Unit 2: Organisms and Evolution, Parasitism Flashcards
What occurs when competitors end up having different tolerances and requirements?
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning by targeting different prey to each other.
What occurs as a result of interspecific competition for identical resources?
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 is parasitism?
Parasitism is a symbiotic interaction between a parasite and its host (+/-)
What is a parasite?
An organism that gains benefit in terms of nutrients at the expense of its host.
What is the difference between an ectoparasite and an endoparasite?
An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host
Why are many parasites degenerate?
Because they rely so much on their hosts to provide them the necessary nutrients as they lack structure and organs found within their organisms
What is the definitive host?
The definitive host is the organism on or in which the parasite reaches sexual maturity.
What is an intermediate host?
Intermediate hosts may also be required for the parasite to complete its life cycle.
What is the function of a vector?
A vector plays an active role in the transmission of the parasite and may also be a host
How does malaria infect a human?
An infected mosquito acts as a vector and bites a human.
Plasmodium now enters the human bloodstream.
When red blood cells burst, gametocytes are then released.
Another mosquito bites an infected human and the gametocytes enter the mosquito which then mature into male and female gametes, allowing sexual reproduction to occur.
Now the mosquito can go and infect other human hosts
How do schistosomes cause schistosomiasis
Schistosomes reproduce sexually in the human intestine.
The fertilised eggs pass out of the body through faeces into water where they develop into larvae.
The larvae then infect water snails, where asexual reproduction occurs.
This then produces another type of motile larvae which escapes the water snail and penetrates the skin of a human, entering the bloodstream.
What are viruses?
Parasites that can only reproduce inside the host cell.
What are viruses’ genetic material protective coat made of?
Protein
Describe the 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 the reverse transcriptase enzyme for?
To form DNA from RNA, which is then inserted into the genome of the host cell.
How are ectoparasites transmitted?
They are generally transmitted through direct contact
How are endoparasites transmitted?
Usually transmitted through vectors or by consumption of intermediate hosts.
What factors 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
Provide examples of non specific defences?
Physical barriers, chemical secretions, inflammatory response, phagocytes, and natural killer cells destroying cells infected with viruses
Explain how non specific defences work?
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.
Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes.
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis.
Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis.
Explain how specific defences work?
White blood cells constantly circulate through the bloodstream, 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
Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of the lymphocyte.
Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells
How are memory lymphocytes formed?
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.
Describe the secondary response of memory lymphocytes
When a secondary response occurs, antibody production is enhanced in speed of production, concentration in blood and the duration it remains in the blood.
How do endoparasites evade the immune system?
Endoparasites mimic the host antigens to avoid detection and modify host immune responses to reduce their chances of destruction.
What does antigenic variation in parasites allow for?
Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host
What can antigenic variation in parasites also potentially cause?
Reinfection of the same host with the new variant
What is herd immunity?
The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic.
What is epidemiology?
Epidemiology is the study of the outbreak and spread of infectious disease
What do vaccines contain?
Vaccines contain antigens that will elicit an immune response
Why is it difficult to find drugs that only target the parasite?
Because the host and parasite metabolisms are too similar.
What can cause rapid spread of parasites?
Challenges arise where parasites spread most rapidly as a result of overcrowding or tropical climates
What are possible solutions to control the spread of parasites?
Civil engineering projects to improve sanitation combined with co-ordinated vector control may often be the only practical control strategies
