Parasitism

Question 1

What is an ecological niche?

Answer 1

An ecological niche is a multi-dimensional summary of tolerances and requirements of a species.

Question 2

What is a fundamental niche?

Answer 2

A species that has a fundamental niche that it occupies in the absence of any interspecific competition.

Question 3

What is a realised niche?

Answer 3

A realised niche is occupied in response to interspecific competition.

Question 4

What is competitive exclusion and how can it occur?

Answer 4

As a result of interspecific competition, competitive exclusion can occur, where the niches of two species are so similar that one declines to local extinction.

Question 5

When can potential competitors co-exist by resource partitioning?

Answer 5

Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning.

Question 6

What is parasitism?

Answer 6

Parasitism is a symbiotic interaction between a parasite and its host.

Question 7

How does a parasite gain benefit?

Answer 7

A parasite gains benefit in terms of nutrients at the expense of its host.

Question 8

What has greater reproductive potential, a parasite or its host?

Answer 8

Unlike in a predator-prey relationship, the reproductive potential of the parasite is greater than that of the host.

Question 9

What niche do parasites have and why?

Answer 9

Most parasites have a narrow niche as they are very host-specifc.

Question 10

Are parasites degenerate and why?

Answer 10

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

Question 11

What is an ectoparasite and an endoparasite?

Answer 11

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

Question 12

How many hosts does a parasite need to complete its life cycle.

Answer 12

Some parasites require only one host to complete their life cycle however others may need more.

Question 13

What is the definitive host?

Answer 13

The definitive host is the organism on or in which the parasite reaches sexual maturity.

Question 14

What would an intermediate host be used for?

Answer 14

Intermediate hosts may also be required for the parasite to complete its life cycle.

Question 15

What does a vector do?

Answer 15

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

Question 16

How is malaria caused by plasmodium?

Answer 16

An infected mosquito, acting as a vector, bites a human.
Plasmodium enters the human bloodstream.
Asexual reproduction occurs in the liver and then in the red blood cells.
When the red blood cells burst gametocytes are released into the bloodstream.
Another mosquito bites an infected human and the gametocytes enter the mosquito maturing into the make and female gametes allowing sexual reproduction to now occur.
The mosquito can then infect another human host.

Question 17

How does schistosomes cause the human disease schistosomiasis?

Answer 17

Schistosomes reproduce sexually in the human intestine.
The fertilised eggs pass out via faeces into water where they develop into larvae.
The larvae then infect water snails where asexual reproduction occurs.
This produces another type of motile larvae, which escape the snail and penetrate the skin of the human, entering the bloodstream.

Question 18

What are viruses?

Answer 18

Viruses are parasites that can only replicate inside a host cell.

Question 19

What do viruses contain?

Answer 19

Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat.

Question 20

What are some viruses surrounded by?

Answer 20

Some viruses are surrounded by a phospholipid membrane derived from the host cell materials.

Question 21

What does the outer surface of a virus contain?

Answer 21

The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign.

Question 22

What are the viral life cycle stages?

Answer 22

Infection of the 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 23

What do RNA retroviruses use?

Answer 23

RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell.

Question 24

What can viral genes be expressed to form?

Answer 24

Viral genes can then be expressed to form new viral particles.

Question 25

What is transmission?

Answer 25

Transmission is the spread of a parasite to a host.

Question 26

What is virulence?

Answer 26

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

Question 27

How are ectoparasites transmitted?

Answer 27

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

Question 28

How are endoparasites transmitted?

Answer 28

Endoparasites of the body tissues are often transmitted by vectors.

Question 29

What increases transmission rates?

Answer 29

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 the infected hosts are incapacitated.

Question 30

How do parasites maximise transmission?

Answer 30

Alteration of host foraging, movement, sexual behaviour, habitat choice and anti-predator behaviour.

Question 31

What becomes part of the extended phenotype of the parasite?

Answer 31

The host behaviour becomes part of the extended phenotype of the parasite.

Question 32

Why do parasites often suppress the host immune system and modify host size and reproductive rate?

Answer 32

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 33

What type of aspects do immune responses in mammals have?>

Answer 33

Immune response in mammals has both non-specific and specific aspects.

Question 34

What are some non-specific defences?

Answer 34

Physical barriers (epithelial tissue blocks the entry of parasites), 
Chemical secretions (hydrolytic enzymes in mucus), 
Inflammatory response (saliva and tears destroy bacterial cell walls),
Phagocytes (injured cells release signalling molecules which results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes.)
natural killer cells (NKC can identify and attach to cells infected with the virus releasing chemicals that lead to cell death by inducing apoptosis) destroying cells infected with viruses are examples of non-specific defences.

Question 35

What are specific cellular defences

Answer 35

A range of white blood cells constantly circulate, monitoring the tissues.
If tissues become damaged or invaded, cells release cytokines that increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of the infection or tissue damage.

Question 36

How do mammals recognise a parasite antigen and kill them?

Answer 36

Mammals contain many different lymphocytes, each possessing a receptor on its surface, which can potentially recognise a parasite antigen.
Binding of an antigen to a lymphocytes 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 37

Where do antibodies possess regions?

Answer 37

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

Question 38

How are memory lymphocytes formed?

Answer 38

Initial antigen exposure produces memory lymphocyte cells specific for that antigen that can produce a secondary response when the same antigen enters the body in the future. When this occurs antibody production enhanced in terms of speed and production, concentration in blood and duration.

Question 39

Why do endopararsites mimic host antigens?

Answer 39

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

Question 40

What allows change between different antigens during the course of infection in a host?

Answer 40

Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host. It mat also allow re-infection of the same host with a new varient.

Question 41

How do some viruses escape immune surveillance?

Answer 41

Some viruses escape immune surveillance by integrating their genome into host genomes, existing in an inactive state known as latency.

Question 42

When do viruses become active again?

Answer 42

The viruses become active again when favourable conditions arise.

Question 43

What is Epidemiology?

Answer 43

Epidemiology is the study of the outbreak and spread of infectious disease.

Question 44

What is the herd immunity threshold?

Answer 44

The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic.

Question 45

What do vaccines contain?

Answer 45

Vaccines contain antigens that will cause an immune response.

Question 46

What makes it difficult to find drug compounds that only target the parasite?

Answer 46

The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite.

Question 47

What has to be reflected in the design of vaccines?

Answer 47

Antigenic variation has to be reflected in the design of vaccines.

Question 48

What does some parasites being difficult to culture mean for designing vaccines?

Answer 48

Some parasites are difficult to culture in the laboratory making it difficult to design vaccines.

Question 49

In terms of parasite spread when do challenges arise?

Answer 49

Challenges arise where parasites spread most rapidly as a result of overcrowding or tropical climates.

Question 50

Where can overcrowding occur?

Answer 50

Overcrowding can occur in refugee camps that result from war or natural disaster or rapidly growing cities in LEDCs(Lower Economically Developed Countries)

Question 51

How does overcrowding and tropical climates affect treatment and control programmes?

Answer 51

These conditions make co-ordinated treatment and control programs difficult to achieve.

Question 52

How can we control parasite spread?

Answer 52

Civil engineering projects to improve sanitation combined with co-ordination vector control may often be the only practical control strategy.

Question 53

Why are improvements in parasite control good?

Answer 53

Improvements in parasite control reduce child mortality and result in population wide-improvements in child development and intelligence, as individuals have more resources for growth and development.