2.5 Parasitism Flashcards
what is a niche
the niche of an organism is the functional role that it plays within an ecosystem
what is an ecological niche
a multi-dimensional summary of tolerances and requirements of a species
what are the types of niches
fundamental
realised
what is a fundamental niche
the niche that an organism occupies when there are no other species present competing for space or resources (no interspecific competition)
what is a realised niche
the niche that an organism occupies when there is competition from other species (interspecific competition)
what can interspecific competition (realised competition) lead to
competitive exclusion
what is competitive exclusion
when two species are in intense competition with one another and the weaker of the two species declines or becomes locally extinct
what can occur if the realised niches are sufficiently different
resource partitioning
what is resource partitioning
where two species occupy different realised niches, allowing them to co-exist by compromising over resources
what is parasitism
a symbiotic interaction between a parasite and its host (+/-)
what does a parasite benefit in at the expense of the host
nutrients and shelter
what is the difference between a predator-prey relationship and parasitism
the reproductive potential of the parasite is greater then that of the host
why do most parasites have a narrow (specialised) niche
the are very host-specific
what does hosts providing many of the parasite’s needs lead to
parasite being degenerate
what does degenerate mean
lacking structures and organs found in other organisms
what is an ectoparasite
a parasite which lives on the surface of its host
what is an endoparasite
a parasite which lives within the tissues of its host
how many hosts do parasites require to complete their cycle
some require 1
most require more than one
what is a definitive (primary) host
host where parasite reaches sexual maturity
what is an intermediate (secondary) host
the host that the parasite might require in order to complete its life cycle or as a means of transmission thus making it a vector
what is a vector
the means of transmitting a parasite
what role does a vector play
an active role in the transmission of the parasite and may also be a host
what is the human disease malaria caused by
Plasmodium
what is the first step in the malaria life cycle
an infected mosquito, acting as a vector, bits a human
what is the second step in the malaria life cycle
Plasmodium enters the human bloodstream
what is the third step in the malaria life cycle
asexual reproduction occurs in the liver and then in the red blood cells
what is the fourth step in the malaria life cycle
when the red blood cells burst gametocytes are released into the bloodstream
what is the fifth step in the malaria life cycle
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 is the human disease schistosomiasis caused by
schistosomes
what is the first step in the schistosomiasis life cycle
schostosomes reproduce sexually in the human intestine
what is the second step in the schistosomiasis life cycle
the fertilised eggs pass out via faeces into water where they develop into larvae
what is the third step in the schistosomiasis life cycle
the larvae then infect water snails where asexual reproduction occurs
what is the fourth step in the schistosomiasis life cycle
this produces another type of motile larvae, which escape the snail and perpetrate the skin of a human, entering the bloodstream
what are viruses
parasite that can only replicate inside a host cell
which genetic information do viruses contain
viruses contain genetic information in the form of DNA or RNA, packaged in a protective protein coat
what are some viruses surrounded by
a phospholipid membrane derived form host cell material
what does the outer surface of a virus contain
antigens that a host cell may or may not be able to detect as foreign
what is the first stage of the viral life cycle
infection of a host cell with genetic material
what is the second stage of the viral life cycle
host cell enzymes replicate viral genome
what is the third stage of the viral life cycle
transcription of viral proteins
what is the fourth stage of the viral life cycle
assembly and release of new viral particles
what are retroviruses
a virus that contains RNA as its nucleic acid
which enzyme does RNA retrovirus use to form DNA
reverse transcriptase which is then inserted into the genome of the host cell
viral genes can be expressed to form…
viral particles
what is transmission
the spread of a parasite to a host
what is virulence
the harm caused to a host species by a parasite
how are ectoparasites transmitted
through direct contact or by consumption of intermediate hosts
how are endoparasites of the body tissues often transmitted
by vectors
name factors which increase transmission rate
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 is extended phenotype
a theory whereby the parasite modifies the host’s behaviour to increase its own transmission
what does the parasite modify in the host’s behaviour
alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour
parasites often suppress the host immune system and modify….
host size and reproductive rate in ways that benefit the parasite growth, reproduction or transmission
types of immune response in mammals
specific
non-specific
what are non-specific defences
immune system defence mechanisms in organisms that attempt to prevent any parasites from infecting the potential host
examples of non-specific defences
physical barriers and chemical secretions
inflammatory response
phagocytes
natural killer cells destroying cells infected with viruses
what are physical barriers and chemical secretions in non-specific defences
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
what is the inflammatory response in non-specific defences
injured cells release signalling molecules
this results in enhanced blood flowing to the site, bringing antimicrobial a theory whereby the parasite modifies the host’s behaviour to increase its own transmission proteins and phagocytes
what is phagocytes in non-specific defences
killing of parasites using powerful enzymes contained in lysosomes, by engulfing them ad storing them inside a vacuole in the process of phagocytosis
what is phagocytosis
non-specific defence where phagocytes engulf foreign antigens and digest them using digestive enzymes present in lysosomes
what is the first step of phagocytosis
phagocyte is attracted to chemical signals produced by a bacterium
what is the second step of phagocytosis
vacuole forms around the bacterium
lysosomes move towards and fuse with the vacuole
what is the third step of phagocytosis
lysosomes release digestive enzymes into the vacuole, the bacterium is broken down by enzymes
what is the fourth step of phagocytosis
vacuole disintegrates releasing digested products into the cytoplasm digested products into the cytoplasm of the phagocyte
what is natural kills cells destroying cells infected with viruses
these cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
what are natural killer cells
lymphocytes responsible for destroying abnormal cells
what is apoptosis
cell death
example of specific cellular defences
a range of white blood cells constantly circulate, monitoring the tissue
it is soecific because teh immune system targets specific antigens on the surface of parasites
what is an antigen
a protein that may induce an immune response if it is foreign
what happens if tissue 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
mammals contain many different lymphocytes…
each possess a receptor on its surface, which can potentially recognise a parasite antigen
what does the binding of an antigen to a lymphocyte receptor do
selects that lymphocyte to then divide and produce a clonal population of this lymphocyte
what do lymphocytes do
some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells
what do antibodies have that vary
antibodies possess regions where the amino acid sequence varies greatly between different antibodies
what does the variable variable region of an antibody give
the antibody’s specificity for binding to antigens
name the parts of an antigen
antigen binding site
variable region
constant region
how is the antigen-antibody complex formed
when the antigen binds to the antigen binding site
what does the formation of the antigen-antibody complex result in
inactivation of the parasite, rendering it susceptible to a phagocyte of can stimulate a response that results in cell lysis
what does initial antigen exposure produce
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
what are memory lymphocyte cells
cloned lymphocytes that remain in the body to respond faster if the individual is exposed to the same antigen a second time
what have parasites evolved
ways of evading the immune system
why do endoparasites mimic host antigens
to evade detection and modify host immune response to reduce their chances of destruction
what does antigenic variation allow
in some parasites, allows them to change between different antigens during the course of infection of a host
what is antigenic variation
where parasites show great variety amongst different strains
what is epidemiology
the study of the outbreak and spread of infectious diseases
what is herd immunity
the resistance to the spread of a contagious disease that results if a sufficiently high proportion of individuals are immune to the disease
what is the herd immunity threshold
the density of resistant hosts in the population required to prevent an epidemic
what do vaccines contain
antigens that will elicit an immune response
what does similarities between host and parasite metabolism result in
difficulty in finding drug compounds that only target the parasite
what has to be reflected in the design of vaccines
antigenic variation
what does parasites being difficult to culture in the lab result in
makes it difficult to design vaccines
where do challenges arise
where parasites spread most rapidly as a result of overcrowding or tropical climates
where does overcrowding happen
in refugee camps that result from war of natural disaster or rapidly growing cities in LEDCs
what does overcrowding result in in terms of treatment
make co-ordinated treatment and control programs difficult to achieve
what is civil engineering
a profession that is involved in the design and manufacture of infrastructure to improve standards of living
what is often the only practical control strategy
civil engineering projects to improve sanitation combined with co-ordinated vector control
what does improvements in parasite control reduce
child mortality and results in population-wide improvements in child development and intelligence, as individuals have more resources for growth and development
