Parasitism

Question 1

What is an ecological niche?

Answer 1

A multi-dimensional summary of tolerances and requirements of a species

Question 2

When does a species have a fundamental niche?

Answer 2

It occupies in the absence of any interspecific competition

Question 3

When is a realised niche occupied?

Answer 3

In response to interspecific competition

Question 4

What is a result of interspecific competition?

Answer 4

Competitive exclusion can occur, where the niches of two species are so similar that one declines to local extinction

Question 5

What happens if the realised niches are sufficiently different?

Answer 5

Potential competitors can co-exist by resource partitioning

Question 6

What is parasitism?

Answer 6

A symbiotic interaction between a parasite and its host (+/-)

Question 7

What is a parasite?

Answer 7

An organism which gains benefit in terms of nutrients at the expense of its host

Question 8

What is the reproductive potential of the parasite?

Answer 8

Greater than that of the host

Question 9

What type of niche do most parasites have?

Answer 9

A narrow (specialised) niche as they are very host-specific

Question 10

Why are many parasites degenerate?

Answer 10

As the host provides so many of the parasite’s needs, many parasites are degenerate, lacking structures and organs found in other organisms

Question 11

What is the difference between an ectoparasite and an endoparasite?

Answer 11

An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host

Question 12

How many hosts does a parasite require to complete their life cycle?

Answer 12

Some parasites require only one host to complete their life cycle. Many parasites require more than one host to complete their life cycle

Question 13

What is a vector in terms of parasites?

Answer 13

A vector plays an active role in the transmission of the parasite and may also be a host

Question 14

What is malaria caused by?

Answer 14

Plasmodium

Question 15

What are schistosomes?

Answer 15

They cause the human disease schistosomiasis

Question 16

What are viruses?

Answer 16

They are parasites that can only replicate inside a host cell

Question 17

What do viruses contain?

Answer 17

Genetic material in the form of DNA or RNA, packaged in a protective protein coat

Question 18

What are some viruses surrounded by?

Answer 18

A phospholipid membrane derived from host cell materials

Question 19

What does the outer surface of a virus contain?

Answer 19

Antigens that a host cell may or may not be able to detect as foreign

Question 20

What are the viral life cycle stages?

Answer 20

Infection of host cell with genetic material, host cell enzymes replicate viral genome, transcription of viral genes and translation of viral proteins, assembly and release of new viral particles

Question 21

What do RNA retroviruses do and how does this affect viral genes?

Answer 21

They use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell. Viral genes can then be expressed to form new viral particles

Question 22

What is transmission?

Answer 22

Transmission is the spread of a parasite to a host

Question 23

What is virulence?

Answer 23

Virulence is the harm caused to a host species by a parasite

Question 24

How are ectoparasites transmitted?

Answer 24

Ectoparasites are generally transmitted through direct contact or by consumption of intermediate hosts

Question 25

How are endoparasites transmitted?

Answer 25

Endoparasites of the body tissues are often transmitted by vectors

Question 26

What are 2 factors that increase transmission rates?

Answer 26

The overcrowding of hosts when they are at high density. Mechanisms, such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacitated

Question 27

How can parasites affect host behaviour?

Answer 27

Host behaviour is often exploited and modified by parasites to maximise transmission. The host behaviour becomes part of the extended phenotype of the parasite.

Question 28

How can parasites affect the host immune system?

Answer 28

Parasites often suppress the host immune system and modify host size and reproductive rate in ways that benefit the parasite growth, reproduction or transmission

Question 29

What types of aspects does the immune response in mammals have?

Answer 29

Both non-specific and specific aspects

Question 30

What are examples of non-specific defences?

Answer 30

Physical barriers, chemical secretions, inflammatory response, phagocytes, and natural killer cells destroying cells infected with viruses are examples of non-specific defences

Question 31

What are examples of specific cellular defences?

Answer 31

A range of white blood cells constantly circulates, monitoring the tissues

Question 32

What happens if tissues become damaged or invaded?

Answer 32

Cells release cytokines that increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage

Question 33

Mammals contain many different lymphocytes, why is this useful against parasites?

Answer 33

Each possesses a receptor on its surface, which can potentially recognise a parasite antigen. Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte. Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells.

Question 34

What do antibodies possess and how does this affect antigen binding?

Answer 34

Antibodies possess regions where the amino acid sequence varies greatly between different antibodies. This variable region gives the antibody its specificity for binding antigen.

Question 35

What happens when the antigen binds to this binding site?

Answer 35

The antigen-antibody complex formed can result in inactivation of the parasite, rendering it susceptible to a phagocyte, or can stimulate a response that results in cell lysis. Memory lymphocyte cells are also formed.

Question 36

How have endoparasites evolved in order to invade the immune system?

Answer 36

They mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction

Question 37

What does antigenic variation do?

Answer 37

In some parasites it allows them to change between different antigens during the course of infection of a host and it may also allow re-infection of the same host with the new variant.

Question 38

How do some viruses escape immune surveillance?

Answer 38

By integrating their genome into host genomes, existing in an inactive state known as latency

Question 39

When does the virus become active again?

Answer 39

When favourable conditions arise

Question 40

What is epidemiology?

Answer 40

The study of the outbreak and spread of infectious disease

Question 41

What is the herd immunity threshold?

Answer 41

The density of resistant hosts in the population required to prevent an epidemic

Question 42

How do vaccines help and why do they find it ‘difficult’?

Answer 42

Vaccines contain antigens that will elicit an immune response. The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite.

Question 43

What has to be reflected in the design of vaccines?

Answer 43

Antigenic variation

Question 44

Why would it be difficult to design vaccines?

Answer 44

Some parasites are difficult to culture in the laboratory

Question 45

What are challenges that could arise?

Answer 45

Where parasites spread most rapidly as a result of overcrowding or tropical climates. These conditions make coordinated treatment and control programs difficult to achieve .

Question 46

How do civil engineering projects help?

Answer 46

Civil engineering projects to improve sanitation combined with coordinated vector control may often be the only practical control strategies

Question 47

How do improvements in parasite control help?

Answer 47

They can reduce child mortality and result in population-wide improvements in child development and intelligence, as individuals have more resources for growth and development