Unit 2: Key Area 5 - Parasitism Flashcards
Define an ecological niche
An ecological niche is a multi-dimensional summary of tolerances and requirements of a species
Why do species have a niche
A species has a fundamental niche that it occupies in the absence of any interspecific competition
Define a realised niche
A realised niche is occupied in response to interspecific competition
What is a result of interspecific competition
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
What happens when realised niches are sufficiently different
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning
Define Parasitism
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
Describe the relationship of a parasite and host
Unlike in a predator-prey relationship, the reproductive potential of the parasite is greater than that of the host
Describe parasite niches
Most parasites have a narrow (specialised) niche as they are very host-specific
Compare a ectoparasite to an endoparasite
An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host
What is the result of the host providing resources for the parasite
As the host provides so many of the parasite’s needs, many parasites are degenerate, lacking structures and organs found in other organisms
How many hosts do parasites require in their life cycle
Some parasites require only one host to complete their life cycle
Many parasites require more than one host to complete their life cycle
Define a definitive host
The definitive host is the organism on or in which the parasite reaches sexual maturity.
Define an intermediate host
Intermediate hosts may also be required for the parasite to complete its life cycle
Describe the role of a vector
A vector plays an active role in the transmission of the parasite and may also be a host
How is the human disease malaria caused
The human disease malaria is caused by Plasmodium
Describe how malaria is caused in humans
- 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 male and female gametes, allowing sexual reproduction to
now occur. - The mosquito can then infect another human host.
What causes the human disease schistosomiasis
Schistosomes cause the human disease schistosomiasis
Describe how schistosomiasis is caused in humans
- 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 a human, entering the bloodstream.
Define a virus
Viruses are parasites that can only replicate inside a host cell
Describe the inner structure of viruses
Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat
What are some viruses surrounded by
Some viruses are surrounded by a phospholipid membrane derived from host cell materials
Describe
a) the outer surface of a virus structure
b) how a host can detect the virus is not a part of itself
a) The outer surface of a virus contains antigens
b) that a host cell may or may not be able to detect as foreign
Describe the stages of the Viral life cycle stages (how new viruses are made within a host cell)
Viral life cycle stages:
- 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
Describe
a) what enzyme RNA retroviruses use
b) what effect does this enzyme have
c) what happens after this enzyme is used
a) RNA retroviruses use the enzyme reverse transcriptase
b) to form DNA, which is then inserted into the genome of the host cell
c) Viral genes can then be expressed to form new viral particles
Define Transmission
Transmission is the spread of a parasite to a host
Define Virulence
Virulence is the harm caused to a host species by a parasite
What factors increase transmission rates
Factors that increase transmission rates:
- 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
What do parasites often do to maximise transmission
Host behaviour is often exploited and modified by parasites to maximise transmission
What happens to the host’s behaviour afterwards
The host behaviour becomes part of the extended phenotype of the parasite
How else does the parasite use its host to benefit itself
Alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour
What type of immune responses do mammals have
Immune response in mammals has both non-specific and specific aspects
Give examples of non-specific defences
- Physical barriers
- chemical secretions
- inflammatory response
- phagocytes
- natural killer cells destroying cells infected with viruses
Give an example of a physical barrier response within the body
Epithelial tissue (skin) blocks the entry of parasites
Give examples of chemical secretion responses within the body
- 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
Describe why does more blood flow to the site of wounds and what the blood carries
Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes
Describe the process of phagocytosis
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis
What do natural killer cells do
Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
Which cells constantly circulate to monitor body tissues as part of a specific cellular defence
Specific cellular defences
A range of white blood cells constantly circulate, monitoring the tissues
Describe what happens
a) If tissues become damaged or invaded what do the cells release
b) what is the result of this
a) If tissues become damaged or invaded, cells release cytokines
b) that increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage
Describe
a) the structure of lymphocytes
b) what does it do
a) Mammals contain many different lymphocytes, each possessing a receptor on its surface
b) which can potentially recognise a parasite antigen
What happens as a result of a binding of an antigen to a lymphocyte’s receptor
Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte
What do selected lymphocytes produce
Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells
What do regions of antibodies posses
Antibodies possess regions where the amino acid sequence varies greatly between different antibodies
What does the variable region give the antibody
This variable region gives the antibody its specificity for binding antigen
Describe
a) what is formed when the antigen bind to the binding site of the antibody
b) what are the 2 results
a) When the antigen binds to this binding site the antigen-antibody complex formed
b) (1) can result in inactivation of the parasite, rendering it susceptible to a phagocytes,
(2) or can stimulate a response that results in cell lysis (bursting)
Describe
a) what else can be formed from antigen-antibody binding
b) how?
c) how is this of advantage to the host
a) Memory lymphocyte cells are also formed
b) 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.
c) When this occurs antibody production is enhanced in terms of speed of production, concentration in blood and duration.
Parasites have evolved ways of evading the immune system to reduce their chances of being detected. How do endoparasites do this?
Endoparasites mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction
Describe
a) antigenic variation in parasites
b) give another advantage of antigenic variation for parasites
a) Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host
b) It may also allow re-infection of the same host with the new variant
Describe latency
Some viruses escape immune surveillance by integrating their genome into host genomes, existing in an inactive state known as latency
When does latency end
Latency ends when favourable conditions arise resulting in the virus becoming active again
What is epidemiology
Epidemiology is the study of the outbreak and spread of infectious disease
What is herd immunity threshold
The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic
Why are vaccines important during an epidemic
As vaccines contain antigens that will elicit an immune response
Why is it difficult to design a vaccine
Because the similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite
AND
Antigenic variation has to be reflected in the
design of vaccines
AND
Some parasites are difficult to culture in the laboratory making it difficult to design vaccines
What conditions make co-ordinated treatment and control programs difficult to achieve
Challenges arise where parasites spread most rapidly as a result of overcrowding (condition 1) or tropical climates (condition 2)
How and where can overcrowding occur
Overcrowding can occur in refugee camps that result from war or natural disaster or rapidly growing cities in LEDCs.
What are often the only practical control strategies
Civil engineering projects to improve sanitation combined with co-ordinated vector control may often be the only practical control strategies
What are the wider impacts of controlling a parasite within a population
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
