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

What do viruses contain?

Answer 11

DNA or RNA, packaged inside a protein coat.

Question 12

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

Answer 12

genetic material, (RNA, DNA), protein

Question 13

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

Answer 13

phospholipid membrane, host cell

Question 14

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

Answer 14

antigens, may or may not, foreign

Question 15

What are the 4 steps to the viral life cycle?

Answer 15

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 16

What do RNA retroviruses do? (2)

Answer 16

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 17

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

Answer 17

reverse transcriptase, DNA, genome, host cell

Question 18

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

Answer 18

reverse transcriptase, expressed, viral particles

Question 19

What is meant by…
Transmission?
Virulence?

Answer 19

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

Question 20

Transmission is the ___ of a ___ to a ___.

Answer 20

spread, parasite, host

Question 21

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

Answer 21

harm, host, parasite

Question 22

How are ectoparasites transmitted?
How are endoparasites transmitted?

Answer 22

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

Question 23

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

Answer 23

direct contact, consumption, intermediate.
vectors.

Question 24

Name some factors that increase transmission rates.

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

behaviour, exploited, modified, transmission

Question 27

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

Answer 27

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

Question 28

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

Answer 28

extended phenotype

Question 29

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 29

immune system, size, reproductive

Question 30

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 30

benefit, growth, reproduction, transmission

Question 31

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

Answer 31

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

Question 32

What is an extended phenotype?

Answer 32

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 33

Why do parasites modify and exploit host behaviour?

Answer 33

to maximise transmission