Biology - Parasitism

define an ecological niche

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

what do species occupy in the absence of any interspecific competition

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

what is a realised niche

a realised niche is occupied in response to interspecific competition

what results from interspecific competition

as a result of interspecific competition, competition 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

when the realised niches are sufficiently different, potential competitors 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 reproductive potential of a parasite compared to the host

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

what do most parasites have

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

describe the structure of a parasite

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

name the types of parasites and where they live

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

how many hosts do parasites need to complete their life cycles

some parasites require only one host to compete their lifecycle however many parasites require more than one host to complete their lifecycle

what is a definitive host

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

what is an intermediate

an intermediate host may be required for the parasite to complete its lifecycle

what is a vector

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

what is the human disease malaria causes by

plasmodium

describe how malaria is transferred pt 1

an infected mosquito that acts as a vector bites a human, plasmodium enters the human bloodstream - asexual reproduction then occurs in the liver and then in the red blood cells

describe how malaria is transferred pt 2

when the red blood cells burst gametocytes are released into the bloodstream, another mosquito bites an infected human and the gametocytes enter the mosquito

describe how malaria is transferred pt 3

the gametocytes then mature into male and female gametes, allowing sexual reproduction to occur, the mosquito can then infect another human host

what causes the human disease schistosomiasis

schistosomes

describe how schistosomiasis is transferred pt 1

schistosomes reproduce sexually in the human intestine, the fertilises eggs pass out via faeces into water where they develop into larvae

describe how schistosomiasis is transferred pt 2

the larvae then infect water snails, where asexual reproduction occurs, this produces another type of motile care which escape the snail and penetrate the skin of a human, entering the bloodstream

what are viruses

viruses parasites that can only replicate inside a host cell

what do viruses contain

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

what does the outer surface of a virus contain

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

what are the 4 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

what do RNA retroviruses use

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

what is transmission

transmission is the spread of a parasite to a host

what is virulence

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

how are ectoparasites transmitted

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

how are endoparasites transmitted

endoparasites of the body tissues are often transmitted by vectors

name a factor that increases transmission rates

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 hosts are incapacitated

how is transmission maximised

host behaviour is often exploited and modified by parasites to maximise transmission

what is the extended phenotype of a parasite

alteration of host foraging, movement, sexual behaviour, habitat or anti-predator behaviour - the host behaviour will become an extended phenotype of the parasite

what do parasites often do that benefits themselves

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

what aspects does the immune response have

the immune response in mammals has both non-specific and specific aspects

give examples of non-specific defences

physical barriers such as chemical secretions, phagocytes, natural killer cells destroying cells infected with viruses, inflammatory response

what does epithelial tissue do

epithelial tissue blocks the entry of parasites

where are hydrolytic enzymes found and what do they do

hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls

what denatures cellular proteins of pathogens

low pH environments of the secretions of stomach, vagina and sweat glands

what do injured cells release

injured cells release signalling molecules, which results in enhanced blood flow to the site which brings in 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.

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 apoptosis

describe specific cellular defences

a range of white blood cells constantly circulates, 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

what do mammals contain

mammals contain many different lymphocytes, each possessing a receptor on its surface which can potentially recognise a parasite antigen

how is a clonal population of lymphocytes produced

binding of an antigen to a lymphocytes receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte

what do some lymphocytes produce

some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells

what do antibodies possess

antibodies possess regions where the amino acid sequence varies greatly between different antibodies

what does the variable region give the antibody

the variable region gives the antibody its specificity for binding antigen

what is formed when an antigen binds

when the antigen binds to this binding site the antigen-antibody complex formed can result in inactivation of the parasite

what can the inactivation of a parasite cause

the inactivation of a parasite can render it susceptible to a phagocyte or can stimulate a response that results in cell lysis, this will also form memory cells

what does initial antigen exposure produce

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

what is the difference between the secondary response and the initial response for antigen exposure

in the secondary response antibody production is enhanced in terms of speed of production, concentration in blood, and duration

how do parasites evade the immune system

by evolution

how do endoparasites evade the immune system

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

what does antigenic variation in some parasites allow

this allows the 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

how do some viruses escape immune surveillance

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

when do inactive viruses become active again

the virus becomes active again when favourable conditions arise

define epidemiology

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

what is the herd immunity threshold

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

what do vaccines contain

vaccines contain antigens that will elicit an immune response

why is it difficult to make drug compounds that only target the parasite

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

what is reflected in the design of vaccines

antigenic variation has to be reflected in the design of vaccines

what makes it difficult to design vaccines in the lab

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

what challenges arise with parasites in overcrowded areas

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

where does overcrowding occur

overcrowding can occur in refugee camps that result from war or natural disaster in rapidly growing cities in LEDCs

what does overcrowding make difficult to achieve

overcrowding conditions makes co-ordinated treatment and control programs difficult to achieve

what do civil engineering projects aim to do

civil engineering projects aim to improve sanitation combined with co-vector control which may often be the only practical control strategies

what do improvements in parasite control reduce

improvements in parasite control reduce child mortality