Parasitism

Question 1

What is a niche?

Answer 1

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

Question 2

What are fundamental and realised niches ?

Answer 2

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

A realised niche is occupied in response to interspecific competition

Question 3

What is competitive exclusion ?

Answer 3

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 4

What is resource partitioning ?

Answer 4

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

Species exploiting different components of the resource

Question 5

What is parasitism ?

Answer 5

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

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

Question 6

What aspects are more unique about a parasite ?

Answer 6

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

Most parasites have a narrow (specialised) niche as they are very host-specific

Question 7

What does degenerate mean ?

Answer 7

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

Production of unused tissue would be a waste of resources.

Question 8

What are the types of parasite ?

Answer 8

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

Question 9

How many hosts do parasites need ?

Answer 9

Some parasites require only one host to complete their life cycle

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

Question 10

What are the types of parasite hosts ?

Answer 10

The definitive host is the organism on or in which the parasite reaches sexual maturity. (produces gametes, undergoes sexual reproduction, meiosis, egg laying, etc)

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

Question 11

What is a vector ?

Answer 11

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

Question 12

Explain malaria

Answer 12

The human disease malaria is caused by Plasmodium

1) An infected mosquito, acting as a vector, bites a human. Plasmodium enters the human bloodstream.

2) Asexual reproduction occurs in the liver and then in the red blood cells.

3) When the red blood cells burst gametocytes are released into the bloodstream.

4) Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to now occur.

5) The mosquito can then infect another human host

Question 13

Explain Schistosomiasis

Answer 13

Schistosomes cause the human disease schistosomiasis

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 then infect water snails, where asexual reproduction occurs.

4) This produces another type of motile larvae, which escape the snail and penetrate the skin of a human, entering the bloodstream.

Question 14

What are viruses ?

Answer 14

Viruses are parasites that can only replicate inside a host cell

Question 15

Describe the structures of a virus ?

Answer 15

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

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

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

Question 16

What are the stages of the viral life cycle ?

Answer 16

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 17

What are retroviruses ?

Answer 17

RNA retroviruses 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 18

What are transmission and virulence ?

Answer 18

-Transmission is the spread of a parasite to a host

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

Question 19

How are ecto and endoparasites transmitted ?

Answer 19

Ectoparasites are generally transmitted through direct contact

Endoparasites of the body tissues are often transmitted by vectors or by consumption of intermediate hosts

Question 20

What are factors that increase transmission rates ?

Answer 20

-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 21

What is exploited by parasites to maximise transmission ?

Answer 21

Host behaviour is often exploited and modified by parasites to maximise transmission, including;
-Alteration of host foraging
-Movement
-Sexual behaviour
-Habitat choice
-Anti-predator behaviour.

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

Question 22

What is modified by parasites ?

Answer 22

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

Question 23

What aspects does the immense response of mammals against parasitic attack have ?

Answer 23

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

Question 24

What are the non-specific defences ?

Answer 24

1) Physical barriers,
2) Chemical secretions,
3) Inflammatory response
4) Phagocytes
5) Natural killer cells destroying cells infected with viruses

Question 25

What are specific examples of non-specific defences ?

Answer 25

-Epithelial tissue blocks the entry of parasites -Hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls -Low pH environments of the secretions of stomach, vagina and sweat glands denatures cellular proteins of pathogens.

Question 26

What are the non-specific defences ?

Answer 26

1) Physical barriers -Epithelial tissue blocks the entry of parasites 2) Chemical secretions -Hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls -Low pH environments of the secretions of stomach, vagina and sweat glands denatures cellular proteins of pathogens. 3) Inflammatory response -Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes 4) Phagocytes -Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis. 5) Natural killer cells destroying cells infected with viruses -Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis.

Question 27

What happens if tissues becomed damaged or invaded ?

Answer 27

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 infection or tissue damage

Question 28

How can lymphocytes recognise a parasite ?

Answer 28

Mammals contain many different lymphocytes, each possessing a receptor on its surface, which can potentially recognise a (specific) parasite antigen

Question 29

What happens when a lymphocytes receptor binds to an antigen?

Answer 29

-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 30

Why are antibodies specific ?

Answer 30

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

Question 31

What do antibodies do ?

Answer 31

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 32

What are memory lymphocyte cells ?

Answer 32

-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 is enhanced in terms of speed of production, concentration in blood and duration. | Antigen bind to lympho receptor, clonal population, some clones r memory

Question 33

What is immume evasion and methods to achieve this ?

Answer 33

Parasites have evolved ways of evading the immune system -Endoparasites mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction -Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host. It may also allow re-infection of the same host with the new variant -Some viruses escape immune surveillance by integrating their genome into host genomes, existing in an inactive state known as latency. The virus becomes active again when favourable conditions arise.

Question 34

What is Epidemiology ?

Answer 34

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

Question 35

What is the herd immunity

Answer 35

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

Question 36

What do vaccines contain ?

Answer 36

Vaccines contain antigens that will elicit an immune response

Question 37

What are challenges in the use of medicine against parasites ?

Answer 37

-The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite. -Antigenic variation has to be reflected in the design of vaccines. -Some parasites are difficult to culture in the laboratory making it difficult to design vaccines.

Question 38

Where do parasites spread most rapidly and what does this mean ?

Answer 38

-Challenges (in treatment and control) arise where parasites spread most rapidly as a result of overcrowding or tropical climates -Overcrowding can occur in refugee camps that result from war or natural disaster or rapidly growing cities in LEDCs. -These conditions make co-ordinated treatment and control programs difficult to achieve

Question 39

What is an example of a control strategy of parasites, and what are the effects of this ?

Answer 39

Civil engineering projects to improve sanitation combined with co-ordinated vector control may often be the only practical control strategies. 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. ## Footnote Civil engineering projects r expensive, more resources for biological and physical g&d