes, and then sexual reproduction occurs
6. the mosquito can then infect another human

Question 7

Schistosomes cause ____.
Plasmodia cause ___.

Answer 7

schistosomiasis.
malaria

Question 8

What are the 4 steps to the life cycle of schistosomes?
1.
2.
3.
4.

Answer 8

1. Schistosomes reproduce sexually in the human intestine
2. the fertilised eggs pass out via faeces, into water, where they develop into larvae
3. the larvae infect water snails, where asexual reproduction occurs, producing another type of motile larvae
4. these larvae escape the snail and penetrate the skin of a human, entering the bloodstream and starting the process again.

Question 9

What are viruses?

Answer 9

viruses are parasites that can only replicate inside a host cell

Question 10

Viruses are ___ that can only replicate inside a ___ cell

Answer 10

parasites,host

Question 11

Viruses contain ___ ___ (in the form of __ or __), packaged inside a ___ coat.

Answer 11

genetic material, (RNA, DNA), protein

Question 12

Some viruses are surrounded by a ___ ___, derived from ___ ___ materials.

Answer 12

phospholipid membrane, host cell

Question 13

The outer surface of a virus contains ___ that a host cell ___ or ___ ___ be able to detect as ___.

Answer 13

antigens, may or may not, foreign

Question 14

What are the 4 steps to the viral life cycle?

Answer 14

1. Infection of host cell with genetic material
2. Host cell enzymes replicate viral genome
3. transcription of viral genes and translation of viral proteins.
4. assembly and release of new viral particles.

Question 15

What do RNA retroviruses do? (2)

Answer 15

they use reverse transcriptase to form double stranded DNA from RNA, and then insert the DNA into the genome of the host cell.
The host cell then expresses the viral genes to form new viral particles

Question 16

RNA retroviruses use the enzyme ___ ___ to form ___, which is then inserted into the ___ of the ___ cell.

Answer 16

reverse transcriptase, DNA, genome, host cell

Question 17

Once viral RNA has been turned into DNA, using ___ ___ enzyme, the viral genes can then be ___ to form new ___ ___.

Answer 17

reverse transcriptase, expressed, viral particles

Question 18

What is meant by…
Transmission?
Virulence?

Answer 18

transmission is the spread of a parasite to a host
virulence is the harm caused to a host by the parasite

Question 19

Transmission is the ___ of a ___ to a ___.

Answer 19

spread, parasite, host

Question 20

Virulence is the ___ caused to a ___ species by a ___.

Answer 20

harm, host, parasite

Question 21

How are ectoparasites transmitted?
How are endoparasites transmitted?

Answer 21

ecto: direct contact or consumption of intermediate host.
endo: vector

Question 22

Ectoparasites are transmitted through ___ ___, or ___ of ___ hosts.
Endoparasites are transmitted through ___.

Answer 22

direct contact, consumption, intermediate.
vectors.

Question 23

Name some factors that increase transmission rates.

Answer 23

Overcrowding / high density of hosts.
vectors/waterborne dispersal stages.

Question 24

Transmission rates are increased by ___, and by mechanisms which allow the ___ to spread, even if ___ ___ are incapacitated, such as ___.

Answer 24

Overcrowding (of hosts),
parasite, infected hosts, vectors

Question 25

Host ___ is often e___ and m___ by parasites in order to maximise ___.

Answer 25

behaviour, exploited, modified, transmission

Question 26

Parasites can modify behaviours of hosts in order to maximise transmission.
Name some of these behaviours.

Answer 26

foraging,
movement,
sexual behaviour,
habitat choice,
anti-predator behaviour

Question 27

If parasites modify their host’s behaviour, then it becomes a part of the ___ ___ of the parasite.

Answer 27

extended phenotype

Question 28

Parasites often suppress the host’s ___ ___ and modify the host’s ___ and ___ rate in ways that benefit the parasite’s growth, reproduction or transmission.

Answer 28

immune system, size, reproductive

Question 29

Parasites often suppress the host’s immune system and modify the host’s size and reproductive rate in ways that ___ the parasite’s ___, ___ or ___.

Answer 29

benefit, growth, reproduction, transmission

Question 30

Parasites often suppress the host’s ___ ___ and modify the host’s ___ and ___ rate in ways that benefit the parasite’s ___, ___ or ___.

Answer 30

immune system, size, reproductive, growth, reproduction or transmission

Question 31

What is an extended phenotype?

Answer 31

the complete phenotype of an organism - including things besides an organism’s body (for example a beaver dam, a bird’s nest or a parasite altering a host’s behaviour or appearance)

Question 32

Why do parasites modify and exploit host behaviour?

Answer 32

bcuz: “Host behaviour is often exploited and modified by parasites to maximise transmission”